Ultra-Thin Lead Sulfide Capping for Stabilizing Tin Halide Perovskite Solar Cells

Addressing the inherent instability of tin-based perovskite solar cells (PSCs), a facile approach is introduced to simultaneously enhance their stability and performance. This study demonstrates the implementation of an ultra-thin (≈3 nm) dual-functional lead sulfide (PbS) capping layer, formed via a sequential deposition. This PbS layer serves a critical dual role: first, as a robust protective barrier against oxidation and moisture, effectively mitigating the degradation of the underlying tin-based perovskite; and second, by improving interfacial electronic properties to facilitate efficient charge extraction. Specifically, the PbS layer not only provides conformal coverage and minimizes non-radiative recombination but also acts as an n-type interfacial layer, promoting electron transport. This synergistic effect results in a significant boost in power conversion efficiency (PCE) from 12.0% to 14.4% with an open-circuit voltage of 0.845 V, and exceptional long-term stability with negligible PCE decay after 1600 h in a nitrogen environment. Operando grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements corroborate enhanced structural stability under operating conditions. These findings establish the PbS capping layer as a practical, facile, and highly effective strategy for advancing stable and high-performance tin-based PSCs, paving the way for their viable application in sustainable photovoltaics.