Evolution of Morphology and Open-circuit Voltage in Alloy-Energy Transfer Coexisted Ternary Organic Solar Cells
The oligomer-type small molecule PDT2FBT-ID is applied in a polymer/small molecule/fullerene ternary system. The PTB7-Th/PDT2FBT-ID/PC71BM ternary active layer shows complementary absorption spectra, enhanced face-on orientation and energy transfer property. Comparing to binary system, the FF of ternary system is improved from 66.72% to 76.14% and the Jsc is improved from 17.90 mA cm−2 to 18.92 mA cm−2. The maximum 11.1% PCE is obtained in ternary system with common inverted devices structure. An alloy-like domain structure and energy transfer between the two donor materials are found coexist in the ternary system. Based on the combined model, the variation of morphology and Voc was discussed in detail and compared with previous publications. More interpretation for the selection of third compound in high performance ternary organic solar cells was provided and this facile design strategy could also be widely used in other systems.