Co‐adsorbed Self‐assembled Monolayer Enables Efficient and Stable Organic Solar Cells

Comprehensive Summary Hole‐selective self‐assembled monolayers (SAMs) are essential for high‐efficiency conventional organic solar cells (OSCs), yet common SAMs like 4PACz often suffer from inhomogeneous coverage on transparent conductive oxide (TCO) substrates, limiting device efficiency, reproducibility, and stability. Herein, we introduce Ph‐IDCz as a co‐adsorbent with 4PACz to form a more uniform SAM that passivates uncovered TCO regions. Strong intermolecular interactions between Ph‐IDCz and 4PACz suppress excessive self‐aggregation of 4PACz, while enhancing anchoring to the ITO substrate and improving stability. The resulting Co‐SAM device achieves a champion power conversion efficiency (PCE) of 20.23%, outperforming the single‐4PACz device (19.43%). Moreover, it exhibits excellent thermal stability, retaining 89.5% of its initial PCE after 2,592 hours at 65 °C under N 2 , compared to only 57.0% for the 4PACz reference. This Co‐SAM strategy provides a new route toward stable and efficient OSCs.