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2018 Volume Issue 2
2018, (2): 1-2
Abstract:
2018, (2): 129-131
doi: 10.11777/j.issn1000-3304.2018.18019
Abstract:
In polymer solar cells (PSCs), the blends of polymer donors and fullerene-based acceptors have been predominantly used for over two decades. This situation has been challenged owing to the rapid progress in non-fullerene (NF) PSCs. Up to now, the power conversion efficiencies (PCEs) of single-junction NF-PSCs have reached over 13% and surpassed that of the fullerene-based counterparts. Tandem double-junction solar cells are intrinsically more potential for enhancing PCE but bring more challenges for material design and device fabrication. Recently, in order to optimize light response spectrum of tandem NF-PSCs and hence to promote PCE, Hou et al. modulated the photoactive layer compositions by adopting a series of polymer donors and NF-acceptors. They found that light response spectrum of the blend of J52-2F:IT-M was well complementary with that of PTB7-Th:IEICO-4F, and as a result, the tandem NF-PSC based on these two blends could offer a broad and strong light response spectra covering 400-1000 nm. After optimizing device fabrication process, they realized a PCE of 14.9%, which is the top value in the field. Herein, by making a brief overview of NF-PSCs and highlighting this outstanding result, this short essay not only aims to attract attention to the rapid progress made by Chinese academic community but also delivers the expectation for the bright future of NF-PSCs.
In polymer solar cells (PSCs), the blends of polymer donors and fullerene-based acceptors have been predominantly used for over two decades. This situation has been challenged owing to the rapid progress in non-fullerene (NF) PSCs. Up to now, the power conversion efficiencies (PCEs) of single-junction NF-PSCs have reached over 13% and surpassed that of the fullerene-based counterparts. Tandem double-junction solar cells are intrinsically more potential for enhancing PCE but bring more challenges for material design and device fabrication. Recently, in order to optimize light response spectrum of tandem NF-PSCs and hence to promote PCE, Hou et al. modulated the photoactive layer compositions by adopting a series of polymer donors and NF-acceptors. They found that light response spectrum of the blend of J52-2F:IT-M was well complementary with that of PTB7-Th:IEICO-4F, and as a result, the tandem NF-PSC based on these two blends could offer a broad and strong light response spectra covering 400-1000 nm. After optimizing device fabrication process, they realized a PCE of 14.9%, which is the top value in the field. Herein, by making a brief overview of NF-PSCs and highlighting this outstanding result, this short essay not only aims to attract attention to the rapid progress made by Chinese academic community but also delivers the expectation for the bright future of NF-PSCs.
2018, (2): 132-144
doi: 10.11777/j.issn1000-3304.2018.17280
Abstract:
Organic luminescent materials have played important roles in optoelectronic device, chemo-/biosensing, and biomedical applications. However, traditional luminescent materials always suffer from the aggregation-caused quenching (ACQ) effect:they are highly emissive in dilute solutions but their emission becomes weaker or totally quenched in the practical application forms, i.e. the aggregate, film and solid states. The ACQ effect has greatly limited the applications of these luminescent materials in many fields. Exactly opposite to the ACQ, the aggregation-induced emission (AIE) can actively utilize the natural aggregation process of a molecule to provide intense emission in the aggregate and solid states. In the AIE area, the research is focusing on the low mass molecules, and the polymers have been paid less attention although they possess the unique properties such as good film-forming ability, amplification effect of the signals, and multiple functionalization, which facilitates their practical applications. In this review, we first accounted the used polymerizations for the construction of AIE polymers, such as polycouplings, radical polymerization, and click polymerizations. Next, we discussed the structure-property relationship of the AIE polymers based on the systematically investigation of the effect of substituent groups, the link of TPE and fluorene groups on the triazole rings, the attachment of TPE-diethynyl groups on phenyl rings with o, m, and p-positions, and the side-chains on their photo-physical properties. Moreover, the interesting non-conjugated AIE polymers without aromatic rings were also discussed and cluster oluminescence was proposed as the cause for this unique emission. Finally, the applications of the AIE polymers in chemo-and biosensors, and tracing were reviewed and the advantages of AIE polymers over AIE low-mass molecules were also emphasized. It is expected that this review could serve as a trigger for future innovation in the AIE research area.
Organic luminescent materials have played important roles in optoelectronic device, chemo-/biosensing, and biomedical applications. However, traditional luminescent materials always suffer from the aggregation-caused quenching (ACQ) effect:they are highly emissive in dilute solutions but their emission becomes weaker or totally quenched in the practical application forms, i.e. the aggregate, film and solid states. The ACQ effect has greatly limited the applications of these luminescent materials in many fields. Exactly opposite to the ACQ, the aggregation-induced emission (AIE) can actively utilize the natural aggregation process of a molecule to provide intense emission in the aggregate and solid states. In the AIE area, the research is focusing on the low mass molecules, and the polymers have been paid less attention although they possess the unique properties such as good film-forming ability, amplification effect of the signals, and multiple functionalization, which facilitates their practical applications. In this review, we first accounted the used polymerizations for the construction of AIE polymers, such as polycouplings, radical polymerization, and click polymerizations. Next, we discussed the structure-property relationship of the AIE polymers based on the systematically investigation of the effect of substituent groups, the link of TPE and fluorene groups on the triazole rings, the attachment of TPE-diethynyl groups on phenyl rings with o, m, and p-positions, and the side-chains on their photo-physical properties. Moreover, the interesting non-conjugated AIE polymers without aromatic rings were also discussed and cluster oluminescence was proposed as the cause for this unique emission. Finally, the applications of the AIE polymers in chemo-and biosensors, and tracing were reviewed and the advantages of AIE polymers over AIE low-mass molecules were also emphasized. It is expected that this review could serve as a trigger for future innovation in the AIE research area.
2018, (2): 145-163
doi: 10.11777/j.issn1000-3304.2018.17236
Abstract:
Compared to the polymer/fullerene system, all-polymer solar cells, based on conjugated polymers as both donor and acceptor, have many potential advantages such as achieving more efficient light absorption and high open-circuit voltage, as well as easily solution processing and large-area fabrication. Strongly promoted by developments of materials and device structure, the power conversion efficiency (PCE) has been reached 9%. However, conjugated polymers have more rigid molecules compared to the flexible polymers and thus will form chain entanglement and π-π interaction with each other, leading to a more complex phase separation process in the conjugated polymer system. Besides, the strong molecular interaction between donor and acceptor polymers may generate a long-range phase domain in the blend films, which will inhibit the excitons to diffuse to the donor/acceptor (D/A) phase interface. In addition, the difference of thermodynamics steady state between the donor and the acceptor polymers may lead to the formation of different molecular orientation, which will impede the exciton dissociation. To solve these problems, by tuning the thermodynamic and dynamics factors, including molecular rigidity and blend ratio, the phase-separated structure of the conjugated polymer blend system was adjusted and the phase separation mechanism was identified, based on which the phase diagram of the conjugated polymer blend was depicted. By controlling phase separation structure, the interpenetrating networks were obtained, facilitating the charge transfer and collection. Besides, the domain size and film crystallinity were adjusted by reducing the solvent-polymer interaction parameter and polymer-polymer interaction parameters. Due to the decreased domain size, the efficiency of the exciton diffusion was enhanced. In addition, the solution state or molecular diffusion rate was adjusted to adjust the molecular orientation. By increasing the aggregation of the polymers in solution and introducing the epitaxial crystallization, the molecular orientation could change from edge-on to face-on. The identical molecular orientation for the donor and the acceptor improved the exciton dissociation efficiency and the device performance.
Compared to the polymer/fullerene system, all-polymer solar cells, based on conjugated polymers as both donor and acceptor, have many potential advantages such as achieving more efficient light absorption and high open-circuit voltage, as well as easily solution processing and large-area fabrication. Strongly promoted by developments of materials and device structure, the power conversion efficiency (PCE) has been reached 9%. However, conjugated polymers have more rigid molecules compared to the flexible polymers and thus will form chain entanglement and π-π interaction with each other, leading to a more complex phase separation process in the conjugated polymer system. Besides, the strong molecular interaction between donor and acceptor polymers may generate a long-range phase domain in the blend films, which will inhibit the excitons to diffuse to the donor/acceptor (D/A) phase interface. In addition, the difference of thermodynamics steady state between the donor and the acceptor polymers may lead to the formation of different molecular orientation, which will impede the exciton dissociation. To solve these problems, by tuning the thermodynamic and dynamics factors, including molecular rigidity and blend ratio, the phase-separated structure of the conjugated polymer blend system was adjusted and the phase separation mechanism was identified, based on which the phase diagram of the conjugated polymer blend was depicted. By controlling phase separation structure, the interpenetrating networks were obtained, facilitating the charge transfer and collection. Besides, the domain size and film crystallinity were adjusted by reducing the solvent-polymer interaction parameter and polymer-polymer interaction parameters. Due to the decreased domain size, the efficiency of the exciton diffusion was enhanced. In addition, the solution state or molecular diffusion rate was adjusted to adjust the molecular orientation. By increasing the aggregation of the polymers in solution and introducing the epitaxial crystallization, the molecular orientation could change from edge-on to face-on. The identical molecular orientation for the donor and the acceptor improved the exciton dissociation efficiency and the device performance.
