Fuzzy-junction organic light-emitting devices

Abstract

A ''fuzzy-junction'' organic light-emitting device ͑OLED͒ containing a graded organic-organic interface is reported. Such graded junction is effectively produced utilizing interdiffusion through an ultrathin interfacial fusing layer sandwiched between two functional layers. With a glass transition temperature (T g) lower than remaining layers, this fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its T g. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices. As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of ϳ20 lm/W, substantially higher than ϳ14 lm/W of a corresponding abrupt-junction device.

Graded doped structure fabricated by vacuum spray method to improve the luminance of polymer light-emitting diodes

“…As there is no interface between the electron and hole transport materials in this structure, it is expected that there will be an increase in the lifetime of the devices. For small organic molecules, graded structures can be fabricated by codeposition processes [4][5][6][7] and annealing [8], but for polymers it is difficult to control the gradient profile in the active layer due to dissolution by the solvent. There have been attempts to achieve polymer graded structures, such as molecular-scale interface engineering [9], self-organization [10], and thermal transfer process [11]; however, the processes involved are not simple.…”

High temperature operation and stability of phosphorescent OLEDs

“…Diffusion can lead to fused mixed layers formation, which is known to improve OLED lifetimes [9]. Thermal treatment of devices has been reported [10] and shown to cause an improvement in efficiency and a reduction in operating voltage. However, from this standpoint it is difficult to explain the large improvement observed in RD07s stability.…”

Dependence of dark spot growth on cathode/organic interfacial adhesion in organic light emitting devices

“…In previous studies on the effect of subjecting the organic layers to high temperatures, it has been reported that depositing HTL and ETL at higher temperature resulted in a fused HTL-ETL interface [56]. The interface was mentioned to have lost its abrupt heterojunction property as a result of heat.…”