Improved photovoltaic performance of D-A1-D-A2 terpolymer via synergetic effects of copolymerization and blending

Abstract A series of copolymers FD10 , FD21 , FD11 , FD12 and FD01 have been designed and synthesized via copolymerization of 3,3′-difluoro-2,2′-bithiophene (FTT) and two electron-deficient units, fluorinated benzothiadiazole (FBT) and diketopyrrolopyrrole (DPP), respectively. These terpolymers exhibit broad absorption ranging from 400 nm to 900 nm. The polymer solar cells (PSC) were prepared from these terpolymers as donor and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) as acceptor. A power conversion efficiency (PCE) value of 6.41% for terpolymer FD21 with a high short-circuit current density ( J sc ) of 12.52 mA cm −2 is achieved via tuning the composition of FBT and DPP unit (FBT:DPP = 2:1). The binary polymer FD10 shows the highest open-circuit voltage ( V oc ) of 0.86 V. In order to further improve the photovoltaic performance of the terpolymer, the blends of FD10 and FD21 with different weight ratio were prepared and applied as donor materials for PSC. The highest PCE of 7.04% with a J sc of 13.79 mA cm −2 and a V oc of 0.77 V for blend FD10 : FD21:PC 71 BM (0.5:0.5:1.5) was attained due to more balanced mobility ( μ h /μ e  = 1.02) and an appropriate microphase separation. This work provides an effective strategy to improve photovoltaic performance of terpolymers via synergetic effects of copolymerization and blending.