Excited state engineering for efficient reverse intersystem crossing

Noda, Haruhiko; Nakanotani, Hajime; Adachi, Chihaya

doi:10.1126/sciadv.aao6910

Cited by 329 publications

(312 citation statements)

References 30 publications

(40 reference statements)

Supporting

Mentioning

289

Contrasting

Order By: Relevance

“…The differences among the maximum EQE (EQE max ) values for each OLED can be explained by the difference between the PL quantum yields (η PL ) of the emitters, which are 74% for 5CzBN and 86% for 3Cz2DPhCzBN, and a difference between their light outcoupling efficiency (η OC ) values because the order parameter of the transition dipole moment vector (S) [21] for 3Cz2DPhCzBN (S = −0.20) showed a slightly higher horizontal orientation than that of 5CzBN (S = −0.13) ( Figure S3, Supporting Information). [17] Note that the slight difference between the lifetime characteristics in this study and those in the previous study can be ascribed to the different fabrication conditions used. The LT 90 (which is the time at which the luminance decreases to 90% of the initial luminance) values for the 5CzBN-and 3Cz2DPhCzBN-based OLEDs are 7.9 and 201 h, respectively ( Figure 1d).…”

Section: Wwwadvelectronicmatdecontrasting

confidence: 54%

“…3Cz2DPhCzBN has a partially modified 5CzBN structure and this modification results in slightly redshifted photoluminescence (PL) and a shorter decay time for the delayed PL component when compared with that of 5CzBN acting as a sky blue emitter. [17] shows much shorter delayed lifetime than that of 3Cz2DPhCzBN, 2Cz3D-PhCzBN has significantly larger difference of the energy gap compared to those of 5CzBN and 3Cz2DPhCzBN. Although 2,4,6-tris(3,6-diphenylcarbazole-9-yl)-3,5-(9H-carbazole-9-yl) benzonitrile (2Cz3DPhCzBN) reported in ref.…”

Section: Device Performance Of Tadf-oledsmentioning

confidence: 92%

“…[11][12][13][14] To suppress unwanted interactions between the triplet excitons and quenching species such as trapped charge carriers, the triplet exciton lifetime of the emitters should be managed carefully because the rates of the exciton annihilation processes are critically dependent on the triplet exciton density. [17] While it was proposed that the improvement in the device's operational lifetime was caused not only by the short triplet lifetime but also by the change in the carrier transport abilities of the TADF molecules, the detailed mechanism that is responsible for the significant observed improvement in the operational lifetime remains unclear. [15,16] Our group recently reported that insertion of different donor units into a parent benzonitrilecarbazole (CzBN) type molecule was effective in shortening the triplet exciton lifetime and successfully improved both the external quantum efficiency (EQE) roll-off and the device's operational stability.…”

Section: Effect Of Carrier Balance On Device Degradation Of Organic Lmentioning

confidence: 99%

See 2 more Smart Citations

Effect of Carrier Balance on Device Degradation of Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters

Tanaka

Noda

Nakanotani

et al. 2019

Adv Elect Materials

Self Cite

View full text Add to dashboard Cite

The relatively short device lifetime of blue organic light‐emitting diodes (OLEDs) when compared with the lifetimes of green and red OLEDs is one of the crucial problems that must be overcome to enable practical application of these devices to full‐color OLED displays. This work focuses on the degradation phenomena of OLEDs that are based on sky‐blue thermally activated delayed fluorescence emitters and clarifies the degradation mechanisms based on spectral change of the electroluminescence, which indicates the formation of electromer emission from an electron transport layer. Additionally, it is determined that the change in the carrier balance that occurs during this degradation process can be ascribed to the formation of electron traps.

show abstract

Section: Wwwadvelectronicmatdecontrasting

confidence: 54%

Section: Device Performance Of Tadf-oledsmentioning

confidence: 92%

Section: Effect Of Carrier Balance On Device Degradation Of Organic Lmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Carrier Balance on Device Degradation of Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters

Tanaka

Noda

Nakanotani

et al. 2019

Adv Elect Materials

Self Cite

View full text Add to dashboard Cite

show abstract

“…[28,29] Recently, efficient and stable blue TADF emitters have been successfully constructed by adopting the benzonitrile as a building block with the combination of two different donor units. [14,30,31] Meanwhile, most reported TADF emitters exhibit broad EL spectra with a FWHM of 80-100 nm or even wider, leading to low color purity and significant energy losses in OLED displays with the use of color filters. However, the sky-blue emission with CIEy > 0.3 is inadequate for the display applications.…”

