Journal
NANO LETTERS
Volume 18, Issue 2, Pages 1044-1048Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b04520
Keywords
Perovskite; microscopy; ultrafast; carriers; cooling
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Funding
- Air Force Office of Scientific Research [FA9550-14-1-0005]
- Packard Foundation [2013-39272]
- U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC-0012541]
- Soft and Hybrid Nano technology Experimental (SHyNE) Resource [NSF ECCS-1542205]
- MRSEC program at the Materials Research Center [NSF DMR-1121262]
- International Institute for Nanotechnology (IIN)
- Keck Foundation
- State of Illinois, through the IIN
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Understanding carrier relaxation in lead halide perovskites at the nanoscale is critical for advancing their device physics. Here, we directly image carrier cooling in polycrystalline CH3NH3PbI3 films with nanometer spatial resolution. We observe that upon photon absorption, highly energetic carriers rapidly thermalize with the lattice at different rates across the film. The initial carrier temperatures vary by many multiples of the lattice temperature across hundreds of nanometers, a factor that cannot be accounted for by excess photon energy above the bandgap alone or in variations of the initial carrier density. Electron microscopy suggests that morphology plays a critical role in determining the initial carrier temperature and that carriers in small crystal domains decay slower than those in large crystal domains. Our results demonstrate that local disorder dominates the observed carrier behavior, highlighting the importance of making local rather than averaged measurements in these materials.
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