膦基电致发光材料及器件的研究进展
|
摘要
芳香膦(氧)基团具有可打断共轭、电子效应适中、位阻大、便于多功能修饰和配位能力强等特点,是少数几个兼具多种功能的基团之一.通过综合运用这些功能,芳香膦(氧)基团在选择性调节分子光电特性等方面显示出了独特的优势.因此,芳香膦(氧)基团不仅适于构建综合性能优异的光电功能材料,进而实现高效的有机电致发光器件,而且能够为选择性研究单一性质变化对材料光电性能的影响提供平台.近年来,膦基光电功能材料逐渐发展成为有机电致发光(organic light-emitting diode, OLED)领域的热点之一,其所展现出的优异性能和清晰的构效关系在丰富OLED材料库、明确材料设计和优化途径,乃至推动OLED技术创新等方面具有重要的理论意义和实际应用价值.我们在膦基电致发光材料及其器件方面开展了比较系统的研究.从材料的设计策略出发,分别开发了膦基主体材料、发光材料和电子传输材料,对这类材料的光物理性质、激发态特性、电学性能以及电致发光器件性能等进行深入研究.本文对这些工作进行了较为系统的总结,以期为今后膦基光电功能材料的开发提供借鉴和参考.
Organic light emitting diodes(OLEDs) have been attracting much attention and have been studied extensively by scientists and engineers in both academic and industrial communities, due to their great advantages of self-emitting, fast response,wide view-angle, full color capacity, high efficiency, low power consumption, ultra-thinness, lightness and flexibility for the applications of new generation flat panel displays and solid-state lighting sources. With the full use of active-matrix OLED(AMOLED) screen in iPhone X, OLED technology has become the mainstream information display technology and has gained more than 40% of market share. In the era of information, liquid crystal display technology will be gradually replaced by OLED technology. However, OLEDs technology still faces many challenges, including low yield, high cost,short service life, environmentally unfriendly and so on, which urgently requires more in-depth and detailed research in material development and device design.Since the first OLED reported by Tang, OLED technology has developed from the first generation of fluorescence(FL)technology, the second generation of phosphorescence(PH) technology to the third generation of thermally activated delayed fluorescence(TADF) technology. In general, PH materials are heavy metal complexes, in which triplet excited state is the main radiative excited state. Since singlet exciton can translate into triplet exciton through intersystem crossing(ISC) process, therefore, in theory, 100% electrogenerated excitons can be used in phosphorescence materials. Compared with the first generation of fluorescence materials, which can only use 25% single state electrogenerated excitons, the electro-optic conversion efficiency is greatly improved in phosphorescence materials. However, heavy metal ions in PH materials not only increase the cost, but also bring some potential environmental pollution. TADF technology can realize the transformation of non-radiative triplet excitons into radiative singlet excitons through reverse ISC(RISC) process, and thus achieving 100% exciton utilization. TADF material is usually pure organic molecule based on a push-pull electron system, thus making up for the defects of phosphorescent material. Therefore, as a kind of molecular electroluminescent devices, innovation of material system is the foundation for the development of OLED technology.With the insulating effect, moderate electronic effect, large steric hindrance, multi-functionalizability and coordination effect, aryl phosphine(oxide) group is one of the few groups with multiple functions. Through comprehensively utilizing these functions, aryl phosphine(oxide) group reveal the unique advantage in selectively optimizing molecular optoelectronic properties, further realizing high-efficiency OLED, and providing a platform for selective investigation of the influence of single property variation on optoelectronic performance. Recently, phosphine optoelectronic materials have been gradually developed as one of the focuses in OLED field, whose excellent performance and clear structureproperty relationship reveal the significant theoretical and application values regarding to enriching OLED material,suggesting the methods in material design and optimization and promoting the OLED technology innovation. Based on material design strategy, we developed phosphine host materials, emitters and electron transporting materials and deeply investigated the photophysical properties, excited-state characteristics, electrical properties and OLED performance. In this paper, the main works are summarized, with the expectation to provide reference for the subsequent study on phosphine optoelectronic materials.
