NIR Photodetectors with Highly Efficient Detectivity Enabled by 2D Fluorinated Dithienopicenocarbazole-Based Ultra-Narrow Bandgap Acceptors

Developing non-fullerene acceptors (NFAs) with strong absorption and optical response in near-infrared region (NIR) is an imperative avenue for achieving efficient organic solar cells (OSCs) and NIR organic photodetectors (OPDs). Herein, four ultra-narrow bandgap NFAs with different alkyl side chains and 2D fluorinated or non-fluorinated phenyl substituents using dithienopyrrolecarbazole as electron-rich core are designed and synthesized for photoelectric devices. The effect of 2D central core fluorination on molecular self-assembly and optoelectronic properties is comprehensively explored. Due to the banana-type molecular conformation of these NFAs, they can easily form honeycomb-like 3D network stacking, and the central core fluorination is confirmed that can reduce π-π stacking distance and enhance intermolecular interaction, which result in smaller molecular stacking density. As a result, the 2D fluorinated acceptors based OSCs display more balanced and higher carrier mobilities, contributing to higher fill factor and efficiency. Moreover, the NIR OPD devices based on PTB7-Th:FDTPC-OD exhibit a superior responsivity of >0.4 A W⁻¹ at 880 nm, a low dark current of ≈8 × 10^–11 A, and an excellent specific detectivity (D*) of >2.5 × 10¹¹ Jones. The NIR OPD also demonstrates excellent performance in photo-plethysmography and shows great potential for application in monitoring heart rate.