Low Band Gap Polymers for Roll-to-Roll Coated Polymer Solar Cells

We present the synthesis of a low band gap copolymer based on dithienothiophene and dialkoxybenzothiadiazole (poly(dithienothiophene-co-dialkoxybenzothiadiazole), PDTTDABT). The optical properties of the polymer showed a band gap of 1.6 eV and a sky-blue color in solid films, The polymer was explored in roll-to-roll coating experiments and was optimized with respect to the manufacturing process and mixing ratio with [60]PCBM through a series of experiments with variation of the composition in steps of 1% w/w of respectively PDTTDABT and [60]PCBM a id a relatively broad optimimum was found around a 1:2 mixing ratio. Roll-to-roll coated polymer solar cell devices were prepared under ambient conditions employing solution processing in all steps including the metallic back electrode that was printed is a grid giving semitransparent solar cell devices. Solar cell modules comprising 16 serially connected cells were prepared with a total module active area of 96 cm(2). The devices were tested for operational stability under simulated sunlight (AM1.5G);old natural sunlight, and the photochemical stability of the polymer was examined using a combination of UV-vis and IR spectroscopy.