Organic light emitting diodes(OLEDs) have been attracting much attention and have been studied extensively by scientists and engineers in both academic and industrial communities, due to their great advantages of self-emitting, fast response,wide view-angle, full color capacity, high efficiency, low power consumption, ultra-thinness, lightness and flexibility for the applications of new generation flat panel displays and solid-state lighting sources. With the full use of active-matrix OLED(AMOLED) screen in iPhone X, OLED technology has become the mainstream information display technology and has gained more than 40% of market share. In the era of information, liquid crystal display technology will be gradually replaced by OLED technology. However, OLEDs technology still faces many challenges, including low yield, high cost,short service life, environmentally unfriendly and so on, which urgently requires more in-depth and detailed research in material development and device design.Since the first OLED reported by Tang, OLED technology has developed from the first generation of fluorescence(FL)technology, the second generation of phosphorescence(PH) technology to the third generation of thermally activated delayed fluorescence(TADF) technology. In general, PH materials are heavy metal complexes, in which triplet excited state is the main radiative excited state. Since singlet exciton can translate into triplet exciton through intersystem crossing(ISC) process, therefore, in theory, 100% electrogenerated excitons can be used in phosphorescence materials. Compared with the first generation of fluorescence materials, which can only use 25% single state electrogenerated excitons, the electro-optic conversion efficiency is greatly improved in phosphorescence materials. However, heavy metal ions in PH materials not only increase the cost, but also bring some potential environmental pollution. TADF technology can realize the transformation of non-radiative triplet excitons into radiative singlet excitons through reverse ISC(RISC) process, and thus achieving 100% exciton utilization. TADF material is usually pure organic molecule based on a push-pull electron system, thus making up for the defects of phosphorescent material. Therefore, as a kind of molecular electroluminescent devices, innovation of material system is the foundation for the development of OLED technology.With the insulating effect, moderate electronic effect, large steric hindrance, multi-functionalizability and coordination effect, aryl phosphine(oxide) group is one of the few groups with multiple functions. Through comprehensively utilizing these functions, aryl phosphine(oxide) group reveal the unique advantage in selectively optimizing molecular optoelectronic properties, further realizing high-efficiency OLED, and providing a platform for selective investigation of the influence of single property variation on optoelectronic performance. Recently, phosphine optoelectronic materials have been gradually developed as one of the focuses in OLED field, whose excellent performance and clear structureproperty relationship reveal the significant theoretical and application values regarding to enriching OLED material,suggesting the methods in material design and optimization and promoting the OLED technology innovation. Based on material design strategy, we developed phosphine host materials, emitters and electron transporting materials and deeply investigated the photophysical properties, excited-state characteristics, electrical properties and OLED performance. In this paper, the main works are summarized, with the expectation to provide reference for the subsequent study on phosphine optoelectronic materials.
引文
1 Tang C W,VanSlyke S A.Organic electroluminescent diodes.Appl Phys Lett,1987,51:913-915
2 Schubert E F.Light-emitting Diodes.2nd ed.Cambridge:Cambridge University Press,2006
3 Huang W,Mi B,Gao Z.Organic Electronics.Beijing:Science Press,2011
4 Baldo M A,O’Brien D F,You Y,et al.Highly efficient phosphorescent emission from organic electroluminescent device.Nature,1998,395:151-154
5 Ma Y,Zhang H,Shen J,et al.Electroluminescence from triplet metal-ligand charge-transfer excited state of transition metal complexes.Synthet Met,1998,94:245-248
6 Endo A,Ogasawara M,Takahashi A,et al.Thermally activated delayed fluorescence from Sn4+-porphyrin complexes and their application to organic light-emitting diodes-A novel mechanism for electroluminescence.Adv Mater,2009,21:4802
7 Uoyama H,Goushi K,Shizu K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence.Nature,2012,492:234-238
8 Chi Y,Chou P T.Transition-metal phosphors with cyclometalating ligands:Fundamentals and applications.Chem Soc Rev,2010,39:638-655
9 Yang X,Zhou G,Wong W Y.Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices.Chem Soc Rev,2015,44:8484-8575
10 Xu H,Chen R,Sun Q,et al.Recent progress in metal-organic complexes for optoelectronic applications.Chem Soc Rev,2014,43:3259-3302
11 Xu H,Sun Q,An Z,et al.Electroluminescence from europium(III)complexes.Coord Chem Rev,2015,293-294:228-249
