Ultra-narrowband perovskite single-crystal photodetector enabled by dynamic space charge region for portable concentration detection.

Narrowband photodetectors with wavelength-selective light response are essential for applications involving environmental monitoring and biomedical sensing. Although perovskites with excellent optoelectronic characteristics and tunable bandgaps have been demonstrated as promising candidates for the realization of narrowband detection, their practical performance still lags behind the combination of traditional photodetectors with optical filters. Here, we construct a dynamic space charge region model for achieving high-performance narrowband detection in perovskite single crystals. In this model, the space charge region formed by mobile ions suppresses the response to above-bandgap photons and amplifies the response to band-edge photons, as well as providing an adjustable narrowband wavelength. As a result, the photodetectors achieve a record narrowband performance with a full width at half maximum of 9.0 nanometers. We further develop a portable application of our narrowband photodetectors to rapidly and effectively detect water pollutant concentrations, showing an order of magnitude less in the limit of detection than commercial silicon photodetectors combined with complex optical filters.