Anomalous Current Decrease Under Illumination In Ambipolar Phototransistors Based On Ptcdi-C-5 Crystals Embedded In C-8-Btbt Thin Film

Most organic thin film-based phototransistors exhibit an increase in current under illumination owing to the trapped photogenerated minority charge carriers, which enhance the accumulation of majority carriers in the semiconductor layer of the device. Recent research reveals that, on employing a unique active layer structure, phototransistor devices exhibit abnormal photoresponse behaviors under certain conditions: hole-dominated current decreases under illumination and shows an anomalous dependence on irradiance. The current decreases with increasing irradiance. When the irradiance is increased further, a moderate current increase is observed. Under a constant negative bias, when a discrete light pulse is turned on, the current decreases sharply and then slowly increases to saturation in the beginning and it starts to increase when illumination is ceased. These anomalies are analyzed, and the changes in current are modeled using a mathematical model based on the simultaneous trapping and release of both photogenerated holes and electrons.