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Long-range hot-carrier transport in hybrid perovskites visualized by ultrafast microscopy

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Science  07 Apr 2017:
Vol. 356, Issue 6333, pp. 59-62
DOI: 10.1126/science.aam7744

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Seeing hot carriers break the limit

If charge carriers in solar cells can be harvested before they cool on their way to equilibrium, then the Shockley-Queisser limit of 33% for solar cell efficiency can potentially be beaten. Long carrier lifetimes (∼100 ps) have been reported for hybrid organic-inorganic metal halide perovskites. Guo et al. imaged charge transport in CH3NH3PbI3 thin films with transient absorption microscopy. Hot carriers could travel up to 600 nm, which suggests that devices that harvest hot carriers may be feasible.

Science, this issue p. 59

Abstract

The Shockley-Queisser limit for solar cell efficiency can be overcome if hot carriers can be harvested before they thermalize. Recently, carrier cooling time up to 100 picoseconds was observed in hybrid perovskites, but it is unclear whether these long-lived hot carriers can migrate long distance for efficient collection. We report direct visualization of hot-carrier migration in methylammonium lead iodide (CH3NH3PbI3) thin films by ultrafast transient absorption microscopy, demonstrating three distinct transport regimes. Quasiballistic transport was observed to correlate with excess kinetic energy, resulting in up to 230 nanometers transport distance that could overcome grain boundaries. The nonequilibrium transport persisted over tens of picoseconds and ~600 nanometers before reaching the diffusive transport limit. These results suggest potential applications of hot-carrier devices based on hybrid perovskites.

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