Modulating Aggregation Behavior and Optimizing Morphology of PM6:Y6-Based Ternary Organic Solar Cells by Introducing a Noncoplanar Indacenodithiophene-Based Small-Molecule Guest

The rational development of the third component is the key to obtaining highly efficient ternary organic solar cells (OSCs). In this contribution, one tetracyanobutadiene-functionalized small molecule, IDT-T-PCN, featuring a noncoplanar molecular backbone, is selected and employed as a third component to construct PM6:Y6:IDT-T-PCN ternary OSCs. Results demonstrate that IDT-T-PCN exhibits complementary absorption and cascade energy-level alignment with the host materials (PM6 and Y6), which are beneficial for improving light-capture capability and charge transfer properties. Absorption spectra and contact angle measurements reveal that there is good compatibility and strong interaction between IDT-T-PCN and Y6, which can affect the crystallization and molecular aggregation of the host materials, especially Y6. The morphology, structure, and formation kinetics characterizations of the active layer film have unveiled that IDT-T-PCN plays a critical role in optimizing phase separation and morphology, modulating molecular aggregation, and enhancing crystallization and orderly molecular stacking of the ternary blend. Therefore, the ternary OSCs exhibit improved charge dissociation and collection probability, enhanced charge transport, and reduced charge recombination, leading to improvements in all photovoltaic parameters. Specially, the ternary OSCs incorporated with IDT-T-PCN achieve a decent PCE of 17.36%, which is obviously higher than that of the host PM6:Y6 binary device (PCE = 15.84%) owing to the simultaneous increase of VOC, JSC, and FF. This work highlights the role of careful material selection and design of the third component with the aim of optimizing device physics processes, crystallinity, and morphology of the blend film, ultimately realizing high-performance ternary OSCs.