Temperature Dependence of the Urbach Energy in Lead Iodide Perovskites.

To gain insight in the properties of photovoltaic and light-emitting materials, detailed information about their optical absorption spectra is essential. Here, we elucidate the temperature dependence of such spectra for methylammonium lead iodide (CH3 NH3 PbI3 ), with specific attention for its sub bandgap absorption edge (often referred to as Urbach energy). Based on these data, firstly, we find clear further evidence for the universality of the correlation between the Urbach energy and open-circuit voltage losses of solar cells. Secondly, we find that for CH3 NH3 PbI3 the static, temperature-independent, contribution of the Urbach energy is 3.8 ± 0.7 meV, which is smaller than that of crystalline silicon (Si), gallium arsenide (GaAs), indium phosphide (InP) or gallium nitride (GaN), underlining the remarkable optoelectronic properties of perovskites.