Rational Regulation of Layer‐by‐Layer Processed Active Layer via Trimer‐Induced Pre‐Swelling Strategy for Efficient and Robust Thick‐Film Organic Solar Cells

Abstract Thick‐film (>300 nm) organic solar cells (OSCs) have garnered intensifying attention due to their compatibility with commercial roll‐to‐roll printing technology for the large‐scale continuous fabrication process. However, due to the uncontrollable donor/acceptor (D/A) arrangement in thick‐film condition, the restricted exciton splitting and severe carrier traps significantly impede the photovoltaic performance and operability. Herein, combined with layer‐by‐layer deposition technology, a twisted 3D star‐shaped trimer (BTT‐Out) is synthesized to develop a trimer‐induced pre‐swelling (TIP) strategy, where the BTT‐Out is incorporated into the buried D18 donor layer to enable the fabrication of thick‐film OSCs. The integrated approach characterizations reveal that the exceptional configuration and spontaneous self‐organization behavior of BTT‐Out trimer could pre‐swell the D18 network to facilitate the acceptor's infiltration and accelerate the formation of D/A interfaces. This enhancement triggers the elevated polarons formation with amplified hole‐transfer kinetics, which is essential for the augmented exciton splitting efficiency. Furthermore, the regulated swelling process can initiate the favorable self‐assembly of L8‐BO acceptors, which would ameliorate carrier transport channels and mitigate carrier traps. As a result, the TIP‐modified thin‐film OSC devices achieve the champion performance of 20.3% (thin‐film) and 18.8% (thick‐film) with upgraded stability, among one of the highest performances reported of thick‐film OSCs.