Role of alkali-metal cations in electronic structure and halide segregation of hybrid perovskites
Siyuan Zhang, Ming Chun Tang, Yuanyuan Fan, Ruipeng Li, Nhan V. Nguyen, Kui Zhao, Thomas D. Anthopoulos, Christina A. Hacker
Triple-cation hybrid perovskites with mixed-halide have become one of the most dominant composition due to superior photovoltaic performance and stability. In this study, we systematically investigate the incorporation of cesium (Cs+) and potassium (K+) at various ratios into formamidinium (FA)-dominated mixed-halide mixed-cation perovskite films. It is found that the electronic structure of the mixed-cation perovskites can be adjusted by the precursor ratio: incorporation of Cs+ and K+ cations shifts the Fermi level further away from the valance band maximum, and the core levels of all components shift toward higher binding energy with increasing lead iodide precursor ratio. The distribution of chemical components in all perovskite films was further investigated by the depth profile analysis. It is observed that high metallic cation ratio (20%), both Cs+ and K+, leads to halide segregation within the perovskite film: the concentration of iodide gradually decreases accompany with the increase of bromide and metal cations concentration as the sampling depth increases. The low metallic concentration films (5%), on the other hand, show uniform composition where the halides and cations are distributed evenly across the films. These observations were confirmed by the angle-dependent GIWAXS: single perovskite 3C (100) phase diffraction was observed for low metallic concentration (5%) films, while two diffraction features which assigned to Br-poor 3C perovskite α1 phase and a Br-rich 3C perovskite α2 phase were observed in high concentration films. This study provides valuable insight into the underlying reasons in tuning the electrical properties and film chemical composition by varying the alkali metal cations concentration, which is critical for hybrid perovskite ink design in the future to achieve improved reproducibility in low-cost and large-scale production of perovskite solar cells.
, Tang, M.
, Fan, Y.
, Li, R.
, Nguyen, N.
, Zhao, K.
, Anthopoulos, T.
and Hacker, C.
Role of alkali-metal cations in electronic structure and halide segregation of hybrid perovskites, ACS Applied Materials and Interfaces, [online], https://doi.org/10.1021/acsami.0c08396
(Accessed February 24, 2024)