The contribution of triplet–triplet annihilation to the lifetime and efficiency of fluorescent polymer organic light emitting diodes

King, Simon; Cass, Michael; Pintani, Martina; Coward, Chris; Dias, Fernando B.; Monkman, Andrew P.; Roberts, Matthew

doi:10.1063/1.3561430

Cited by 80 publications

(71 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Also consistent with our observations, the importance of the layers immediately adjacent to the EML was emphasized. Interestingly, despite the large differences in device architectures and the chemical nature of the EML materials, the polymer-based OLEDs benefited from TTA to a similar degree [32,33].…”

Section: Ubiquitous Nature Of Triplet-triplet Annihilation In Efficiementioning

confidence: 99%

Triplet–triplet annihilation in highly efficient fluorescent organic light-emitting diodes: current state and future outlook

Kondakov

2015

Phil. Trans. R. Soc. A.

137

119

View full text Add to dashboard Cite

Studies of delayed electroluminescence in highly efficient fluorescent organic light-emitting diodes (OLEDs) of many dissimilar architectures indicate that the triplet–triplet annihilation (TTA) significantly increases yield of excited singlet states—emitting molecules in this type of device thereby contributes substantially to their efficiency. Towards the end of the 2000s, the essential role of TTA in realizing highly efficient fluorescent devices was widely recognized. Analysis of a diverse set of fluorescent OLEDs shows that high efficiencies are often cor-related to TTA extents. It is therefore likely that it is the long-term empirical optimization of OLED efficiencies that has resulted in fortuitous emergence of TTA as a large and ubiquitous contributor to efficiency. TTA contributions as high as 20–30% are common in the state-of-the-art OLEDs, and even become dominant in special cases, where TTA is shown to substantially exceed the spin-statistical limit. The fundamental features of OLED efficiency enhancement via TTA—molecular structure-dependent contributions, current density-dependent intensities in practical devices and frequently observed antagonistic relationships between TTA extent and OLED lifetime—came to be understood over the course of the next few years. More recently, however, there was much less reported progress with respect to all-important quantitative details of the TTA mechanism. It should be emphasized that, to this day and despite the decades of work on improving blue phosphorescent OLEDs as well as the recent advent of thermally activated delayed fluorescence OLEDs, the majority of practical blue OLEDs still rely on TTA. Considering such practical importance of fluorescent blue OLEDs, the design of blue OLED-compatible materials capable of substantially exceeding the spin-statistical limit in TTA, elimination of the antagonistic relationship between TTA-related efficiency gains and lifetime losses, and designing devices with an extended range of current densities producing near-maximum TTA electroluminescence are the areas where future improvements would be most beneficial.

show abstract

Section: Ubiquitous Nature Of Triplet-triplet Annihilation In Efficiementioning

confidence: 99%

Triplet–triplet annihilation in highly efficient fluorescent organic light-emitting diodes: current state and future outlook

Kondakov

2015

Phil. Trans. R. Soc. A.

137

119

View full text Add to dashboard Cite

show abstract

“…Two possible explanations for such a high EQE are as follows: (i) the value of Z s attributable to electrical injection may be higher than 25% because of the triplet-triplet annihilation process 37,38 and the fact that the singlet-formation cross-section of F8BT is greater than the triplet-formation cross-section of F8BT 39 and (ii) the enhanced light extraction (Z e ) of the iPLEDs achieved by using ZnO-R may also contribute to the high EQE value. EA, ethanolamine; EQE, external quantum efficiency; FTO, fluorine-doped tin oxide; iPLED, inverted-structured polymer light-emitting diode; L, luminance; LE, luminous efficiency; ME, methoxyethanol; PE, power eddiciency.…”

Section: Ripplementioning

confidence: 99%

Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer

et al. 2014

View full text Add to dashboard Cite

Organic light-emitting diodes have been recently focused for flexible display and solid-state lighting applications and so much effort has been devoted to achieve highly efficient organic light-emitting diodes. Here, we improve the efficiency of inverted polymer light-emitting diodes by introducing a spontaneously formed ripple-shaped nanostructure of ZnO and applying an amine-based polar solvent treatment to the nanostructure of ZnO. The nanostructure of the ZnO layer improves the extraction of the waveguide modes inside the device structure, and a 2-ME þ EA interlayer enhances the electron injection and hole blocking in addition to reducing exciton quenching between the polar-solvent-treated ZnO and the emissive layer. Therefore, our optimized inverted polymer light-emitting diodes have a luminous efficiency of 61.6 cd A À 1 and an external quantum efficiency of 17.8%, which are the highest efficiency values among polymer-based fluorescent light-emitting diodes that contain a single emissive layer.

show abstract

Section: Introductionmentioning

confidence: 99%

“…In this case, the yield of singlet emissive states is highly dependent on the relative energy order of the excited singlet and triplet energy levels in the molecule, and the maximum total singlet yield is limited to 62.5%. OLEDs with TTA contribution as large as 40% have been demonstrated but the relative merit of this approach is still unsatisfactory [6,7].The TADF mechanism uses the thermal energy to assist reverse intersystem crossing and promote the up-conversion of lower triplet states into more energetic but emissive singlet states [8]. The efficiency of the TADF mechanism is controlled by two main parameters, the energy splitting between the singlet and triplet states ( E ST ) and the efficiency of non-radiative pathways available for the excited singlet and triplet states to decay [9,10].…”

mentioning

confidence: 99%

Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet–triplet energy gap

Dias

2015

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

The kinetics of thermally activated delayed fluorescence (TADF) is investigated in dilute solutions of organic materials with application in blue lightemitting diodes (OLEDs). A method to accurately determine the energy barrier ( E a ) and the rate of reverse intersystem crossing (k Risc ) in TADF emitters is developed, and applied to investigate the tripletharvesting mechanism in blue-emitting materials with large singlet-triplet energy gap ( E ST ). In these materials, triplet-triplet annihilation (TTA) is the dominant mechanism for triplet harvesting; however, above a threshold temperature TADF is able to compete with TTA and give enhanced delayed fluorescence. Evidence is obtained for the interplay between the TTA and the TADF mechanisms in these materials. IntroductionThermally activated delayed fluorescence (TADF) has recently become one of the favorite methods to overcome the 25% limitation on the internal quantum efficiency of organic light-emitting diodes (OLEDs) due to spin statistics [1,2]. The ratio (1 : 3) between singlet and triplet excited states created from charge recombination in OLEDs imposes that only 25% of the charge recombination events will give origin to emissive singlet states, the rest is wasted by other non-radiative processes [3]. This imposes a serious limitation for the application of organic materials in displays and lighting devices [4]. Different methods have been used when trying to overcome this limitation, including the use of organic phosphors containing Ir(III), Pt(II) or other heavy metals, which can convert dark triplet states into emissive 2015 The Author(s) Published by the Royal Society. All rights reserved. species with 100% efficiency due to the enhanced intersystem crossing via the heavy atom effect. These emitting complexes have to be dispersed in charge-transporting host materials with relatively higher energy triplet levels to avoid emission quenching. Finding appropriate host materials for emitters in the blue region is difficult. Also, the performance of blue-emitting phosphors is affected by substantial degradation, thus obtaining stable, long lifetime and deep blue-emitting phosphors has been difficult. Owing to these reasons, deep blue phosphorescent OLEDs with long operation lifetime have not yet been demonstrated [5]. Moreover, heavy metals are not abundant elements in nature, which will cause unnecessary stress on the fabrication costs of these devices.Using triplet-triplet annihilation (TTA) to up-convert non-emissive triplet states to emissive singlet states has also been attempted. In this case, the yield of singlet emissive states is highly dependent on the relative energy order of the excited singlet and triplet energy levels in the molecule, and the maximum total singlet yield is limited to 62.5%. OLEDs with TTA contribution as large as 40% have been demonstrated but the relative merit of this approach is still unsatisfactory [6,7].The TADF mechanism uses the thermal energy to assist reverse intersystem crossing and promote the up-conversion of lowe...

show abstract

The contribution of triplet–triplet annihilation to the lifetime and efficiency of fluorescent polymer organic light emitting diodes

Cited by 80 publications

References 28 publications

Triplet–triplet annihilation in highly efficient fluorescent organic light-emitting diodes: current state and future outlook

Triplet–triplet annihilation in highly efficient fluorescent organic light-emitting diodes: current state and future outlook

Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer

Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet–triplet energy gap

Contact Info

Product

Resources

About