2018, (2): 164-173
doi: 10.11777/j.issn1000-3304.2018.17251
Abstract:
Third generation solar cells including organic solar cells, perovskite solar cells have attracted much attention due to their advantages of low cost, solution processability and flexibility. The rapid progress in this field is attributed to the development of absorbing layers, interfacial materials or interfacial modification, device architectures and so on. Especially, the interfaces in the devices significantly affect the exciton dissociation, charge carrier transport and collection, and subsequently affect the device performance. This review focuses on the interface engineering in organic solar cells, polymer/nanocrystal hybrid solar cells and perovskite solar cells in our group. We summarize the strategies of designing effective interfacial materials including hole-transporting materials, electron-transporting materials and their modification to achieve ohmic contact at the interface of active layer and electrodes. A series of low-temperature solution processed low-cost inorganic materials and organic small molecules are developed. With appropriate energy levels, high mobility and low defect or ability to passivate perovskites, highly efficient organic and perovskite solar cells are achieved. Self-assembly monolayer technologies are also discussed here. It is an efficient way to modify the work function of electrodes to obtain ohmic contact between electrodes and active layer. On one hand, the self-assembly monolayer can also be used to passivate the defect of metal oxide buffer layer such as ZnO or TiO2 to reduce recombination, which may improve the morphology of perovskite film to enhance the performance. Plasmonic effect is introduced to enhance the light absorption of active layer by incorporating Au or Ag nanoparticles into the interface layers. At last, the optimized strategies for interface modification between polymer and nanocrystals to improve the exciton dissociation and charge transport are discussed in details. By attaching benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry, the nanocrystal-nanocrystal or polymer-nanocrystal distance is minimized. Furthermore, the "electroactive" π-orbitals of the benzenedithiol can further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. On the other hand, judicious choice of ligands with appropriate molecular dipoles has a strong impact on chemical and electronic structures at the polymer-nanocrystal interface and subsequently on photovoltaic device performance. With these strategies, highly efficient polymer/CdSe nanocrystal hybrid solar cells have been achieved. A few viewpoints on further developing interface engineering for high-performance solar cells are also provided.
Third generation solar cells including organic solar cells, perovskite solar cells have attracted much attention due to their advantages of low cost, solution processability and flexibility. The rapid progress in this field is attributed to the development of absorbing layers, interfacial materials or interfacial modification, device architectures and so on. Especially, the interfaces in the devices significantly affect the exciton dissociation, charge carrier transport and collection, and subsequently affect the device performance. This review focuses on the interface engineering in organic solar cells, polymer/nanocrystal hybrid solar cells and perovskite solar cells in our group. We summarize the strategies of designing effective interfacial materials including hole-transporting materials, electron-transporting materials and their modification to achieve ohmic contact at the interface of active layer and electrodes. A series of low-temperature solution processed low-cost inorganic materials and organic small molecules are developed. With appropriate energy levels, high mobility and low defect or ability to passivate perovskites, highly efficient organic and perovskite solar cells are achieved. Self-assembly monolayer technologies are also discussed here. It is an efficient way to modify the work function of electrodes to obtain ohmic contact between electrodes and active layer. On one hand, the self-assembly monolayer can also be used to passivate the defect of metal oxide buffer layer such as ZnO or TiO2 to reduce recombination, which may improve the morphology of perovskite film to enhance the performance. Plasmonic effect is introduced to enhance the light absorption of active layer by incorporating Au or Ag nanoparticles into the interface layers. At last, the optimized strategies for interface modification between polymer and nanocrystals to improve the exciton dissociation and charge transport are discussed in details. By attaching benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry, the nanocrystal-nanocrystal or polymer-nanocrystal distance is minimized. Furthermore, the "electroactive" π-orbitals of the benzenedithiol can further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. On the other hand, judicious choice of ligands with appropriate molecular dipoles has a strong impact on chemical and electronic structures at the polymer-nanocrystal interface and subsequently on photovoltaic device performance. With these strategies, highly efficient polymer/CdSe nanocrystal hybrid solar cells have been achieved. A few viewpoints on further developing interface engineering for high-performance solar cells are also provided.
2018, (2): 174-185
doi: 10.11777/j.issn1000-3304.2018.17268
Abstract:
Bulk-heterojunction (BHJ) polymer solar cells (PSCs) have attracted attention over the past decades due to their distinct advantages of low cost, light weight, and the suitability for flexible-device fabrications. Despite the remarkable success in improving the efficiency of PSCs, fullerene-based acceptors have shown evident limitations. Accordingly, increased research efforts have been invested in developing non-fullerene acceptors, and great development has been witnessed in this field in recent years. Among all different kinds of BHJ PSCs, all polymer solar cells (all-PSCs) potentially possess the most stable donor-acceptor phase separation morphology, and all-polymer films are expected to boast superior mechanical properties. Yet, the bottle neck of enhancing the power conversion efficiency (PCE) of all-PSCs currently lies in the performance of the polymer acceptors. In the past years, we have been focusing on designing new polymer acceptors using perylenediimide (PDI) as the main building block and studying their performance in all-PSCs. A series of PDI-based polymer acceptors have been synthesized and studied since 2013. Due to the steric hindrance induced by the bay-region substitution, the PDI polymers mostly manifest low crystallinity. Accordingly, by enhancing the conjugation and rigidity of the polymer backbone, and thereby improving the aggregation and crystallization ability of the polymers, increased PCE has been achieved with all-PSC devices. Consistently, experimental evidence has also been collected showing improved morphology of the active layer. As a result of the continued and systematic studies on designing and synthesizing new polymer acceptors, along with the optimization of device fabrication conditions, the best PCE of all-PSC incorporating a PDI polymer acceptor has now been boosted to 8.59%. Very similar PCE values can be obtained from devices fabricated under ambient conditions, proving the high chemo-stability of the active-layer materials. The synthetic methods of these PDI-based polymers and the device fabrication conditions are much more convenient and economical. All these properties are friendly to the large-scale material preparation and device production.
Bulk-heterojunction (BHJ) polymer solar cells (PSCs) have attracted attention over the past decades due to their distinct advantages of low cost, light weight, and the suitability for flexible-device fabrications. Despite the remarkable success in improving the efficiency of PSCs, fullerene-based acceptors have shown evident limitations. Accordingly, increased research efforts have been invested in developing non-fullerene acceptors, and great development has been witnessed in this field in recent years. Among all different kinds of BHJ PSCs, all polymer solar cells (all-PSCs) potentially possess the most stable donor-acceptor phase separation morphology, and all-polymer films are expected to boast superior mechanical properties. Yet, the bottle neck of enhancing the power conversion efficiency (PCE) of all-PSCs currently lies in the performance of the polymer acceptors. In the past years, we have been focusing on designing new polymer acceptors using perylenediimide (PDI) as the main building block and studying their performance in all-PSCs. A series of PDI-based polymer acceptors have been synthesized and studied since 2013. Due to the steric hindrance induced by the bay-region substitution, the PDI polymers mostly manifest low crystallinity. Accordingly, by enhancing the conjugation and rigidity of the polymer backbone, and thereby improving the aggregation and crystallization ability of the polymers, increased PCE has been achieved with all-PSC devices. Consistently, experimental evidence has also been collected showing improved morphology of the active layer. As a result of the continued and systematic studies on designing and synthesizing new polymer acceptors, along with the optimization of device fabrication conditions, the best PCE of all-PSC incorporating a PDI polymer acceptor has now been boosted to 8.59%. Very similar PCE values can be obtained from devices fabricated under ambient conditions, proving the high chemo-stability of the active-layer materials. The synthetic methods of these PDI-based polymers and the device fabrication conditions are much more convenient and economical. All these properties are friendly to the large-scale material preparation and device production.
