Optimizing fibril morphology of polymer donors by increasing dipole–dipole interactions using additives for efficient organic solar cells

Abstract

The extension of polymer fibrils is anticipated to enhance charge transport in organic solar cells (OSCs). However, further extending the length of polymer fibrils remains challenging due to the weak intermolecular interactions among polymer chains. This work reports a fibrillization strategy that enables pronounced extension of polymer donor D18 fibrils (from 264 nm to 391 nm) by selectively strengthening packing between the acceptor units (A) in D18 fibrils. By introducing a volatile solid additive, 2,4-dichloro-5-cyanothiazole (DCCTz), dipole–dipole interactions are established between the additive and the A units of the polymer donor D18, effectively reducing the energetic barrier for intermolecular packing. Importantly, the extended fibril network and optimized molecular packing are well preserved in D18/L8-BO layer-by-layer (LbL) processed active layers without disturbing acceptor ordering. Consequently, this optimized donor fibril morphology facilitates charge transport and collection in D18/L8-BO LbL fabricated organic solar cells (OSCs), yielding a significantly improved power conversion efficiency of 19.30%. This work demonstrates an effective strategy to carefully control the dipole–dipole interaction between the solid additive and polymer donor, offering a promising approach for advancing the performance of OSCs.