ITO-Free, Fully Solution Processed Transparent Organic Light-Emitting Electrochemical Cells on Thin Glass

Abstract

Organic light emitting diodes (OLEDs) have the advantages of self-emitting property, high luminous efficiency, full-colour capability, wide viewing angle, high contrast, low power consumption, low weight and flexibility. All these capacitate OLEDs to be an attractive optical source for display and lighting applications. However, the current manufacturing cost is still relative high, which obstacle its success in the display and lighting market. The main problems are indispensable low work function material for cathode and/or electron injection layer such as Ba, LiF, which require vacuum deposition and/or inert fabrication atmosphere, and widely used anode ITO which are not solution processable. Therefore, the fully solution processing manufacturing techniques are under intense investigation in order to reduce the cost. Compared to OLEDs, its derivation, organic light-emitting electrochemical cells (OLECs), show an intrinsic advantage in fully solution processing. By mixing metal ions and a solid electrolyte with light-emitting polymers as active materials, an in-situ doping and in-situ PN-junction can be generated within a three layer sandwich device. Because of this doping effect, work function adaption is not necessary and air-stable flexible electrodes like PEDOT:PSS can be used. Hereby, a manufacturing process for fully solution-processed transparent OLECs is presented, which consist of inkjet printed PEDOT:PSS anode and cathode, spin-coated ZnO interlayer, and spin-coated yellow light-emitting polymer plus dopant. Inkjet printing the electrode give the advantages of mask-free and spin-coating provides the homogeneous active layers. Furthermore, by manufacturing on 70 µm thin glass, a relative flexible transparent light source can be realized and enable the potential emerging applications like signal display on textiles.