Transport Layer Engineering by Hydrochloric Acid for Efficient Perovskite Solar Cells with a High Open-Circuit Voltage

A large number of defect states that exist at the interface between a perovskite film and an electron transport layer (ETL) are detrimental to the efficiency and the stability of perovskite solar cells (PSCs). It is still a challenge to simultaneously passivate the defects on both sides by a stable and low-cost ion compound. Herein, we demonstrate a simple and effective versatile strategy by introducing hydrochloric acid into SnO₂ precursor solution to passivate the defects in both SnO₂ and perovskite layers and simultaneously reduce the interface energy barrier, ultimately achieving a high-performance and hysteresis-free PSCs. Hydrogen ions can neutralize −OH groups on the SnO₂ surface, whereas the Cl^– can not only combine with Sn⁴⁺ in ETL but also suppress the Pb–I antisite defects formed at the buried interface. The reduced nonradiative recombination and the favorable energy level alignment result in a significantly increased efficiency from 20.71 to 22.06% of PSCs due to the enhancement of open-circuit voltage. In addition, the stability of the device can also be improved. This work presents a facile and promising approach for the development of highly efficient PSCs.