The effect of CO2-doped spiro-OMeTAD hole transport layer on FA(1−x)CsxPbI3 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. FA 0.85 Cs 0.15 PbI 3 shows the highest power conversion efficiency of 10.63% (V oc = 1.04 V, J sc = 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 cm 2 , 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 CO 2 or O 2 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 FA 0.85 Cs 0.15 PbI 3 solar cells by CO 2 -doped hole transport layer for 90 s exhibited the highest power conversion efficiency of 16.11% (V OC = 1.11 V, J SC = 19.73 mA cm −2 , and fill factor = 0.74). The improved photovoltaic performance is attributed to CO 2 -doped spiro-OMeTAD increasing charge carrier density and accelerating charge separation, thereby inducing higher conductivity. CO 2 or O 2 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.