Optimized Lead‐Free Double Perovskite‐Based Vertical Photodetector for Low‐Power Light Detection

Lead‐free double perovskites (DPs), such as Cs 2 AgBiI 6 , have garnered significant attention as sustainable alternatives to lead‐based perovskites for optoelectronic applications. However, challenges in defect management, interface engineering, and device optimization have limited their performance. Herein, a comprehensive design and optimization of a Cs 2 AgBiI 6 ‐based vertical photodetector using a combination of first‐principles density functional theory (DFT) and SCAPS‐1D simulations are presented. The DFT calculations reveal an indirect bandgap of 1.53 eV, ideal for visible‐light absorption and charge transport. Systematic optimization of the device architecture, including charge transport layers, thickness, doping concentrations, and defect densities, leads to an optimal structure of FTO/ReS 2 /Cs 2 AgBiI 6 /CdTe/Au. The optimized device achieves a responsivity of 0.552 A W −1 and a detectivity of 1.542 × 10 12 Jones at 700 nm illumination. Remarkably, the photodetector demonstrates excellent low‐power light detection capabilities, with responsivity and detectivity values of 0.72 A W −1 and 2.01 × 10 12 Jones, respectively, at an incident power of 0.03 W m −2 . These findings highlight the potential of Cs 2 AgBiI 6 ‐based DPs for sustainable, high‐performance photodetectors and provide a roadmap for their experimental realization and broader optoelectronic applications.