Light: A new handle to control the structure of cesium lead iodide

CsPbI3 is of high interest for photovoltaic applications owing to its low band gap, provided it could be stabilized in its gamma perovskite phase. Instead, it energetically prefers to adopt a so-called yellow, 8 phase, with a much larger band gap and reduced photovoltaic properties. Here, using an original constrained density functional theory method, we mimic the effect of thermalized photoexcited carriers, and show that larger concentrations in photoexcited carriers (i.e., larger optical pump fluences) effectively reduce the energy difference between the 8 nonperovskite ground state and the gamma perovskite phase. Even further, the stability of the phases could be potentially reversed and therefore the gamma phase stabilized under strong illumination. We also report large photostriction, i.e., large photoinduced strain for all phases in this material, making CsPbI3 suitable for other applications such as photodriven relays and photoactuators.

Automated summary

CsPbI3 is of high interest for photovoltaic applications, but it prefers to adopt a yellow phase rather than the γ perovskite phase. However, using an original constrained density functional theory method, we show that larger concentrations of photoexcited carriers can effectively reduce the energy difference between the nonperovskite ground state and the γ perovskite phase. This could potentially stabilize the γ phase under strong illumination and make CsPbI3 suitable for other applications.