Origins of high performance and degradation in the mixed perovskite solar cells

Abstract: The origins of the high device performance and degradation in the air are the greatest issues for commercialization of perovskite solar cells. Here we investigated the possible origins of the mixed perovskite cells by monitoring defect states and compositional changes of the perovskite layer over the time. The results of deep-level transient spectroscopy analysis revealed that a newly identified defect formed by Br atoms exists at deep levels of the mixed perovskite film, and its defect states shift when the film was aged in the air. The change of the defect state was originated from loss of the methylammonium molecules of the perovskite layer, which resulted in decreased JSC, deterioration of the power conversion efficiency and long-term stability of perovskite solar cells. Our results provide a powerful strategy to diagnose and manage the efficiency and stability of perovskite solar cells.