12 Tao Y,Yuan K,Chen T,et al.Thermally activated delayed fluorescence materials towards the breakthrough of organoelectronics.Adv Mater,2014,26:7931-7958
13 Wong M Y,Zysman C E.Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes.Adv Mater,2017,29:160544
14 Yang Z,Mao Z,Xie Z,et al.Recent advances in organic thermally activated delayed fluorescence materials.Chem Soc Rev,2017,46:915-1016
15 Song F,Xu Z,Zhang Q,et al.Highly efficient circularly polarized electroluminescence from aggregation-induced emission luminogens with amplified chirality and delayed fluorescence.Adv Funct Mater,2018,28:1800051
16 Hong Y,Lam J W Y,Tang B Z.Aggregation-induced emission:Phenomenon,mechanism and applications.Chem Commun,2009,1:4332-4353
17 Hong Y,Lam J W Y,Tang B Z.Aggregation-induced emission.Chem Soc Rev,2011,40:5361-5388
18 Baldo M A,Lamansky S,Burrows P E,et al.Very high-efficiency green organic light-emitting devices based on electrophosphorescence.Appl Phys Lett,1999,75:4-6
19 Chatterjee T,Wong K T.Perspective on host materials for thermally activated delayed fluorescence organic light emitting diodes.Adv Opt Mater,2018,6:1800565
20 Adachi C,Kwong R C,Djurovich P,et al.Endothermic energy transfer:A mechanism for generating very efficient high-energy phosphorescent emission in organic materials.Appl Phys Lett,2001,79:2082-2084
21 Kawamura Y,Yanagida S,Forrest S R.Energy transfer in polymer electrophosphorescent light emitting devices with single and multiple doped luminescent layers.J Appl Phys,2002,92:87-93
22 Holmes R J,Forrest S R,Tung Y J,et al.Blue organic electrophosphorescence using exothermic host-guest energy transfer.Appl Phys Lett,2003,82:2422-2424
23 Tokito S,Iijima T,Suzuri Y,et al.Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices.Appl Phys Lett,2003,83:569-571
24 Xiao L,Chen Z,Qu B,et al.Recent progresses on materials for electrophosphorescent organic light-emitting devices.Adv Mater,2011,23:926-952
25 Burrows P E,Padmaperuma A B,Sapochak L S,et al.Ultraviolet electroluminescence and blue-green phosphorescence using an organic diphosphine oxide charge transporting layer.Appl Phys Lett,2006,88:183503
26 Padmaperuma A B,Sapochak L S,Burrows P E.New charge transporting host material for short wavelength organic electrophosphorescence:2,7-bis(diphenylphosphine oxide)-9,9-dimethylfluorene.Chem Mater,2006,18:2389-2396
27 Sapochak L S,Padmaperuma A B,Cai X,et al.Inductive effects of diphenylphosphoryl moieties on carbazole host materials:Design rules for blue electrophosphorescent organic light-emitting devices.J Phys Chem C,2008,112:7989-7996
28 Vecchi P A,Padmaperuma A B,Qiao H,et al.A dibenzofuran-based host material for blue electrophosphorescence.Org Lett,2006,8:4211-4214
29 Cai X,Padmaperuma A B,Sapochak L S,et al.Electron and hole transport in a wide bandgap organic phosphine oxide for blue electrophosphorescence.Appl Phys Lett,2008,92:083308
30 Jeon S O,Yook K S,Joo C W,et al.High-efficiency deep-blue-phosphorescent organic light-emitting diodes using a phosphine oxide and a phosphine sulfide high-triplet-energy host material with bipolar charge-transport properties.Adv Mater,2010,22:1872-1876
31 Han C,Xie G,Xu H,et al.Towards highly efficient blue-phosphorescent organic light-emitting diodes with low operating voltage and excellent efficiency stability.Chem Eur J,2011,17:445-449
32 Han C,Xie G,Li J,et al.A new phosphine oxide host based on ortho-disubstituted dibenzofuran for efficient electrophosphorescence:Towards high triplet state excited levels and excellent thermal,morphological and efficiency stability.Chem Eur J,2011,17:8947-8956
33 Han C,Xie G,Xu H,et al.A single phosphine oxide host for high-efficiency white organic light-emitting diodes with extremely low operating voltages and reduced efficiency roll-off.Adv Mater,2011,23:2491-2496
34 Han C,Zhao Y,Xu H,et al.A simple phosphine-oxide host with a multi-insulating structure:High triplet energy level for efficient blue electrophosphorescence.Chem Eur J,2011,17:5800-5803
35 Yu D,Zhao Y,Xu H,et al.Fluorene-based phosphine oxide host materials for blue electrophosphorescence:An effective strategy for a high triplet energy level.Chem Eur J,2011,17:2592-2596
36 Yu D,Zhao F,Han C,et al.Ternary ambipolar phosphine oxide hosts based on indirect linkage for highly efficient blue electrophosphorescence:Towards high triplet energy,low driving voltage and stable efficiencies.Adv Mater,2012,24:509-514
37 Han C,Zhang Z,Xu H,et al.Short-axis substitution approach selectively optimizes electrical properties of dibenzothiophene-based phosphine oxide hosts.J Am Chem Soc,2012,134:19179-19188
38 Yang W,Zhang Z,Han C,et al.Controlling optoelectronic properties of carbazole-phosphine oxide hosts by short-axis substitution for low-voltagedriving PHOLEDs.Chem Commun,2013,49:2822-2824
39 Li J,Ding D,Wei Y,et al.A“Si-locked”phosphine oxide host with suppressed structural relaxation for highly efficient deep-blue TADF diodes.Adv Opt Mater,2016,4:522-528
40 Fan C,Duan C,Han C,et al.Dibenzothiophene sulfone-based phosphine oxide electron transporters with unique asymmetry for high-efficiency blue thermally activated delayed fluorescence diodes.ACS Appl Mater Interfaces,2016,8:27383-27393
