Heat Transformation and Dissipation in Photoexcited Perovskites

The partitioning of energy into heat dictates the performance of all conceivable devices. In solar cells, heat is produced through the sequential exchange of energy between photons, electrons and phonons. The past decade has shown that the initial photon-to-charge conversion step is remarkably efficient for metal-halide perovskites, but there is still much to learn about the redistribution of thermal energy between the electronic and vibrational degrees of freedom in these materials, and the implications of these processes toward the performance and stability of emerging optoelectronic devices. In this talk I will outline our recent efforts to visualize heat flow in photoexcited perovskite materials and devices using a suite of non-contact and lattice-sensitive techniques. Starting in the ultrafast regime, I will discuss the development and implementation of a novel optical pump-infrared push-terahertz probe experiment to monitor the real-time conductivity of cooling carriers and localized heating of the surrounding perovskite lattice within the polaron volume. I will then go on to show how the more wide-scale dissipation of this heat plays a major role in defining the structural response and equilibration of the lattice across the pico-to-microsecond time domains through in-operando time-resolved X-ray diffraction measurements on perovskite devices. These findings bring new insight into the unusual thermal properties of metal-halide perovskites and their interplay with the electronic and structural dynamics.