Formation of Organic Alloys in Ternary-Blend Solar Cells with Two Acceptors Having Energy Level Offsets Exceeding 0.4 eV

Recent studies demonstrated that with proper selection of chemically compatible constituents the open-circuit voltage (V-oc) of ternary-blend solar cells can be tuned across the composition window of the active layer. In this study, we probed the limit of the offset between the lowest unoccupied molecular orbital (LUMO) energy levels of the two acceptors in ternary blends containing one donor and two acceptors. We demonstrate, for the first time, that ternary-blend active layers with two acceptors having an energy-level difference between their LUMO levels exceeding 0.4 eV can still result in solar cells exhibiting composition dependent open-circuit voltage (V-oc). Our results suggest strong electronic interactions between the acceptors, with the electron wave function delocalized over multiple molecules. These findings have broadened the library of possible candidates for active layers of ternary-blend solar cells with tunable V-oc, and established guidelines for the design of next-generation materials for efficient performance of such devices.