Self-Powered Photodetection and Optical Information Recognition in a Mixed-Dimensional WSe₂/CdSe Heterojunction

Mixed-dimensional van der Waals heterojunctions offer opportunities for self-powered optical sensing and information processing, yet identifying the spatial origin of zero-bias photoresponse remains important for understanding device operation. Here, a vertical WSe₂/CdSe heterojunction composed of a WSe₂ nanosheet and a CdSe nanobelt is investigated for visible photodetection. Under 610 nm illumination, the device exhibits a photovoltaic response with an open-circuit voltage of 0.403 V and a short-circuit current of 4.77 × 10^-10 A. Quantitative photocurrent mapping reveals a mean response of 5.94 nA in the heterojunction overlap region, approximately 50 times that near the metal contacts. Scanning Kelvin probe microscopy yields a reproducible contact-potential-difference contrast of 293 ± 15 mV, whereas electronic-structure calculations support a type-II band-edge configuration and interfacial charge redistribution. At 100 Hz, the measured rise/fall times are 1.09/0.99 ms at 0 V and 165/191 μs at +3 V. Under +3 V bias, approximately 97% of the reference modulation amplitude is retained at 1 kHz. Self-powered optical imaging and wavelength- and time-window-dependent 8-bit information recognition are further demonstrated, with all 96 tested bits correctly decoded. These results highlight the potential of mixed-dimensional WSe₂/CdSe heterojunctions for self-powered visible-light sensing and optical information recognition.