We have studied the mechanisms of CH3NH3PbI3 degradation and its transformation to PbI2 by means of X–ray diffraction and the density functional theory. The experimental analysis has shown that the material can degrade in both air and vacuum conditions, with humidity and temperature–annealing strongly accelerating such process. Based on ab–initio calculations, we have argued that even in the absence of humidity, a decomposition of the perovskite structure can take place through the statistical formation of molecular defects with a non–ionic character, whose volatility at surfaces should break the thermodynamic defect equilibrium.
Contact person: Ioannis Deretzis, IMM–CNR Catania