Hybrid organic-inorganic halide perovskite based semiconductor materials have emerged as promising candidates for multiple optoelectronic applications because of their superior properties with respect to charge carrier transport, despite 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 exceptionally sharp onset as reflected in small Urbach energies over the full composition space (0 ≤ x ≤ 1, with corresponding bandgaps of 1.6 eV ≤ Eg ≤ 2.3 eV). The Urbach energies range from 15 and 23 meV and outperform conventional semiconductors with similar bandgaps, especially for Eg &gt; 1.9 eV. Intentional degradation under laboratory conditions (no encapsulation, ~22°C, 55 +/- 5% relative humidity, in the dark) for up to 1000 hours, as monitored by formation of PbI2, does not reveal any change in Urbach energy. These results confirm high degree of crystal ordering clearly outperforming semiconductors with similar bandgaps, most strikingly wide gap semiconductors with bandgap &gt; 1.9 eV. Moreover, sub-bandgap EQE measurements reveal states in the bandgap that are not in vicinity of the conduction nor valence band.

Small Urbach energies in CH3NH3PbI3-xBrx perovskites that remain constant under degradation

253rd National Meeting (2017)

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