Upright Orientation of Asymmetric Conjugated SAM Enables High-Performance Perovskite Solar Cells.

Abstract

Self-assembled monolayers (SAMs) are promising hole-transporting interlayers for inverted perovskite solar cells (PSCs) owing to their ultrathin thickness and tunable work function. However, conventional SAMs such as Me-4PACz tend to adopt lying-down or tilted conformations on substrates, leading to disordered dipole orientation, inadequate substrate coverage, and buried terminal groups that are unable to passivate interface defects. In this study, we design an asymmetric conjugated SAM molecule, BCPA-Ph, to address these limitations. Its vertically oriented π-conjugated backbones build direct hole transport pathways, thereby accelerating carrier extraction, while the fully exposed terminal carbazole N─H groups form intermolecular hydrogen bonds with perovskite surface iodine species and eliminate iodide vacancy traps. As a result, the inverted PSCs based on BCPA-Ph achieve a certified power conversion efficiency (PCE) of 27.21%, along with markedly enhanced thermal and operational stability. Moreover, BCPA-Ph presents outstanding universality for large-area and wide-bandgap perovskite devices, yielding a high PCE of 26.34% for 1 cm2 devices and 23.77% for 1.68 eV wide-bandgap PSCs. This work underscores the critical importance of molecular configuration engineering in the rational design of SAMs for high-performance PSCs.