Binary Organic Solar Cells with >19.6% Efficiency: The Significance of Self-Assembled Monolayer Modification

Improving the uniformity and density of self-assembled monolayers (SAMs) is crucial to elevate the photovoltaic performance of organic solar cells (OSCs). Herein, we introduced the small molecules 1-hydroxybenzotriazole (HOBT) to modulate the distribution and electrical properties of (4-(7H-dibenzoc,gcarbazol-7-yl)butyl)phosphonic acid (4PADCB) on indium tin oxide (ITO) transparent electrodes in an innovative manner. The hydroxyl group of HOBT interacts with the phosphate group of SAMs, while the steric repulsion exerted by the HOBT backbone efficiently regulates the distribution of SAMs. This led to a more uniform and dense distribution of SAMs on ITO. Furthermore, HOBT-modified SAMs have improved the crystallization and vertical phase separation of the upper active layer. Consequently, the PM6:BTP-eC9 binary OSCs based on HOBT-modified SAMs exhibit an impressive PCE of 19.66%. Our work presents an effective strategy for regulating the SAM morphology and offers a promising approach for advancing OSCs.