41 Duan C,Fan C,Wei Y,et al.Optimizing the intralayer and interlayer compatibility for high-efficiency blue thermally activated delayed fluorescence diodes.Sci Rep,2016,6:19904
42 Fan C,Duan C,Wei Y,et al.Dibenzothiophene-based phosphine oxide host and electron-transporting materials for efficient blue thermally activated delayed fluorescence diodes through compatibility optimization.Chem Mater,2015,27:5131-5140
43 Li J,Ding D,Tao Y,et al.A significantly twisted spirocyclic phosphine oxide as a universal host for high-efficiency full-color thermally activated delayed fluorescence diodes.Adv Mater,2016,28:3122-3130
44 Ishimatsu R,Matsunami S,Shizu K,et al.Solvent effect on thermally activated delayed fluorescence by 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene.J Phys Chem A,2013,117:5607-5612
45 Han C,Duan C,Yang W,et al.Allochroic thermally activated delayed fluorescence diodes through field-induced solvatochromic effect.Sci Adv,2017,3:e1700904
46 Zhang J,Ding D,Wei Y,et al.Extremely condensing triplet states of DPEPO-type hosts through constitutional isomerization for high-efficiency deep-blue thermally activated delayed fluorescence diodes.Chem Sci,2016,7:2870-2882
47 Zhang J,Ding D,Wei Y,et al.Multiphosphine-oxide hosts for ultralow-voltage-driven true-blue thermally activated delayed fluorescence diodes with external quantum efficiency beyond 20%.Adv Mater,2016,28:479-485
48 Yang H,Liang Q,Han C,et al.A phosphanthrene oxide host with close sphere packing for ultralow-voltage-driven efficient blue thermally activated delayed fluorescence diodes.Adv Mater,2017,29:1700553
49 Fan C,Wei Y,Ding D,et al.Linkage engineering in hosts for dramatic efficiency enhancement of blue phosphorescent organic light-emitting diodes.Opt Express,2015,23:12887-12899
50 Zhang Z,Zhang Z,Ding D,et al.Selectively investigating molecular configuration effect on blue electrophosphorescent host performance through a series of hydrocarbon oligomers.J Phys Chem C,2014,118:20559-20570
51 Zhang Z,Zhang Z,Chen R,et al.Modulating the optoelectronic properties of large,conjugated,high-energy gap,quaternary phosphine oxide hosts:Impact of the triplet-excited-state location.Chem Eur J,2013,19:9549-9561
52 Han C,Zhang Z,Xu H,et al.Controllably tuning excited-state energy in ternary hosts for ultralow-voltage-driven blue electrophosphorescence.Angew Chem Int Ed,2012,51:10104-10108
53 Han C,Zhang Z,Xu H,et al.Elevating the triplet energy levels of dibenzofuran-based ambipolar phosphine oxide hosts for ultralow-voltage-driven efficient blue electrophosphorescence:from D-A to D-π-A systems.Chem Eur J,2013,19:1385-1396
54 Han C,Zhang Z,Xu H,et al.Convergent modulation of singlet and triplet excited states of phosphine-oxide hosts through the management of molecular structure and functional-group linkages for low-voltage-driven electrophosphorescence.Chem Eur J,2013,19:141-154
55 Han C,Zhu L,Li J,et al.Rationally investigating the influence of T1location on electroluminescence performance of aryl amine modified phosphine oxide materials.Chem Eur J,2014,20:16350-16359
56 Reineke S,Walzer K,Leo K.Triplet-exciton quenching in organic phosphorescent light-emitting diodes with Ir-based emitters.Phys Rev B,2007,75:125328
57 Zamani Siboni H,Aziz H.Triplet-polaron quenching by charges on guest molecules in phosphorescent organic light emitting devices.Appl Phys Lett,2012,101:063502
58 Han C,Zhu L,Li J,et al.Highly efficient multifluorenyl host materials with unsymmetrical molecular configurations and localized triplet states for green and red phosphorescent devices.Adv Mater,2014,26:7070-7077
59 Zhang Q,Li B,Huang S,et al.Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence.Nat Photon,2014,8:326-332
60 Hirata S,Sakai Y,Masui K,et al.Highly efficient blue electroluminescence based on thermally activated delayed fluorescence.Nat Mater,2015,14:330-336
61 Wada Y,Kubo S,Kaji H.Adamantyl substitution strategy for realizing solution-processable thermally stable deep-blue thermally activated delayed fluorescence materials.Adv Mater,2018,30:1705641
62 Han C,Zhang Z,Ding D,et al.Dipole-dipole interaction management for efficient blue thermally activated delayed fluorescence diodes.Chem,2018,4:2154-2167
63 Duan C,Li J,Han C,et al.Multi-dipolar chromophores featuring phosphine oxide as joint acceptor:A new strategy toward high-efficiency blue thermally activated delayed fluorescence dyes.Chem Mater,2016,28:5667-5679
64 Li C,Duan C,Han C,et al.Secondary acceptor optimization for full-exciton radiation:Toward sky-blue thermally activated delayed fluorescence diodes with external quantum efficiency of~30%.Adv Mater,2018,30:1804228
65 Liang Q,Han C,Duan C,et al.Blue thermally activated delayed fluorescence-emitting phosphine oxide hosts for ultrasimple and highly efficient white organic light-emitting diodes.Adv Opt Mater,2018,6:1800020
66 Xu H,Yin K,Huang W.Highly improved electroluminescence from a series of novel Eu(III)complexes with functional single-coordinate phosphine oxide ligands:Tuning the intramolecular energy transfer,morphology,and carrier injection ability of the complexes.Chem Eur J,2007,13:10281-10293
