Wavelength‐Selective Near‐Infrared Organic Upconversion Detectors for Miniaturized Light Detection and Visualization

Upconversion detectors monolithically combining a detection unit and a light emitting unit, enables light detection and visualization in a compact structure, promising great advances in miniaturized multifunctional optoelectronics. The detection range of upconversion detectors usually covers a broadband spectrum, limiting their use in spectroscopic fields. This work investigates two wavelength‐selective upconversion detectors made with organic semiconductors to realize narrowband near‐infrared (NIR) light detection and visualization dual function. Two non‐fullerene‐based NIR‐sensitive bulk‐heterojunctions (BHJs) are exploited to make wavelength‐selective upconversion detectors, achieving peak sensitivity at 860 and 890 nm, with full width at half maximum of 125 and 170 nm, respectively. Each NIR‐sensitive BHJ comprises a donor polymer and a non‐fullerene acceptor, both of which are selectively sensitive to NIR light. The cumulative analysis of the optical properties of the absorber and current–voltage characteristics of the device indicates that the wavelength selectivity stems mainly from the wavelength‐dependent absorption. In particular, the upconversion detectors exhibit wavelength‐selective electronic and optical dual‐readouts, which are appealing for miniaturized spectroscopic applications, including health monitoring, optical communication, and microbead imaging, paving the way for practical applications.