English

In situ and Ex situ Investigation of the Organic-Organic Interface Effect

• Lianlian Ji ^{1, †,} ,
• Xianpeng Wang ^{4, †,} ,
• Yingying Zhang ^1, ,
• Xueli Shen ^1, ,
• Di Xue ^1, ,
• Lu Wang ^1, ,
• Zi Wang ^{2, ,} ,
• Wenchong Wang ^{3, ,} ,
• Lizhen Huang ^{1, ,} ,
• Lifeng Chi ^{1, 4, ,}

• 1.

  Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou 215123, Jiangsu Province, China

• 2.

  Gusu Laboratory of Materials, Suzhou 215123, Jiangsu Province, China

• 3.

  Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität Münster, Münster 48149, Germany

• 4.

  Macao Institute of Materials Science and Engineering (MIMSE), MUST-SUDA Joint Research Center for Advanced Functional Materials, Macau University of Science and Technology, Taipa 999078, Macao, China

• ^†These authors contributed equally to this work.

Corresponding author: Zi Wang, wangz2020@gusulab.ac.cn Wenchong Wang, wangw@uni-muenster.de Lizhen Huang, lzhuang@suda.edu.cn Lifeng Chi, chilf@suda.edu.cn

• Received Date: 03 April 2023
  Accepted Date: 09 May 2023
  Revised Date: 05 May 2023
  Available Online: 15 January 2024
• Fund Project:

Abstract: Organic-organic heterostructures have been widely applied in various organic electronic devices, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells. A thorough understanding of the interface effect in these heterostructures is of crucial importance for device design and optimization. However, owing to the diverse chemical properties and weak van der Waals interactions of organic semiconductors, interface charge transport is critically related to the organic-organic electronic structure and environmental atmosphere. Therefore, an in situ real-time investigation of the electrical properties in vacuum could efficiently avoid atmospheric influence and aid determination of the instinct interactions at the organic-organic interface. Herein, we report in situ real-time electrical property monitoring of the pentacene/vanadyl phthalocyanine (VOPc) heterostructure with top layer pentacene growth. The hole mobility of the heterostructure transistors decreases from 0.4 cm²∙V⁻¹∙s⁻¹ to approximately 0.2 cm²∙V⁻¹∙s⁻¹, while the electron mobility increases rapidly from 0.01 cm²∙V⁻¹∙s⁻¹ to approximately 0.9 cm²∙V⁻¹∙s⁻¹ as the pentacene thickness increases. This enhanced electron transport is attributed to the interface electron transfer from pentacene to VOPc, leading to filling of trap states in the VOPc layer and an improvement in the charge mobility and n-channel current. In contrast, the ex situ processing results indicate that atmospheric exposure will significantly suppress this charge transfer effect, resulting to a negligible improvement in the electron transport. The film morphology, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy characterizations suggest electron transfer occurs from pentacene to VOPc. Additionally, density functional theory (DFT) calculations confirm that the interaction between pentacene and VOPc is strong and the pentacene molecule tends to transfer electrons to VOPc with a calculated charge transfer value of approximately 0.15 e. Moreover, this interface charge transfer is significantly suppressed with the presence of either O₂ or H₂O, which is highly consistent with our experiment results. In this paper, we provide a clear understanding of the instinct organic-organic interface charge transfer effect by using in situ characterization, which will be helpful for further device performance optimization and analysis.

Key words:
• Organic-organic heterostructure
•  /  In situ characterization
•  /  Charge transfer effect
•  /  Organic field effect transistors
•  /  O₂/H₂O doping

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