To gain insight into 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 (CH 3 NH 3 PbI 3 ), with specific attention to its sub-band gap absorption edge (often termed Urbach energy). On the basis of these data, we first find clear further evidence for the universality of the correlation between the Urbach energy and open-circuit voltage losses of solar cells. Second, we find that for CH 3 NH 3 PbI 3 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.

We report on the experimental realization of amorphous/microcrystalline silicon tandem solar cells (Micromorph) based on our three-dimensional design. An enhancement is reached in the short-circuit current by 40%, with an excellent open-circuit voltage of 1.41V and a fill factor of 72%. We have used nanoholes or microholes dry etched into the ZnO front contact layer. Monte Carlo optical modeling shows that stable efficiency of amorphous silicon p-i-n solar cells in over 12% range is possible. For the Micromorph cells, efficiency over 15% with the thickness of amorphous Si below 200 nm and of microcrystalline Si around 500 nm is possible.

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