The effect of CO2-doped spiro-OMeTAD hole transport layer on FA(1−x)Cs x PbI3 perovskite solar cells

Black-phase formamidinium lead iodine with 1.48 eV bandgap is considered to be the most promising material for improving the near-theoretical limit efficiency of perovskite solar cells, but at room temperature, black-phase formamidinium lead iodine easily transforms into the yellow non-perovskite phase formamidinium lead iodine. Here, different ratios of Cs+-incorporated formamidinium lead iodine prepared by one-step processing with the stability and power conversion efficiency of formamidinium lead iodine perovskite solar cells are investigated. FA0.85Cs0.15PbI3 shows the highest power conversion efficiency of 10.63% (Voc = 1.04 V, Jsc = 16.81 mA cm−2, and fill factor = 0.60), and the unencapsulated device maintained 60% of the initial power conversion efficiency after storage in air with 40% humidity for 186 h with an active area of 0.1 cm2, when the ratios of Cs+ reached 15% (x = 0.15) in formamidinium lead iodine. However, the efficiency of perovskite solar cell–based formamidinium lead iodine is still low. In this work, a simple but an effective strategy was carried out to rapidly and fully oxidize hole transport layer solution by doping CO2 or O2 under ultraviolet light irradiation to increase the conductivity of hole transport layer, thereby improving the power conversion efficiency of solar cells. The results show that FA0.85Cs0.15PbI3 solar cells by CO2-doped hole transport layer for 90 s exhibited the highest power conversion efficiency of 16.11% (VOC = 1.11 V, JSC = 19.73 mA cm−2, and fill factor = 0.74). The improved photovoltaic performance is attributed to CO2-doped spiro-OMeTAD increasing charge carrier density and accelerating charge separation, thereby inducing higher conductivity. CO2 or O2 doped can rapidly and fully oxidize spiro-OMeTAD, and reduce the solar cell fabrication time; it is beneficial to the commercial use of perovskite solar cells.