67 Xu H,Yin K,Huang W.Comparison of the electrochemical and luminescence properties of two carbazole-based phosphine oxide Eu(III)complexes:Effect of different bipolar ligand structures.ChemPhysChem,2008,9:1752-1760
68 Xu H,Wang L H,Zhu X H,et al.Application of chelate phosphine oxide ligand in Eu-III complex with mezzo triplet energy level,highly efficient photoluminescent,and electroluminescent performances.J Phys Chem B,2006,110:3023-3029
69 Xu H,Yin K,Wang L,et al.Bright electroluminescence from a chelate phosphine oxide Eu(III)complex with high thermal performance.Thin Solid Films,2008,516:8487-8492
70 Xu H,Wei Y,Zhao B,et al.Influence of bidentate structure of an aryl phosphine oxide ligand on photophysical properties of its Eu(III)complex.JRare Earths,2010,28:666-670
71 Xu H,Yin K,Huang W.Novel light-emitting ternary Eu3+complexes based on multifunctional bidentate aryl phosphine oxide derivatives:Tuning photophysical and electrochemical properties toward bright electroluminescence.J Phys Chem C,2010,114:1674-1683
72 Xu H,Yin K,Huang W.Synthesis,photophysical and electroluminescent properties of a novel bright light-emitting Eu3+complex based on a fluorene-containing bidentate aryl phosphine oxide.Synth Met,2010,160:2197-2202
73 Wang J,Han C,Xie G,et al.Solution-processible brilliantly luminescent Eu(III)complexes with host-featured phosphine oxide ligands for monochromic red-light-emitting diodes.Chem Eur J,2014,20:11137-11148
74 Xu H,Zhu R,Zhao P,et al.Photophysical and electroluminescent properties of a series of monochromatic red-emitting europium-complexed nonconjugated copolymers based on diphenylphosphine oxide modified polyvinylcarbazole.Polymer,2011,52:804-813
75 Xu H,Wang J,Wei Y,et al.A unique white electroluminescent one-dimensional europium(III)coordination polymer.J Mater Chem C,2015,3:1893-1903
76 Zhang Q,Zhou Q,Cheng Y,et al.Highly efficient green phosphorescent organic light-emitting diodes based on CuI complexes.Adv Mater,2004,16:432-436
77 Hashimoto M,Igawa S,Yashima M,et al.Highly efficient green organic light-emitting diodes containing luminescent three-coordinate copper(I)complexes.J Am Chem Soc,2011,133:10348-10351
78 Liu Z,Qayyum M F,Wu C,et al.A codeposition route to CuI-pyridine coordination complexes for organic light-emitting diodes.J Am Chem Soc,2011,133:3700-3703
79 Chen X L,Yu R,Zhang Q K,et al.Rational design of strongly blue-emitting cuprous complexes with thermally activated delayed fluorescence and application in solution-processed OLEDs.Chem Mater,2013,25:3910-3920
80 Volz D,Chen Y,Wallesch M,et al.Bridging the efficiency gap:Fully bridged dinuclear Cu(I)-complexes for singlet harvesting in high-efficiency OLEDs.Adv Mater,2015,27:2538-2543
81 Zhang J,Duan C,Han C,et al.Balanced dual emissions from tridentate phosphine-coordinate copper(I)complexes toward highly efficient yellow OLEDs.Adv Mater,2016,28:5975-5979
82 Xie M,Han C,Zhang J,et al.White electroluminescent phosphine-chelated copper iodide nanoclusters.Chem Mater,2017,29:6606-6610
83 Duan C,Han C,Du R,et al.High-efficiency blue dual-emissive exciplex boosts full-radiative white electroluminescence.Adv Opt Mater,2018,6:1800437
84 Jia J,Zhu L,Wei Y,et al.Triazine-phosphine oxide electron transporter for ultralow-voltage-driven sky blue PHOLEDs.J Mater Chem C,2015,3:4890-4902
85 Kan W,Zhu L,Wei Y,et al.Phosphine oxide-jointed electron transporters for the reduction of interfacial quenching in highly efficient blue PHOLEDs.J Mater Chem C,2015,3:5430-5439
86 Kan W,Duan C,Sun M,et al.Dual encapsulation of electron transporting materials to simplify high-efficiency blue thermally activated delayed fluorescence devices.Chem Mater,2016,28:7145-7157
87 Lin N,Qiao J,Duan L,et al.Molecular understanding of the chemical stability of organic materials for OLEDs:A comparative study on sulfonyl,phosphine-oxide,and carbonyl-containing host materials.J Phys Chem C,2014,118:7569-7578
88 Lin N,Qiao J,Duan L,et al.Achilles heels of phosphine oxide materials for OLEDs:Chemical stability and degradation mechanism of a bipolar phosphine oxide/carbazole hybrid host material.J Phys Chem C,2012,116:19451-19457
89 Tan W Y,Zou J H,Gao D Y,et al.Promising operational stability of potentially high power efficiency organic light-emitting diodes utilizing a simple and versatile electron-transport/hole-blocking layer.Adv Electron Mater,2016,2:1600101
2 Schubert E F.Light-emitting Diodes.2nd ed.Cambridge:Cambridge University Press,2006
3 Huang W,Mi B,Gao Z.Organic Electronics.Beijing:Science Press,2011
4 Baldo M A,O’Brien D F,You Y,et al.Highly efficient phosphorescent emission from organic electroluminescent device.Nature,1998,395:151-154
5 Ma Y,Zhang H,Shen J,et al.Electroluminescence from triplet metal-ligand charge-transfer excited state of transition metal complexes.Synthet Met,1998,94:245-248
6 Endo A,Ogasawara M,Takahashi A,et al.Thermally activated delayed fluorescence from Sn4+-porphyrin complexes and their application to organic light-emitting diodes-A novel mechanism for electroluminescence.Adv Mater,2009,21:4802
