Solution‐Processed Resonant Microcavity‐Enhanced Organic Photodetectors with Extended Shortwave Infrared Response beyond 1800 nm

Shortwave infrared (SWIR) plays a pivotal role in shaping the next generation of optical sensing technologies, driving innovation in emerging materials and device architectures. Among the promising candidates, organic photodetectors (OPDs) have garnered considerable attention. However, their development is often hindered by the limited long‐wavelength responsiveness and constrained external quantum efficiency (EQE) of organic semiconductors. In this study, an ultranarrow bandgap polymer specifically designed for efficient SWIR absorption is presented. When paired with a nonfullerene acceptor (NFA) to form a bulk‐heterojunction (BHJ) blend, and integrated into a resonant microcavity device utilizing a transparent electrode with high SWIR reflectivity, the resulting OPD successfully extended its spectral response beyond 1800 nm while maintaining an exceptional EQE. As the active layer thickness (i.e., cavity length) increases, the device achieved EQEs of 12.6%, 4.2%, and 2.1% at 1620, 1750, and 1800 nm, respectively. To the best of knowledge, these represent the highest performance to date for OPD in the SWIR range beyond 1600 nm. Furthermore, the entire device can be fabricated using cost‐effective, solution‐processable, and scalable techniques. This breakthrough marks a significant milestone for OPD technology and opens an exciting new chapter in the advancement of organic electronic technologies is believed.