Overcoming the PCBM/Ag Interface Issues in Inverted Perovskite Solar Cells by Rhodamine‐Functionalized Dodecahydro‐Closo‐Dodecaborate Derivate Interlayer

Abstract Efficient modification of the interface between metal cathode and electron transport layer are critical for achieving high performance and stability of the inverted perovskite solar cells (PSCs). Herein, a new alcohol‐soluble rhodamine‐functionalized dodecahydro‐ closo ‐dodecaborate derivate, RBH, is developed and applied as an efficient cathode interlayer to overcome the (6,6)‐phenyl‐C 61 butyrie acid methyl ester (PCBM)/Ag interface issues. By introducing RBH cathode interlayer, the functions of the interface traps passivation, interfacial hydrophobicity enhancement, interface contact improvement as well as built‐in potential enhancement are realized at the same time and thus correspondingly improve the device performance and stability. Consequently, a power conversion efficiency (PCE) of 21.08% and high fill factor of 83.37% are achieved, which is one of the highest values based on solution‐processed MAPbI 3 /PCBM heterojunction PSCs. Moreover, RBH can act as a shielding layer to slow down moisture erosion and self‐corrosion. The PCE of the RBH devices still maintain 84% for 456 h (85 °C @ N 2 ), 87% for 360 h (23 °C @ relative humidity (RH) 35%) of its initial PCE value, while the control device can only maintain ≈23%, 58% of its initial PCE value under the same exposure conditions, respectively.