Journal of Materials Chemistry A, 2017, vol 5, 20, pp. 9859-9866
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 properties. Compared to the binary system, the FF of the 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 PCE of 11.1% is obtained in the ternary system with a common inverted device structure. Additionally, an alloy-like domain structure and energy transfer between the two donor materials are found to coexist in the ternary system. Based on the combined model, the variation in morphology and Voc is discussed in detail and compared with previous publications. An in-depth interpretation for the selection of a third compound in high performance ternary organic solar cells is provided. Finally, this facile design strategy could also be widely used in other systems.