Improving the Stability of FAPbI ₃ Based‐Inverted Perovskite Solar Cells Through In Situ Passivation of Grain Boundaries at the Buried Interface

Inverted perovskite solar cells (PSCs) offer superior operational stability in comparison to their normal-structure counterparts. However, the efficiency and stability of p-i-n perovskite solar cells prepared in air are still less than those prepared in an inert atmosphere. In this work, it is found that introducing a precise amount of RbCl into the perovskite precursor solution results in the in situ formation of (PbI₂)₂RbCl at the grain boundaries of the buried interface of the perovskite film, which can passivate the defects at the buried interface, suppresses ion migration, and enhance the stability of perovskite films. Moreover, the introduction of RbCl can also eliminate cracks and pinholes at the buried interface, improving the contact between the perovskite film and the hole transport layer. Consequently, inverted solar cells utilizing an FAPbI₃ perovskite layer, prepared under ambient conditions (T≈25 °C, RH≈50%), achieve a power conversion efficiency (PCE) of 25.14%, comparable to the state-of-the-art PSCs fabricated in an inert atmosphere. Moreover, the unencapsulated devices retain 90% of their initial PCE after 950 h of maximum power point tracking at 65 °C under 1-sun illumination. This work presents a novel approach for fabricating efficient and stable inverted devices under ambient conditions.