Section: Introductionmentioning

confidence: 99%

High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

Zou

Xie

et al. 2019

Advanced Science

View full text Add to dashboard Cite

TADF) materials without using heavy metals have gained great attention as the third-generation organic light-emitting diode (OLED) emitters. [8][9][10][11][12][13][14][15][16][17][18][19][20] The use of pure organic TADF emitters allows almost 100% internal electroluminescence (EL) quantum efficiency by harvesting the triplet excitons (T 1 ) to the emissive singlet excited states (S 1 ) via reverse intersystem crossing (RISC). To date, high external quantum efficiency (EQE) exceeding 20% has been achieved for blue, green, and red TADF emitters in OLEDs. [8][9][10][11][12][13][14][15][16][17][18][19][20] However, achieving high-performance deep blue TADF OLEDs is still challenging, since most of them suffer from poor color purity, low brightness, severe EL efficiency roll-off, as well as short operational stability. [21][22][23][24][25] It remains an urgent demand to develop new blue TADF emitters that can simultaneously achieve high efficiency, high brightness, low driving voltage, long operational lifetime, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) for various applications.Several strategies have been proposed to realize highly efficient blue TADF emitters. Generally, the TADF molecules are designed with a donor-acceptor-type rigid and symmetrical molecular configuration, exhibiting high optical bandgap (E g ), small S 1 -T 1 energy splitting (ΔE ST ), and high photoluminescence quantum yield (PLQY). [26][27][28] For narrowband emission, Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light-emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile-based TADF emitters (namely 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile (2PhCz2CzBn) and 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert-butyl group can weaken the intermolecular π-π stacking in the nondoped TADF emitter, and thus significantly suppress self-aggregation-caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn-based nondoped device with an extremely low turn-on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m −2 , a narrow fullwidth at half-maximum of 70 nm, and CIE color coordinates of (0.167, 0.248).

show abstract

“…As we know, the fluorescent LED originates from the radiative recombination of singlet excitons, and the maximum of internal quantum efficiency is constrained to 25% due to the spin statistics. The efficient use of the remaining 75% triplet excitonic states for generating fluorescence, rather than phosphorescence, relies on the thermally activated delayed fluorescence (TADF) in an organic fluorescent material with a smaller exchange energy, triplet–triplet annihilation (TTA), and exciton‐charge reaction . From the calculation shown in Figure d, TADF can be ignored for ITIC due to the large energy difference of the singlet and triplet.…”

Section: Resultsmentioning

confidence: 99%

Spin‐Dependent Electron–Hole Recombination and Dissociation in Nonfullerene Acceptor ITIC‐Based Organic Photovoltaic Systems

et al. 2019

View full text Add to dashboard Cite

A nonfullerene acceptor (NFA), named 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′] dithiophene (ITIC) with the fused aromatic conjugated backbone structure, is an intriguing small molecular semiconductor in the application of organic bulk heterojunction (BHJ) solar cells. However, the underlying spin‐dependent photo‐physics in the photovoltaic process remains deficient. Here, ITIC‐based thin solid film, binary, and ternary organic blends are designed and fabricated with two polymeric donors, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]‐dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) and poly[(2,6‐(4,8‐Bis(3‐((2‐ethylhexyl)oxy)‐phenyl)‐benzo[1,2‐b:4,5‐b′]‐dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBPD‐Th). With the spin‐sensitive magneto‐photocurrent and magneto‐electroluminescence measurements, ITIC always exhibits large magnetic field effects with negative signs in the ambient temperature. The effect is attributed to the exciton‐charge reaction. However, both positive and negative signs are detected in the binary and ternary organic blends at small and large fields, respectively. The results elucidate that the mutual combination of the spin‐dependent polaron pair dissociation and exciton‐charge reaction plays a decisive role in the photovoltaic process. Furthermore, with photo‐induced electron paramagnetic resonance (EPR) studies, the full width at half maximum (FWHM) of the line shape for the positive magneto‐photocurrent is firmly associated to the magnitude of the effective g‐factor. The present study may shed a new light on the deep understanding of spin‐dependent photo‐physical process in NFA‐based solar cells for organic opto‐spintronic developments.

show abstract

Excited state engineering for efficient reverse intersystem crossing

Abstract: Excited state engineering in purely organic molecules provides highly efficient and stable TADF-OLEDs.

Cited by 329 publications

References 30 publications

Effect of Carrier Balance on Device Degradation of Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters

Effect of Carrier Balance on Device Degradation of Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters

High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

Spin‐Dependent Electron–Hole Recombination and Dissociation in Nonfullerene Acceptor ITIC‐Based Organic Photovoltaic Systems

Contact Info

Product

Resources

About