Guarding the heterogeneous interface of perovskite solar cells by the anion-barrier synthesized using residual PbI₂

Ion migration and diffusion, particularly in the case of halide ions, are among the bottlenecks of the efficiency and stability of perovskite solar cells (PSCs). The residue of lead iodide (PbI₂) is easily produced by the spin-coating deposition of the perovskite film, which introduces more uncertainty to the active layer and even leads to adverse effects across the interface. In this study, a clever strategy of in situ synthesis anion-barrier was used to lock the iodide ions at the heterogeneous interface. The solution is to convert the residual PbI₂ into δ-CsPbI₃, which is more capable to bind iodine. These in situ synthesized δ-CsPbI₃ not only blocked the diffusion of iodide ions into Spiro-OMeTAD but also promoted the energy level alignment about 0.3 eV between perovskite and Spiro-OMeTAD. Fortunately, this also improved the quality of the active layer. In the end, the device based on in situ synthesized anion-barrier achieved an increased power conversion efficiency (PCE) of 21.21% from 19.62% of the reference without such a treatment. Meanwhile, the stability of the treated PSCs maintained 88.2% of their initial PCE after being stored for about 1200 h under dark conditions and controlled RH of 15-25%. This study provides a new solution and technical reference for the inhibition of ion diffusion in PSCs.