Study on degradation mechanism of perovskite solar cell and their recovering effects by introducing CH3NH3I layers

We demonstrate the degradation mechanism of CH3NH3PbI3 perovskite solar cells (PSCs) and their recovery effects by introduction of CH3NH3I layers. After degradation by exposure to air under a 1-sun condition for 18 h, the absorption of the CH3NH3PbI3 perovskite between 530 and 800 nm decreases, and thereby the energy band gap increases. X-ray diffraction (XRD) patterns indicate that moisture with sunlight corrodes the CH3NH3PbI3 perovskite into PbI2, which generates cracklike voids on the surface of illumination-degraded CH3NH3PbI3 perovskite thin films. As a result, the PSC photovoltaic performance is degraded and the power conversion efficiency (PCE) is reduced from 16.8 to 0.7%. However, the PCE is recovered to 7.6% by spin-coating a CH3NH3I layer into the illumination-degraded CH3NH3PbI3 perovskite thin films. The recovery of the absorption between 530 and 800 nm and the CH3NH3PbI3-perovskitc-assigned peaks in the XRD patterns verifies that the illumination-induced PbI2 is recombined with spin coated CH3NH3I and that the CH3NH3PbI3 perovskite structure is recrystallized. (C) 2017 Elsevier B.V. All rights reserved.