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Nonfullerene acceptors have boosted the power conversion efficiencies (PCE) of organic solar cells (OSCs). Rigid fused-ring molecular skeletons enable decent molecular planarity and stacking orientations, but suffer from tedious synthesis procedures for those with large π-backbones. Promisingly, the π-bridge strategy provides an alternative to readily manipulate the light utilization, but sometimes increases the conformation complexity. To rationally regulate the performance of π-bridged acceptors, herein, we report two new acceptors WA1 and WA2, functionalized with single or dual π-bridges flanking the phenylalkyl modified indacenodithiophene (IDT) backbone. The unilateral π-bridge endows WA1 with an asymmetric electron cloud distribution, affording a greater dipole moment and well-organized molecular orientation. In contrast, the bilateral π-bridges endow WA2 with two disparate molecular dipoles and disordered stacking orientations, generating inferior PCEs below 10%. Notably, the PM6:WA1 device shows a remarkable PCE of up to 15.45% with an impressive fill factor (FF) of up to 79.31%, both of which rank among the highest values of OSCs with π-bridged acceptors. More importantly, the PM6:Y6:WA1 ternary organic solar cell (TOSC) affords a high PCE of up to 18.15%, which is the best efficiency among Y6-based bulk-heterojunction TOSCs and the first example of an efficient ternary cell featuring a π-bridged guest acceptor. [ABSTRACT FROM AUTHOR]

Ternary polymer solar cells (PSCs) exhibit broader absorption bands, greater potential in micro-morphology regulation, energy level tuning, and other advantages compared with binary PSCs, and is a facile and efficient approach for further enhancing photovoltaic performances. Because of its much more complicated morphology-forming process, the ternary devices with two donors and one non-fullerene acceptor are difficult to regulate. In contrast, the ternary devices with one donor and two acceptors show greater potential in improving the morphology stability of the active layer film, which is one of the biggest obstacles that hinder the commercialization of PSCs. This review systematically summarizes the principles and functions of the third component of high-performance non-fullerenes ternary PSCs, and outlines the recent advancements of ternary PSCs with two donors and one non-fullerene acceptor, including two polymer donors and small molecular acceptor, all-polymer PSCs, and PSCs with small molecule donors. The relationship between the composition and property was carefully examined and outlined. In addition, the valuable guidelines in developing high-efficiency and high-stability non-fullerene ternary PSCs are demonstrated. [ABSTRACT FROM AUTHOR]