7 Uoyama H,Goushi K,Shizu K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence.Nature,2012,492:234-238
8 Chi Y,Chou P T.Transition-metal phosphors with cyclometalating ligands:Fundamentals and applications.Chem Soc Rev,2010,39:638-655
9 Yang X,Zhou G,Wong W Y.Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices.Chem Soc Rev,2015,44:8484-8575
10 Xu H,Chen R,Sun Q,et al.Recent progress in metal-organic complexes for optoelectronic applications.Chem Soc Rev,2014,43:3259-3302
11 Xu H,Sun Q,An Z,et al.Electroluminescence from europium(III)complexes.Coord Chem Rev,2015,293-294:228-249
12 Tao Y,Yuan K,Chen T,et al.Thermally activated delayed fluorescence materials towards the breakthrough of organoelectronics.Adv Mater,2014,26:7931-7958
13 Wong M Y,Zysman C E.Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes.Adv Mater,2017,29:160544
14 Yang Z,Mao Z,Xie Z,et al.Recent advances in organic thermally activated delayed fluorescence materials.Chem Soc Rev,2017,46:915-1016
15 Song F,Xu Z,Zhang Q,et al.Highly efficient circularly polarized electroluminescence from aggregation-induced emission luminogens with amplified chirality and delayed fluorescence.Adv Funct Mater,2018,28:1800051
16 Hong Y,Lam J W Y,Tang B Z.Aggregation-induced emission:Phenomenon,mechanism and applications.Chem Commun,2009,1:4332-4353
17 Hong Y,Lam J W Y,Tang B Z.Aggregation-induced emission.Chem Soc Rev,2011,40:5361-5388
18 Baldo M A,Lamansky S,Burrows P E,et al.Very high-efficiency green organic light-emitting devices based on electrophosphorescence.Appl Phys Lett,1999,75:4-6
19 Chatterjee T,Wong K T.Perspective on host materials for thermally activated delayed fluorescence organic light emitting diodes.Adv Opt Mater,2018,6:1800565
20 Adachi C,Kwong R C,Djurovich P,et al.Endothermic energy transfer:A mechanism for generating very efficient high-energy phosphorescent emission in organic materials.Appl Phys Lett,2001,79:2082-2084
21 Kawamura Y,Yanagida S,Forrest S R.Energy transfer in polymer electrophosphorescent light emitting devices with single and multiple doped luminescent layers.J Appl Phys,2002,92:87-93
22 Holmes R J,Forrest S R,Tung Y J,et al.Blue organic electrophosphorescence using exothermic host-guest energy transfer.Appl Phys Lett,2003,82:2422-2424
23 Tokito S,Iijima T,Suzuri Y,et al.Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices.Appl Phys Lett,2003,83:569-571
24 Xiao L,Chen Z,Qu B,et al.Recent progresses on materials for electrophosphorescent organic light-emitting devices.Adv Mater,2011,23:926-952
25 Burrows P E,Padmaperuma A B,Sapochak L S,et al.Ultraviolet electroluminescence and blue-green phosphorescence using an organic diphosphine oxide charge transporting layer.Appl Phys Lett,2006,88:183503
26 Padmaperuma A B,Sapochak L S,Burrows P E.New charge transporting host material for short wavelength organic electrophosphorescence:2,7-bis(diphenylphosphine oxide)-9,9-dimethylfluorene.Chem Mater,2006,18:2389-2396
27 Sapochak L S,Padmaperuma A B,Cai X,et al.Inductive effects of diphenylphosphoryl moieties on carbazole host materials:Design rules for blue electrophosphorescent organic light-emitting devices.J Phys Chem C,2008,112:7989-7996
28 Vecchi P A,Padmaperuma A B,Qiao H,et al.A dibenzofuran-based host material for blue electrophosphorescence.Org Lett,2006,8:4211-4214
29 Cai X,Padmaperuma A B,Sapochak L S,et al.Electron and hole transport in a wide bandgap organic phosphine oxide for blue electrophosphorescence.Appl Phys Lett,2008,92:083308
30 Jeon S O,Yook K S,Joo C W,et al.High-efficiency deep-blue-phosphorescent organic light-emitting diodes using a phosphine oxide and a phosphine sulfide high-triplet-energy host material with bipolar charge-transport properties.Adv Mater,2010,22:1872-1876
31 Han C,Xie G,Xu H,et al.Towards highly efficient blue-phosphorescent organic light-emitting diodes with low operating voltage and excellent efficiency stability.Chem Eur J,2011,17:445-449
32 Han C,Xie G,Li J,et al.A new phosphine oxide host based on ortho-disubstituted dibenzofuran for efficient electrophosphorescence:Towards high triplet state excited levels and excellent thermal,morphological and efficiency stability.Chem Eur J,2011,17:8947-8956
33 Han C,Xie G,Xu H,et al.A single phosphine oxide host for high-efficiency white organic light-emitting diodes with extremely low operating voltages and reduced efficiency roll-off.Adv Mater,2011,23:2491-2496
34 Han C,Zhao Y,Xu H,et al.A simple phosphine-oxide host with a multi-insulating structure:High triplet energy level for efficient blue electrophosphorescence.Chem Eur J,2011,17:5800-5803
35 Yu D,Zhao Y,Xu H,et al.Fluorene-based phosphine oxide host materials for blue electrophosphorescence:An effective strategy for a high triplet energy level.Chem Eur J,2011,17:2592-2596
36 Yu D,Zhao F,Han C,et al.Ternary ambipolar phosphine oxide hosts based on indirect linkage for highly efficient blue electrophosphorescence:Towards high triplet energy,low driving voltage and stable efficiencies.Adv Mater,2012,24:509-514
