Direct Observation of Efficient Triplet–Triplet Energy Transfer in Phosphorescent Organic Light-Emitting Diode

Fukagawa, Hirohiko; Shimizu, Takahisa; Osada, Yoshihito; Kamada, Taisuke; Kiribayashi, Yukihiro; Yamamoto, Toshihiro; Shimidzu, Naoki

doi:10.7567/apex.6.052104

Cited by 10 publications

(8 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Some of the residual SEs in SY-PPV can be converted to TEs by direct ISC. TEs in SY-PPV near the enclosed fullerenes could be converted to fullerene TEs by Dexter type energy transfer, a process reported in a number of host-guest blends, [49][50][51][52]54] polymer:fullerene blends of low fullerene concentration, [53] and polymer-polymer blend films. [33,56] Our EDMR detection of TE signature of SY-PPV in these devices of low fullerene concentration shows that the TE-TE energy transfer does not completely quench the polymer TEs.…”

Section: Energy Of the Charge Transfer State And Triplet Formation Pathwaysmentioning

confidence: 83%

Understanding Triplet Formation Pathways in Bulk Heterojunction Polymer:Fullerene Photovoltaic Devices

Tedlla

Zhu

Cox

et al. 2014

Advanced Energy Materials

View full text Add to dashboard Cite

Triplet exciton (TE) formation pathways have systematically been investigated in prototype bulk heterojunction (BHJ) SY-PPV:PCBM, SY-PPV:PC70BM, and SY-PPV:ICBA solar cell devices of varying compositions using complementary optoelectrical and electrically detected magnetic resonance (EDMR) spectroscopies. In this investigation it is shown that EDMR spectroscopy allows the unambiguous demonstration of fullerene triplet production in BHJ polymer:fullerene solar cells. EDMR triplet detection under selective photoexcitation of each blend component and of the interfacial charge transfer (CT) state unravels that low lying fullerene TEs are produced by direct intersystem crossing from singlet excitons (SEs). The direct CT-TE recombination pathway, although energetically feasible, is kinetically suppressed in these devices. However, high energy CT states in the CT manifold can contribute to the population of the fullerene triplet state via a direct CT-SE conversion. This undesirable energetic alignment could be one of the causes for the severe reduction in photocurrent observed when the open circuit voltage of polymer:fullerene solar cells is pushed to or beyond 1.0 V.

show abstract

Section: Energy Of the Charge Transfer State And Triplet Formation Pathwaysmentioning

confidence: 83%

Understanding Triplet Formation Pathways in Bulk Heterojunction Polymer:Fullerene Photovoltaic Devices

Tedlla

Zhu

Cox

et al. 2014

Advanced Energy Materials

View full text Add to dashboard Cite

show abstract

“…The Bepp 2 -based PHOLED exhibits the high η EQE of 23.6%. [ 12,14,15 ] The operational stability of the Bepp 2 -based PHOLED is much higher than that of the CBP-based PHOLED. [ 13 ] Effi cient energy transfer from Bepp 2 to Ir(mppy) 3 is expected, as for the Bebq 2 /phosphorescent dopant confi guration, since high effi ciency is obtained even in the 1-wt% doped PHOLED.…”

Section: Host-dependent Device Characteristics Of Green Pholedsmentioning

confidence: 99%

Highly Efficient and Stable Phosphorescent Organic Light‐Emitting Diodes Utilizing Reverse Intersystem Crossing of the Host Material

