Slow carrier relaxation in tin-based perovskite nanocrystals

Tin-based perovskite nanocrystals with slower than usual relaxation dynamics holds promise for superior lead-free perovskite optoelectronic devices. The conversion efficiency of solar energy in semiconductors is fundamentally limited by ultrafast hot-carrier relaxation processes, and slowing down these processes is critical for improved energy harvesting. Here we report formamidinium tin iodide (FASnI(3)) nanocrystals where quantum confinement effects yield an evolution from a continuous band structure to separate energy states with decreasing nanocrystal size, as observed by transient absorption spectroscopy. The appearance of separate energy levels slows down the relaxation of hot carriers by two orders of magnitude at low injected carrier densities (<1 carrier pair per nanoparticle). The observed build up time of the ground-state bleach at the band edge is two orders of magnitude slower in FASnI(3) nanocrystals than in lead halide perovskite bulk and nanocrystals, which we attribute to a phonon bottleneck effect. Our results highlight the promise of lead-free perovskite nanocrystals for high-efficiency photovoltaic applications operating above the Shockley-Queisser limit.

Automated summary

Tin-based perovskite nanocrystals exhibit slower relaxation dynamics due to quantum confinement effects, resulting in different energy states that slow down hot carrier relaxation at low carrier densities. This suggests potential for high-efficiency photovoltaic applications above the Shockley-Queisser limit.