37 Han C,Zhang Z,Xu H,et al.Short-axis substitution approach selectively optimizes electrical properties of dibenzothiophene-based phosphine oxide hosts.J Am Chem Soc,2012,134:19179-19188
38 Yang W,Zhang Z,Han C,et al.Controlling optoelectronic properties of carbazole-phosphine oxide hosts by short-axis substitution for low-voltagedriving PHOLEDs.Chem Commun,2013,49:2822-2824
39 Li J,Ding D,Wei Y,et al.A“Si-locked”phosphine oxide host with suppressed structural relaxation for highly efficient deep-blue TADF diodes.Adv Opt Mater,2016,4:522-528
40 Fan C,Duan C,Han C,et al.Dibenzothiophene sulfone-based phosphine oxide electron transporters with unique asymmetry for high-efficiency blue thermally activated delayed fluorescence diodes.ACS Appl Mater Interfaces,2016,8:27383-27393
41 Duan C,Fan C,Wei Y,et al.Optimizing the intralayer and interlayer compatibility for high-efficiency blue thermally activated delayed fluorescence diodes.Sci Rep,2016,6:19904
42 Fan C,Duan C,Wei Y,et al.Dibenzothiophene-based phosphine oxide host and electron-transporting materials for efficient blue thermally activated delayed fluorescence diodes through compatibility optimization.Chem Mater,2015,27:5131-5140
43 Li J,Ding D,Tao Y,et al.A significantly twisted spirocyclic phosphine oxide as a universal host for high-efficiency full-color thermally activated delayed fluorescence diodes.Adv Mater,2016,28:3122-3130
44 Ishimatsu R,Matsunami S,Shizu K,et al.Solvent effect on thermally activated delayed fluorescence by 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene.J Phys Chem A,2013,117:5607-5612
45 Han C,Duan C,Yang W,et al.Allochroic thermally activated delayed fluorescence diodes through field-induced solvatochromic effect.Sci Adv,2017,3:e1700904
46 Zhang J,Ding D,Wei Y,et al.Extremely condensing triplet states of DPEPO-type hosts through constitutional isomerization for high-efficiency deep-blue thermally activated delayed fluorescence diodes.Chem Sci,2016,7:2870-2882
47 Zhang J,Ding D,Wei Y,et al.Multiphosphine-oxide hosts for ultralow-voltage-driven true-blue thermally activated delayed fluorescence diodes with external quantum efficiency beyond 20%.Adv Mater,2016,28:479-485
48 Yang H,Liang Q,Han C,et al.A phosphanthrene oxide host with close sphere packing for ultralow-voltage-driven efficient blue thermally activated delayed fluorescence diodes.Adv Mater,2017,29:1700553
49 Fan C,Wei Y,Ding D,et al.Linkage engineering in hosts for dramatic efficiency enhancement of blue phosphorescent organic light-emitting diodes.Opt Express,2015,23:12887-12899
50 Zhang Z,Zhang Z,Ding D,et al.Selectively investigating molecular configuration effect on blue electrophosphorescent host performance through a series of hydrocarbon oligomers.J Phys Chem C,2014,118:20559-20570
51 Zhang Z,Zhang Z,Chen R,et al.Modulating the optoelectronic properties of large,conjugated,high-energy gap,quaternary phosphine oxide hosts:Impact of the triplet-excited-state location.Chem Eur J,2013,19:9549-9561
52 Han C,Zhang Z,Xu H,et al.Controllably tuning excited-state energy in ternary hosts for ultralow-voltage-driven blue electrophosphorescence.Angew Chem Int Ed,2012,51:10104-10108
53 Han C,Zhang Z,Xu H,et al.Elevating the triplet energy levels of dibenzofuran-based ambipolar phosphine oxide hosts for ultralow-voltage-driven efficient blue electrophosphorescence:from D-A to D-π-A systems.Chem Eur J,2013,19:1385-1396
54 Han C,Zhang Z,Xu H,et al.Convergent modulation of singlet and triplet excited states of phosphine-oxide hosts through the management of molecular structure and functional-group linkages for low-voltage-driven electrophosphorescence.Chem Eur J,2013,19:141-154
55 Han C,Zhu L,Li J,et al.Rationally investigating the influence of T1location on electroluminescence performance of aryl amine modified phosphine oxide materials.Chem Eur J,2014,20:16350-16359
56 Reineke S,Walzer K,Leo K.Triplet-exciton quenching in organic phosphorescent light-emitting diodes with Ir-based emitters.Phys Rev B,2007,75:125328
57 Zamani Siboni H,Aziz H.Triplet-polaron quenching by charges on guest molecules in phosphorescent organic light emitting devices.Appl Phys Lett,2012,101:063502
58 Han C,Zhu L,Li J,et al.Highly efficient multifluorenyl host materials with unsymmetrical molecular configurations and localized triplet states for green and red phosphorescent devices.Adv Mater,2014,26:7070-7077
59 Zhang Q,Li B,Huang S,et al.Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence.Nat Photon,2014,8:326-332
60 Hirata S,Sakai Y,Masui K,et al.Highly efficient blue electroluminescence based on thermally activated delayed fluorescence.Nat Mater,2015,14:330-336
61 Wada Y,Kubo S,Kaji H.Adamantyl substitution strategy for realizing solution-processable thermally stable deep-blue thermally activated delayed fluorescence materials.Adv Mater,2018,30:1705641
62 Han C,Zhang Z,Ding D,et al.Dipole-dipole interaction management for efficient blue thermally activated delayed fluorescence diodes.Chem,2018,4:2154-2167
63 Duan C,Li J,Han C,et al.Multi-dipolar chromophores featuring phosphine oxide as joint acceptor:A new strategy toward high-efficiency blue thermally activated delayed fluorescence dyes.Chem Mater,2016,28:5667-5679
