Chiral Polyacetylene with Thermally Activated Delayed Fluorescence Feature for High-Performance Circularly Polarized Light Detection

Organic semiconductors with chemically tailored photoelectric properties and deliberately engineered chiral-optical activity, along with their cost-effectiveness and superior processing efficiency, exhibit considerable potential as promising candidates for circularly polarized light (CPL) detection. Nevertheless, traditional organic materials for constructing high-performance CPL photodetectors remain challenging due to the constrained triplet exciton utilization, resulting in a moderate responsivity. Herein, a self-powered CPL photodetector is fabricated by using a series of chiral polyacetylenes (PAs) with thermally activated delayed fluorescence (TADF) characteristics, including (R)-PADB3Cz7, (R)-PADB1Cz9, and (R)-PADB0.5Cz9.5. The TADF polymers with tiny energy gap between singlet and triplet (<13 meV) can boost up-conversion from triplet to singlet states, which is favorable for an efficient recycled ISC and RISC processes between singlet and triplet excitons. By effectively harvesting both the singlet and triplet excitons, they present a novel spin photovoltaic effect where efficient exciton separation enables CPL detection without an external bias. The detectors possess an outstanding CPL detection responsivity of 0.18 A W−1 with a relatively high dissymmetry factor (gph) of 0.08. The high gph value originates from the helical conformations of the PA backbones induced by the chiral side chains. Meanwhile, the hydrogen bonds between amide groups allow for a high degree of stereoregularity for PA backbones, which is advantageous in promoting carrier transport. Additionally, the photodetector demonstrates excellent reproducibility and long-term stability, rendering it a prospective candidate for sensitive and robust CPL detectors.