Asymmetric ITO/Ag/ZTO and ZTO/Ag/ITO anodes prepared by roll-to-roll sputtering for flexible organic light-emitting diodes

We report highly transparent and flexible asymmetric InSnO (ITO)/Ag/ZnSnO (ZTO) and ZTO/Ag/ITO multilayer anodes prepared by roll-to-roll sputtering for use as electrodes in flexible organic light-emitting diodes (OLEDs). The electrical, optical, mechanical, and morphological properties of the asymmetric ITO/Ag/ZTO and ZTO/Ag/ITO films were comprehensively compared. Due to the presence of the nano-sized Ag interlayer, the roll-to-roll sputtered asymmetric electrodes exhibited very low sheet resistance and good mechanical flexibility. Despite the similar electrical and optical properties of the ITO/Ag/ZTO and ZTO/Ag/ITO multilayers, the performance of flexible OLEDs fabricated with ITO/Ag/ZTO was better than that of OLEDs fabricated with ZTO/Ag/ITO; this is because hole injection from the multilayer is closely related to the work function of the top oxide layer. The successful operation of flexible OLEDs on asymmetric ITO/Ag/ZTO anodes indicates that roll-to-roll sputtered ITO/Ag/ZTO multilayers are a viable alternative to brittle ITO films for use as highly flexible and transparent electrodes.