Novel Oligomer Enables Green Solvent Processed 17.5% Ternary Organic Solar Cells: Synergistic Energy Loss Reduction and Morphology Fine‐Tuning

Abstract The large non‐radiative recombination is the main factor that limits state‐of‐the‐art organic solar cells (OSCs). In this work, two novel structurally similar oligomers (named 5BDTBDD and 5BDDBDT) with D‐A‐D‐A‐D and A‐D‐A‐D‐A configuration are synthesized for high‐performance ternary OSCs with low energy loss. As third components, these PM6 analogue oligomers effectively suppress the non‐radiative recombination in OSCs. Although the highest occupied molecular orbital (HOMO) levels of 5BDTBDD and 5BDDBDT are higher than that of PM6, the oligomers enabled ultra‐high electroluminescence quantum efficiency (EQE_EL) of 0.05% and improved V_OC, indicating suppressing non‐radiative recombination overweighs the common belief of deeper HOMO requirement in third component selection. Moreover, the different compatibility of 5BDTBDD and 5BDDBDT with PM6 and BTP‐BO4Cl fine‐tunes the active layer morphology with synergistic effects. The ternary devices based on PM6:5BDTBDD:BTPBO4Cl and PM6:5BDDBDT:BTP‐BO4Cl achieve a significantly improved PCEs of 17.54% and 17.32%, representing the state‐of‐the art OSCs processed by green solvent of o‐xylene. The strategy using novel oligomer as third component also has very wide composition tolerance in ternary OSCs. This is the first work that demonstrates novel structurally compatible D‐A type oligomers are effective third components, and provides new understanding of synergetic energy loss mechanisms towards high performance OSCs.