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Organic solar cells are a favorable alternative to their inorganic counterparts because the functional layers of these devices can be processed with printing or coating on a large scale. In this study, a novel absorber polymer was synthesized, blended with fullerene and deposited with inkjet printing for solar cell applications. A fluorene based terpolymer with dialkyl substituted diphenyl-dithienylbenzopyrazine and triphenylamine units was synthesized by Suzuki polymerization with high molecular weights. The introduction of dialkyl substituted diphenyldithienylbenzopyrazine in the fluorene main chain leads to LUMO-energy level of -3.1 eV and to an open circuit voltage of 0.96 V in solar cells. All the requirements were fulfilled to achieve absorber polymers with high efficiencies including a HOMO energy level which is lower than -5.2 eV, a band gap in the range of 1.3-1.9 eV and a hole mobility in OTFTs greater than 1 x 10-3cm2/Vs. Solar cells with printed layers were compared to those with spin coated films in order to evaluate inkjet printing as a thin film deposition method. Efficiency values of 3.7% were found for devices with inkjet printed layers or spin coated layers when using chlorinated solvents. In order to be able to use inkjet printing on a large scale, hazardous, chlorinated solvents should be avoided when depositing the functional materials. Anisol/tetralin was used as an alternative solvent system. It was found that devices prepared from the chlorine-free system showed only slightly lower efficiencies of 2.7% with respect to the chlorinated system. A coarser phase separation was found with energy filtered transmission electron microscopy plasmon mapping which most likely resulted in the performance differences for the chlorinated and chlorine-free solvent systems. This paper, originally published on 17 October 2013, was replaced with the correct version on 30 January 2014. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
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