2018, (2): 186-197
doi: 10.11777/j.issn1000-3304.2018.17269
Abstract:
In recent years, conjugated polymers (CPs) with characteristic and excellent photochemical and photophysical properties have become particularly popular in scientific research and are widely used for biological sensing. Conjugated polymers are characterized by a delocalized electronic structure along their backbones and exhibit electronic coupling between each optoelectronic segments. Owing to unique delocalized π-conjugated structure, CPs are endowed with distinguished optical properties, such as light-harvesting and amplification capability and high energy transfer efficiency. Water-soluble conjugated polymers (WSCPs) introduced with charged groups or selectively-recognition elements on the side chains can specifically diagnose through electrostatic interaction or specific binding with targets. In addition, WSCPs with diverse absorption and emission characteristics have been designed and synthesized by tuning the constitution and conformation of the backbones. In contrast with fluorescence proteins, small organic molecules and quantum dots, CPs with greatly unique properties have greater advantages that directed to sensing and imaging in biochemical and biomedical fields. This review article is aimed to summarize recent research progresses on applications of WSCPs as biosensors for the detection of a series of biological targets. Firstly, according to electrostatics interaction of CPs and targeted DNA, different novel strategies are used for detection of DNA mutations (section 2). Meanwhile, CPs modified with recognition moieties can be utilized to detect specific proteins (section 3). In addition, based on different interaction modes between CPs and cells and pathogens, identification and discrimination of microbial pathogens and cells are realized (section 4). CPs can also be used for cell imaging due to their advantageous optical properties (section 5). The structures, characteristics and advantages of CPs, as well as various nove lidentifications and detections strategies are also discussed. Through a variety of design and modification, novel CPs can be obtained and used for identification and detection, which is complementary to traditional CPs in biosensor and widens the range of biological applications. It is worth mentioning that, with the development of inter-discipline, more attention should be paid to the combination of new methods and strategies for exploiting functions of CPs in biological sensing.
In recent years, conjugated polymers (CPs) with characteristic and excellent photochemical and photophysical properties have become particularly popular in scientific research and are widely used for biological sensing. Conjugated polymers are characterized by a delocalized electronic structure along their backbones and exhibit electronic coupling between each optoelectronic segments. Owing to unique delocalized π-conjugated structure, CPs are endowed with distinguished optical properties, such as light-harvesting and amplification capability and high energy transfer efficiency. Water-soluble conjugated polymers (WSCPs) introduced with charged groups or selectively-recognition elements on the side chains can specifically diagnose through electrostatic interaction or specific binding with targets. In addition, WSCPs with diverse absorption and emission characteristics have been designed and synthesized by tuning the constitution and conformation of the backbones. In contrast with fluorescence proteins, small organic molecules and quantum dots, CPs with greatly unique properties have greater advantages that directed to sensing and imaging in biochemical and biomedical fields. This review article is aimed to summarize recent research progresses on applications of WSCPs as biosensors for the detection of a series of biological targets. Firstly, according to electrostatics interaction of CPs and targeted DNA, different novel strategies are used for detection of DNA mutations (section 2). Meanwhile, CPs modified with recognition moieties can be utilized to detect specific proteins (section 3). In addition, based on different interaction modes between CPs and cells and pathogens, identification and discrimination of microbial pathogens and cells are realized (section 4). CPs can also be used for cell imaging due to their advantageous optical properties (section 5). The structures, characteristics and advantages of CPs, as well as various nove lidentifications and detections strategies are also discussed. Through a variety of design and modification, novel CPs can be obtained and used for identification and detection, which is complementary to traditional CPs in biosensor and widens the range of biological applications. It is worth mentioning that, with the development of inter-discipline, more attention should be paid to the combination of new methods and strategies for exploiting functions of CPs in biological sensing.
2018, (2): 198-216
doi: 10.11777/j.issn1000-3304.2018.17289
Abstract:
Electroluminescent polymers hold great promise in penal display and solid-state lighting applications because of their advantages of solution processability, large-scale manufacturing and ability to produce flexible devices based on plastic substrates. In the past decades, great progress has been made in electroluminescent polymers including their working mechanism, material systems and device performance. Basically, electroluminescent polymers can be divided into three classes:fluorescent polymers, phosphorescent polymers and thermally activated delayed fluorescence (TADF) polymers. For fluorescent polymers, the internal quantum efficiency (IQE) is limited to 25% because they can use only singlet excitons in the electroluminescent device. In comparison, IQE of phosphorescent polymers can reach 100% because of the strong spin-orbital coupling induced by the heavy-atoms in the phosphorescent dopants. Recently, TADF polymers have evolved rapidly as the new kind of electroluminescent polymers because they are able to utilize triplet excitons through rapid reverse intersystem crossing process from the lowest triplet state to the lowest singlet state, thereby providing a promising approach to reach 100% IQE without the use of noble metal elements. With these developments, the device performance of the polymers has been enhanced greatly and many indexes have met the commercialization requirements. This review is aimed to summarize the research progresses on electroluminescent polymers used for organic light-emitting diodes, including the molecular design and device performance of representative examples of fluorescent polymers, phosphorescent polymers and TADF polymers. The emphasis of this review is especially focused on the color tuning and performance improvement approaches for the fluorescent polymers, the optimization of the phosphorescent dopant, the polymer host and the topological structure of the phosphorescent polymers, as well as the design principles of the thermally activated delayed fluorescence polymers. Finally, the perspectives and the key challenges of the electroluminescent polymers are discussed, and future directions of efforts toward further developing low-cost, efficient, and stable electroluminescent polymers are also demonstrated.
Electroluminescent polymers hold great promise in penal display and solid-state lighting applications because of their advantages of solution processability, large-scale manufacturing and ability to produce flexible devices based on plastic substrates. In the past decades, great progress has been made in electroluminescent polymers including their working mechanism, material systems and device performance. Basically, electroluminescent polymers can be divided into three classes:fluorescent polymers, phosphorescent polymers and thermally activated delayed fluorescence (TADF) polymers. For fluorescent polymers, the internal quantum efficiency (IQE) is limited to 25% because they can use only singlet excitons in the electroluminescent device. In comparison, IQE of phosphorescent polymers can reach 100% because of the strong spin-orbital coupling induced by the heavy-atoms in the phosphorescent dopants. Recently, TADF polymers have evolved rapidly as the new kind of electroluminescent polymers because they are able to utilize triplet excitons through rapid reverse intersystem crossing process from the lowest triplet state to the lowest singlet state, thereby providing a promising approach to reach 100% IQE without the use of noble metal elements. With these developments, the device performance of the polymers has been enhanced greatly and many indexes have met the commercialization requirements. This review is aimed to summarize the research progresses on electroluminescent polymers used for organic light-emitting diodes, including the molecular design and device performance of representative examples of fluorescent polymers, phosphorescent polymers and TADF polymers. The emphasis of this review is especially focused on the color tuning and performance improvement approaches for the fluorescent polymers, the optimization of the phosphorescent dopant, the polymer host and the topological structure of the phosphorescent polymers, as well as the design principles of the thermally activated delayed fluorescence polymers. Finally, the perspectives and the key challenges of the electroluminescent polymers are discussed, and future directions of efforts toward further developing low-cost, efficient, and stable electroluminescent polymers are also demonstrated.
2018, (2): 217-222
doi: 10.11777/j.issn1000-3304.2018.17242
Abstract:
Naphtho[1, 2-c:5, 6-c']bis([1, 2, 5]thiadiazole) (NT) unit with centro-symmetric and enlarged planar π-conjugated structure is one of the most promising electron-withdrawing moieties for the construction of high-performance conjugated polymers for solar cells and organic field-effect transistors. Recently, an NT based narrow-bandgap conjugated polymer (NTOD), consisting of NT as the electron-withdrawing unit and 2, 5-bis(3-alkylthiophen-2-yl)thieno[3, 2-b]thiophene as the electron-donating unit, has been developed, which exhibited a remarkable power conversion efficiency exceeding 10% and might be used to construct device with thick active layer over 300 nm. Considering the impressive photovoltaic performances achieved based on the NT-polymers, here we designed and fabricated solution-processed polymer photodetectors using NTOD as the electron donor. Device with architecture of ITO/PEDOT:PSS/active layer/Al was fabricated to investigate the performance of the photodetector. The active layer was comprised of NTOD as the electron donor and a fullerene derivative of (6, 6)-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor, which displayed broad absorption spectra ranging from 400 nm to 830 nm. We noted that the dark current density of the photodetectors was effectively suppressed by increasing the thickness of the NTOD:PC71BM based active layer, while the external quantum efficiency (EQE) of the devices maintained relatively high. It is also worth pointing out that, when the thickness of the active layer increased up to 385 nm, the device exhibited low dark current density of 6.69×10-10 A cm-2 at -0.1 V, for which the specific detectivity (D*) is higher than 1013 cm Hz1/2 W-1 in the range of 440-800 nm, with champion detectivity of 1.50×1013 cm Hz1/2 W-1 and responsivity of 0.22 A W-1 at 750 nm. Moreover, the polymer photodetector exhibited a high detectivity of 1.10×1013 cm Hz1/2 W-1 at 800 nm, suggesting the good detectivity extending to near-infrared (NIR) region. These results indicate that the NTOD polymer has great potential for the construction of high performance polymer photodetectors.
