Pressure Response of Halide Ion Mobility in Mixed Halide Perovskites

River Leversee, University of Colorado Boulder

Photo of River Leversee

Mixed methylammonium lead iodide/bromide perovskites undergo spontaneous demixing when exposed to visible light, on a time scale that depends on the light intensity. Demixing leads to the formation of iodide rich domains, which preferentially emit light when excited, surrounded by bromide rich domain walls. When light exposure is ceased, spontaneous remixing occurs. The dynamics of the demixing and remixing are slowed dramatically by the application of pressure. This presents an interesting set of effects in a system which is both chemically relevant, and applicable to high efficiency solar cells. Here, we investigate the demixing dynamics using photoluminescence spectroscopy at pressures up to 200 MPa. Photoluminescence spectroscopy reveals information on the formation and growth of light emitting iodide rich regions. The trends in iodide rich domain formation become more apparent at high pressure due to the slower halide ion migration through the material. We explore different models of growth, as the observed trends in emission cannot be explained by a simple monoexponential kinetic model. These new models are based on including the effects of bromide wall formation during demixing.

Abstract Author(s): River Leversee, Mathias Weber