Transient Sub-bandgap States in Halide Perovskite Thin Films

S. Nah, B. Spokoyny, X. Jiang, C. Stoumpos, C. M.M. Soe, M. G. Kanatzidis, E. Harel

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)827-831
Number of pages5
JournalNano letters
Issue number2
Publication statusPublished - Feb 14 2018


  • Metal halide perovskite
  • polaron states
  • spatially resolved measurements
  • transient absorption microscopy
  • ultrafast spectroscopy

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering

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