Light enhanced moisture degradation of perovskite solar cell material CH3NH3PbI3

To understand the light enhanced moisture degradation of CH3NH3PbI3 (MAPbI(3)) material, we carry out a series of first principles calculations and find the decisive role played by the giant photostriction effect. The photostriction effect in MAPbI(3) material changes the charge distribution and thus the bonding interactions between atoms. This effect enhances the adsorption and penetration of H2O molecules nearby the MAPbI(3) surface after the above band gap illumination, which is ascribed to the alternation of bonding interactions between MA molecules, H2O molecules and PbI networks. Owing to the straightening of the PbI networks induced by the photostriction effect, the band gap of MAPbI(3) decreases, leading to more photon absorption and thus self-accelerated photostriction processes. Hence the photostriction effect could accelerate the moisture decomposition of MAPbI(3) perovskite under illumination. Therefore, to develop perovskite solar cells with strong moisture resistance, an effective strategy is to develop perovskite materials with no or a minor photostriction effect.