Near‐Infrared Organic Phototransistors Based on Thermally Evaporated Planar Heterojunctions

Heterostructures are widely used in organic phototransistors (OPTs) to balance carrier dynamics, including exciton dissociation, transport, and recombination inhibition. Planar heterojunctions (PHJs) offer direct pathways and fewer recombination sites for photo‐induced carriers. However, PHJ‐based OPTs' performance remains unsatisfactory due to challenges in achieving high‐quality organic planar interfaces with uniformity, large area, low roughness, and low defect density. Herein, a PHJ structure is designed for near‐infrared (NIR) photodetection. The PHJ consists of a polymer semiconductor, PDPPBTT, and a fullerene derivative, PC 61 BM. The PDPPBTT acts as the NIR photoactive layer, electron donor, and channel, while PC 61 BM is the acceptor. A simple evaporation technique is developed to deposit the PC 61 BM film on PDPPBTT to form a stable and uniform planar interface. Owing to the balanced dynamic characteristics, highly sensitive NIR photodetection is achieved as demonstrated by peak photosensitivity of 2.59 × 10 4 , photoresponsivity of 1.42 × 10 5 A W −1 , detectivity of 1.83 × 10 16 Jones upon weak irradiation of 0.072 μW cm −2 . To confirm the practicality of NIR imaging, a 7 × 7 array device is demonstrated. The results reveal a simple and effective strategy to prepare high‐performance PHJ‐based OPTs and provide insights into the development of advanced photodetection and imaging systems.