Enhanced Stability and Efficiency of Quasi‐2D Perovskite Self‐Powered Photodetectors Enabled by Sulfur‐Doped Inorganic Hole Transport Layer

Self-powered photodetectors (SPPDs) offer significant advantages for next-generation optoelectronic applications, attributed to their bias-free operation character. Copper-based hole transport layers (HTL) are a promising inorganic candidate due to high stability and low cost compared to their organic counterparts. However, issues involving low visible-range transmittance and fine-tuning energy band levels restrict compatibility with diverse active layers such as emerging quasi-2D perovskite (Q2D PVK). To address these challenges, sulfur-doped CuI (S-CuI) is introduced as a promising inorganic HTL for PVK SPPDs. Through a vapor-phase synthesis approach, uniform S-CuI films with tunable energy band levels and optoelectronic properties are achieved. Systematic sulfur doping enhances hole mobility, reduces interfacial defects, and improves energy band alignment with Q2D PVKs, leading to efficient charge extraction and suppressed nonradiative recombination. The optimized S-CuI-based SPPD demonstrates a peak responsivity of 0.357 A W^-1, a detectivity of 4.7 × 10¹² Jones, and fast response times of t_r = 4.34 µs and t_f = 1.87 µs. Notably, the device retains 93.4% of its initial photocurrent after 3 h of continuous operation in ambient air, outperforming its counterparts. This work highlights the potential of S-CuI as a stable, high-performance HTL for PVK SPPDs, paving the way for durable, energy-efficient optoelectronic devices.