Key issues and recent progress of high efficient organic light-emitting diodes

•Summary innovated and efficient light out-coupling technology.•Novel transparent conducting electrodes for flexible OLEDs.•Ideas for improving white emission OLEDs performance.

Organic light-emitting diodes (OLEDs) are considered as an ideal in next generation of flat panel displays and solid state lighting source. Still, the stability and efficiency of OLEDs remain great challenges for its commercialization application. This article provides an overview on working principle of different kinds of luminescence, effective methods to improve quantum efficiency, recent progress of white emission OLEDs, novel types of transparency electrode for flexible OLEDs and the stability of OLEDs. A series of interesting and promising ideas to improve the performance of OLEDs are summarized from physical engineering based on the recent achievement of high brightness, high efficient and good stability of OLEDs.