Improving the Active Layer\nCrystallization Process\nby Promoting Acceptor Aggregation for High-Performance Near-Infrared\nOrganic Photodetectors

Near-infrared\norganic photodetectors (NIR-OPDs) have been extensively\nemployed in biomedicine, alcohol detection, and image sensing areas.\nThe crystallization state of the active layer of NIR-OPDs has a significant\nimpact on the performance of organic photodetectors in terms of detection.\nThe combination of a polymer donor and a nonfullerene small molecule\nacceptor as an active layer has recently emerged as a promising approach\nin the field of NIR-OPDs for its favorable balance of stability and\nmutual solubility. However, this combination has been observed to\nexhibit suboptimal exciton dissociation and collection, as well as\nserver trap-assisted complexation, due to its inherent challenges\nin crystallization. These limitations have been shown to impede the\nimprovement of the external quantum efficiency (EQE) of the device.\nFurthermore, this combination increases the trap state density, which\nis unfavorable for dark current density (<i>J</i><sub>D</sub>) reduction. To address these issues, the crystallization process\nof the acceptors was enhanced by promoting the aggregation of nonfullerene\nsmall molecule acceptors using the liquid crystal small molecule BTR-Cl\nas a third component. Finally, the <i>J</i><sub>D</sub> of\nthe device is effectively suppressed from 5.04 × 10<sup>–10</sup> to 2.05 × 10<sup>–10</sup> A/cm<sup>2</sup> at −0.2\nV. The EQE of the device is improved from 74.12% to 78.48% at 800\nnm. The specific detection rate (<i>D</i>*) of 5.50 ×\n10<sup>13</sup> Jones is achieved at −0.2 V and 800 nm. Furthermore,\nthe device is employed for the detection of heart rate and the real-time\nmonitoring of the pulse. This study presents an effective method for\nenhancing the performance of NIR-OPDs and elucidates the impact of\nthe active layer crystallization process on the performance of NIR-OPDs.\nThis is of significant guiding value for the enhancement of the NIR-OPDs’\nperformance.