Synchronous defect passivation of all-inorganic perovskite solar cells enabled by fullerene interlayer

All-inorganic CsPbI_3–xBr_x perovskite solar cells (PSCs) are advantageous in terms of high thermal stability, while its efficiency lags behind those of organic-inorganic hybrid perovskite counterparts. Defect passivations have been extensively applied for enhancing efficiency of all-inorganic PSCs, which are mainly based on univocal defect passivation of perovskite layer. Herein, we incorporated a bis-dimethylamino-functionalized fullerene derivative (abbreviated as PCBDMAM) as an interlayer between ZnO electron transport layer (ETL) and all-inorganic CsPbI_2.25Br_0.75 perovskite layer, accomplishing synchronous defect passivations of both layers and consequently dramatic enhancements of efficiency and thermal stability of PSC devices. Upon spin-coating PCBDMAM onto ZnO ETL, the surface defects of ZnO especially oxygen vacancies can be effectively passivated due to the formation of Zn−N ionic bonds. In addition, PCBDMAM incorporation affords effective passivation of Pb_I and I_Pb antisite defects within the atop perovskite layer as well via coordination bonding with Pb²⁺. As a result, the regular-structure planar CsPbI_2.25Br_0.75 PSC device delivers a champion power conversion efficiency (PCE) of 17.04%, which surpasses that of the control device (15.44%). Moreover, the PCBDMAM-incorporated PSC device maintains ~ 80% of its initial PCE after 600 h heating at 85 °C hot plate in N₂ atmosphere, whereas PCE of the control device degrades rapidly to ~ 62% after 460 h heating under identical conditions. Hence, PCBDMAM incorporation benefited dramatic improvement of the thermal stability of PSC device.