Low-Noise Near-Infrared Photomultiplication Organic Photodetectors Enabled by Donor-Sidechain Steric Engineering

Abstract Achieving low dark current remains a major challenge for photomultiplication-type organic photodetectors (PM-OPDs). In this work, we show that steric engineering of donor side chains, through incorporation of bulky fluorinated alkoxyphenyl sidechains into a BDT-based polymer donor, is an effective approach to reduce dark current while enhancing photomultiplication. The polymer PDJ15 exhibits a more twisted backbone, reduced donor–acceptor packing and a higher hole reorganization energy (0.24 eV) relative to PM6, collectively impeding hole transport and assisting in trap-assisted charge injection. A specific detectivity of 4.6 × 1012 Jones at 800 nm was achieved for a PDJ15:BTP-eC9 PM-OPD under 1.0 V, outperforming the PM6:BTP-eC9-based control device (2.7 × 1011 Jones) operated under the same condition. The results reveal that donor-sidechain engineering is an effective molecular design strategy for high-gain and low-noise near-infrared PM-OPDs.