HYBRID SOLAR CELLS Perovskites under the Sun

The groups of Henry J. Snaith and colleagues and Nripan Mathews, Tze C. Sum and collaborators independently report on diffusion-length measurements performed on hybrid perovskites, which shed light on the dynamics of photoexcited species in these materials. Both teams used photoluminescence quenching experiments to measure the electron-hole diffusion length. They deposited on top of a perovskite thin-film a layer of quenching molecules, which act as a sink for the photoexcited species that, traveling in the film, reach the interface between the perovskite and the quencher. Both teams obtain LD of about 100 nm for electrons and holes in CH3NH3PbI 3. Furthermore, the group of Snaith also investigated the mixed-halide perovskite CH3NH3PbI3-xCl x, obtaining in this case a LD exceeding 1 μm. The studies reported by the two teams highlight that, after the initial excitement and surprise of the high efficiency of the solar cells, it is now time to investigate the physical properties that make hybrid perovskites so promising for solar-energy conversion.