Trilayer OLEDs Using LEPs

There are several reports of trilayer OLEDs using three distinct layers for electron transport, hole transport and emission. This device configuration has the advantage that each layer can be optimised for one distinct function, i.e. hole-transport, electron-transport and light emission. The problems associated with the fabrication of OLEDs with three distinct polymer layers of controlled thickness, integrity and homogeneity by the technique of deposition from solution by spin-coating are not inconsiderable. 

An early example of a trilayer OLED used PVK (62) as the HTL, a polymer blend of PBD in poly(methacrylate) as the ETL and a 

Conjugated organic polymers such as those shown in the Tables have been used in multilayer OLEDs as the HTL or combined HTL and emission layers or as the ETL or combined ETL and emission layer. The combined polymers (75-77) shown in Table 6.15 have been used as combined ETL, HTL and emission layers in various OLED configurations. Blends of these polymers have also been used to maximise OLED efficiency, although phase separation is always a problem with mixtures (blends) of main-chain polymers. 

Trilayer OLEDs using LEPs have been fabricated with external quantum efficiencies (rjeff 4-10%) comparable to those obtained for analogous OLEDs using small molecules or LEDs. The low threshold and operating voltages ( 5 V) of these multilayer polymer OLEDs means that they can be used as displays in battery operated devices. 

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