Ultraviolet Absorbers Stabilize the Self‐Assembled Monolayers and Passivate the Buried Interface for Highly Efficient and Stable Inverted Perovskite Solar Cells

ABSTRACT Self‐assembled monolayers (SAMs) have played a pivotal role in advancing the efficiency of inverted PSCs, with [4‐(3,6‐Dimethyl‐9H‐carbazol‐9‐yl)butyl] phosphonic acid (Me‐4PACz) emerging as one of the most promising SAMs materials, enabling devices to achieve record PCEs exceeding 27%. However, the operational stability of highly efficient devices is still hampered by the susceptibility of Me‐4PACz molecules to light‐induced degradation. Specifically, UV exposure leads to cleavage of the carbon‐phosphorus bond in Me‐4PACz, resulting in anchor group detachment and consequent deterioration of device performance. Addressing this challenge, two ultraviolet absorbers, 7‐Amino‐4‐methylcoumarin and 7‐Hydroxy‐4‐methylcoumarin as multifunctional additives were introduced into the Me‐4PACZ solution, and can not only effectively filter harmful UV radiation, preserving the structural integrity of SAMs, but also enhance the uniformity and compactness of the monolayer and passivate defects at the perovskite buried interface by coordinating with uncoordinated lead ions. As a result, the modified devices achieved a significant boost in PCE from 23% to over 25%, along with improved V oc and J sc. Furthermore, the photostability of the devices was substantially enhanced under continuous illumination. Thus, such a work could offer a simple and effective interfacial engineering strategy to simultaneously improve the efficiency and photostability of inverted perovskite solar cells.