Suppressing charge recombination in small-molecule ternary organic solar cells by modulating donor-acceptor...

The ternary blending strategy has been a widely used method to achieve high performance in organic photovoltaics. However, the impact of the third component on the donor-acceptor interface geometries is still unclear, especially with regard to the microscopic structures in the mixed regions. In this study, we have investigated the donor-acceptor molecular packing structures in the mixed region as well as the exciton dissociation and charge recombination properties in all-small-molecule ternary solar cells based on the new DR3TBDTT:DR3TBDTT-E:PC71BM system by means of molecular dynamics simulations combined with electronic-structure calculations. The simulated results reveal that the incorporation of 10% DR3TBDTT-E in the ternary blend can lead to a decrease in the probability of finding PC71BM close to the central electron-donating benzodithiophene moiety, and thus this can reduce the binding energy of the lowest charge-transfer state and the electronic coupling of charge recombination. However, with a further increase of the doping ratio, PC71BM aggregation becomes weak, which is harmful to electron transport. Therefore, superior performance can be only obtained with a proper amount of the third component for ternary blend solar cells.