Cross-Linked Interfacial Layer for Enhanced Performance in n-Channel Organic Thin Film Transistors

Abstract

Interfacial engineering has proven to be important in regulating the performance of optoelectronics. However, immobilized interlayer molecules may diffuse between adjacent layers in devices and induce an inferior electrical performance. In this study, the polyethylenimine ethoxylated (PEIE) modification layer at the source−drain contacts/semiconductor interface was cross-linked with siloxane cross-linking agents (SCAs) to enhance the performance of organic thin film transistors (OTFTs) based on diketopyrrolopyrroletype conjugated polymer (P4FTVT-C32). Our results demonstrate that the improvement of device performance is closely related to the electron-donating ability and the surface energy-modifying capabilities of the functional group on SCAs. Tertiary amino group-containing (N,N-dimethylaminopropyl)trimethoxysilane (NTMS) is in favor of stronger electron-donating ability for higher carrier density and further reduced work function of Au contacts and moderate surface potential for large semiconductor crystalline domains. As a result, OTFTs modified by NTMS-cross-linked PEIE exhibited increased electron mobility to over 7 cm 2 V −1 s −1 from ∼3 cm 2 V −1 s −1 , together with increased on/off ratio by ∼1 order of magnitude as compared to that modified by un-cross-linked PEIE. On the other hand, cross-linking of PEIE interlayer with alkyl-substituted SCA trimethoxy(octyl)silane (TOTS) led to the largest surface tension for largest crystalline domain size, highest alignment degree, and compact stacking of P4FTVT-C32 and thus increased the electron mobility over 5 cm 2 V −1 s −1 . The PEIE interlayer cross-linking strategy was also verified in isoindigo-and naphthalenediimide-based n-channel OTFTs in terms of enhanced electron mobility and on/off ratio. This work highlighted the potential of interlayer cross-linking strategy using functional crosslinkers in enhancing the performance of organic electronics.