Photocurrent Response in Ambipolar Transistors Based on Single Laterally Stacked Crystals: The Role of Charge Trapping and Release

Abstract

Organic semiconductors are currently implemented in photoresponsive devices due to their versatility. The aim of this study was to investigate the photoresponsive properties of an ambipolar field-effect transistor with only one laterally stacked C8-BTBT/PTCDI-C5 semiconductor crystal wire prepared using solution processing and mechanical cutting. The photoresponsive characteristics of the device were investigated under different irradiance levels, and the photogating effect was found to be the major contributor to the photocurrent. From the dynamic response of the device under light pulses, it was found that the trapping and release processes are dependent on the irradiance. A mathematical description of the dynamic response was proposed based on the trapping and release of photogenerated holes at deep and shallow trap sites with two discrete energy levels. Although the trapped charge density and trapping rates in the shallow traps exhibited expected trends under different irradiances, the charges in the deep traps exhibited anomalous irradiance dependence. On the basis of the findings, a description for the trapping behavior in the laterally stacked C8-BTBT/PTCDI-C5 system was proposed, and the usefulness of the simple kinetic model of trapping and release was analyzed.