The Blue Problem: OLED Stability and Degradation Mechanisms

Abstract

OLED technology has revolutionized the display industry and is promising for lighting. Despite its maturity, there remain outstanding device and materials challenges to address. Particularly, achieving stable and highly efficient blue OLEDs is still proving to be difficult; the vast array of degradation mechanisms at play, coupled with the precise balance of device parameters needed for blue high-performance OLEDs, creates a unique set of challenges in the quest for a suitably stable yet high-performance device. Here, we discuss recent progress in the understanding of device degradation pathways and provide an overview of possible strategies to increase device lifetimes without a significant efficiency trade-off. Only careful consideration of all variables that go into OLED development, from the choice of materials to a deep understanding of which degradation mechanisms need to be suppressed for the particular structure, can lead to a meaningful positive change toward commercializable blue devices.

Figure 1

Working principles for fluorescent, phosphorescent and TADF OLEDs.

Figure 2

Structures of emitter materials.

Figure 3

Structures of host materials.

Figure 4

Principal schemes for exciton harvesting mechanisms including (a) an exciplex with a TADF-type acceptor, (b) an intermediate phosphor, (c) a distributing TADF compound. Singlet and triplet states without indices correspond to a range of excited states.

Figure 5

Reported OLED LT95 values, sampled focusing on blue devices, and reported lifetimes of OLEDs used in industry.^{,,−,,,−,−,−,−}