Synthesis and photovoltaic properties of an alternating phenylenevinylene copolymer with substituted-triphenylamine units along the backbone for bulk heterojunction and dye-sensitized solar cells

Abstract

We have fabricated bulk heterojunction (BHJ) photovoltaic devices based on the as cast and thermally annealed P:[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) blends and found that these devices gave power conversion efficiency (PCE) of about 1.15 and 1.60% respectively. P is a novel alternating phenylenevinylene copolymer which contains 2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid units along the backbone and was synthesized by Heck coupling. This copolymer was soluble in common organic solvents and showed long-wavelength absorption maximum at 390–420 nm with optical band gap of 1.94 eV. The improvement of PCE after thermal annealing of the device based on the P:PCBM blend was attributed to the increase in hole mobility due to the enhanced crystallinity of P induced by thermal treatment. In addition, we have fabricated BHJ photovoltaic devices based on the as cast and thermally annealed PB: P:PCBM ternary blend. PB is a low band gap alternating phenylenevinylene copolymer with BF 2–azopyrrole complex units, which has been previously synthesized in our laboratory. We found that the device based on this ternary blend exhibited higher PCE (2.56%) as compared to either P:PCBM (1.15%) or PB:PCBM (1.57%) blend. This feature was associated with the well energy level alignment of P, PB and PCBM, the higher donor–acceptor interfaces for the exciton dissociation and the improved light harvesting property of the ternary blend. The further increase in the PCE with thermally annealed ternary blend (3.48%) has been correlated with the increase in the crystallinity of both P and PB. Finally, we used copolymer P as sensitizer for quasi solid state dye-sensitized solar cell and we achieved PCE of approximately 3.78%.