A new approach to the solvent system for inkjet-printed P3HT:PCBM solar cells and its use in devices with printed passive and active layers
Inkjet-printing is a suitable method to generate patterned structures from solvents containing active components. However, the process of inkjet-printing imposes severe limitations on the properties of the inkjet ink. This paper presents a new approach to solvent systems suitable for inkjet-printing common organic solar cell materials, poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C-61 as active layers in solar cells. Typically, low boiling point chlorinated solvents are used to dissolve P3HT and PCBM because both components are well soluble in these materials. During inkjet-printing, nozzle clogging due to evaporation of the ink in the inkjet print head is reduced when a high boiling point solvent is incorporated. Solar cells with active layers that were printed from an ink with a solvent system of chlorobenzene and trichlorobenzene showed power conversion efficiencies of 2.4% when active layer was dried at 130 degrees C. This compares to 2.6% for spin-coated solar cells from the same materials. In addition, devices with printed passive and printed active layers were prepared and power conversion efficiencies of 1.5% were achieved.