Binary all-polymer solar cells with 19.30% efficiency enabled by bromodibenzothiophene-based solid additive

All-polymer solar cells (all-PSCs) are thought to be the most promising candidates for the practical application of organic solar cells (OSCs). However, the efficiencies of all-PSCs remain lower than those of small molecule acceptor (SMA)-based OSCs due to their unfavorable active-layer morphology. The complicated molecular interaction and aggregation behavior involved in all-polymer blends make it highly challenging to achieve optimal morphology. Herein, two volatile solid additives named dibenzothiophene (DBTP) and 4-bromodibenzothiophene (4-BDBTP) were developed to finely modulate the morphology of all-PSCs. We clarify that the subtle bromine substitution enables 4-BDBTP to form enhanced intermolecular interactions with the host material, which is beneficial to control the molecular aggregation and crystallization, thus facilitating the formation of more ordered molecular stacking and well-defined fibril networks in the all-polymer blend. As a result, the 4-BDBTP-treated-PM6:PY-DT all-PSC achieved a high efficiency of 19.30% (certified as 18.82%). Moreover, three other all-polymer systems validate the broad applicability of 4-BDBTP, and these devices all showed enhanced efficiencies. Our work demonstrates the promising role of solid additive in regulating molecular aggregation and packing in all-polymer blends, offering valuable insight into fabricating high-performance all-PSCs.