Polymer Bulk Heterojunction Photovoltaic Devices with Multilayer Structures Prepared by Thermal Lamination

Multilayer structures consisting of two blend layers of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61 butyric acid methyl ester (PCBM) and poly{N-[1-(2′-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2-b:2′,3′-d]pyrrole-2,6-diyl-alt-4,7-di(2-thienyl)-2,1,3-benzothiadiazole-5′, 5′ ′ -diyl} (PDTPDTBT):PCBM were prepared by a simple thermal lamination technique. Both of the layers contributed to the photocurrent generation simultaneously, as shown by external quantum efficiency spectra. The recombination rate at the interfaces was largely affected by the stacking order of the layers, resulting in the difference of the fill factors. The broadened light absorption range of the multilayer devices compared to that of single-layer P3HT:PCBM devices improved the short-circuit current from 8.83 to 9.41 mA cm−2 because of the absorption of the PDTPDTBT:PCBM layer, resulting in a power conversion efficiency of 3.0% with an open circuit voltage of 0.58 V and a fill factor of 54%.