21.26% Efficiency Organic Solar Cells Enabled by Mixed Self‐Assembled Multilayers

Abstract

ABSTRACT Insufficient surface coverage persists as a critical limitation for self‐assembled monolayers/multilayers (SAMs/SAMULs) in photovoltaic field. The co‐assembled SAMULs (Co‐SAMULs) strategy, which incorporates a guest self‐assembled molecule, offers an effective solution. However, the working mechanism of the guest molecule is still not fully understood. Herein, benzo[b]thien‐2‐ylboronic acid (BBA) was introduced as a guest material into the host molecule system based on (4‐(3,6‐di(thiophen‐3‐yl)‐9H‐carbazol‐9‐yl)butyl) phosphonate (4PAThCz) to construct efficient Co‐SAMULs. We found that BBA can fused into 4PAThCz micelles rather than forming individual micelles, respectively, thereby inhibiting micelle growth. During the film‐forming process, BBA engages in synergistic adsorption with the host molecules, selectively fills the voids between host molecule and substantially improving surface coverage. Such a homogeneous and high‐quality film effectively suppresses surface defect states, enhances interfacial charge transport capacity and minimizes non‐radiative exciton recombination. As a result, a champion power conversion efficiency (PCE) of 21.26% (certificated as 20.79%) with an outstanding fill factor (FF) of 83.54% is achieved, representing the highest performances reported for organic solar cells (OSCs) to date.