Interspersed Assembled Monolayers Enhance Hole Transport in High-Efficiency Organic and Perovskite Solar Cells

We propose a novel concept called interspersed assembled monolayers (IAMs), which leverage a dispersant molecule sharing a similar backbone with the host self-assembled monolayer (SAM) but possessing a distinct donor-acceptor (D-A) strength, aimed to suppress micelle formation. We designed two dispersant backbones, NNN (triazolo) and NSN (thiadiazolo), both featuring electron-withdrawing backbones, but NSN exhibits a substantially larger dipole moment, which in the current study seems to reduce interfacial energy barriers. Compared to SAMs, employing an IAM strategy with a long side chain (BO) raises power conversion efficiencies (PCE) across various organic solar cell (OSC) architectures. In the PM6:Y6 system, the original PCE of 16.46% improves to 16.72% when using NNN-BO, and further increases to 18.04% with NSN-BO, which has a stronger dipole moment. Perovskite solar cells (PSCs) also benefit, with PCE rising from 23.84 to 24.17% (NNN-BO) and 25.01% (NSN-BO). Moreover, short-side-chain variants NSN-C4 and NSN-IB in PM6:L8-BO-based OSCs yield PCE of 19.01 and 18.94%, respectively, while in PSCs, these dispersants achieve 24.95 and 24.94%, which all closely approximate the performance of long-side-chain NSN-BO (19.23 and 25.01%). Systematic investigation thus demonstrates that, in the design of IAM molecules, both the conjugated backbone and appended side chains must be taken into account. The underlying mechanisms have been revealed through comprehensive femtosecond transient absorption and time-resolved photoluminescence, showing the key to dispersants in promoting charge extraction, mitigating recombination and film morphology. These IAM-integrated components also exhibit environmental and thermal stability, paving a practical way to high-performance IAM-based PSCs and OSCs.