Band Engineering via Back Surface Field Layer for High‐Performance Self‐Powered CZTSSe Thin‐Film Near‐Infrared Photodetectors

ABSTRACT

To meet the application requirements of high sensitivity, low dark current, and self‐powered near‐infrared photodetection, a Cu ₂ ZnSn(S,Se) ₄ (CZTSSe) thin‐film photodetector is designed and optimized in this work via SCAPS‐1D numerical simulation. This study investigates the effects of key parameters of the absorber layer, window layer, and back surface field (BSF) layer on the quantum efficiency, dark current, responsivity, and detectivity of the device. It also clarifies the performance enhancement mechanism from the perspectives of band structure engineering and dark current suppression. The introduction of the BSF layer creates a favorable back surface field at the rear interface of the device, which effectively suppresses the transport of minority carriers to the back electrode, reduces interface recombination and dark current, and thus significantly improves the device performance. Among the investigated BSF materials, Cu ₂ O exhibits the optimal performance enhancement effect owing to its well‐matched band alignment with CZTSSe. After further optimization of the layer thickness, doping concentration, and defect density, the photodetector achieves a high responsivity (0.79 A/W) and detectivity (9.32 × 10 ¹² Jones) at a wavelength of 1020 nm, while maintaining a low dark current. The results demonstrate that the optimized device holds promising application potential in near‐infrared photodetection.