Magnetic field effects on the quenching of triplet excitons in exciplex-based organic light emitting diodes

2018 ◽  
Vol 6 (21) ◽  
pp. 5721-5726 ◽  
Author(s):  
Peisen Yuan ◽  
Xianfeng Qiao ◽  
Donghang Yan ◽  
Dongge Ma
Keyword(s):  
Excited States ◽  
Light Emitting Diodes ◽  
Energy Levels ◽  
Organic Light Emitting Diodes ◽  
Magnetic Field Effects ◽  
Triplet Energy ◽  
Light Emitting ◽  
Organic Light ◽  
Triplet Excited States ◽  
Triplet Excitons

Triplet excited states in exciplex-based organic light emitting diodes (OLEDs) can be wasted by transferring their energy to the host material in a system with smaller triplet energy levels.

scholarly journals Triplet–triplet upconversion enhanced by spin–orbit coupling in organic light-emitting diodes

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Ryota Ieuji ◽  
Kenichi Goushi ◽  
Chihaya Adachi
Keyword(s):  
Excited States ◽  
Light Emitting Diodes ◽  
Energy Levels ◽  
Molecular Structures ◽  
Organic Light Emitting Diodes ◽  
Triplet Energy ◽  
Light Emitting ◽  
Singlet Exciton ◽  
Organic Light ◽  
Triplet Excited States

AbstractTriplet–triplet upconversion, in which two triplet excitons are converted to one singlet exciton, is a well-known approach to exceed the limit of electroluminescence quantum efficiency in conventional fluorescence-based organic light-emitting diodes. Considering the spin multiplicity of triplet pairs, upconversion efficiency is usually limited to 20%. Although this limit can be exceeded when the energy of a triplet pair is lower than that of a second triplet excited state, such as for rubrene, it is generally difficult to engineer the energy levels of higher triplet excited states. Here, we investigate the upconversion efficiency of a series of new anthracene derivatives with different substituents. Some of these derivatives show upconversion efficiencies close to 50% even though the calculated energy levels of the second triplet excited states are lower than twice the lowest triplet energy. A possible upconversion mechanism is proposed based on the molecular structures and quantum chemical calculations.

scholarly journals Suppression of external quantum efficiency rolloff in organic light emitting diodes by scavenging triplet excitons

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Buddhika S. B. Karunathilaka ◽  
Umamahesh Balijapalli ◽  
Chathuranganie A. M. Senevirathne ◽  
Seiya Yoshida ◽  
Yu Esaki ◽  
...  
Keyword(s):  
Quantum Efficiency ◽  
External Quantum Efficiency ◽  
Light Emitting Diodes ◽  
Energy Levels ◽  
Organic Light Emitting Diodes ◽  
Triplet Energy ◽  
Light Emitting ◽  
Organic Light ◽  
Current Densities ◽  
Triplet Excitons

Abstract Large external quantum efficiency rolloff at high current densities in organic light-emitting diodes (OLEDs) is frequently caused by the quenching of radiative singlet excitons by long-lived triplet excitons [singlet–triplet annihilation (STA)]. In this study, we adopted a triplet scavenging strategy to overcome the aforementioned STA issue. To construct a model system for the triplet scavenging, we selected 2,6-dicyano-1,1-diphenyl-λ5σ4-phosphinine (DCNP) as the emitter and 4,4′-bis[(N-carbazole)styryl]biphenyl (BSBCz) as the host material by considering their singlet and triplet energy levels. In this system, the DCNP’s triplets are effectively scavenged by BSBCz while the DCNP’s singlets are intact, resulting in the suppressed STA under electrical excitation. Therefore, OLEDs with a 1 wt.%-DCNP-doped BSBCz emitting layer demonstrated the greatly suppressed efficiency rolloff even at higher current densities. This finding favourably provides the advanced light-emitting performance for OLEDs and organic semiconductor laser diodes from the aspect of the suppressed efficiency rolloff.

scholarly journals Delayed Fluorescence from Inverted Singlet and Triplet Excited States for Efficient Organic Light-Emitting Diodes

2021 ◽  
Author(s):  
Daigo Miyajima ◽  
Naoya Aizawa ◽  
Yong-Jin Pu ◽  
Atsuko Nihonyanagi ◽  
Ryotaro Ibuka ◽  
...  
Keyword(s):  
Excited States ◽  
Light Emitting Diodes ◽  
Energy Gap ◽  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Positive Energy ◽  
Light Emitting ◽  
Organic Light ◽  
Spin Singlet ◽  
Triplet Excited States

Abstract Hund’s multiplicity rule states that for a given electronic configuration, a higher spin state has a lower energy. Rephrasing this rule for molecular excited states predicts a positive energy gap between spin-singlet and spin-triplet excited states, which has been consistent with numerous experimental observations over almost a century. Here, we report a fluorescent molecule that disobeys Hund’s rule, possessing a negative singlet–triplet energy gap of –11 meV. The energy inversion of the singlet and triplet excited states results in delayed fluorescence with short time constants of 0.2 μs, which anomalously decrease with decreasing temperature due to the emissive singlet character of the lowest-energy excited state. Organic light-emitting diodes using this molecule exhibited a fast transient electroluminescence decay with a peak external quantum efficiency of 17%, demonstrating potential implications for optoelectronic devices, including displays, lighting, and lasers.

scholarly journals High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Maria Vasilopoulou ◽  
Abd. Rashid bin Mohd Yusoff ◽  
Matyas Daboczi ◽  
Julio Conforto ◽  
Anderson Emanuel Ximim Gavim ◽  
...  
Keyword(s):  
High Efficiency ◽  
Light Emitting Diodes ◽  
High Mobility ◽  
Organic Light Emitting Diodes ◽  
Triplet Energy ◽  
Material Interface ◽  
Light Emitting ◽  
Thermally Activated ◽  
Organic Light ◽  
Hole Transporting

AbstractBlue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light-emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency (EQE) of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m−2. Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures.

Lowest unoccupied molecular orbital managing function of CN-substituted dibenzofuran in high triplet energy hosts for blue thermally-activated delayed fluorescent organic light-emitting diodes

2021 ◽  
Author(s):  
Sung Yong Byun ◽  
Kyung Hyung Lee ◽  
Jun Yeob Lee
Keyword(s):  
Molecular Orbital ◽  
Light Emitting Diodes ◽  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Organic Light ◽  
Lowest Unoccupied Molecular Orbital

The effect of lowest unoccupied molecular orbital (LUMO) management of high triplet energy electron transport type hosts on the device performance of blue thermally-activated delayed fluorescence (TADF) organic light-emitting diodes...

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