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  Rappich, J.; Lang, F.; Brus, V.V.; Shargaieva, O.; Dittrich, T.; Nickel, N.H.: Light-induced defect generation in CH₃NH₃PbI₃ thin films and single crystals. Solar RRL 4 (2020), p. 1900216/1-6

10.1002/solr.201900216
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Abstract:
In a period of only a few years the power conversion efficiency of organic-inorganic perovskite solar cells has surpassed a value of 24.2 %. However, a major drawback is the lack of long-term stability, which is partially related to the dissociation of organic cations under prolonged illumination. This degradation mechanism is not limited to ambient temperatures. At low temperatures (T = 5 K) illumination of methyl ammonium lead iodide (CH3NH3PbI3) thin films with a photon energy of Eph = 3.4 eV results in the formation of localized trap states located about 100 meV within the band gap. These light-induced defects are metastable and annealing at T >= 15 K removes the localized states. Defect creation is not limited to polycrystalline perovskites but has also been observed in single crystal CH3NH3PbI3. The experimental data are discussed in terms of a two-level model where the metastable state is separated from the annealed state by an energy barrier.