Fukagawa

Shimizu

Kamada

et al. 2014

Advanced Optical Materials

Self Cite

View full text Add to dashboard Cite

high reliability, their internal electroluminescence quantum effi ciency ( η int ), defi ned as the number of photons generated per injected carrier, is limited to 25% because of the exciton-branching ratio of singlet excited states under electrical excitation. [ 2 ] To increase the value of η int , several methods were proposed, such as employing phosphorescent materials with heavy atoms, utilizing triplet-triplet exciton annihilation for extra singlet generation, and employing thermally activated delayed fl uorescence (TADF) materials. [3][4][5][6] In particular, an η int value of 100% is expected by employing phosphorescent and TADF materials. In 1999, effi cient electrophosphorescence was fi rst demonstrated using iridium complexes, and an η int value of almost 100% was achieved afterwards. [ 7,8 ] Many highly effi cient phosphorescent OLEDs (PHOLEDs) with values of η int of about 100% were demonstrated by using a device architecture that can confi ne charges and excitons inside the phosphorescence-emitting layer. [ 9,10 ] Although PHOLEDs have a longer history than OLEDs fabricated with TADF materials, the basic concept for improving both the effi ciency and operational stability is not clear; this is the greatest challenge for the practical application of PHOLEDs.In recent years, several PHOLEDs with high effi ciency and high operational stability were reported. [ 11,12 ] The confi guration of the emitting layer, i.e., the combination of the phosphorescent dopant and the surrounding host material, was proposed as a key parameter determining the effi ciency and stability of PHOLEDs. Particular metal complexes such as bis(benzo[h]quinolin-10-olato-kN,kO)beryllium( II ) (Bebq 2 ) and bis[2-(2-hydroxyphenyl) benzothiazolato]zinc( II ) [Zn(BTZ) 2 ] are effective hosts for red PHOLEDs; however, an effective host for green/blue PHOLEDs with high operational stability was not yet reported. If the role of effective hosts such as metal complexes in a highly effi cient and stable PHOLED is revealed, the development of useful host materials for green/blue PHOLEDs is expected to be accelerated.Herein, to investigate a possible strategy for realizing highly effi cient and stable PHOLEDs, we examine the energy-transfer mechanism in such PHOLEDs. A highly effi cient green PHOLED that exhibits a half lifetime of over 10000 h with an initial luminance of 1000 cd m -2 is realized by using a Phosphorescent organic-light emitting diodes (PHOLEDs) exhibit an internal quantum effi ciency of 100% and their early practical realization is expected. One of the main challenges in PHOLEDs is to improve the operational stability of green and blue devices. Triplet exciton dynamics in stable PHOLEDs, which are different from those in unstable PHOLEDs, are shown. An effi cient and stable green PHOLED is demonstrated by employing a suitable host that surrounds the phosphorescent dopant. The transient photoluminescence characteristics show that the triplet excitons of the host, which are generally unstable, are rapidly transferred to the dop...

show abstract

“…However, phosphorescent materials have the disadvantages of high cost, limited resources, and environment pollution because of heavy metal atoms. [ 4–6 ] Compared to traditional fluorescent and phosphorescent materials, thermally activated delayed fluorescence (TADF) materials have drawn enormous research interest because they can harvest both singlets and triplets without heavy metal atoms. [ 7,8 ]…”

Section: Introductionmentioning

confidence: 99%

High‐Efficiency Nondoped White Organic Light‐Emitting Diodes Based on All‐Exciplex Emission

Zhao

Zhou

et al. 2021

Physica Status Solidi (a)

View full text Add to dashboard Cite

A nondoped full‐exciplex approach is applied in white organic light‐emitting diodes (WOLEDs). Both the blue emission and yellow emission are from exciplex, which makes it possible to exceed the 25% internal quantum efficiency limit of normal fluorescent OLEDs via reverse intersystem crossing from triplet to singlet states because of the small energy gap between them. White emission can be realized by simply stacking the blue and yellow exciplex materials because the same acceptor material is used in the emitting systems. And a two‐color WOLED with an external quantum efficiency (EQE) of 6.11% is demonstrated, exceeding the efficiencies of the exciplex‐based blue and yellow monochrome devices. The higher efficiency is attributed to redistribution of the exciplex excitons, which suppresses the exciton concentration quenching at the emission interface. By adopting a quantum‐well‐like structure, the EQE can be further improved. This approach sheds light on the simple fabrication of high‐efficiency WOLEDs in the future.

show abstract

Direct Observation of Efficient Triplet–Triplet Energy Transfer in Phosphorescent Organic Light-Emitting Diode

Cited by 10 publications

References 18 publications

Understanding Triplet Formation Pathways in Bulk Heterojunction Polymer:Fullerene Photovoltaic Devices

Understanding Triplet Formation Pathways in Bulk Heterojunction Polymer:Fullerene Photovoltaic Devices

Highly Efficient and Stable Phosphorescent Organic Light‐Emitting Diodes Utilizing Reverse Intersystem Crossing of the Host Material

High‐Efficiency Nondoped White Organic Light‐Emitting Diodes Based on All‐Exciplex Emission

Contact Info

Product

Resources

About