Synergistic Optimization of Buried Interface via Hydrochloric Acid for Efficient and Stable Perovskite Solar Cells

Incorporating chlorine into the SnO₂ electron transport layer (ETL) has proven effective in enhancing the interfacial contact between SnO₂ and perovskite in perovskite solar cells (PSCs). However, previous studies have primarily focused on the role of chlorine in passivating surface trap defects in SnO₂, without considering its influence on the buried interface. Here, hydrochloric acid (HCl) is introduced as a chlorine source into commercial SnO₂ to form Cl-capped SnO₂ (Cl-SnO₂) ETL, aiming to optimize the buried interface of the PSC. The incorporation of HCl into the SnO₂ precursor solution works in two key ways. First, it converts the detrimental KOH stabilizer into KCl through an acid-base reaction. Second, it regulates the crystallization process of the perovskite, reducing PbI₂ residues and voids at the buried interface. As a result, the efficiency of the PSC increases from 21.93% to 25.39%, with a certified efficiency of 25.69%, the highest efficiency reported for Cl-SnO₂ ETL-based PSCs. Moreover, the target PSC exhibits excellent air stability, retaining 90% of its initial efficiency after 2900 h of air exposure, compared to only 56.1% for the control PSC. This investigation highlights the effectiveness of HCl in the synergistic optimization of the buried interface in PSCs.