@article{32d5385e90ff41d38ae4824ebc579e28,
title = "Transient Sub-bandgap States in Halide Perovskite Thin Films",
abstract = "Metal halide perovskites are promising solar energy materials, but their mechanism of action remains poorly understood. It has been conjectured that energetically stabilized states such as those corresponding to polarons, quasiparticles in which the carriers are dressed with phonons, are responsible for their remarkable photophysical properties. Yet, no direct evidence of polarons or other low-energy states have been reported despite extensive efforts. Such states should manifest as below bandgap features in transient absorption and photoluminescence measurements. Here, we use single-particle transient absorption microscopy on MAPbI3 (MA = methylammonium) to unambiguously identify spectrally narrow sub-bandgap states directly; we demonstrate that such signals are completely averaged away in ensemble measurements. Carrier temperature-dependent studies suggest that hot carriers are directed toward transient low-energy states which are immune from permanent defects and traps, thereby giving rise to low carrier recombination rates and ultimately high power conversion efficiency in devices. The utilization of short-lived sub-bandgap states may be a key design principle that propels widespread use of highly heterogeneous materials in optoelectronic applications.",
keywords = "Metal halide perovskite, polaron states, spatially resolved measurements, transient absorption microscopy, ultrafast spectroscopy",
author = "S. Nah and B. Spokoyny and X. Jiang and C. Stoumpos and Soe, {C. M.M.} and Kanatzidis, {M. G.} and E. Harel",
note = "Funding Information: E.H. acknowledges support by the Air Force Office of Scientific Research (FA9550-14-1-0005), and the Packard Foundation (2013-39272) in part. M.G.K. acknowledges support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (DE-SC-0012541, sample synthesis and physical characterization). The electron microscopy work made use of the EPIC facility of Northwestern University's NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Funding Information: E.H. acknowledges support by the Air Force Office of Scientific Research (FA9550-14-1-0005), and the Packard Foundation (2013-39272) in part. M.G.K. acknowledges support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (DE-SC-0012541, sample synthesis and physical characterization). The electron microscopy work made use of the EPIC facility of Northwestern University{\textquoteright}s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Publisher Copyright: {\textcopyright} 2018 American Chemical Society.",
year = "2018",
month = feb,
day = "14",
doi = "10.1021/acs.nanolett.7b04078",
language = "English",
volume = "18",
pages = "827--831",
journal = "Nano Letters",
issn = "1530-6984",
publisher = "American Chemical Society",
number = "2",
}