Hybrid organic–inorganic perovskites exhibit extraordinary photovoltaic performance. This is believed to arise from almost liquid-like low-energy interactions among lattice ions and charge carriers. While spatial variations have recently been identified over multiple length scales in the optoelectronic response of perovskites, the relationship between the heterogeneity and the soft cation–lattice interactions has remained elusive.<br/>Here, we apply multivariate infrared vibrational nanoimaging to lead halide perovskites by using vibrational resonances of molecular cations as sensitive probes of their local chemical environments.<br/>In a formamidinium-methylammonium-cesium triple cation perovskite, we characterize the nano-localized vibrational signal arising from the CN anti-symmetric stretch mode of the formamidinium cation. The derived correlation among nanoscale composition, cation–lattice coupling, and associated few-picosecond vibrational dynamics implies a heterogeneous reaction field and lattice contraction that we attribute to a spatially nonuniform distribution of cesium cations. The associated spatial variation in elasticity of the lattice leads to disorder in charge–phonon coupling and related polaron formation - the control of which is central to improving perovskite photovoltaics.<br/>Infrared vibrational nano-imaging, with the access to molecular structures and interactions, is widely applicable to other types of perovskites and associated intriguing topics, such as local disorder in quasi-two-dimensional perovskites and photoinduced ion migration in mixed anion perovskites.

Heterogeneous cation-lattice interaction and dynamics in head halide perovskites probed by infrared vibrational nano-spectroscopy

ACS Fall 2020 Virtual Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.