Optimizing the performance of metal grid conductors for light-emitting electrochemical cell devices by modifying printing conditions

Printed metal grid conductors can be used in thin, flexible and large-area lighting sources based on, e.g., light-emitting electrochemical cells (LECs). Similar to organic light-emitting diodes (OLEDs), LECs are thin-film electroluminescent devices, which can be processed from solution. However, LECs have a simpler architecture, and do not rely on air-sensitive charge-injection layers or metals for electron injection. This offers simplicity for manufacturing process, cost-efficiency and easier large-scale manufacture. Printing methods such as inkjet and flexography are suitable for manufacturing the metal grid conductors needed in LEC devices. The goal of this article is to evaluate the potential of flexographic and inkjet printing to manufacture metal grid conductors on an industrial scale. Printing equipment that can be up-scaled to industrial scale is used and the printing conditions are modified to meet the device requirements. The performance and properties of inkjet and flexographic printed conductors are compared. Finally, the performance of full LEC devices is evaluated. As a conclusion, both inkjet and flexographic printing were found to be suitable for fabricating metal grid conductors since the surface roughness, layer thickness and electrical performance met the target values when the printing conditions were carefully optimized. Some compromises had to be made between adhesion, surface roughness, layer thickness and process reliability requirements. Finally, the performance of inkjet printed LEC devices has been demonstrated.