Correlating nanoscale electronic uniformity and device performance in mixed-cation perovskite solar cells driven by sequential deposition

Perovskite solar cells have garnered substantial attention in recent years owing to their high efficiency and the tunable bandgaps of their perovskite absorbers. Among various fabrication techniques, vacuum-based thermal evaporation offers particularly advantageous by minimizing environmental influences such as humidity, thereby enabling enhanced phase stability and reproducibility. In particular, sequential thermal evaporation allows precise control over the deposition rate, thickness, and stacking order of individual precursor layers, providing a versatile platform for nanoscale materials engineering. In this study, mixed-cation perovskite thin films based on formamidinium lead iodide (FAPbI3) and cesium lead iodide (CsPbI3) were fabricated via sequential thermal evaporation. By optimizing the deposition sequence of organic and inorganic precursors, a well-defined solid-state diffusion pathway was established for efficient Cs+ incorporation into the perovskite layer. Structural and optical analyses, including X-ray diffraction and photoluminescence spectroscopy, revealed that Cs+ incorporation stabilizes the alpha-phase and enhances crystallinity while suppressing non-radiative recombination. Among the optical characterization, time-resolved photoluminescence and surface photovoltage measurements demonstrate prolonged carrier lifetimes, a stabilized local potential landscape under illumination, and reduced charge trapping. These structural and electronic enhancements resulted in superior device stability and performance, characterized by improved photocurrent generation and suppressed J-V hysteresis. As a result, the fill factor and the short-circuit current density increases and the power conversion efficiency of the devices improved dramatically—from 8.89% to 16.88%. Overall, this work demonstrates that sequential deposition engineering serves as a critical nanoscale design strategy for controlling cation distribution and phase stability in vacuum-processed perovskite thin films, thereby enabling robust and high-performance perovskite solar cells.