Oxygen aging time: A dominant step for spiro-OMeTAD in perovskite solar cells

Perovskite solar cells (PSCs) are emerging as a new type of energy device which have drawn tremendous attention in the scientific community. However, details of the fabrication process, such as about the aging time of the hole transport layer, are worth clarified. Commonly, PSCs were sealed in oxygen conditions over 24 h, but further long-time-aging lacks a deep study. In this article, PSCs were sealed in oxygen from 0 h to 120 h. We have found that trapping centers and accumulated charges in perovskite crystals increased after 48-h aging treatment, leading to an increased recombination rate. As a result, the short circuit current density decreased from initially 20 mA/cm2 to lower than 10 mA/cm2, which was the main reason for the decrease in the power conversion efficiency. The current falling was further checked by the transient photocurrent technique. Although the current dropping was slightly related to differential capacitance, the accumulated charge in the bulk of cells strongly increased by 50% along with the aging time. Compared to 24-h-sealed PSCs, the lifetime of free carriers in both open circuit and short circuit conditions was significantly decreased after 48-h aging treatment, indicating that the decomposition occurred inside perovskite crystals.