Ultrafast selective extraction of hot holes from cesium lead iodide perovskite films

Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells, LEDs and lasers. One important and expected application of perovskite halide semiconductors is solar cell operation including hot carriers. This advanced solar cell concept allows overcoming the Shockley-Queisser efficiency limit, thereby achieving energy conversion efficiency as high as 66% by extracting hot carriers. Understanding ultrafast photoexcited carrier dynamics and extraction in lead halide perovskites is crucial for these applications. Here, we clarify the hot carrier cooling and transfer dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy and Al2O3, poly(3-hexylthiophene-2,5-diyl) (P3HT) and TiO2 as selective contacts. We find that slow hot carrier cooling occurs on a timescale longer than 10 ps in the cases of CsPbI3/Al2O3 and CsPbI3/TiO2, which is attributed to hot phonon bottleneck for the high photoexcited carrier density. An efficient ultrafast hole transfer from CsPbI3 to the P3HT hole extracting layer is observed. These results suggest that hot holes can be extracted by appropriate selective contacts before energy dissipation into the halide perovskite lattice and that CsPbI3 has a potential for hot carrier solar cell applications. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.