Multiple Passivation on High-Quality Perovskite Crystals Based on Low-Cost Polyfunctional Food Additive for High-Performance Perovskite Solar Cells in Ambient Air.

The two-step deposition of FAPbI3 perovskite films in ambient air faces multiple challenges, such as incomplete PbI2-to-perovskite conversion and moisture-induced degradation, leading to residual PbI2, grain boundary defects, and unstable phase formation. To solve these issues, a low-cost polyfunctional food-grade food additive, sodium cyclamate (SC), was introduced into the PbI2 precursor for the air-processed device fabrication process. The multiple cooperative interactions between SC and perovskite precursors effectively inhibit the unfavorable defect generation and greatly improve moisture tolerance. The sulfonic acid group (-SO3-) in SC coordinates with Pb2+ vacancies, while the amino group (-NH-) passivates I- vacancies via hydrogen bonding. Additionally, SC facilitates the crystallization kinetics of perovskite films via forming a porous PbI2 intermediate, which promotes the complete FAI penetration and stabilizes the α-phase against δ-phase transition. The perovskite films with enlarged grain size, reduced trap density, and improved phase purity were achieved in ambient air. Consequently, the champion device achieves an improved power conversion efficiency (PCE) with a high open-circuit voltage (Voc) in ambient air. The unencapsulated devices with SC exhibit superior long-term stability compared with the control devices under ambient conditions.