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

Abstract

AbstractDeveloping 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.