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Impact of Structure and Morphology on Charge Transport in Semiconducting Oligomeric Thin‐Film Devices
Author(s) -
Melzer Christian,
Brinkmann Martin,
Krasnikov Victor V.,
Hadziioannou Georges
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500142
Subject(s) - morphology (biology) , materials science , thin film , charge (physics) , nanotechnology , optoelectronics , chemical physics , chemistry , physics , genetics , quantum mechanics , biology
We investigated various thin‐film morphologies of vacuum‐deposited highly luminescent 2,5‐di‐ n ‐octyloxy‐1,4‐bis[4′‐(styryl)styryl]benzene (Ooct‐OPV5) in a typical light‐emitting‐diode device structure. Important modifications in the thin‐film morphology and structure were obtained by changing the substrate temperature in the range 23–90 °C. Structural analysis by X‐ray and electron diffraction provided clear evidence for polymorphism in evaporated thin films of Ooct‐OPV5. Concomitantly, the hole mobility in the corresponding devices was determined by transient electroluminescence measurements. We demonstrate that the substrate temperature T sub is a key parameter that controls the hole mobility of the devices. Increasing T sub between 23 and 84 °C results in a progressive increase of the zero‐field hole mobility from 10 −6 to 10 −4 cm 2 V −1 s −1 . The increase in hole mobility is correlated to the average grain size in the thin films. In addition, we give evidence for the existence of a peculiar growth mode in the bulk crystal structure of Ooct‐OPV5, whereby the ( a,b ) and ( b,c ) planes can grow in a homoepitaxial manner.