| Summary: | Organic-inorganic lead-halide perovskites have recently drawn great attention as novel absorbers and charge transporters in low-cost solar cells. It is still largely unknown what makes these materials so phenomenally well-suited for charge generation and conduction. Here we show that both CH3NH3PbI3 and CH3NH3PbI3−xClx exhibit exceptionally low mono-molecular and bi-molecular charge-carrier decay rates, defying the Langevin limit by at least 4 orders of magnitude. Using transient THz spectroscopy, we establish lower bounds for the high-frequency charge mobility of 11.6 cm 2/Vs for CH3NH3PbI3−xClx and 8cm2/Vs for CH3NH3PbI3, which are remarkably high for solution-processed materials. We deduce charge-carrier diffusion lengths as a function of charge density and find values exceeding a few microns for CH3NH3PbI3−xClx, under typical device operating conditions. For CH3NH3PbI3, diffusion lengths are a factor∼4 lower because of higher mono- and bi-molecular recombination rates. These findings underline the suitability of this material class for planarheterojunction device structures and highlight the potential for performance tuning through manipulation of the polar metal-halide bond.
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