Few‐Layer Organic Crystalline van der Waals Heterojunctions for Ultrafast UV Phototransistors

Abstract

AbstractOrganic UV photodetectors using a transistor architecture can yield higher photoresponsivity than diode‐based devices because of the presence of a gate electrode. However, a long‐term issue of these phototransistor devices is the slow response speed, which hinders their practical applications. Here, organic UV phototransistors are constructed using few‐layer organic crystalline van der Waals (vdW) heterojunctions as the photoactive layers. The thickness of the photoactive layers is even less than the exciton diffusion length, thus removing the exciton‐diffusion bottleneck and giving rise to the confinement of charge separation and recombination within the adjacent molecular layers across the heterojunction interface. Hence, the phototransistor devices can exhibit a remarkably enhanced response speed (rise and decay times as short as only ≈4 and 6 ms, respectively). The layer‐dependent photoresponse characteristics are also observed, reinforcing the great importance of few‐layer organic heterostructures in phototransistor devices. This work not only provides a promising avenue toward fast response optoelectronic devices but also presents an in‐depth understanding on the microscopic nature of photogenerated charge carriers at the precision of molecular layers.