Yuanhong Gao1 Ya Yi1 Jia Li1 Xue-Feng Yu1

1, Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, , China

Recently, extensive research efforts have been focused on improving the photosensitivity of organic phototransistors (OPTs) by taking advantages of charge trapping and charge transfer effect (CTE). In particular, by integrating electron acceptor materials (i.e., polar polymers such as PMMA and PLA, or specific dispersed nanoparticles such as ZnO QDs, C60, PC61BM) into the organic semiconductors, the exciton dissociation efficiency can be enhanced due to the introduction of electron-withdrawing groups in polymers or the enough energy offset between organic semiconductors and dispersed nanoparticles. Despite the great advances, there are still several critical challenges remained. First of all, in the layered heterojunction devices, photoinduced electrons need to travel through a certain thickness of the organic layers, which leads to the electron trapping in the acceptor materials, and thus the higher electron-hole recombination probability. Secondly, in the blended heterojunction devices, the added electron acceptor materials may also serve as defects and increase the channel resistance, which is unfavorable for the carrier transporting in the channel. To overcome these challenges, we propose a novel hybrid-layered phototransistor architecture, which is composed of an organic bulk heterojunction acting as the photoactive layers and thin organic semiconductor films serving as the efficient carrier transporting channel. This architecture allows us to simultaneously take advantages of CTE and fast carrier transporting in pure organic semiconductors. The photogenerated electrons can be effectively trapped by their surrounding nanoparticles and at the same time holes can freely inject to the channel, which results in both the efficient carrier separation and charge transporting in the device. As a result, the significantly enhanced device performance can be expected. In this work, we have fabricated hybrid-layered OPTs consisting of C8-BTBT as the channel layers and C8-BTBT/PC61BM bulk heterojunction upon the channel region as the photoactive layers. Upon illumination with 365 nm UV light, the significant enhancement of photodetection performance has been obtained from the hybrid-layered OPTs. In contrast with the devices solely with C8-BTBT/PC61BM films as the channel layer (i.e., hybrid OPTs), the hybrid-layered OPTs have demonstrated the maximum 3-fold enhancement of photoresponsivity. In addition, the channel resistance of the hybrid OPTs was almost 2 times higher than that for the hybrid-layered OPTs, which explained the limited photodetection performance of the hybrid OPTs. This mechanism significantly improves the photoresponsivity, detectivity and response speed, opening up opportunities to realize high-performance OPTs and other organic optoelectronis.