| Abstract Scope |
The metal halide perovskite solar cells have achieved efficiency over 25%, while the main challenge is its instability. To understand the structure-function relationship of perovskite materials, we utilize femtosecond laser spectroscopy to study photophysics of different structures. For example, we manipulate the phase distribution of quasi-2D perovskite, verified by transient absorption spectroscopy. We find that solar cell performance is more sensitive to phase purity than vertical phase distribution. In another example, a small amount of hydrophobic cation is added to improve efficiency and stability simultaneously. The cations preferentially segregate at the grain boundaries and surface, verified by transient reflection spectroscopy. Such passivation enhances device efficiency and stability. Compared with organic cation, inorganic perovskite exhibits better thermal and photo stability, but its black phase is not stable. We find that the vertical phase distribution is substrate dependent, which ultimately affects the film and device stability. |