Phenolphthalein: A Potent Small-Molecule Additive for High-Performance and Ambient-Air-Stable FAPbI₃ Perovskite Solar Cells

We assessed the impact of phenolphthalein (PHTH) on the efficacy and robustness of FAPbI3 perovskite solar cells (PSCs) fabricated in ambient air. The experimental methodology entailed the integration of PHTH into the perovskite precursor solution. The optimized concentration of 10 mg/mL significantly elevated the power conversion efficiency (PCE), experiencing an enhancement from 14.62 to 19.9%, while manifesting minimal hysteresis. PHTH-treated PSCs maintained approximately 90% of their initial PCE following a storage duration of 720 h in ambient air at 25 °C with 30% relative humidity. In contrast, control devices exhibited swift degradation, retaining only 30% of their initial value within 720 h under identical environmental conditions. The observed enhancement in the performance of PHTH-treated PSCs is attributed to PHTH acting as an intermolecular bonding agent, facilitating the crystallization of the FAPbI3 film. This improvement is primarily rooted in the intermolecular interaction between the O-donor Lewis base PHTH and both Pb2+ and FA+ ions in the FAPbI3 perovskite. This interaction effectively mitigates trap-assisted recombination processes and expedites the conversion of the less desirable δ-phase to the highly photoactive and stable α-phase of FAPbI3. Overall, these outcomes underscore the potential of black phosphorus as a promising additive for enhancing the performance and stability of PSCs.