Improved charge carrier mobility in copper phthalocyanine based field effect transistors by insertion of a thin poorly conducting layer as gate insulator extension

The charge carrier mobility is an important parameter that directly affects the performance of organic field-effect transistors. We use copper phthalocyanine (CuPc)-based transistors having crosslinked poly(vinyl alcohol) (cr-PVA) as gate insulator to study the variation of the mobility in CuPc with the distance from the gate insulator interface. By measuring the mobility of the charge carriers flowing along the channel as a function of the minimum thickness of the effective channel near to the transistor source, we demonstrate that the mobility is low near to the interface and shows a maximum at approximately 5 nm from the interface. The mobility dependence on distance from interface can be modified through the inclusion of a poorly conducting thin PEDOT:PSS layer between gate insulator and channel semiconductor, which effectively acts as a gate insulator extension. This procedure is a simple but efficient strategy to improve organic field-effect transistor performance, positively affecting the transconductance and the mobility, which in the studied devices is increased by a factor 20. The improvement is attributed to the suppression of the deleterious consequences of interface charge traps on transport along the channel and is, in principle, a general approach applicable to other organic field-effect transistor materials combinations. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim