Tenfold increase in the lifetime of blue phosphorescent organic light-emitting diodes

Abstract

Organic light-emitting diodes are a major driving force of the current information display revolution due to their low power consumption and potentially long operational lifetime. Although electrophosphorescent organic emitters have significantly lower power consumption than fluorescent emitters, the short lifetime of electrophosphorescent blue devices has prevented their application in displays for more than a decade. Here, we demonstrate a novel blue electrophosphorescent device with a graded dopant concentration profile in a broadened emissive layer, leading to a lower exciton density compared with a conventional device. Thus, triplet-polaron annihilation that leads to long-term luminescent degradation is suppressed, resulting in a more than threefold lifetime improvement. When this strategy is applied to a two-unit stacked device, we demonstrate a lifetime of 616±10 h (time to 80% of the 1,000 cd m À 2 initial luminance) with chromaticity coordinates of [0.15, 0.29], representing a tenfold lifetime improvement over a conventional blue electrophosphorescent device.

Electroplex as a New Concept of Universal Host for Improved Efficiency and Lifetime in Red, Yellow, Green, and Blue Phosphorescent Organic Light‐Emitting Diodes

“…Two types of mixed hosts, i.e., exciplex free mixed hosts and exciplex mixed hosts, are known to provide high efficiency and long lifetimes in red, green, and blue PhOLEDs 6. However, exciplex free hosts were not useful to improve the lifetime of PhOLEDs due to TPA by charge trapping 7. Exciplex hosts were effective in green PhOLEDs,8 but they have rarely been used in blue PhOLEDs.…”

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

“…The general expression from Eq. 2.35 then simplifies to 36) with the site (rather than state) occupation probabilities p A (t), p B (t) and charge transfer rates k A→B , k B→A between the conjugated segments A and B. For N > 1, i.e., multiple charge carriers, the number of system configurations increases dramatically.…”

“…Severe stability issues are most prominent in OLEDs, but in principle extend to any device, notably organic thin-film transistors with high-mobility n-type conductors [35]. Deep-blue emitters for OLEDs, for example, are still vulnerable to degradation processes related to the long lifetime of the highly energetic excited triplet state [36]. In this context, thermally activated delayed fluorescence is a mechanism that repopulates singlet via triplet states [37], thus not only maintaining high external quantum efficiencies, but also rendering heavy metal complexation for spin-orbit coupling redundant.…”

“…3.29. The resulting linear system of equations for ∆Q p(s) 36) and is best solved iteratively via successive over-relaxation [110,117] , based on an aperiodic-periodic-type decomposition, is therefore needed: To this end, the foreground density in its neutral charge and polarization state P (n) is again added toB * ; the potentials generated by the resulting periodic charge density B * can be computed efficiently after an Ewald transformation, which starts from the decomposition of the 1/r charge-charge interaction into 1/r = erf(βr)/r + erfc(βr)/r. Here, the first term absorbs the long-range contribution to be evaluated in reciprocal space, following a Fourier transformation of the sum over periodic images.…”

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…It could be that the extensive charge delocalization in the conjugated polymers may significantly lower the triplet energy level (T 1 ) 79, and; hence, the tripletpolaron annihilation (TPA) and TTA processes would not be able to produce excessive energy that causes structural disruption of the emitting species, where the former has been regarded as the major degradation cause for the blue phosphorescent materials. 141 Moreover, the conjugated backbone might result in better intrachain or interchain bimolecular triplet exciton communication to allow a more efficient TTA process. Of course, it could also be that the currently reported PLED efficiencies of fluorescent polymers with non-conjugated backbone…”