The effect of oxygen molecule adsorption on lead iodide perovskite surface by first-principles calculation

Oxygen molecule has a negative effect on perovskite solar cells, which has been investigated experimentally. However, detailed theoretical research is still rare. This study presents a microscopic view to reveal the interaction mechanism between O ₂ and perovskite based on the first-principles calculation. The results show that O ₂ is adsorbed on the (100) surface of MAPbI ₃ perovskite mainly by Van der Waals force. O ₂ adsorption makes the MAPbI ₃ surface generate a small number of positive charges, which leads to the increase of the work function of the MAPbI ₃ surface. This is in agreement with the experimental measurement. And increased work function of MAPbI ₃ surface is not beneficial to electron transfer from perovskite to electronic extraction layer (such as TiO ₂ ). Comparison of the density of states (DOS) of the clean (100) surface and the adsorbed system shows that an in-gap state belonging to O ₂ appears, which can explain the phenomenon observed from experiments that electron transfers from the surface of perovskite to O ₂ to form superoxide. The theoretical power conversion efficiency of the system with and without O ₂ adsorption is evaluated, and it turns out that the power conversion efficiency of the system with O ₂ adsorption is slightly lower than that of the system without O ₂ adsorption. This result indicates that avoiding the introduction of O ₂ molecules between perovskite and electronic extraction layer is beneficial to the perovskite solar cell.