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Molecular Structure‐Dependent Charge Injection and Doping Efficiencies of Organic Semiconductors: Impact of Side Chain Substitution
Author(s) -
Yang Jinpeng,
Li Yanqing,
Duhm Steffen,
Tang Jianxin,
Kera Satoshi,
Ueno Nobuo
Publication year - 2014
Publication title -
advanced materials interfaces
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.671
H-Index - 65
ISSN - 2196-7350
DOI - 10.1002/admi.201300128
Subject(s) - materials science , side chain , doping , fluorene , organic semiconductor , alkyl , oled , density functional theory , computational chemistry , organic chemistry , chemistry , nanotechnology , optoelectronics , polymer , layer (electronics) , composite material
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 (F 4 ‐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.