Solution-Phase PbI₂ Coordination Controls Perovskite Film Formation and Photovoltaic Performance

Additive engineering is an effective strategy for achieving high quality, defectless perovskite films in the solution process. To explore the role of additives and their chemical interactions with precursors, two different additives of 4-hydroxybenzenesulfonamide (4HBSA) and 4-aminophenol (4AP) were examined. 4HBSA bearing sulfonyl group interacted well with PbI 2, while 4AP without sulfonyl showed negligible interaction. Such a strong 4HBSA–PbI 2 interaction led to pinhole-free, defectless perovskite films, which reduced defect-mediated traps, whereas 4AP increased traps. Power conversion efficiency (PCE) was thus increased from 23.52% to 25.04% by 4HBSA, while a significant decrease in PCE to 18.66% was observed in 4AP. Additionally, the 1 sun light-soaking stability test demonstrated that 4HBSA-treated device maintained 97.5% of its initial maximum PCE after ∼1600 h, while 4AP-treated device retained only 54.2% after ∼850 h. This work highlights the importance of controlling PbI 2 through additives in the precursor solution for defectless, high quality perovskite films.