Synergistically Minimized Nonradiative Energy Loss and Optimized Morphology Achieved via the Incorporation of Small Molecule Donor in 17.7% Efficiency Ternary Polymer Solar Cells

Abstract To further improve the photovoltaic performance of the polymer solar cells (PSCs), it is an essential and significantly challenging issue to synergistically minimize non-radiative energy loss and optimize morphology. In this work, ternary PSCs are fabricated by incorporating a small molecule donor, namely BTTzR, into the state-of-the-art PM6:Y6 binary system. Detailed investigations suggest that BTTzR can form energy cascade with binary components to facilitate charge transfer. Furthermore, the integration of BTTzR can enhance crystallization and domain purity of the binary blend, and effectively suppress the aggregation of Y6, which ultimately leads to more efficient charge transport and lower non-radiative energy loss (ΔEnr). As a result, compared to the binary devices with PCE of 15.8% and ΔEnr of 0.23 eV, the ternary PSCs with 20% BTTzR contents achieved a significantly enhanced performance with PCE of 17.7% and lower ΔEnr of 0.19 eV, which are among the best results reported in the literatures to date. Therefore, this work not only offers a high-efficiency ternary blend system but also provides an efficient strategy to synergistically minimize non-radiative energy loss and optimize the morphology for the development of PSCs.