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Molecular Structure-Dependent Charge Injection and Doping Efficiencies of Organic Semiconductors: Impact of Side Chain Substitution

Authors

  • Jinpeng Yang,

    1. Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based, Functional Materials & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, People's Republic of China
    2. Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan
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  • Yanqing Li,

    1. Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based, Functional Materials & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, People's Republic of China
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  • Steffen Duhm,

    Corresponding author
    1. Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based, Functional Materials & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, People's Republic of China
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  • Jianxin Tang,

    Corresponding author
    1. Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based, Functional Materials & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, People's Republic of China
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  • Satoshi Kera,

    1. Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan
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  • Nobuo Ueno

    1. Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan
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Abstract

Due to the highly anisotropic nature of π -conjugated molecules, the molecular structure of organic semiconductors can significantly affect the device performance of organic optoelectronics. Here, the molecular structure dependence on charge injection and doping efficiencies is investigated by characterizing the typical hole transport material of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) and its derivatives N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-9,9-dimethyl-fluorene (DMFL-NPB) and N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-9,9-diphenyl-fluorene (DPFL-NPB)]. Using photoelectron spectroscopy data and density functional theory calculation, it is identified that the side chain substitution in NPB and its derivatives plays a crucial role in the intrinsic injection and transport properties, and doping efficiency. The inner twist of the two main benzene rings in NPB is changed from out-of-plane to in-plane due to the alkyl or phenyl side chains of DMFL-NPB or DPFL-NPB, which reduces the ionization energies and thus decreases the hole injection barriers at the indium tin oxide/organic interface. The doping efficiency in 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped systems is also highly dependent on the degree of intermolecular orbital energy hybridization with respect to the side chain substitution. These findings show that the rational design of molecular structures with suitable side chains is crucial for achieving high-performance organic devices.

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