Carbazole–pyrene back surface field–induced performance enhancement in CZTSSe-Based photodetectors

In this study, a high-performance CZTSSe-based photodetector incorporating a carbazole–pyrene (Cz-Pyr) back surface field (BSF) layer is numerically investigated using SCAPS-1D simulation. The proposed ZnO:Al/Zn(O,S)/CZTSSe/Cz-Pyr device architecture aims to enhance charge collection and suppress recombination losses while maintaining broadband spectral sensitivity. The introduction of the BSF layer leads to a notable improvement in device performance, yielding an open-circuit voltage of approximately 1.15 V and a short-circuit current density of about 32 mA cm −2 under illumination. The quantum efficiency reaches nearly 100% across the 450–900 nm wavelength range, confirming efficient photon absorption and carrier collection. With optimized absorber thickness (∼1100 nm), the photodetector achieves a maximum responsivity of ∼ 0.7 A W −1 and a detectivity on the order of 10 14 Jones. Parametric analysis reveals that higher BSF doping concentrations (10 17 –10 19 cm −3 ) enhance internal electric field without degrading the spectral response, while low defect densities (≤10 12 cm −3 ) are essential to minimizing recombination and noise. Additionally, low series resistance and high shunt resistance are found to be critical for preserving fill factor and current output. Temperature-dependent analysis shows a slight increase in J SC with temperature (300–400 K) accompanied by a marginal reduction in V OC , whereas C–V characteristics confirm good junction quality and electrical stability. These results demonstrate that BSF-engineered CZTSSe photodetectors offer a promising route toward efficient, low-cost, and environmentally benign optoelectronic devices.