Naphtho[1, 2-c:5, 6-c']bis([1, 2, 5]thiadiazole) (NT) unit with centro-symmetric and enlarged planar π-conjugated structure is one of the most promising electron-withdrawing moieties for the construction of high-performance conjugated polymers for solar cells and organic field-effect transistors. Recently, an NT based narrow-bandgap conjugated polymer (NTOD), consisting of NT as the electron-withdrawing unit and 2, 5-bis(3-alkylthiophen-2-yl)thieno[3, 2-b]thiophene as the electron-donating unit, has been developed, which exhibited a remarkable power conversion efficiency exceeding 10% and might be used to construct device with thick active layer over 300 nm. Considering the impressive photovoltaic performances achieved based on the NT-polymers, here we designed and fabricated solution-processed polymer photodetectors using NTOD as the electron donor. Device with architecture of ITO/PEDOT:PSS/active layer/Al was fabricated to investigate the performance of the photodetector. The active layer was comprised of NTOD as the electron donor and a fullerene derivative of (6, 6)-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor, which displayed broad absorption spectra ranging from 400 nm to 830 nm. We noted that the dark current density of the photodetectors was effectively suppressed by increasing the thickness of the NTOD:PC71BM based active layer, while the external quantum efficiency (EQE) of the devices maintained relatively high. It is also worth pointing out that, when the thickness of the active layer increased up to 385 nm, the device exhibited low dark current density of 6.69×10-10 A cm-2 at -0.1 V, for which the specific detectivity (D*) is higher than 1013 cm Hz1/2 W-1 in the range of 440-800 nm, with champion detectivity of 1.50×1013 cm Hz1/2 W-1 and responsivity of 0.22 A W-1 at 750 nm. Moreover, the polymer photodetector exhibited a high detectivity of 1.10×1013 cm Hz1/2 W-1 at 800 nm, suggesting the good detectivity extending to near-infrared (NIR) region. These results indicate that the NTOD polymer has great potential for the construction of high performance polymer photodetectors.
2018, (2): 223-230
doi: 10.11777/j.issn1000-3304.2018.17297
Abstract:
In this work, we focus on the fine-tuning of absorption spectra to achieve well-matched light response and reducing the energy loss (Eloss=Egopt-e*VOC, where Egopt is the optical bandgap, and VOC is the open circuit voltage) for the sub-cells of tandem organic solar cells (OSCs) to improve photovoltaic performance. We select PTB7-Th:IEICO-4F with a band gap of 1.24 eV as the rear cell and J52-2F:IT-M with a band gap of 1.59 eV as the front cell to fabricate the tandem OSCs. The absorption spectra of PTB7-Th:IEICO-4F is mainly located in the region of 600-950 nm, while that of J52-2F:IT-M is mainly located in the region of 450-750 nm. Their response spectra are very complementary, and both of the sub-cells show high external quantum efficiency, prompting the tandem OSCs to realize high-efficiency utilization of solar spectrum in the range of 300-1000 nm. In this tandem OSC, the Eloss in both front and rear cells are also effectively controlled to be 0.64 and 0.53 eV, respectively. In addition, an efficient interconnection layer (ICL) of ZnO/PCP-Na is used to connect the front and the rear sub-cells, which shows outstanding diode characteristics and high light transmittance in the long wavelength direction. In view of these excellent properties, the tandem solar cells manufactured in this work possess the advantages of high short-circuit current density (JSC) and VOC, reaching 13.3 mA/cm2 and 1.65 V, respectively. The highest power conversion efficiency (PCE) of the tandem OSC reaches 14.9%. The device parameters decrease slightly after encapsulation due to the intense ultraviolet irradiation, and a certified PCE of 14.0%, with a VOC of 1.64 V, a JSC of 12.9 mA/cm2, and a fill factor (FF) of 0.664, recorded by National Institute of Metrology (NIM), China. This result is the best obtained in the organic photovoltaic field.
In this work, we focus on the fine-tuning of absorption spectra to achieve well-matched light response and reducing the energy loss (Eloss=Egopt-e*VOC, where Egopt is the optical bandgap, and VOC is the open circuit voltage) for the sub-cells of tandem organic solar cells (OSCs) to improve photovoltaic performance. We select PTB7-Th:IEICO-4F with a band gap of 1.24 eV as the rear cell and J52-2F:IT-M with a band gap of 1.59 eV as the front cell to fabricate the tandem OSCs. The absorption spectra of PTB7-Th:IEICO-4F is mainly located in the region of 600-950 nm, while that of J52-2F:IT-M is mainly located in the region of 450-750 nm. Their response spectra are very complementary, and both of the sub-cells show high external quantum efficiency, prompting the tandem OSCs to realize high-efficiency utilization of solar spectrum in the range of 300-1000 nm. In this tandem OSC, the Eloss in both front and rear cells are also effectively controlled to be 0.64 and 0.53 eV, respectively. In addition, an efficient interconnection layer (ICL) of ZnO/PCP-Na is used to connect the front and the rear sub-cells, which shows outstanding diode characteristics and high light transmittance in the long wavelength direction. In view of these excellent properties, the tandem solar cells manufactured in this work possess the advantages of high short-circuit current density (JSC) and VOC, reaching 13.3 mA/cm2 and 1.65 V, respectively. The highest power conversion efficiency (PCE) of the tandem OSC reaches 14.9%. The device parameters decrease slightly after encapsulation due to the intense ultraviolet irradiation, and a certified PCE of 14.0%, with a VOC of 1.64 V, a JSC of 12.9 mA/cm2, and a fill factor (FF) of 0.664, recorded by National Institute of Metrology (NIM), China. This result is the best obtained in the organic photovoltaic field.
2018, (2): 231-238
doi: 10.11777/j.issn1000-3304.2018.17128
Abstract:
A series of C60 derivatives functionalized by carbazole group with great electrochemical activity were designed and synthesized via Bingel reaction. Three monomers (2Cz-C60, 4Cz-C60, 6Cz-C60) were finally obtained with different molar ratios between C60 and malonate used in Bingel reaction. The molecular structure of these monomers were fully characterized by proton nuclear magnetic resonance spectra, Matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), Fourier transform infrared spectroscopy (FTIR), and UV-Vis absorption. Electrochemical polymerization of these monomers were processed to form linear or cross-linked organic conducting polymer films, denoted as Poly[2Cz-C60], Poly[4Cz-C60] and Poly[6Cz-C60], which were attributed to the coupling of electrochemical activity group of N-alkyl carbazole. Their electrochemical polymerization was processed under three-electrode system of the electrochemical workstation (ITO or glassy carbon as working electrode, titanium plate or Pt wire as counter electrode and Ag/Ag+ as reference electrode). The chemical structures of the polymers obtained were clearly dependent on the definite electrochemical condition such as potential, electrolyte, concentration and scan rate during the polymerization. The thickness of the films obtained by the electrochemical polymerization could be controlled precisely by controlling the cycles of cyclic voltammetry (CV). The electrochemical polymerization of the polymers had the same features of instantaneous nucleation and layered growth concluded by the atomic force microscope images of the films under different CV cycles. Finally, the films show globular stacking features. After CV test, the bipolar characters (N-alkyl carbazole group as the p-doping and C60 group as the n-doping), fast and reversible redox properties of the organic conducting polymers films have been found. Then we explored the charge storage ability of the polymers as the electrode materials, which possessed considerable development potential to some extent.
A series of C60 derivatives functionalized by carbazole group with great electrochemical activity were designed and synthesized via Bingel reaction. Three monomers (2Cz-C60, 4Cz-C60, 6Cz-C60) were finally obtained with different molar ratios between C60 and malonate used in Bingel reaction. The molecular structure of these monomers were fully characterized by proton nuclear magnetic resonance spectra, Matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), Fourier transform infrared spectroscopy (FTIR), and UV-Vis absorption. Electrochemical polymerization of these monomers were processed to form linear or cross-linked organic conducting polymer films, denoted as Poly[2Cz-C60], Poly[4Cz-C60] and Poly[6Cz-C60], which were attributed to the coupling of electrochemical activity group of N-alkyl carbazole. Their electrochemical polymerization was processed under three-electrode system of the electrochemical workstation (ITO or glassy carbon as working electrode, titanium plate or Pt wire as counter electrode and Ag/Ag+ as reference electrode). The chemical structures of the polymers obtained were clearly dependent on the definite electrochemical condition such as potential, electrolyte, concentration and scan rate during the polymerization. The thickness of the films obtained by the electrochemical polymerization could be controlled precisely by controlling the cycles of cyclic voltammetry (CV). The electrochemical polymerization of the polymers had the same features of instantaneous nucleation and layered growth concluded by the atomic force microscope images of the films under different CV cycles. Finally, the films show globular stacking features. After CV test, the bipolar characters (N-alkyl carbazole group as the p-doping and C60 group as the n-doping), fast and reversible redox properties of the organic conducting polymers films have been found. Then we explored the charge storage ability of the polymers as the electrode materials, which possessed considerable development potential to some extent.
