Cesium Iodide Incorporation Enables High-Efficiency and Thermally Stable Inverted Perovskite Solar Cells with Low-Temperature NiO_<i>x</i>

Achieving efficient, stable, and flexible perovskite solar cells (PSCs) requires low-temperature processing and precise interfacial control at the nanoscale. Here, we develop a cesium iodide (CsI) incorporation strategy for nickel oxide (NiOx) hole transport layers processed at 100 °C to improve the performance of inverted PSCs. CsI incorporation improves the conductivity and energy level alignment of NiOx while enabling partial CsI diffusion into the perovskite layer. This interfacial modification leads to enhanced crystallinity, enlarged grain size, and reduced trap density in the perovskite film. The optimized device exhibits a power conversion efficiency of 24.1%, with excellent thermal stability─retaining 89% of its initial efficiency after 42 days at 85 °C. This work demonstrates an effective route for nanoscale interfacial engineering toward high-performance, low-temperature PSCs.