Interface Field Engineering of Weakly Alkaline-Treated PEDOT:PSS for Enhanced Performance and Stability of Tin-Based Perovskite Solar Cells

State-of-the-art tin-based perovskite solar cells (TPSCs) commonly use a water-based poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer. However, the strong acidity of PEDOT:PSS, arising from the deprotonation of its -SO₃H group in PSS chains due to the low acid dissociation constant (p<i>K</i>_a), often degrades tin perovskite films, compromising both the device performance and stability of TPSCs. Here, we present a novel interface engineering strategy using ammonium hydroxide (NH₄OH) treated PEDOT:PSS, which effectively neutralizes acidic groups in PSS while simultaneously improving the quality of tin perovskite films due to preferentially oriented crystal growth. Besides, this strategy improves conductivity of the hole transport layer and effectively suppresses charge recombination due to the high-quality perovskite films. As a result, the devices achieve a remarkable power conversion efficiency of 13.3%, alongside significant improvements in stability. Notably, the unencapsulated devices retain 85% of their initial efficiency after approximately 1600 h in N₂. Our method marks a significant advancement, integrating enhanced efficiency with improved durability and offering a scalable pathway for the commercialization of tin-based perovskite photovoltaics.