Weak‑Light Self‑Powered UV–Blue Photodetection via Cs₂AgBiBr₆/SnS₂ Heterojunction

Lead-free double perovskite Cs₂AgBiBr₆ has emerged as a promising candidate for environmentally friendly optoelectronic devices. However, its application in self-powered photodetectors, especially under weak light conditions, remains challenging. In this work, we propose and numerically investigate a heterojunction structure consisting of ITO/SnS₂/Cs₂AgBiBr₆/Ni for weak-light UV–blue photodetection. The device operates at zero bias and shows improved performance compared to conventional SnO₂-based and Au-based structures. Compared to the reference, the SnS₂ ETL significantly enhances the photoresponse in the near-UV region (300–340 nm), improving responsivity by up to 77% at 300 nm. The proposed structure exhibits an external quantum efficiency (EQE) of 41.4% at 350 nm and 47.1% at 440 nm under 100 mW/cm² illumination, corresponding to responsivities of 0.117 A/W and 0.167 A/W, respectively. The specific detectivity (D*) reaches 1.90 × 10⁹ Jones at 350 nm for the reference devices, while the SnS₂/Ni device achieves 2.39 × 10¹⁰ Jones, a 15‑fold improvement. The device maintains stable performance down to 0.001 mW/cm², with a limit of detection (LOD) of 2.88 × 10⁻⁶ mW/cm². The superior performance makes it suitable for biomedical imaging, secure optical communications, and UV early warning systems. These results indicate that the Cs₂AgBiBr₆/SnS₂/Ni heterojunction is a highly efficient and stable self-powered photodetector for the UV–blue spectral range, particularly suitable for low-light environments.