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Long-term Chemical Aging of Hybrid Halide Perovskites.

Since the power conversion efficiency (PCE) of hybrid halide perovskite solar cells (PSCs) could exceed 24%, extensive research has been focused on improving their long-term stability for commercialization in the near future. In a previous study, we reported that the addition of a certain amount of ionized iodide (triiodide: I3-) ions during the perovskite film formation significantly improved the efficiency of PSCs by reducing deep-level defects in the perovskite layer. Understanding the relationship between the concentration of these defects and the long-term chemical aging of PSCs is important not only for obtaining fundamental insight into the perovskite materials, but also for studying the long-term chemical stability of PSCs. Herein we aim to identify the origin of the natural decay in PCE during long-term chemical aging in the dark of PSCs based on formamidinium lead triiodide, by comparing the performance of control and low-defect (LD) devices. After aging for 200 days, the change in PCE of the LD devices (1.3%) was found to be half that of the control devices (2.6%). We investigated this difference using grazing incidence wide-angle X-ray scattering, deep-level transient spectroscopy, scanning photoemission microscopy, and X-ray photo emission spectroscopy. The addition of I3- was found to reduce the amounts of hydroxide and Ox in the halide perovskites (HPs), affecting the migration of defects and the structural transformation of the HPs.