2018, (2): 239-247
doi: 10.11777/j.issn1000-3304.2018.17193
Abstract:
A series of bipolar blue-emitting poly(spirobifluorene)s, named PSFCzPO10, PSFCzPO20 and PSFCzPO30, have been designed and synthesized via Suzuki polycondensation, where carbazole and arylphosphine oxide are incorporated as the hole-and electron-transporting units, respectively. These resultant poly(spirobifluorene)s are thermally stable with decomposition temperatures up to 380 ℃ and no glass transition or melting behaviors are observed in the range of 25-280 ℃, which are beneficial for the fabrication of long-trem PLEDs. Moreover, compared to the reference polymer Cz-PSF only containing carbazole, the introduction of the arylphosphine oxide unit does not obviously affect their photoluminescence (PL) and the corresponding PL quantum yields of PSFCzPO10-PSFCzPO30 in solid states. However, with increasing content of the arylphosphine oxide, the lowest unoccupied molecular orbital (LUMO) levels are lowered from -2.22 eV for Cz-PSF to -2.68 eV for PSFCzPO30, whereas the highest occupied molecular orbital (HOMO) levels remain nearly unchanged (-5.39~-5.40 eV). This trend implies the favored electron injection and transporting although the hole injection barriers seem to be the same for all the polymers. That is, the bipolar transporting and thus charge balance to some degree are within our expectation for PSFCzPO10-PSFCzPO30. Among them, PSFCzPO10 exhibits the best current efficiency of 1.19 cd A-1 based on a single-layer device structure, which is about twofolds higher than that of Cz-PSF (0.39 cd A-1). In addition, with PSFCzPO10 as the emitting layer and TPPO as the alcohol-soluble electron-transporting layer, the corresponding all-solution-processed multilayer device is successfully assembled through orthogonal sequential solvent processing. And its current efficiency is further up to 1.93 cd A-1 together with CIE coordinates of (0.16, 0.14). Meanwhile, the electroluminescence is nearly independent of the driving voltages, indicative of the good blue spectral stability. These results clearly demonstrate that the bipolar design is a promising strategy to improve the efficiency and stability of blue-emitting poly(spirobifluorene)s applied in PLEDs.
A series of bipolar blue-emitting poly(spirobifluorene)s, named PSFCzPO10, PSFCzPO20 and PSFCzPO30, have been designed and synthesized via Suzuki polycondensation, where carbazole and arylphosphine oxide are incorporated as the hole-and electron-transporting units, respectively. These resultant poly(spirobifluorene)s are thermally stable with decomposition temperatures up to 380 ℃ and no glass transition or melting behaviors are observed in the range of 25-280 ℃, which are beneficial for the fabrication of long-trem PLEDs. Moreover, compared to the reference polymer Cz-PSF only containing carbazole, the introduction of the arylphosphine oxide unit does not obviously affect their photoluminescence (PL) and the corresponding PL quantum yields of PSFCzPO10-PSFCzPO30 in solid states. However, with increasing content of the arylphosphine oxide, the lowest unoccupied molecular orbital (LUMO) levels are lowered from -2.22 eV for Cz-PSF to -2.68 eV for PSFCzPO30, whereas the highest occupied molecular orbital (HOMO) levels remain nearly unchanged (-5.39~-5.40 eV). This trend implies the favored electron injection and transporting although the hole injection barriers seem to be the same for all the polymers. That is, the bipolar transporting and thus charge balance to some degree are within our expectation for PSFCzPO10-PSFCzPO30. Among them, PSFCzPO10 exhibits the best current efficiency of 1.19 cd A-1 based on a single-layer device structure, which is about twofolds higher than that of Cz-PSF (0.39 cd A-1). In addition, with PSFCzPO10 as the emitting layer and TPPO as the alcohol-soluble electron-transporting layer, the corresponding all-solution-processed multilayer device is successfully assembled through orthogonal sequential solvent processing. And its current efficiency is further up to 1.93 cd A-1 together with CIE coordinates of (0.16, 0.14). Meanwhile, the electroluminescence is nearly independent of the driving voltages, indicative of the good blue spectral stability. These results clearly demonstrate that the bipolar design is a promising strategy to improve the efficiency and stability of blue-emitting poly(spirobifluorene)s applied in PLEDs.
2018, (2): 248-256
doi: 10.11777/j.issn1000-3304.2018.17194
Abstract:
Water-dispersed hyperbranched conjugated polymer nanoparticles (HCPN-QA) with quaternary ammonium salt as terminal groups were prepared by Suzuki polymerization in miniemulsion, followed by post-functionalization reaction, for highly sensitive and selective sensing of picric acid (PA) in aqueous solutions. By taking advantage of the positively charged quaternary ammonium salt terminal groups and hydrophobic cavities inside the hyperbranched core, bright blue emissive HCPN-QA can efficiently bind with PA in water by electrostatic attraction and hydrophobic encapsulation interaction, leading to highly efficient fluorescence quenching. The quenching constant of HCPN-QA was 6.36×107 L/mol, which was three orders higher than that of its organic solution-dispersed hyperbranched conjugated polymer nanoparticle analogue (HCPN-OMe). HCPN-QA was capable of sensing PA in water with a detection limit of 7.8×10-10 mol/L (0.18 μg/L), which was four orders of magnitude lower than that of HCPN-OMe (0.34 mg/L). Meanwhile, this value was also lower than the maximum permissible level (1 μg/L) for PA in drinking water set by World Health Organization (WHO). Moreover, by decreasing the amount of surfactants during the polymerization, nanoparticles with small diameter were obtained for further studying the relationship between particle size and the sensitivity for PA sensing. The fluorescent titration study indicated that particle size of HCPN-QA had little effect on the sensitivity for PA sensing. Furthermore, by combining electrostatic attraction and hydrophobic encapsulation interaction, HCPN-QA also showed much higher fluorescence quenching response to PA over other analytes, including 2, 4, 6-trinitrotoluene (TNT), 2, 4-dinitrotoluene (DNT), nitrobenzene, cyclotetramethylenetetranitramine (HMX), 1, 3, 5-trinitro-1, 3, 5-triazinane (RDX), nitromethane, ammonium nitrate, chlorobenzene, toluene and phenol in water. Especially, HCPN-QA showed nearly 60-fold higher quenching constant for PA than that of TNT, indicating that HCPN-QA had not only a high sensitivity, but also a good selectivity for PA sensing. In addition, contact mode detection was further performed using fluorescent paper strips based on HCPN-QA for naked eye detection of PA with a detection limit of 66 pg/mm2.
Water-dispersed hyperbranched conjugated polymer nanoparticles (HCPN-QA) with quaternary ammonium salt as terminal groups were prepared by Suzuki polymerization in miniemulsion, followed by post-functionalization reaction, for highly sensitive and selective sensing of picric acid (PA) in aqueous solutions. By taking advantage of the positively charged quaternary ammonium salt terminal groups and hydrophobic cavities inside the hyperbranched core, bright blue emissive HCPN-QA can efficiently bind with PA in water by electrostatic attraction and hydrophobic encapsulation interaction, leading to highly efficient fluorescence quenching. The quenching constant of HCPN-QA was 6.36×107 L/mol, which was three orders higher than that of its organic solution-dispersed hyperbranched conjugated polymer nanoparticle analogue (HCPN-OMe). HCPN-QA was capable of sensing PA in water with a detection limit of 7.8×10-10 mol/L (0.18 μg/L), which was four orders of magnitude lower than that of HCPN-OMe (0.34 mg/L). Meanwhile, this value was also lower than the maximum permissible level (1 μg/L) for PA in drinking water set by World Health Organization (WHO). Moreover, by decreasing the amount of surfactants during the polymerization, nanoparticles with small diameter were obtained for further studying the relationship between particle size and the sensitivity for PA sensing. The fluorescent titration study indicated that particle size of HCPN-QA had little effect on the sensitivity for PA sensing. Furthermore, by combining electrostatic attraction and hydrophobic encapsulation interaction, HCPN-QA also showed much higher fluorescence quenching response to PA over other analytes, including 2, 4, 6-trinitrotoluene (TNT), 2, 4-dinitrotoluene (DNT), nitrobenzene, cyclotetramethylenetetranitramine (HMX), 1, 3, 5-trinitro-1, 3, 5-triazinane (RDX), nitromethane, ammonium nitrate, chlorobenzene, toluene and phenol in water. Especially, HCPN-QA showed nearly 60-fold higher quenching constant for PA than that of TNT, indicating that HCPN-QA had not only a high sensitivity, but also a good selectivity for PA sensing. In addition, contact mode detection was further performed using fluorescent paper strips based on HCPN-QA for naked eye detection of PA with a detection limit of 66 pg/mm2.
