The Mechanism and Effective Connecting Structure for Tandem Organic Light-Emitting Devices

We introduce an effective connecting structure in which an ultrathin middle metal layer is sandwiched between efficient electron-and hole-injection layers for the tandem OLEDs, which in essence, avoids the use of reactive metals during fabrication. A model based on the Fermi-level pinning effect has been proposed as the mechanism of the connecting structure in the tandem devices. This model is also consistent with the results obtained from the photovoltaic effect measurements in tandem OLEDs.