Light induced defect generation in CH3NH3PbI3 thin films and single crystals

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 gt; 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 barrie