Photo-response modulation of organic transistors for multi-level light sensing using active layer microstructure control

Abstract

Annealing processes are widely used to alter the morphology of organic films and optimize the electrical properties of organic field-effect transistors (OFETs). However, the impact of annealing processes on the photo-response characteristics of phototransistors is not widely studied. We analyze the photo-response modulation of OFETs functioning as multi-level light sensors using active layer microstructure control through annealing processes. We apply solvent vapor annealing with dichloromethane vapor or thermal annealing to an N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide film, a widely used photosensitive n-type active layer. The annealing processes lead to significant changes in the morphology of the film, altering the charge transport and trapping processes. These changes affect the charge carrier mobility and photo-response characteristics of the device. The difference in static and dynamic photo-response of the OFET devices with respect to the processing conditions is believed to be due to changes in the mechanism of charge transport and the trapping of photogenerated charge carriers in the active layers with altered morphologies. We analyze the active layer morphologies considering the processing conditions and explain their impact on device characteristics based on the charge transport and photo-response characteristics. We demonstrate that simple annealing processes enable the control of charge carrier mobility and photosensitivity of OFETs which highlights the importance of morphology control in the semiconductor film when fabricating multi-level light sensor.