Carrier Diffusion Lengths of over 500 nm in Lead-Free Perovskite CH 3 NH 3 SnI 3 Films.

The dynamics of photoexcited lead-free perovskite films, CH3 NH3 SnI3 , were studied using broadband transient absorption and time-resolved fluorescence spectroscopy. Similar to its lead analogue CH3 NH3 PbI3 , we show that free carrier (electrons and holes) recombination is also the dominant relaxation pathway in CH3 NH3 SnI3 films. The slow hot carrier relaxation time is 0.5 ps. Long carrier diffusion lengths for electrons (279 ± 88 nm) and holes (193 ± 46 nm) were obtained from fluorescence quenching measurements. We also show that SnF2 doping in the CH3 NH3 SnI3 film effectively increases the fluorescence lifetime up to 10 times and gives diffusion lengths exceeding 500 nm. These results suggest that the photophysics of CH3 NH3 SnI3 perovskite are as favorable as those of CH3 NH3 PbI3 , demonstrating that it is a promising nontoxic lead-free replacement for lead iodide perovskite-based solar cells.