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Band filling with free charge carriers in organometal halide perovskites

Abstract

The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Additionally, charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein–Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier density and serve to elucidate the behaviour of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.

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Figure 1: Ground- and excited-state absorption spectra of CH3NH3PbI3.
Figure 2: Excited-state dynamics of CH3NH3PbI3.
Figure 3: Dynamic Burstein–Moss analysis.

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Acknowledgements

The authors thank J. Christians for his input on perovskite film preparation and discussion of experimental outcomes. The authors thank G. Hartland and M. Kuno for their commentary and interpretation of experimental results. The authors acknowledge the Center for Sustainable Energy at Notre Dame (cSEND) Materials Characterization Facilities for the use of the Bruker DektakXT profilometer. The research described herein was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy (award DE-FC02-04ER15533). This is contribution number NDRL No. 5004 from the Notre Dame Radiation Laboratory.

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J.S.M. and P.V.K. conceived the original experimental ideas and details. J.S.M. carried out all aspects of film preparation and optical measurements. J.S.M. prepared the figures and wrote the initial draft. Both authors contributed to the discussion, analysis and writing of the final paper.

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Correspondence to Prashant V. Kamat.

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Manser, J., Kamat, P. Band filling with free charge carriers in organometal halide perovskites. Nature Photon 8, 737–743 (2014). https://doi.org/10.1038/nphoton.2014.171

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