The mechanism of photogenerated minority carrier movement in organic phototransistors

Abstract

The acceptor phase, which affects the free carrier transport by trapping the photogenerated minority carrier in the active layer, plays an important role in organic phototransistors (OPTs) based on a bulk heterojunction (BHJ). In this work, the FBT-Th₄(1,4):PC₆₁BM blend film with high mobility is selected as the active layer to construct the OPT. A model of the action of minority carrier movement on hole transmission is established by using the change rule of device performance under different donor/acceptor ratios. This model is tested and validated using PTB7:PC₆₁BM-based OPT with low mobility. The results show that a continuous transmission channel of photogenerated minority carrier tends to form in the OPT under high concentration doping, which increases the probability that a minority carrier would recombine with the holes, leading to poor device performance. These results can provide practical guidance for the preparation of high-performance OPT devices. The optimized FBT-Th₄(1,4) : PC₆₁BM device with a low D/A ratio (∼10 : 1) obtained shows ultrahigh photoelectric detection performance (gain = 4.7 × 10⁵, D* = 1.4 × 10¹⁶ Jones).