Digital fabrication of organic solar cells by Inkjet printing using non-halogenated solvents

Abstract

Inkjet printing offers versatility and flexibility for the sequential deposition of functional layers for the production of large area organic photovoltaics (OPV). Four layers of an OPV cell are inkjet printed, comprising an ITO-free semi-transparent front electrode (a metal current collecting grid, inkjet printed PEDOT:PSS and ZnO nanoparticle layers), and the photo-active layer combined with PEDOT:PSS as hole transport layer. To render the process R2R compatible, large area printing is performed using a 3.5cm wide printhead and non-halogenated ink formulations only. Similar performance is achieved for the inkjet printed cells as for cells with only spin coated layers and ITO. For the P3HT/PCBM bulk-heterojunction, a mixture of non-halogenated solvents ensured good solubility, proper printing behavior and a blend morphology that yields similar performance to a layer spin-coated from chlorinated solvents. The potential of inkjet printing for large area OPV was demonstrated by the fabrication of a module with 92cm2 active area, which showed an efficiency of 0.98%. Losses due to front and back electrode resistances are modeled and used to explain the recorded I-V curve. Combining these functional layers with inkjet printed electrodes lays out the roadmap toward fully roll-to-roll compatible digital fabrication of OPV.