2018, (2): 257-265
doi: 10.11777/j.issn1000-3304.2018.17215
Abstract:
Poly(3, 4-ethylenedioxythiophene) (PEDOT) is usually dispersed in water by incorporating polystyrene sulfonate (PSS) as a charge compensator and a template for polymerization. The polymerization behavior of 3, 4-ethylenedioxythiophene (EDOT) without assistance of insulating PSS was explored. Due to their semiconducting and hydrophilic characteristics, π-conjugated polyelectrolytes with sulfonic acid groups, namely PCPDT-T and PCPDT-2T, were used as template for in situ oxidative polymerization of PEDOT. The obtained PEDOT:polyelectrolyte composites showed good dispersibility in aqueous solution, which was used as hole transport layer (HTL) in polymer solar cells (PSCs). The morphologies and photoelectric properties of PEDOT:PSS and PEDOT:polyelectrolyte composites were characterized by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, ultraviolet photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy and contact angle test, respectively. PEDOT:polyelectrolyte composites displayed suitable energy level, transmittance up to 95% (30 nm), hydrophobic surface morphology, as well as superior hole mobility, which were in favour of forming Ω contact with the active layer and increasing the injection and collection efficiency of the holes. Thus, improving the device photovoltaic performance. The current density-voltage (J-V) characteristics of the PSCs with the structure of Glass/ITO/HTL/PTB7-Th:PC71BM/PFN/Al were measured under one standard sun by solar simulator with an Air Mass 1.5 global (AM 1.5G) and an irradiation intensity of 100 mW/cm2. Compared to the photovoltaic characteristics for PEDOT:PSS based device, PSCs with PEDOT:T (1:2) as HTL yielded the highest power conversion efficiency (PCE) of 8.6% with a short current density (JSC) of 18.07 mA/cm2, open circuit voltage (VOC) of 0.77 and fill factor (FF) of 61.31%, respectively. Compared to that of PEDOT:PSS, the obvious increased JSC for PEDOT:polyelectrolyte composites based PSCs was ascribed to the high hole mobility and transmittance, which were consistent with the results from the space-charge limited current (SCLC) method and the external quantum efficiency (EQE) measurement.
Poly(3, 4-ethylenedioxythiophene) (PEDOT) is usually dispersed in water by incorporating polystyrene sulfonate (PSS) as a charge compensator and a template for polymerization. The polymerization behavior of 3, 4-ethylenedioxythiophene (EDOT) without assistance of insulating PSS was explored. Due to their semiconducting and hydrophilic characteristics, π-conjugated polyelectrolytes with sulfonic acid groups, namely PCPDT-T and PCPDT-2T, were used as template for in situ oxidative polymerization of PEDOT. The obtained PEDOT:polyelectrolyte composites showed good dispersibility in aqueous solution, which was used as hole transport layer (HTL) in polymer solar cells (PSCs). The morphologies and photoelectric properties of PEDOT:PSS and PEDOT:polyelectrolyte composites were characterized by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, ultraviolet photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy and contact angle test, respectively. PEDOT:polyelectrolyte composites displayed suitable energy level, transmittance up to 95% (30 nm), hydrophobic surface morphology, as well as superior hole mobility, which were in favour of forming Ω contact with the active layer and increasing the injection and collection efficiency of the holes. Thus, improving the device photovoltaic performance. The current density-voltage (J-V) characteristics of the PSCs with the structure of Glass/ITO/HTL/PTB7-Th:PC71BM/PFN/Al were measured under one standard sun by solar simulator with an Air Mass 1.5 global (AM 1.5G) and an irradiation intensity of 100 mW/cm2. Compared to the photovoltaic characteristics for PEDOT:PSS based device, PSCs with PEDOT:T (1:2) as HTL yielded the highest power conversion efficiency (PCE) of 8.6% with a short current density (JSC) of 18.07 mA/cm2, open circuit voltage (VOC) of 0.77 and fill factor (FF) of 61.31%, respectively. Compared to that of PEDOT:PSS, the obvious increased JSC for PEDOT:polyelectrolyte composites based PSCs was ascribed to the high hole mobility and transmittance, which were consistent with the results from the space-charge limited current (SCLC) method and the external quantum efficiency (EQE) measurement.
2018, (2): 266-272
doi: 10.11777/j.issn1000-3304.2018.17234
Abstract:
Bulk-heterojunction polymer solar cells (PSCs) have attracted great research attention owing to their advantages of low cost, light weight, and their feasibility to fabricate flexible devices. Power conversion efficiency (PCEs) exceeding 12% for single-junction invertedpolymer solar cells (IPSCs) has been reported in the last years. Fast advancement of PCE benefits mainly from new materials synthesized, morphology optimization of active layer and interfacial engineering. Especially, the interfacial engineering has drawn great attention in recent years. To fabricate efficient IPSCs, a cathode interlayer (CIL) is usually needed between the ITO cathode and the photoactive layer to reduce the work function (WF) of the ITO cathode and to lower the energy barriersfor efficient charge-transfer due to an energy-level mismatch between the high WF of ITO cathode and the lowest unoccupied molecular orbital (LUMO) level of fullerene acceptor. In this work, we employed ionic liquids with different halogen anions as CILs for efficient IPSCs, and explored the influence of such halogen anions on the PCE of the IPSCs. A PCE of 6.55% was achieved for the IPSCs with ionic liquids as the CIL and PBDTTT-C:PC71BM as the active layer, much higher than those without the CIL. When using the PTB7-Th:PC71BM as the active layer, a higher PCE of 8.24% was obtained. Ionic liquids could effectively reduce the contact barrier and the series resistance between the ITO cathode and the active layer due to the interfacial dipole, and thus improving the PCE of the IPSCs. Meanwhile, it was found that the IPSC with iodide ionic liquid ([BzMIM]Ⅰ) as the CIL could afford a higher PCE than that with bromide or chloride ionic liquids ([BzMIM]Cl, [BzMIM]Br), mainly attributing to the greater decreases of the ITO work function and the contact resistance in the case with the former ([BzMIM]Ⅰ) as the CIL.
Bulk-heterojunction polymer solar cells (PSCs) have attracted great research attention owing to their advantages of low cost, light weight, and their feasibility to fabricate flexible devices. Power conversion efficiency (PCEs) exceeding 12% for single-junction invertedpolymer solar cells (IPSCs) has been reported in the last years. Fast advancement of PCE benefits mainly from new materials synthesized, morphology optimization of active layer and interfacial engineering. Especially, the interfacial engineering has drawn great attention in recent years. To fabricate efficient IPSCs, a cathode interlayer (CIL) is usually needed between the ITO cathode and the photoactive layer to reduce the work function (WF) of the ITO cathode and to lower the energy barriersfor efficient charge-transfer due to an energy-level mismatch between the high WF of ITO cathode and the lowest unoccupied molecular orbital (LUMO) level of fullerene acceptor. In this work, we employed ionic liquids with different halogen anions as CILs for efficient IPSCs, and explored the influence of such halogen anions on the PCE of the IPSCs. A PCE of 6.55% was achieved for the IPSCs with ionic liquids as the CIL and PBDTTT-C:PC71BM as the active layer, much higher than those without the CIL. When using the PTB7-Th:PC71BM as the active layer, a higher PCE of 8.24% was obtained. Ionic liquids could effectively reduce the contact barrier and the series resistance between the ITO cathode and the active layer due to the interfacial dipole, and thus improving the PCE of the IPSCs. Meanwhile, it was found that the IPSC with iodide ionic liquid ([BzMIM]Ⅰ) as the CIL could afford a higher PCE than that with bromide or chloride ionic liquids ([BzMIM]Cl, [BzMIM]Br), mainly attributing to the greater decreases of the ITO work function and the contact resistance in the case with the former ([BzMIM]Ⅰ) as the CIL.
2018, (2): 273-283
doi: 10.11777/j.issn1000-3304.2018.17243
Abstract:
Halogen substituted benzothiadiazole polymers with different length of alkyl side chains were synthesized via Stille coupling and used as donor materials in polymer solar cells (PSC). These polymers exhibited good solubility in common organic solvents, excellent film forming ability, and broad absorption properly towards the sun light. By introducing the halogen atoms to the backbone, in particularly the large chlorine atoms, fullerene-based (PC71BM) bulk heterojunction PSCs of these polymers could achieve enhanced open-circuit voltage and short-circuit current, and eventually the power conversion efficiency could be dramatically improved. It was found that the halogen substitution and various alkyl side chains could highly affect the polymers' band gaps and charge transport properties, through influencing the molecular orientation and crystallinity. With regard to tuning the energy levels, compared with fluorine atom, chlorine atom with a bigger atomic radius could reduce more efficiently the energy levels, thereby further improving the open-circuit voltage of the corresponding PSCs. In this study, the PSCs based on one-chlorine-and-one-fluorine-substituted PCFBT4T-2OD, with PC71BM used as the acceptor, exhibited an open-circuit voltage of 0.72 V, a short-circuit current of 17.61 mA cm-2, and the highest power conversion efficiency of 8.84%. From the grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments, those polymers with the halogen atoms substitutions showed a mixed "face-on" and "edge-on" conformation in their blended films. The introduction of fluorine atoms in the polymer PCFBT4T-2OD further enhanced the π-π stacking, compared with the one-chlorine substituted PCBT4T-2BO, which was helpful for the charge transport in the active layer and to enhance the device performance in PSCs. Those results demonstrated that the halogen substitution was an effective molecular design strategy to modify the polymer aggregation and morphology for optimized polymer solar cell applications.
