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

TL;DR: In this paper, a review summarizes the recent achievements in flexible transparent conductive electrodes, device fabrication as well as light extraction technologies, and the device operation stability is discussed with a focus on device degradation mechanisms and encapsulation methods.

Abstract: White organic light-emitting devices (WOLEDs) have drawn intense attention in both scientific and industrial communities due to their potential applications in full-color flat-panel displays, back-lighting sources for liquid-crystal displays and solid-state lighting sources. [1,2] To achieve white emission, mixtures of the three red, green and blue (RGB) primary colors or two complementary colors, are typically required. Various approaches towards realizing WOLEDs have been re-ported, including multilayer structures capable of sequential energy transfer, [3–5] multiple component emissive layers containing an appropriate ratio of RGB phosphorescent or fluorescent dopants, [6–14] polymer blends containing RGB emitting species, [8–16] charge transfer exciplexes or excimers broad emission [4,17] and single component layers that utilize a polymer with broad emission. [18–21] Polymer light-emitting devices (PLEDs) [8–15] offer the advantages of solution processing, including screen printing and ink-jet deposition, large area coverage, and low power consumption. However, white emission PLEDs are less efficient with respect to power efficiency (PE) and luminous efficiency (LE), when compared with devices fabricated using vacuum-deposition technologies. For example, vacuum deposited WO-LEDs have efficiencies that exceed that of the incandescent light bulb (12–17 lm W –1 ). [1] In contrast, to the best of our knowledge, the most efficient white emission PLEDs are below 10 lm W –1 , [12–14] still far away from practical applications for solid-state lighting. In