Designing a Third Component for Ternary Organic Solar Cells by Tailoring the Acceptor Structure

The incorporation of a third component into a binary blend, known as the ternary strategy, has proven to be a straightforward and promising method to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs). Tailoring a third-component molecule with a similar chemical structure to the host material is crucial for improving the miscibility and thus the film morphology of the ternary blend. In this study, we design a novel third-component molecule by cleaving the end group of a highly efficient acceptor material BTP-eC9, termed as BTP-Br2Cl. When introduced into a binary system of PM6/BTP-eC9, BTP-Br2Cl forms an alloy-like phase with the acceptor BTP-eC9 owing to their quite similar structures, which optimizes the morphology of the ternary film. Meanwhile, the ternary blend exhibits complementary absorption spectra and cascade energy-level alignments. As a result, BTP-Br2Cl-based ternary OSCs present simultaneous increases in each photovoltaic parameter, providing a PCE of 17.6% (16.6% for the control binary devices). This work offers a new strategy for designing third-component molecules by molecularly tailoring the host acceptor material to realize efficient ternary OSCs.