Improving the Active Layer Crystallization Process by Promoting Acceptor Aggregation for High-Performance Near-Infrared Organic Photodetectors

Abstract

Near-infrared organic photodetectors (NIR-OPDs) have been extensively employed in biomedicine, alcohol detection, and image sensing areas. The crystallization state of the active layer of NIR-OPDs has a significant impact on the performance of organic photodetectors in terms of detection. The combination of a polymer donor and a nonfullerene small molecule acceptor as an active layer has recently emerged as a promising approach in the field of NIR-OPDs for its favorable balance of stability and mutual solubility. However, this combination has been observed to exhibit suboptimal exciton dissociation and collection, as well as server trap-assisted complexation, due to its inherent challenges in crystallization. These limitations have been shown to impede the improvement of the external quantum efficiency (EQE) of the device. Furthermore, this combination increases the trap state density, which is unfavorable for dark current density (J D ) reduction. To address these issues, the crystallization process of the acceptors was enhanced by promoting the aggregation of nonfullerene small molecule acceptors using the liquid crystal small molecule BTR-Cl as a third component. Finally, the J D of the device is effectively suppressed from 5.04 × 10 −10 to 2.05 × 10 −10 A/cm 2 at −0.2 V. The EQE of the device is improved from 74.12% to 78.48% at 800 nm. The specific detection rate (D*) of 5.50 × 10 13 Jones is achieved at −0.2 V and 800 nm. Furthermore, the device is employed for the detection of heart rate and the real-time monitoring of the pulse. This study presents an effective method for enhancing the performance of NIR-OPDs and elucidates the impact of the active layer crystallization process on the performance of NIR-OPDs. This is of significant guiding value for the enhancement of the NIR-OPDs' performance.