Unveiling the Role of Fluorination in Suppressing Dark Current and Enhancing Photocurrent to Enable Thick-Film Near-Infrared Organic Photodetectors

Abstract

Thick active layers are crucial for scalable production of organic photodetectors (OPDs). However, most OPDs with active layers thicker than 200 nm typically exhibit decreased photocurrents and responsivities due to exciton diffusion and prolonged charge transport pathways. To address these limitations, we designed and synthesized PFBDT-8ttTPD, a fluorinated polymer donor. The strategic incorporation of fluorine effectively enhanced the charge carrier mobility, enabling more efficient charge transport, even in thicker films. OPDs combining PFBDT-8ttTPD with IT-4F or Y6 non-fullerene acceptors showed a substantially lower dark current density (Jd) for active layer thicknesses of 250-450 nm. Notably, Jd in the IT-4F-based devices declined from 8.74 x 10-9 to 4.08 x 10-10 A cm-2 under a reverse bias of -2 V, resulting in a maximum specific detectivity of 3.78 x 1013 Jones. Meanwhile, Y6 integration provided near-infrared sensitivity, with the devices achieving responsivity above 0.48 A W-1 at 850 nm and detectivity over 1013 Jones up to 900 nm, supporting broadband imaging. Importantly, high-quality thick films (>= 400 nm) free of pinholes or defects were fabricated, enabling scalable production without performance loss. This advancement ensures robust photodetection in thick uniform layers and marks a significant step toward the development of industrially viable OPDs.