Thermally Activated Delayed Fluorescence Triplet State Excitons for High‐Performance Organic Photodetectors: A Novel Strategy

Abstract

AbstractPhotoinduced charge‐trapping is a promising strategy for boosting the photosensitivity of organic photodetectors at the expense of their response time. In addition, they have a low carrier extraction yield due to the formation of low‐energy triplet excitons through the recombination of a photogenerated hole–electron pair. Materials with thermally activated delayed fluorescence (TADF) exhibit a long‐lived (≈µs) excited spin‐triplet nearly iso‐energetically aligned with that of an excited spin‐singlet, which results in suppressed exciton losses and is widely used in organic light‐emitting diodes. The extraction and population of triplet state excitons in TADFs is a sought‐after but underexplored aspect of photoinduced gating in photodetectors. A 1,2,3,5‐tetrakis(carbazol‐9‐yl)4,6‐Dicyanobenzene (4CzIPN) TADF blend with a high‐mobility Poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT‐C14) polymer via bulk type‐II offset can increase free carrier extraction yield (fast response) and retain trapped electrons in TADF triplet states (high gain). The PBTTT‐C14/4CzIPN ultraviolet photodetector device maintains a trade‐off between high photogain (≈103) and fast response time (79 ms) at 300 nm while operating at a shallow dark current (≈pA). Furthermore, the device shows high external quantum efficiency (≈104 %) and detectivity (≈1011 Jones) for low light power (<pW). The innovative application of TADF material can lead to exciting new developments in organic‐based high‐performance photodetection.