Band tailing and deep defect states in CH3NH3Pb(I1-xBrx)3 perovskites as revealed by sub-bandgap photocurrent

Carolin M. Sutter-Fella, D. Westley Miller, Quynh P. Ngo, Ellis T. Roe, Francesca M. Toma, Ian D. Sharp, Mark C. Lonergan, Ali Javey

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104 Scopus citations


Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. Here, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH3NH3Pb(I1-xBrx)3/TiO2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (Eu) over the full halide composition space. The Urbach energies are 15-23 meV, lower than those for most semiconductors with similar bandgaps (especially with Eg > 1.9 eV). Intentional aging of CH3NH3Pb(I1-xBrx)3 for up to 2300 h, reveals no change in Eu, despite the appearance of the PbI2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH3NH3PbI3 or mixed CH3NH3Pb(I1-xBrx)3 compositions, respectively. The study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH3NH3Pb(I1-xBrx)3 alloys.

Original languageEnglish
Pages (from-to)709-715
Number of pages7
JournalACS Energy Letters
Issue number3
StatePublished - 10 Mar 2017
Externally publishedYes


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