The selenium substitution of solvent additive enables efficient polymer solar cells with efficiency of 19.4 %

Solvent additives, which are widely used as versatile tools for refining active layer morphology, have been considered as important role in enhancing the power conversion efficiency (PCE) of polymer solar cells (PSCs). Herein, innovative solvent additive 2,5-dibromoselenophene (BrS), is devised and synthesized by substituting the sulfur atom in 2,5-dibromothiophene (BrT) with selenium atom. The facile polarization properties of selenium atoms enable selenophene to participate in intermolecular interactions with oxygen or sulfur atoms. Therefore, incorporating BrS into the blend solution leads to refined intermolecular interactions and molecular packing, and crystallinity, resulting in a refined bulk heterojunction (BHJ) morphology compared to using the solvent additives 1-chloronaphthalene (CN) and BrT. Consequently, the BrS outperform their BrT and CN in improving photon absorption, exciton dissociation, and charge collection properties of PSCs, yielding an enhanced PCE of 18.0 % in PM6:Y6 BHJ devices. Moreover, the BrS solvent additive exhibit general applicability in both non-fullerene small molecules PSCs and all-polymer PSCs. High efficiency of 18.8 %, 19.4 % and 18.1 % are obtained in PM6:L8-BO, D18:L8-BO, and PM6:PY-IT BHJ solar cells, respectively, which is rankable among the paramount performance reported to date. Our results highlight the potential of selenophene-based solvent additives as an observable pathway for nanomorphology of active layer and effective enhancement of PCE in PSCs.