Complementary Light Absorption and Efficient Exciton Dissociation Lead to Efficient and Excellent Ternary Polymer Solar Cells
Inverted structure ternary polymer solar cells (PSCs) are designed by blending J61 and PffBTT2-DPPT2 as the donor and Y6 as the acceptor. J61:PffBTT2-DPPT2:Y6 ternary films can replenish the weak absorption of PffBTT2-DPPT2:Y6 binary films at medium wavelengths and broaden near-infrared wavelength absorption windows. The more efficient exciton dissociation at the J61/PffBTT2-DPPT2, J61/Y6 and PffBTT2-DPPT2/Y6 interface, the electron transport channels can be formed in the ternary photoactive layers due to the good compatibility among J61, PffBTT2-DPPT2 and Y6. Simultaneously, effective hole transport occurs at the blend donors due to the smooth highest occupied molecular orbital (HOMO) energy levels of both J61 and PffBTT2-DPPT2. Optimized ternary PSCs have a power conversion efficiency (PCE) of 14.88%, with a short-circuit current density (JSC) of 25.79 mA cm-2, an open-circuit voltage (VOC) of 0.82 V and a fill factor (FF) of 70.4%. Approximately 10.1% and 14.5% PCE improvements are obtained compared to J61:Y6 and PffBTT2-DPPT2:Y6 binary PSCs, respectively, as a result of the simultaneous increase of the JSC and the FF of the optimized ternary PSCs. The broad and weak crystallized peak and high crystallization temperatures of the optimized ternary photoactive layer are beneficial for better thermal stability. After 80°C and 20 hours of a thermal annealing treatment for optimized ternary PSCs, 79% of the initial PCE was observed compared with only 72% and 70% of the initial PCE for J61:Y6 and PffBTT2-DPPT2:Y6 binary PSCs, respectively, under the same thermal stress conditions.