Interface-engineering additives of poly(oxyethylene tridecyl ether) for low-band gap polymer solar cells consisting of PCDTBT:PCBM70 bulk-heterojunction layers

We herein report on the improved photovoltaic (PV) effects of using a polymer bulk-heterojunction (BHJ) layer that consists of a low-band gap electron donor polymer of poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-( 4', 7'-di-2-thienyl-2', 1', 3'-benzothiadiazole)) (PCDTBT) and an acceptor of [6,6]-phenyl C-71 butyric acid methyl ester (PCBM70), doped with an interface-engineering surfactant additive of poly(oxyethylene tridecyl ether) (PTE). The presence of an interface-engineering additive in the PV layer results in excellent performance; the addition of PTE to a PCDTBT:PCBM70 system produces a power conversion efficiency (PCE) of 6.0%, which is much higher than that of a reference device without the additive (4.9%). We attribute this improvement to an increased charge carrier lifetime, which is likely to be the result of the presence of PTE molecules oriented at the interfaces between the BHJ PV layer and the anode and cathode, as well as at the interfaces between the phase-separated BHJ domains. Our results suggest that the incorporation of the PTE interface-engineering additive in the PCDTBT:PCBM70 PV layer results in a functional composite system that shows considerable promise for use in efficient polymer BHJ PV cells. (C) 2012 Optical Society of America