Investigation of Double-Layered Pb-Sn Perovskite Absorbers: Formation, Structure, Band Alignment, and Stability

Mixed Pb/Sn halide perovskites have shown wide band gap tunability, allowing these materials to become practical components. Nevertheless, a high density of Sn vacancies and an undesirable oxidation of Sn(II) to Sn(IV), even in the absence of any oxidant species, diminish film performance and air-stability due to recombination losses of charge carriers. More recently, A-site substitution by several organic halide compounds as additives has been engaged to improve film stability through dangling bond passivation. However, exploring the roles of passivation via A-site doping in Pb/Sn perovskites requires a more insightful investigation. Here, we explicate the structural design of 2D perovskite formation on the 2D/3D mixed Pb/Sn perovskite layer and its effects on electronic properties and stability. Surprisingly, we observe that PEAI treatment causes 2D perovskite formation at the interface of the layered perovskite. In situ growth of the 2D perovskite significantly suppresses Sn and I vacancies via Lewis base passivation. With the control of the conversion process, the interfacial 2D establishes on top of the layered perovskite, resulting in valence-band maximum down-shifting, which in turn adjusts the energy level. Remarkably, the crystallinity along with the more preferred (100) orientation is significantly improved by the PEAI treatment. The phase stability under ambient conditions is enhanced as a result of the 2D passivation. Through various characterization methods, the deep investigation of 2D perovskite interfacial formation was carefully engaged, yielding insights highly beneficial for various optoelectronic applications.