Large Area Inkjet Printing for Organic Photovoltaics and Organic Light Emitting Diodes Using Non-Halogenated Ink Formulations

Abstract

The transfer of laboratory scale solution processing of organic electronics to large area roll-to-roll production requires the use of up-scalable deposition techniques. Furthermore, industrial production demands the omission of halogenated and other harmful solvents. Here, the authors discuss large area inkjet printing using industrial printheads for organic light emitting diodes (OLEDs) or organic photovoltaics (OPVs) applying halogen-free ink formulations. For the inkjet printing of the small molecule OLED emissive layer a low viscosity ink was selected (1.5 mPa s) to obtain layers with outstanding thickness homogeneity. Devices with 3.75 cm2 active area showed a uniform light emission similar to a device with a spin-coated emissive layer. Ink selection for the photo-active layer for OPVs was mostly determined by the device performance and the solubility of the polymer:electron acceptor blend. The inkjet printed layer showed a significant coffee stain effect, which was dependent on the printed layer thickness as well as the printed area. The loss of active material became smaller for larger printed areas. Devices with the inkjet printed photo-active layer from the halogen-free ink showed similar performance to a layer spin-coated from chlorinated solvents. This shows the potential of inkjet printing as a development and production tool for a variety of large area organic electronics.