Over 16.5% efficiency in ternary organic solar cells by adding an alloyed acceptor with energy transfer process

Ternary organic solar cells (OSCs) based on ternary blends of light-absorption materials are simple and impactful strategies to boost the power conversion efficiency (PCE) of single-junction OSCs. In the work, a non-fullerene molecule ITIC with a medium bandgap (1.59 eV) is added to PM6:Y6 binary system as the third component. Compared with the 15.5% and 9.2% of PM6:Y6 and PM6:ITIC binary OSCs, respectively, PM6:Y6:ITIC ternary OSCs achieve a PCE of 16.6% by incorporating 5 wt% ITIC that results from simultaneously enhanced open-circuit voltage of 0.879 V, short-circuit current density of 25.50 mA cm⁻² and fill factor of 74.20%. The extended absorption, enhanced fluorescence resonance energy transfer, balanced carrier transport with increased electron and hole mobility, and reduced energy loss in PM6:Y6:ITIC ternary films enhance the photovoltaic performance of ternary OSCs. The work illustrates that adding an alloyed second acceptor with efficient energy transfer processes in ternary OSCs has great potential to further improve the performance of OSCs.