Spatially segregated free-carrier and exciton populations in individual lead halide perovskite grains

S. Nah; B. Spokoyny; C. Stoumpos; C. M.M. Soe; M. Kanatzidis; E. Harel

doi:10.1038/nphoton.2017.36

Spatially segregated free-carrier and exciton populations in individual lead halide perovskite grains

S. Nah, B. Spokoyny, C. Stoumpos, C. M.M. Soe, M. Kanatzidis, E. Harel^*

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

52 Scopus citations

Abstract

The nature of charge carriers in methylammonium lead iodide perovskites (MAPbI 3) at room temperature is still a matter of considerable debate. Here, we demonstrate that within single grains of MAPbI 3, strong spatial heterogeneities on the nanometre length scale are present and associated with simultaneous free-carrier and exciton populations. These heterogeneous populations, hidden in ensemble measurements, have a signature of spatially resolved relaxation dynamics for above-bandgap photoexcitation. Using spectrally resolved transient absorption microscopy, we directly observe both red- and blueshifts of the band-edge absorption across individual grains due to a dynamic Stark shift and screening of excitonic transitions by hot carriers. These observations help address a long-standing debate on the identity of the charge carriers, showing that both excitons and free carriers coexist, but are spatially segregated on the length scale of hundreds of nanometres.

Original language	English (US)
Pages (from-to)	285-289
Number of pages	5
Journal	Nature Photonics
Volume	11
Issue number	5
DOIs	https://doi.org/10.1038/nphoton.2017.36
State	Published - May 1 2017

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Atomic and Molecular Physics, and Optics

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title = "Spatially segregated free-carrier and exciton populations in individual lead halide perovskite grains",

abstract = "The nature of charge carriers in methylammonium lead iodide perovskites (MAPbI 3) at room temperature is still a matter of considerable debate. Here, we demonstrate that within single grains of MAPbI 3, strong spatial heterogeneities on the nanometre length scale are present and associated with simultaneous free-carrier and exciton populations. These heterogeneous populations, hidden in ensemble measurements, have a signature of spatially resolved relaxation dynamics for above-bandgap photoexcitation. Using spectrally resolved transient absorption microscopy, we directly observe both red- and blueshifts of the band-edge absorption across individual grains due to a dynamic Stark shift and screening of excitonic transitions by hot carriers. These observations help address a long-standing debate on the identity of the charge carriers, showing that both excitons and free carriers coexist, but are spatially segregated on the length scale of hundreds of nanometres.",

author = "S. Nah and B. Spokoyny and C. Stoumpos and Soe, {C. M.M.} and M. Kanatzidis and E. Harel",

note = "Funding Information: E.H. acknowledges support, in part, from the Air Force Office of Scientific Research (FA9550-14-1-0005) and the Packard Foundation (2013-39272). M.K. acknowledges support from the US Department of Energy, Office of Science, Basic Energy Sciences (DE-SC-0012541). 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 programme (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). S.N. acknowledges support from the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry.",

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AU - Stoumpos, C.

AU - Soe, C. M.M.

AU - Kanatzidis, M.

AU - Harel, E.

N1 - Funding Information: E.H. acknowledges support, in part, from the Air Force Office of Scientific Research (FA9550-14-1-0005) and the Packard Foundation (2013-39272). M.K. acknowledges support from the US Department of Energy, Office of Science, Basic Energy Sciences (DE-SC-0012541). 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 programme (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). S.N. acknowledges support from the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry.

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N2 - The nature of charge carriers in methylammonium lead iodide perovskites (MAPbI 3) at room temperature is still a matter of considerable debate. Here, we demonstrate that within single grains of MAPbI 3, strong spatial heterogeneities on the nanometre length scale are present and associated with simultaneous free-carrier and exciton populations. These heterogeneous populations, hidden in ensemble measurements, have a signature of spatially resolved relaxation dynamics for above-bandgap photoexcitation. Using spectrally resolved transient absorption microscopy, we directly observe both red- and blueshifts of the band-edge absorption across individual grains due to a dynamic Stark shift and screening of excitonic transitions by hot carriers. These observations help address a long-standing debate on the identity of the charge carriers, showing that both excitons and free carriers coexist, but are spatially segregated on the length scale of hundreds of nanometres.

AB - The nature of charge carriers in methylammonium lead iodide perovskites (MAPbI 3) at room temperature is still a matter of considerable debate. Here, we demonstrate that within single grains of MAPbI 3, strong spatial heterogeneities on the nanometre length scale are present and associated with simultaneous free-carrier and exciton populations. These heterogeneous populations, hidden in ensemble measurements, have a signature of spatially resolved relaxation dynamics for above-bandgap photoexcitation. Using spectrally resolved transient absorption microscopy, we directly observe both red- and blueshifts of the band-edge absorption across individual grains due to a dynamic Stark shift and screening of excitonic transitions by hot carriers. These observations help address a long-standing debate on the identity of the charge carriers, showing that both excitons and free carriers coexist, but are spatially segregated on the length scale of hundreds of nanometres.

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Spatially segregated free-carrier and exciton populations in individual lead halide perovskite grains

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