The impacts of processing conditions and molecular structures on the performance of diketopyrrolopyrrole-based solution processed organic solar cells

Furan and thiophene-substituted acceptor–donor–acceptor type soluble small molecules (SM1 and SM2) with absorption extending to 800 nm were synthesized and evaluated in solar cells combining with [6,6]-phenyl-C-61-butyric acid methyl ester (PC₆₁BM). The organic solar cells (OSCs) were optimized with different processing conditions, such as thermal annealing. The performances of the OSCs were more than double enhanced by thermal annealing. The highest power conversion efficiency of 5.5% was achieved in OSCs based on SM2:PC₆₁BM in a weight ratio of 1:1 annealed at 120 °C. In addition, the correlations between molecular structures and opto-electric properties as well as the performance of OSCs were also investigated, which indicates that replacing oxygen O with sulfur S on a main chain has much stronger influence on molecular property. These results will be very useful for further designing new molecules with even better property for OSCs.