Water-Processable Amphiphilic Low Band Gap Block Copolymer:Fullerene Blend Nanoparticles as Alternative Sustainable Approach for Organic Solar Cells

The preparation of water-processable nanoparticles (NPs) of polymer semiconductors assembled using an amphiphilic rod-coil block copolymer (BCP), and their application to active layer sustainable fabrication of organic photovoltaic devices are reported. The hydrophobic rod is a p-type semiconductor, while the hydrophilic coil is a short chain of poly-4-vinylpyridine strongly interacting with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). Through miniemulsion technique stable water-suspended blend NPs are obtained, avoiding nonconducting surfactant use. The amphiphilic BCP fulfills a dual function, as surfactant for stabilizing the blend NPs and as electron donor material in the active layer. After mild annealing of obtained films, blend NPs interconnect with each other forming compact and uniform layers with adequate morphology for efficient charge percolation to the electrodes. Space-charge limited hole mobility of ?5 × 10-3 cm2 V-1 s-1 in BCP-only NP films annealed at 120 °C (corresponding to a tenfold increase in mobility as compared to the p-type semiconductor films spin-coated from chlorinated solvents) indicates strong p-p interactions in the self-assembled NPs. Blend NPs were covered with thin PC61BM layer and used as active layers in photovoltaic devices displaying high photocurrents (11.5 mA cm-2) and average power conversion efficiency of 2.53% after annealing at 90 °C.