Molecular packing of spin-cast conjugated polymer films and its effect on charge carrier mobility
Date Issued
2008
Date
2008
Author(s)
Chang, Chia-Rong
Abstract
The correlation between morphology and charge carrier transport for films spin-cast from MEH-PPV/chlorobenzene solution are investigated by means of UV-vis absorption spectrometer, photoluminescence spectrometer, transient electroluminescence, X-ray reflectivity and grazing incident wide angle X-ray scattering techniques. Film morphology is controlled by using various spin speeds as well as by thermal heat treatment. The result shows there is one thin layer of high electron density (due to the molecular packing) formed near the substrate for films prepared by using spin-cast method. This high electron density layer in spin-cast films is the key factor reducing the carrier mobility compared with drop cast films (reported in previous works). The thinner film (spun at higher spin speed) reveals a lower mobility due to the higher centrifugal force leading to higher molecular packing. With subsequent thermal annealing, the film morphology is changed from “nearly” amorphous to ordered lamellar structure. Each lamellar board is constructed by the stacked MEH-PPV backbones, thus carriers can move quickly within the board by hopping across the neighboring chains resulting in a higher mobility compared with the as spin-cast film.
Subjects
Transient Electroluminescence (TrEL)
Mobility
Spin-cast method
Morphology
Optical properties
X-ray reflectivity
X-ray scattering.
Type
thesis
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