64 Li C,Duan C,Han C,et al.Secondary acceptor optimization for full-exciton radiation:Toward sky-blue thermally activated delayed fluorescence diodes with external quantum efficiency of~30%.Adv Mater,2018,30:1804228
65 Liang Q,Han C,Duan C,et al.Blue thermally activated delayed fluorescence-emitting phosphine oxide hosts for ultrasimple and highly efficient white organic light-emitting diodes.Adv Opt Mater,2018,6:1800020
66 Xu H,Yin K,Huang W.Highly improved electroluminescence from a series of novel Eu(III)complexes with functional single-coordinate phosphine oxide ligands:Tuning the intramolecular energy transfer,morphology,and carrier injection ability of the complexes.Chem Eur J,2007,13:10281-10293
67 Xu H,Yin K,Huang W.Comparison of the electrochemical and luminescence properties of two carbazole-based phosphine oxide Eu(III)complexes:Effect of different bipolar ligand structures.ChemPhysChem,2008,9:1752-1760
68 Xu H,Wang L H,Zhu X H,et al.Application of chelate phosphine oxide ligand in Eu-III complex with mezzo triplet energy level,highly efficient photoluminescent,and electroluminescent performances.J Phys Chem B,2006,110:3023-3029
69 Xu H,Yin K,Wang L,et al.Bright electroluminescence from a chelate phosphine oxide Eu(III)complex with high thermal performance.Thin Solid Films,2008,516:8487-8492
70 Xu H,Wei Y,Zhao B,et al.Influence of bidentate structure of an aryl phosphine oxide ligand on photophysical properties of its Eu(III)complex.JRare Earths,2010,28:666-670
71 Xu H,Yin K,Huang W.Novel light-emitting ternary Eu3+complexes based on multifunctional bidentate aryl phosphine oxide derivatives:Tuning photophysical and electrochemical properties toward bright electroluminescence.J Phys Chem C,2010,114:1674-1683
72 Xu H,Yin K,Huang W.Synthesis,photophysical and electroluminescent properties of a novel bright light-emitting Eu3+complex based on a fluorene-containing bidentate aryl phosphine oxide.Synth Met,2010,160:2197-2202
73 Wang J,Han C,Xie G,et al.Solution-processible brilliantly luminescent Eu(III)complexes with host-featured phosphine oxide ligands for monochromic red-light-emitting diodes.Chem Eur J,2014,20:11137-11148
74 Xu H,Zhu R,Zhao P,et al.Photophysical and electroluminescent properties of a series of monochromatic red-emitting europium-complexed nonconjugated copolymers based on diphenylphosphine oxide modified polyvinylcarbazole.Polymer,2011,52:804-813
75 Xu H,Wang J,Wei Y,et al.A unique white electroluminescent one-dimensional europium(III)coordination polymer.J Mater Chem C,2015,3:1893-1903
76 Zhang Q,Zhou Q,Cheng Y,et al.Highly efficient green phosphorescent organic light-emitting diodes based on CuI complexes.Adv Mater,2004,16:432-436
77 Hashimoto M,Igawa S,Yashima M,et al.Highly efficient green organic light-emitting diodes containing luminescent three-coordinate copper(I)complexes.J Am Chem Soc,2011,133:10348-10351
78 Liu Z,Qayyum M F,Wu C,et al.A codeposition route to CuI-pyridine coordination complexes for organic light-emitting diodes.J Am Chem Soc,2011,133:3700-3703
79 Chen X L,Yu R,Zhang Q K,et al.Rational design of strongly blue-emitting cuprous complexes with thermally activated delayed fluorescence and application in solution-processed OLEDs.Chem Mater,2013,25:3910-3920
80 Volz D,Chen Y,Wallesch M,et al.Bridging the efficiency gap:Fully bridged dinuclear Cu(I)-complexes for singlet harvesting in high-efficiency OLEDs.Adv Mater,2015,27:2538-2543
81 Zhang J,Duan C,Han C,et al.Balanced dual emissions from tridentate phosphine-coordinate copper(I)complexes toward highly efficient yellow OLEDs.Adv Mater,2016,28:5975-5979
82 Xie M,Han C,Zhang J,et al.White electroluminescent phosphine-chelated copper iodide nanoclusters.Chem Mater,2017,29:6606-6610
83 Duan C,Han C,Du R,et al.High-efficiency blue dual-emissive exciplex boosts full-radiative white electroluminescence.Adv Opt Mater,2018,6:1800437
84 Jia J,Zhu L,Wei Y,et al.Triazine-phosphine oxide electron transporter for ultralow-voltage-driven sky blue PHOLEDs.J Mater Chem C,2015,3:4890-4902
85 Kan W,Zhu L,Wei Y,et al.Phosphine oxide-jointed electron transporters for the reduction of interfacial quenching in highly efficient blue PHOLEDs.J Mater Chem C,2015,3:5430-5439
86 Kan W,Duan C,Sun M,et al.Dual encapsulation of electron transporting materials to simplify high-efficiency blue thermally activated delayed fluorescence devices.Chem Mater,2016,28:7145-7157
87 Lin N,Qiao J,Duan L,et al.Molecular understanding of the chemical stability of organic materials for OLEDs:A comparative study on sulfonyl,phosphine-oxide,and carbonyl-containing host materials.J Phys Chem C,2014,118:7569-7578
88 Lin N,Qiao J,Duan L,et al.Achilles heels of phosphine oxide materials for OLEDs:Chemical stability and degradation mechanism of a bipolar phosphine oxide/carbazole hybrid host material.J Phys Chem C,2012,116:19451-19457
89 Tan W Y,Zou J H,Gao D Y,et al.Promising operational stability of potentially high power efficiency organic light-emitting diodes utilizing a simple and versatile electron-transport/hole-blocking layer.Adv Electron Mater,2016,2:1600101