Overcoming the Shockley-Queisser limit for solar cell efficiency is possible if hot carriers can be harvested before they reach thermal equilibrium with the surrounding lattice. To efficiently extract hot carriers, they need to migrate sufficiently long distances for collection at the electrodes. We have developed transient absorption microscopy (TAM) with a time resolution of ~ 200 fs and ~ 50 nm spatial precision to directly visualize hot carrier propagating in hybrid organic-inorganic perovskite (CH3NH3PbI3) thin films and single crystals. Three distinctive transport regimes are observed. 1) quasiballistic transport, 2) nonequilibrium transport, and 3) diffusive transport. The nonequilibrium transport persisted over tens of picoseconds and ~ 600 nanometers before reaching the diffusive transport limit. These results suggest a potential for hot carrier based devices, in which the Shockley-Queisser limit could be overcome. To further increase the likelihood of hot carriers being harvested, it is crucial to have the hot carriers live longer (i.e. cool slower). We observe a low threshold hot phonon bottleneck in hybrid perovskite films that possess rubidium and cesium cations incorporated into the lattice. This slow cooling (~50 ps) also promotes enhanced carrier diffusion for ~300 ps, which further corroborates the possibility of a hot carrier solar cell.
Jordan Snaider is a graduate student working under advisement of Prof. Libai Huang in the Department of Chemistry. His current research focus is utilizing ultrafast microscopy and spectroscopy to elucidate challenges of charge transport in perovskite solar cells. Jordan received his B.S. degree from St. John’s University in 2014, as well as his M.S. degree in Chemistry in 2015.
Cite this work
Researchers should cite this work as follows:
4102 Brown, Purdue University, West Lafayette, IN