Halogen substituted benzothiadiazole polymers with different length of alkyl side chains were synthesized via Stille coupling and used as donor materials in polymer solar cells (PSC). These polymers exhibited good solubility in common organic solvents, excellent film forming ability, and broad absorption properly towards the sun light. By introducing the halogen atoms to the backbone, in particularly the large chlorine atoms, fullerene-based (PC71BM) bulk heterojunction PSCs of these polymers could achieve enhanced open-circuit voltage and short-circuit current, and eventually the power conversion efficiency could be dramatically improved. It was found that the halogen substitution and various alkyl side chains could highly affect the polymers' band gaps and charge transport properties, through influencing the molecular orientation and crystallinity. With regard to tuning the energy levels, compared with fluorine atom, chlorine atom with a bigger atomic radius could reduce more efficiently the energy levels, thereby further improving the open-circuit voltage of the corresponding PSCs. In this study, the PSCs based on one-chlorine-and-one-fluorine-substituted PCFBT4T-2OD, with PC71BM used as the acceptor, exhibited an open-circuit voltage of 0.72 V, a short-circuit current of 17.61 mA cm-2, and the highest power conversion efficiency of 8.84%. From the grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments, those polymers with the halogen atoms substitutions showed a mixed "face-on" and "edge-on" conformation in their blended films. The introduction of fluorine atoms in the polymer PCFBT4T-2OD further enhanced the π-π stacking, compared with the one-chlorine substituted PCBT4T-2BO, which was helpful for the charge transport in the active layer and to enhance the device performance in PSCs. Those results demonstrated that the halogen substitution was an effective molecular design strategy to modify the polymer aggregation and morphology for optimized polymer solar cell applications.
2018, (2): 284-294
doi: 10.11777/j.issn1000-3304.2018.17247
Abstract:
The development of deep-blue light-emitting materials is of vital importance in organic light emitting diodes (OLEDs). Deep blue emission can efficiently reduce the power consumption in full-color displays. In this study, aiming at developing solution-processable materials for low-cost OLEDs, a series of wide bandgap polymers using tetraphenylsilane as the main chain and phenanthro[9, 10-d] imidazole (PPI) as the side chain were designed and successfully synthesized via Suzuki coupling reactions. The silane group provides the polymers with wide bandgaps, and PPI unit entitles the polymers with high quantum efficiencies. All the polymers show good solubility in common organic solvents even without long alkyl chains. The emission spectra are all located in deep-blue region in THF peaking at 421 nm. P1 , P2 and P4 show high quantum efficiencies of 82.3%-99.6% in THF. P3 exhibits a relatively low efficiency of 34.0% due to the intramolecular interactions caused by the dibenzo[b, d]thiophene-5, 5-dioxide in the mainchain. And only a few red-shifts in emission spectra are observed in the solid state. They also possess high thermal stability, good morphological stability and appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. AFM characterization presents that the spin-coating film of the polymers display fairly homogenous and smooth surface morphology with the root mean square roughness of 0.57-0.71 nm. The non-doped solution-processed devices are fabricated with a configuration of ITO/PEDOT:PSS (40 nm)/EML (20 nm)/TPBi (30 nm)/LiF (1.2 nm)/Al (120 nm). Among them, the device using P1 as emissive layer shows the best performance with a relatively high external quantum efficiency of 0.65% and deep blue CIE coordinates of (0.163, 0.099). The maximum peak of EL emission was at 420 nm with narrow full width at half maximum (FWHM). All of these results gives us a new foreground for the design of deep-blue light-emitting polymers and inspire its application in the future.
The development of deep-blue light-emitting materials is of vital importance in organic light emitting diodes (OLEDs). Deep blue emission can efficiently reduce the power consumption in full-color displays. In this study, aiming at developing solution-processable materials for low-cost OLEDs, a series of wide bandgap polymers using tetraphenylsilane as the main chain and phenanthro[9, 10-d] imidazole (PPI) as the side chain were designed and successfully synthesized via Suzuki coupling reactions. The silane group provides the polymers with wide bandgaps, and PPI unit entitles the polymers with high quantum efficiencies. All the polymers show good solubility in common organic solvents even without long alkyl chains. The emission spectra are all located in deep-blue region in THF peaking at 421 nm. P1 , P2 and P4 show high quantum efficiencies of 82.3%-99.6% in THF. P3 exhibits a relatively low efficiency of 34.0% due to the intramolecular interactions caused by the dibenzo[b, d]thiophene-5, 5-dioxide in the mainchain. And only a few red-shifts in emission spectra are observed in the solid state. They also possess high thermal stability, good morphological stability and appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. AFM characterization presents that the spin-coating film of the polymers display fairly homogenous and smooth surface morphology with the root mean square roughness of 0.57-0.71 nm. The non-doped solution-processed devices are fabricated with a configuration of ITO/PEDOT:PSS (40 nm)/EML (20 nm)/TPBi (30 nm)/LiF (1.2 nm)/Al (120 nm). Among them, the device using P1 as emissive layer shows the best performance with a relatively high external quantum efficiency of 0.65% and deep blue CIE coordinates of (0.163, 0.099). The maximum peak of EL emission was at 420 nm with narrow full width at half maximum (FWHM). All of these results gives us a new foreground for the design of deep-blue light-emitting polymers and inspire its application in the future.
2018, (2): 295-303
doi: 10.11777/j.issn1000-3304.2018.17253
Abstract:
Diketopyrrolopyrrole (DPP) is attractive for building conjugated polymers for polymer solar cell (PSC) and organic field effect transistor (OFET). Yet the usual access to DPP conjugated polymers is via donor-acceptor (D-A) two-component polymerization. However, the number of excellent polymers based on the D-A combination is still limited, which promotes researchers to explore new strategy for preparation of novel conjugated polymers and to understand their structure-property relationship. In this work, a DPP-based polymer P1 was first obtained with co-polymerization of DPP (A) and alkoxyl benzene (D). Further, two novel polymers ( P2 and P3 ) were developed via introducing a third electron-deficient monomer X (difluoro-benzothiadiazole or naphthalene diimide) in the polymerization process. P1 - P3 polymers (molecular weight:3.83×104, 5.30×104 and 6.56×104) showed good solubility in common organic solvents. Due to the hybridization of the molecular orbitals between their three components (D, A and X), P2 and P3 showed narrower bandgaps (1.26 and 1.27 eV) than P1 , and their absorption thus red-shifted up to 1000 nm in comparison to that of D-A polymer P1 (bandgap of 1.50 eV). The introduction of electron-deficient monomers also deepened the highest occupied molecular orbital (HOMO) levels of P2 and P3 to -5.28 and -5.33 eV, which was beneficial to a larger open circuit voltage (VOC) in PSCs. Moreover, the introduction of the third monomer X altered the film properties of the polymers. It showed that P1 with preference of face-on orientation exhibited a good power conversion efficiency (PCE) in PSCs, while P2 demonstrated an improved hole mobility in OFET due to the preferable edge-on orientation. When blended with [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM), P1 showed a PCE of 2.56%, with a VOC of 0.68 V, a short circuit current density (JSC) of 5.71 mA cm-2 and a fill factor (FF) of 0.66, while P2 gave a lower PCE of 1.79%, with a VOC of 0.71 V, a JSC of 3.91 mA cm-2 and a FF of 0.65. This work provides references for the design of novel conjugated polymers for PSCs and OFETs.
Diketopyrrolopyrrole (DPP) is attractive for building conjugated polymers for polymer solar cell (PSC) and organic field effect transistor (OFET). Yet the usual access to DPP conjugated polymers is via donor-acceptor (D-A) two-component polymerization. However, the number of excellent polymers based on the D-A combination is still limited, which promotes researchers to explore new strategy for preparation of novel conjugated polymers and to understand their structure-property relationship. In this work, a DPP-based polymer P1 was first obtained with co-polymerization of DPP (A) and alkoxyl benzene (D). Further, two novel polymers ( P2 and P3 ) were developed via introducing a third electron-deficient monomer X (difluoro-benzothiadiazole or naphthalene diimide) in the polymerization process. P1 - P3 polymers (molecular weight:3.83×104, 5.30×104 and 6.56×104) showed good solubility in common organic solvents. Due to the hybridization of the molecular orbitals between their three components (D, A and X), P2 and P3 showed narrower bandgaps (1.26 and 1.27 eV) than P1 , and their absorption thus red-shifted up to 1000 nm in comparison to that of D-A polymer P1 (bandgap of 1.50 eV). The introduction of electron-deficient monomers also deepened the highest occupied molecular orbital (HOMO) levels of P2 and P3 to -5.28 and -5.33 eV, which was beneficial to a larger open circuit voltage (VOC) in PSCs. Moreover, the introduction of the third monomer X altered the film properties of the polymers. It showed that P1 with preference of face-on orientation exhibited a good power conversion efficiency (PCE) in PSCs, while P2 demonstrated an improved hole mobility in OFET due to the preferable edge-on orientation. When blended with [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM), P1 showed a PCE of 2.56%, with a VOC of 0.68 V, a short circuit current density (JSC) of 5.71 mA cm-2 and a fill factor (FF) of 0.66, while P2 gave a lower PCE of 1.79%, with a VOC of 0.71 V, a JSC of 3.91 mA cm-2 and a FF of 0.65. This work provides references for the design of novel conjugated polymers for PSCs and OFETs.
