A Co‐Self‐Assembled Monolayer With Enhanced Coverage and Defect Passivation for Efficient Inverted Perovskite Solar Cells

The combination of nickel oxide (NiO x ) and [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) butyl] phosphonic acid (Me‐4PACz) has been broadly applied in the hole transport layer (HTL) of high‐efficiency inverted perovskite solar cells (PSCs). However, the limitations of Me‐4PACz, including its inadequate uniformity of coverage on nickel oxide and insufficient defect passivation effect, restrict further enhancement of device performance. Through the co‐self‐assembled monolayer (Co‐SAM) strategy, we blended [4‐(9H‐9′‐Phenyl‐3,3′‐bicarbazol‐9‐yl) butyl] phosphonic acid (4PABCz) with Me‐4PACz, obtaining a Co‐SAM that exhibits enhanced NiO x substrate coverage. The study found that these two molecules can synergistically passivate defects on the bottom surface of perovskite and suppress non‐radiative recombination. Assisted by the Co‐SAMs, the efficiency of the champion device reached 26.33%, and the unencapsulated device still maintained over 90% of its peak performance after being stored in the nitrogen‐filled glovebox for 1800 h. This work demonstrates the significant potential of the Co‐SAM strategy for advancing self‐assembled monolayer (SAM) performance.