Stepwise Volatilization Induced by Nature-Sourced Volatile Solid Additives Improving Efficiency and Stability of Perovskite Solar Cells

Abstract

In contrast to the substantial efforts dedicated to additive engineering in the field of perovskite solar cells (PSCs), the exploration of volatile solid additives has received surprisingly little attention. This study introduces a novel approach for fabricating highly efficient and stable PSCs by employing "naturally sourced volatile solid additives" (CP and CQ), which exhibit distinct volatilization rates and varying degrees of Lewis base–acid interactions with perovskite. During the PSC fabrication process involving a two-stage thermal annealing, CP completely volatilized after the initial annealing step, resulting in the formation of a densely packed PbI2 film. Conversely, owing to its robust Lewis base–acid interaction with perovskite through bidentate coordination, a certain amount of CQ tends to persist after the first annealing step. However, no residue was observed after the second annealing step (stepwise-volatilization mechanism). This process yields high-quality FA-based perovskite crystallinity characterized by large-grained perovskite and highly preferred crystallite orientation. Consequently, CQ-based PSCs achieve promising power conversion efficiency (PCE) of 25.00% (independently certified at 24.89%) with exceptional MPPT stability (PCE retentions of 90.1% after 1000 h, ISOS-L-1). This study underscores the viability of the naturally sourced volatile solid additives for ecofriendly manufacturing PSCs.