Ternary organic solar cells are promising
candidates for bulk heterojunction
solar cells; however, improving the power conversion efficiency (PCE)
is quite challenging because the ternary system is complicated on
phase separation behavior. In this study, a ternary organic solar
cell (OSC) with two donors, including one polymer (PTB7-Th), one small
molecule (<i>p</i>-DTS(FBTTH<sub>2</sub>)<sub>2</sub>),
and one acceptor (PC<sub>71</sub>BM), is fabricated. We propose the
two donors in the ternary blend forms an alloy. A notable averaged
PCE of 10.5% for ternary OSC is obtained due to the improvement of
the fill factor (FF) and the short-circuit current density (<i>J</i><sub>sc</sub>), and the open-circuit voltage (<i>V</i><sub>oc</sub>) does not pin to the smaller <i>V</i><sub>oc</sub> of the corresponding binary blends. A highly ordered face-on
orientation of polymer molecules is obtained due to the formation
of an alloy structure, which facilitates the enhancement of charge
separation and transport and the reduction of charge recombination.
This work indicates that a high crystallinity and the face-on orientation
of polymers could be obtained by forming alloy with two miscible donors,
thus paving a way to largely enhance the PCE of OSCs by using the
ternary blend strategy
