Time-resolved neutron reflectometry and photovoltaic device studies on sequentially deposited PCDTBT-fullerenel layers

We have used steady-state and time-resolved neutron reflectometry to study the diffusion of fullerene derivatives into the narrow optical gap polymer poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to explore the sequential processing of the donor and acceptor for the preparation of efficient organic solar cells. It was found that when [6,6]-phenyl-C61-butyric-acid-methyl-ester (60-PCBM) was deposited onto a thin film of PCDTBT from dichloromethane (DCM), a three-layer structure was formed that was stable below the glass-transition temperature of the polymer. When good solvents for the polymer were used in conjunction with DCM, both 60-PCBM and [6,6]-phenyl-C71-butyric-acid-methyl-ester (70-PCBM) were seen to form films that had a thick fullerene layer containing little polymer and a PCDTBT-rich layer near the interface with the substrate. Devices composed of films prepared by sequential deposition of the polymer and fullerene had efficiencies of up to 5.3%, with those based on 60-PCBM close to optimized bulk heterojunction (BHJ) cells processed in the conventional manner. Sequential deposition of pure components to form the active layer is attractive for large-area device fabrication, and the results demonstrate that this processing method can give efficient solar cells. © 2014, American Chemical Society.

Keywords

Neutron reflectors, Diffusion, Solar cells, Polymers, Solvents, Films

Citation

Clulow, A. J., Tao, C., Lee, K. H., Velusamy, M., McEwan, J. A., Shaw, P. E., Yamada, N. L., James, M., Burn, P. L., Gentle, T. R., & Meredith, P. (2014). Time-resolved neutron reflectometry and photovoltaic device studies on sequentially deposited PCDTBT-fullerenel layers. Langmuir, 30(38), 11474-11484. doi:10.1021/la5020779