In Situ Formation of High-p<i>K</i>_a Cations for Perovskite Solar Cells

Surface passivation is one of the most promising strategies for improving the illumination stability at high temperatures for perovskite solar cells. However, commonly used surface agents should be presynthesized and were usually located at the perovskite surface or interfaces, making it challenging to suppress bulk defects simultaneously. Here, we present an approach for the in situ formation of high-pKa cations ([N(Z)]-N-(Aminomethylene)guanidinium) to eliminate charge defects in bulk and interfacial sites simultaneously. Consequently, the performance is enhanced for both n-i-p and p-i-n structures, with the highest reaching ∼25.4% and 20.1% (64 cm2 aperture area). Additionally, the treatment can be applied to extensive perovskite compositions, including triple cations, double cations, and single cation-based perovskites. The devices retain 94% of their initial efficiency after 2000 h continuous light illumination under the maximum power point tracking (ISOS-L-1), representing the best photostability among n-i-p structured devices(>25%)reported to date.