Solution processable narrow bandgap polymers composed of asymmetrically alkyl-substituted 4H-cyclopenta[2,1-b;3,4-b']dithiophene units were synthesized by Suzuki polycondensation and characterized with thermal analysis and X-ray diffraction. Some of the materials showed a semi-crystalline nature of the material. When blended with PC71BM and integrated in bulk heterojunction organic solar cells, a moderate power conversion efficiency of about 2.5 % under AM 1.5 G (100 mW/cm2) conditions were obtained. However, upon purification of the semiconducting copolymers by preparative gel permeation chromatography, a noticeable rise in power conversion efficiency to more than 4 % was achieved. The purified polymer materials exhibited an enhanced high field-effect carrier mobility . The active layer morphology was explored by atomic force microscopy and transmission electron microscopy studies, showing phase segregation on the nanometer scale.

Photovoltaic performance of narrow bandgap copolymer derivatives based on 4H-Cyclopenta[2,1-b;3,4-b']dithiophene units

243rd National Meeting (2012)

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