Effect of thermal annealing on the performance of ternary organic photovoltaics based on PTB7:PC71BM:F8BT

The effect of thermal annealing on the inverted PTB7:PC71BM:F8BT ternary organic photovoltaics (OPVs) was systematically investigated, which was the first study about the effect of thermal annealing on the performance of PTB7-based OPVs. The results showed that the devices thermal annealed at 120 degrees C leading to 60 % increase of power conversion efficiency (PCE) compared with the asspun ternary OPVs and 3 % enhancement compared with the reference PTB7: PC71BM binary OPVs coated from chlorobenzene. The performance improvement was mainly attributed to formation of fine nanomorphology of the ternary blend film which could secure both charge separation and charge percolation path. However, the PCE decreased to 1.90 % with temperature higher than 140 degrees C, which was due to the disruptive morphology change and low quantum yield. The results also showed that the thermal annealing process could not only maintain optimized self-assembled morphology of the ternary blend film, but also influence the quantum yield and improve charge transfer efficiency further.