MORPHOLOGIES AND PERFORMANCE OF ORGANIC SOLAR CELLS USING LOW POLYMERIZATION DEGREE ALTERNATING COPOLYMER

The ternary blend films composed of low polymerization degree poly[2,6-(4,4-bis-(2-ethylhexyl) - 4H-cyclopenta[2,1-b; 3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (LDP-PCPDTBT), [6, 6]-phenyl-C61-butyric acid methyl ester (PC61BM), and polymethylmethacrylate (PMMA) were fabricated with and without using 1, 8-dibromooctane (DBO) as solvent additive. The role of PMMA was to enable the formation of the smooth and continuous thin films spun from the solution onto the conducting substrate. In addition, the good stability of the PMMA against the heat, oxygen and water attacks was useful for achieving the long lifetime of organic solar cells. The LDP-PCPDTBT and PC BM phases in the PMMA matrix were amorphous and crystalline, respectively, regardless of the additive processing. The crystalline aggregation of the LDP-PCPDTBT was hampered by the PC BM molecules, though the additive processing was able to promote the degree of crystallinity of the LDP-PCPDTBT. However, with the additive processing the phase separation of the LDP-PCPDTBT and PC BM components in the PMMA matrix was optimized, leading to the improved electron-transporting property and thereby an increase of 32.4% in the power conversion efficiency of solar cell, compared to without the additive processing. The current research indicates that the low polymerization degree alternating copolymers can be recycled as efficient electron donors in association with PMMA, helpful for reducing the material cost of organic solar cells.