2018, (2): 304-314
doi: 10.11777/j.issn1000-3304.2018.17261
Abstract:
A set of novel ladder-type conjugated copolymers (2LF-An, 2LF-BT and 2LF-TBT) were designed, synthesized, and investigated as efficient gain media for organic lasers. The polymers were synthesized via Suzuki polymerization of indenefluorene units with varying blue, green, and red emitting units to afford RGB conjugated polymers with the emission wavelength ranging from 448 nm to 632 nm, covering the full visible spectrum. The thermal, morphological, photophysical, electrochemical, electroluminescent, and optical gain properties of the resulting conjugated polymers were systematically investigated and compared with those of the poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT) counterpart. With the ladder-type backbone structures incorporated, the resulting indenofluorene-based conjugated polymers exhibited enhanced optical and electrical properties with low ASE thresholds and high net gain coefficients. Organic light-emitting diodes (OLEDs) based on 2LF-An, 2LF-BT and 2LF-TBT were fabricated. The current efficiency of the 2LF-An, 2LF-BT and 2LF-TBT devices was 1.10, 3.11 and 0.50 cd/A, respectively, while the maximum brightness was 2772, 8582, 1682 cd/m2, respectively. Low amplified spontaneous emission (ASE) thresholds were achieved for 2LF-An (20.90 μJ/cm2) and 2LF-BT (65.84 μJ/cm2) with high gain coefficients of 62.40 cm-1 for 2LF-An and 66.07 cm-1 for 2LF-BT, respectively. By blending 1% 2LF-TBT into 2LF-BT, high optical gain coefficients of g=68 cm-1 were recorded for 2LF-TBT with the ASE peak at 600 nm and the ASE threshold of 68 cm-1. For comparison, the optical gain coefficient of F8BT was recorded at around 26.88 cm-1 under identical test conditions. The results suggested that the incorporation of ladder-type indenofluorene chain structures played a positive role on improving the optical gain properties. More impressively, the low ASE thresholds were almost unchanged for the samples even upon annealing up to 200 ℃ for the polymers, indicating excellent optical stability. The excellent optical stability, low ASE thresholds, and high net gain coefficients of the resulting polymers have promised their great potential to be used as efficient gain media for organic lasing.
A set of novel ladder-type conjugated copolymers (2LF-An, 2LF-BT and 2LF-TBT) were designed, synthesized, and investigated as efficient gain media for organic lasers. The polymers were synthesized via Suzuki polymerization of indenefluorene units with varying blue, green, and red emitting units to afford RGB conjugated polymers with the emission wavelength ranging from 448 nm to 632 nm, covering the full visible spectrum. The thermal, morphological, photophysical, electrochemical, electroluminescent, and optical gain properties of the resulting conjugated polymers were systematically investigated and compared with those of the poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT) counterpart. With the ladder-type backbone structures incorporated, the resulting indenofluorene-based conjugated polymers exhibited enhanced optical and electrical properties with low ASE thresholds and high net gain coefficients. Organic light-emitting diodes (OLEDs) based on 2LF-An, 2LF-BT and 2LF-TBT were fabricated. The current efficiency of the 2LF-An, 2LF-BT and 2LF-TBT devices was 1.10, 3.11 and 0.50 cd/A, respectively, while the maximum brightness was 2772, 8582, 1682 cd/m2, respectively. Low amplified spontaneous emission (ASE) thresholds were achieved for 2LF-An (20.90 μJ/cm2) and 2LF-BT (65.84 μJ/cm2) with high gain coefficients of 62.40 cm-1 for 2LF-An and 66.07 cm-1 for 2LF-BT, respectively. By blending 1% 2LF-TBT into 2LF-BT, high optical gain coefficients of g=68 cm-1 were recorded for 2LF-TBT with the ASE peak at 600 nm and the ASE threshold of 68 cm-1. For comparison, the optical gain coefficient of F8BT was recorded at around 26.88 cm-1 under identical test conditions. The results suggested that the incorporation of ladder-type indenofluorene chain structures played a positive role on improving the optical gain properties. More impressively, the low ASE thresholds were almost unchanged for the samples even upon annealing up to 200 ℃ for the polymers, indicating excellent optical stability. The excellent optical stability, low ASE thresholds, and high net gain coefficients of the resulting polymers have promised their great potential to be used as efficient gain media for organic lasing.
2018, (2): 315-320
doi: 10.11777/j.issn1000-3304.2018.17267
Abstract:
Despite the rapid progress that has been made in increasing the power conversion efficiency (PCE) of organic solar cells (OSCs) over the past decade, it is a challenge to realize efficient and environment-friendly OSCs. In this contribution, all polymer solar cells were fabricated with a blend of poly[4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1, 2-b:4, 5-b']dithiophene-co-3-fluorothieno[3, 4-b]thiophene-2-carboxylate] (PTB7-Th) donor and vinylene-bridged perylenediimide-based polymer (PDI-V) acceptor, in which non-halogenated tetrahydrofuran (THF) was used as the host solvent. A conventional device structure of ITO/poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/PTB7-Th:PDI-V/zirconium acetylacetonate (ZrAcac)/Al was employed, where PEDOT:PSS functioned as the hole transporting layer (HTL) and ZrAcac functioned as the electron transporting layer (ETL). The mixed solution of PTB7-Th and PDI-V was spin cast on the top of PEDOT:PSS layer to form the active layer. After that, ZrAcac solution was spin cast on the top of PTB7-Th:PDI-V layer. Different thermal annealing temperatures were used to optimize the active layer morphology. In details, OSCs without thermal annealing showed a PCE of 7.1%, with a short-circuit current (JSC) of 14.9 mA/cm2, an open-circuit voltage (VOC) of 0.74 V, and a fill factor (FF) of 64%. The devices annealed at 120℃ showed a high PCE of 8.1% with a JSC of 15.5 mA/cm2, a VOC of 0.74 V, and a FF of 70%. Further increasing the annealing temperature to 150℃ led to decreased FF and thereby a relatively lower PCE (7.4%). To the best of our knowledge, the PCE of~8.1% is one of the highest PCE values reported in the literature so far for all polymer solar cells. The high and balanced hole and electron mobility partially contributed to such a high performance. These results suggest that THF as good non-halogenated solvent can be used to fabricate high-performance all polymer solar cells. Higher efficiency can be achieved for OSCs with THF solvent when better polymer acceptors are employed.
Despite the rapid progress that has been made in increasing the power conversion efficiency (PCE) of organic solar cells (OSCs) over the past decade, it is a challenge to realize efficient and environment-friendly OSCs. In this contribution, all polymer solar cells were fabricated with a blend of poly[4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1, 2-b:4, 5-b']dithiophene-co-3-fluorothieno[3, 4-b]thiophene-2-carboxylate] (PTB7-Th) donor and vinylene-bridged perylenediimide-based polymer (PDI-V) acceptor, in which non-halogenated tetrahydrofuran (THF) was used as the host solvent. A conventional device structure of ITO/poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/PTB7-Th:PDI-V/zirconium acetylacetonate (ZrAcac)/Al was employed, where PEDOT:PSS functioned as the hole transporting layer (HTL) and ZrAcac functioned as the electron transporting layer (ETL). The mixed solution of PTB7-Th and PDI-V was spin cast on the top of PEDOT:PSS layer to form the active layer. After that, ZrAcac solution was spin cast on the top of PTB7-Th:PDI-V layer. Different thermal annealing temperatures were used to optimize the active layer morphology. In details, OSCs without thermal annealing showed a PCE of 7.1%, with a short-circuit current (JSC) of 14.9 mA/cm2, an open-circuit voltage (VOC) of 0.74 V, and a fill factor (FF) of 64%. The devices annealed at 120℃ showed a high PCE of 8.1% with a JSC of 15.5 mA/cm2, a VOC of 0.74 V, and a FF of 70%. Further increasing the annealing temperature to 150℃ led to decreased FF and thereby a relatively lower PCE (7.4%). To the best of our knowledge, the PCE of~8.1% is one of the highest PCE values reported in the literature so far for all polymer solar cells. The high and balanced hole and electron mobility partially contributed to such a high performance. These results suggest that THF as good non-halogenated solvent can be used to fabricate high-performance all polymer solar cells. Higher efficiency can be achieved for OSCs with THF solvent when better polymer acceptors are employed.
