Crystallinity Effects on Near‐Infrared Photoresponse in Y6‐Based Organic Phototransistors

ABSTRACT Organic phototransistors (OPTs) are appealing devices for the fabrication of low‐cost, tuneable and highly sensitive light detectors. This study investigates the potential of single‐component OPTs based on the non‐fullerene acceptor Y6 to detect near‐infrared (NIR) light. Y6 films are deposited via blade coating and subjected to thermal annealing between 200°C and 250°C. Morphological and structural characterization reveals a transition from amorphous to a polycrystalline phase above 200°C. Electrical measurements demonstrate enhanced electron mobility and reduced hysteresis in annealed devices. Under 840 nm illumination, amorphous films exhibit photoconductive behavior, while polycrystalline films show photogating/photogain effects, resulting in a significantly higher photoresponsivity and faster transient response times. The highest photoresponsivity of 127 A·W −1 and shot‐noise‐limited specific detectivity of 6·10 12 Jones (6·10 10 Jones under full noise analysis) are achieved in polycrystalline devices under low NIR light intensity (0.32 µW·cm −2 ) at V DS = V GS = 10 V, associated with enhanced charge carrier mobility rather than enhanced free charge generation. The devices also exhibit high cycling stability under continuous measurements and long‐term shelf‐stability when encapsulated. These findings establish thermally annealed Y6 films as a viable single‐component material for efficient NIR photodetection.