Achieving 17.7% Efficiency of Ternary Organic Solar Cells by Incorporating a High Lowest Unoccupied Molecular Orbital Level and Miscible Third Component

Abstract

A ternary strategy has been demonstrated as being an effective method to improve the power conversion efficiency (PCE); however, general rules for materials selection are not fully comprehended. Herein, nonfullerene acceptor ITIC-M and fullerene acceptor PC70BM possessing higher lowest unoccupied molecular orbital (LUMO) and good miscibility with nonfullerene acceptor Y7 are incorporated as third components in the state-of-the-art of PM6:Y7 binary blend. As a result, the device PCE for both ternary devices improves from 16.46% for binary host to 17.73% and 17.67% for ITIC-M- and PC70BM-based ternary devices, respectively. The higher LUMO of the guest acceptor can play multiple roles to elevate the open-circuit voltage such as reducing energy-loss and reverse saturation current, creating less-localized shallow trap sites along with suppressing charge recombination, and decreasing Urbach energy. Moreover, the good miscibility facilitates an alloy-like phase in acceptors domain for efficient exciton dissociation and electron transport, which leads to improved short-circuit current density and fill factor in ternary devices. The results provide a promising approach to realize high-performance ternary organic solar cells by synergizing the compatible third component with host acceptor.