Linearly tunable bipolar photoresponse in parallel-architecture all-inorganic CsPbBr3/Si photodetectors for encrypted imaging

Bipolar photodetectors have attracted considerable attention in secure communication and encrypted imaging systems owing to their strong dual-band selectivity and intrinsic bipolar coding capabilities. However, achieving well-balanced responses for both the dual optical inputs and their bipolar electrical outputs remains challenging, primarily due to the absence of effective strategies for linearly modulating photoelectric conversion performance. Here, we report a bipolar photodetector based on a Pt/CsPbBr3 microcrystalline thin film/Si heterostructure fabricated via chemical vapor deposition. Through interface characterization, band structure analysis, and comparative device structure experiments, we elucidate the unique parallel configuration comprising CsPbBr3/Si and Pt/Si junctions, along with the underlying mechanism enabling bipolar photoresponse. Leveraging this parallel architecture, we achieve linear control over the photoelectric output by tuning the Pt electrode area. Furthermore, under power-matched dual-band illumination at 520 and 785 nm wavelengths, the device enables effective encryption and decryption of dual-band images, validating its potential for secure imaging applications. This work provides a promising pathway for developing bipolar photodetectors with well-balanced optical-to-electrical conversion, advancing their practical implementation in encrypted imaging systems.