Stoichiometric Gradient Rebalancing Achieves Surface Reconstruction and Bulk Homogenization in High-Performance Vapor-deposited Perovskite Solar Cells†

Abstract

Vapor-deposited perovskites offer excellent reproducibility and scalability, making them highly promising for commercialization. However, limited understanding of the compositional and structural characteristics of their films hinders further improvements in crystal quality and device performance. In this work, we reveal an inherent stoichiometric gradient imbalance in vapor-solid reaction perovskite films, arising from a diffusion-limited top-down crystallization process. To address this issue, we propose a Stoichiometric Gradient Rebalancing (SGR) strategy, which involves the vapor deposition of PbI2 and PbCl2 in precise ratios followed by a re-reaction step. This simple yet effective approach homogenizes the vertical composition, reduces trap density, and enhances crystal quality. As a result, a power conversion efficiency (PCE) of 22.45% is achieved in small-area devices (0.148 cm2) and 19.92% in mini-modules (5 × 5 cm2). Moreover, the devices retain over 80% of their initial efficiency after 500 hours of continuous operation at the maximum power point. This work provides a viable strategy for improving the crystal quality of vapor-deposited perovskites and deepens the understanding of their crystallization, offering valuable insights for future advancements in vapor-deposited perovskites.