Abstract High and balanced open‐circuit voltage ( V OC ) and short‐circuit current density ( J SC ) are crucial for the efficiency of organic solar cells (OSCs). Generally, the π‐bridge strategy serving as an effective molecular functionalization route with the potential to balance the V OC ‐ J SC pair. Herein, the study designs and synthesizes three non‐fused ring electron acceptors (NFREAs): 2T‐T‐EH , 2T‐T‐2EH , and 2T‐TT‐2EH , by systematically regulating the π‐bridge at size, number, and position of the lateral alkyl chains. Introducing inner alkyl side chains result in twisted backbones, which elevated the lowest unoccupied molecular orbital (LUMO) energy levels, and reduced energy loss, facilitating a higher V OC . Single crystal analysis also reveals that the π‐extending in 2T‐TT‐2EH can effectively relieve the congestion of dual lateral chains, leave more space for the terminal overlapping, which promotes efficient charge transport and enhancing J SC . Consequently, a compromise between V OC (0.916 V) and J SC (21.21 mA cm −2 ) is accomplished in the binary OSCs. The elevated LUMO energy level and V OC provides 2T‐TT‐2EH to serve as a third component in ternary OSCs, achieving an impressive power conversion efficiency (PCE) of 19.07% in the D18:BTP‐eC9‐4F: 2T‐TT‐2EH ‐based device. These findings in this study suggest that fine‐tuning the π‐bridges is a simple method for optimizing photovoltaic performance in NFREAs, ensuring a well‐balanced V OC and J SC .
Translating high-performance organic solar cell (OSC) materials from spin-coating to scalable processing is imperative for advancing organic photovoltaics. For bridging the gap between laboratory research and industrialization, it is essential to understand the structural formation dynamics within the photoactive layer during printing processes. In this study, two typical printing-compatible solvents in the doctor-blading process are employed to explore the intricate mechanisms governing the thin-film formation in the state-of-the-art photovoltaic system PM6:L8-BO. Our findings highlight the synergistic influence of both the donor polymer PM6 and the solvent with a high boiling point on the structural dynamics of L8-BO within the photoactive layer, significantly influencing its morphological properties. The optimized processing strategy effectively suppresses the excessive aggregation of L8-BO during the slow drying process in doctor-blading, enhancing thin-film crystallization with preferential molecular orientation. These improvements facilitate more efficient charge transport, suppress thin-film defects and charge recombination, and finally enhance the upscaling potential. Consequently, the optimized PM6:L8-BO OSCs demonstrate power conversion efficiencies of 18.42% in small-area devices (0.064 cm
Conjugated polymer donors have always been one of the important components of organic solar cells (OSCs), particularly those featuring simple synthetic routes, proper energy levels, and appropriate aggregation behavior. In this work, we employed a nonfused electron-deficient building block, dicyanobithiophene (2CT), for constructing high-performance donors. Combining this with side-chain engineering, two novel halogen-free polymer donors, PB2CT-BO and PB2CT-HD, were reported. PB2CT-BO with shorter alkyl chains on the thiophene π bridges exhibited enhanced packing ordering and improved polymer crystallinity. When paired with BTP-CN-HD as the electron acceptor, the PB2CT-BO-based OSC attained an impressive power conversion efficiency (PCE) of 14.2% within a bulk-heterojunction (BHJ) configuration. Additionally, the active layers were refined through a layer-by-layer (LbL) approach, leading to a more organized molecular packing and an improved fibrillar network. Consequently, the OSC employing PB2CT-BO processed with the LbL approach achieved a notable PCE of 15.3%. This enhancement is credited to a reduced energy loss (Eloss) of 0.514 eV and the formation of a favorable morphology. This study highlights the considerable promise of the 2CT unit in the progression of high-efficiency polymer donors with a reduced Eloss.
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