Isomeric acceptors incorporation enables 18.1% efficiency ternary organic solar cells with reduced trap-assisted charge recombination

The donor-acceptor miscibility is one of the most critical factors in controlling the active layer morphologies with multiple components. However, how to practically select the third component with the desired miscibility for efficient ternary organic solar cells remains unresolved. Herein, we demonstrate that the surface energy of thin films could be manipulated by altering the weight ratios of the isomeric acceptors in the blend films and, therefore, the regulation of donor-acceptor miscibility. When the acceptor weight ratio (M- Cl:O-Cl) is 1:0.3, low miscibility (chi = 5.43 x 10-2K) with PM6 is achieved, and the power conversion efficiency of organic solar cells composed of PM6:M-Cl (17.1%) is enhanced to 18.1% (PM6:M-Cl:O-Cl). The increased power conversion ef-ficiency resulted from the surface energy-driven active layer morphology and donor-acceptor phase separations, associated with the significantly lower energetic disorder, trap density, and thus reduced free charge recombi-nation. Our findings underline the significance of the isomeric approach to managing the blend film surface energy and, therefore, the donor-acceptor miscibility for improving the device performance, providing guide-lines for the fabrication of high-performed ternary OSCs and material designs.

Automated summary

The donor-acceptor miscibility is crucial in controlling the active layer morphologies of ternary organic solar cells. This study demonstrates that the surface energy of blend films can be manipulated by altering the weight ratios of isomeric acceptors, leading to improved miscibility and device performance. By achieving low miscibility with PM6 through controlling acceptor weight ratios, the power conversion efficiency of PM6:M-Cl-based solar cells is enhanced from 17.1% to 18.1%. These improvements are attributed to the surface energy-driven active layer morphology and reduced energetic disorder and charge recombination.