In-situ thermally induced fibrous-mesoporous PbBr₂ frameworks for sequential deposited high-performance FAPbBr₃-based solar cells

Wide-bandgap FAPbBr₃ perovskite solar cells (PSCs) show great potential due to their high open-circuit voltage, semitransparency, and excellent stability. However, the uncontrollable crystallization kinetics of FAPbBr₃ lead to non-uniform film, insufficient light absorption and interfacial defect accumulation, collectively limiting the device performance. Here, we propose a novel sequential deposition strategy combining precursor engineering and crystallization control to overcome these challenges. The expensive high-purity PbBr₂ in conventional precursors is replaced with low-cost Pb(Ac)₂ and NH₄Br. In-situ thermal decomposition of the precursor generates a three-dimensional fibrous mesoporous PbBr₂ framework, which creates efficient mass transport channels and abundant active sites for subsequent infiltration with formamidinium bromide (FABr) solution. This fibrous architecture enhances reaction homogeneity and reduces unreacted PbBr₂ residue significantly. Furthermore, urea is incorporated into the Pb(Ac)₂/NH₄Br solution system, effectively modulating the perovskite crystallization process and promoting grain growth. Through these synergistic optimizations, the champion devices achieve a remarkable efficiency of 10.77%, representing one of the highest values reported for FAPbBr₃-based PSCs, along with exceptional thermal stability (retaining 97% their champion efficiency after 30 days at 85°C and 10–30% relative humidity without encapsulation). This work presents a novel cost-effective approach to high-performance and stable wide-bandgap PSCs.