Please wait a minute...
材料研究学报  2015, Vol. 29 Issue (5): 321-336    DOI: 10.11901/1005.3093.2014.724
  本期目录 | 过刊浏览 |
有机发光材料与器件研究进展
段炼(),邱勇()
清华大学化学系 北京 100084
Recent Advances in Organic Electroluminescent Materials and Devices
Lian DUAN(),Yong QIU()
Department of Chemistry, Tsinghua University, Beijing 100084, China
引用本文:

段炼,邱勇. 有机发光材料与器件研究进展[J]. 材料研究学报, 2015, 29(5): 321-336.
Lian DUAN, Yong QIU. Recent Advances in Organic Electroluminescent Materials and Devices[J]. Chinese Journal of Materials Research, 2015, 29(5): 321-336.

全文: PDF(4603 KB)   HTML
摘要: 

自从1987年邓青云博士发明有机发光二极管(OLED)以来, 相关领域的研究蓬勃兴起。近年来, OLED已在中小尺寸显示领域得到广泛的应用, 并逐步进入大面积显示和照明等领域。有机发光技术的不断发展, 对有机发光材料与器件的研究提出了更高的要求。本报告综述了近年来国内外有机发光材料与器件研究领域关注的重要问题和其中的主要进展。随着OLED技术的深入发展, 该领域的研究体现出基础理论与技术创新并重的特点, 在材料与器件技术和有机半导体传输理论方面都取得了丰硕成果。在材料与器件技术方面, 本文主要综述了新型磷光材料分子设计, 新型荧光材料及其发光机理研究, 白光器件技术, 湿法制备技术及柔性制备技术等几个方面的最重要进展。在有机半导体传输理论方面, 本文主要综述了从分子堆积、薄膜无序度及掺杂等角度对有机半导体传输理论进行的研究工作。最后, 报告对国际有机显示技术和有机照明技术的产业现状及发展方向进行了概述。

关键词 综述有机发光二极管发光材料发光机理有机半导体电荷传输    
Abstract

Since the invention of organic light-emitting diodes (OLEDs) by Dr. CW Tang in 1987, researches in related fields have been developed rapidly. Now, small to medium size OLED displays have already been commercialized. Large OLED TVs and OLED lightings have also emerged in real applications. The further development of the OLED technology calls for intensive research on organic light-emitting materials and devices. This report reviewed the most focused issues as well as the main progress in the field of OLEDs in the recent years. It is shown that researchers have paid attentions to both technical innovations and theoretical researches, such as the design of new molecules, developing of new device technology, and understanding of light-emitting and transporting mechanisms of organic semiconductors. The developing trends of organic light-emitting materials and devices are summarized as follows: 1) molecular design for high performance phosphorescent materials; 2) novel fluorescent materials and their light emitting mechanisms; 3) new technologies for high performance white OLEDs; 4) new technologies for solution-processed devices and flexible devices; 5) the influences of molecular packing, disorder and doping on the charge transporting properties of organic semiconductors. Moreover, the current situations and developing trends of international OLED display and lighting industries are discussed.

Key wordsreview    organic light emitting diodes    organic light-emitting materials    light-emitting mechanisms    charge transport in organic semiconductors
收稿日期: 2014-08-21     
作者简介: 段炼,邱勇, 院士
图1  文献报道的苯基磷氧类磷光主体材料的结构[5-7, 9]
图2  已报道的含氮芳杂环类磷光主体材料的结构[10-15]
图3  报道的铱等金属配合物的结构[16-19]
图4  报道的TTA延迟荧光材料的结构[20-25]
图5  文献报道的热活化延迟荧光材料[26-28]
图6  低单-三线态能隙材料作为主体实现热活化敏化荧光示意图[31]
图7  湿法制备WO3空穴传输层的有机电致发光器件及其与PEDOT: PSS器件性能对比[49]
图8  Pei等报道的柔性阳极纳米复合物光驱出LEC器件及效率[52]
图9  狭缝涂布方式印刷制备柔性高分子有机电致发光器件[56]
Classification Company/Institution Time Size/cm2 Efficiency /(lm/W) Lifetime/LT50 (h) CRI
Device level (<4 mm2) Visionox 2013 / 99 > 50,000 87
NEC/Yamagata University 2013 / 156 / /
Panasonic /Idemitsu 2012 / 142 50,000 85
Panasonic /Idemitsu 2011 / 128 30,000 83
UDC 2010 / 113 30,000 /
Screen level LG Chemistry 2013 81 80 >100,000 84
Visionox 2013 41 40 10,000 87
NEC/Yamagata University 2013 20 75 / /
Panasonic /Idemitsu 2012 25 87 100,000 82
Philips/ Konica 2011 37 45 10,000 85
表1  白光OLED器件和屏体水平性能(1000 cd/m2)
1 M. Pope, H. Kallmann, P. Magnante,Electrolum inescence in organic crystals, J. Chem. Phys., 38, 2042(1963)
2 C. W. Tang, S. A VanSlyke,Organic electroluminescent diodes, Appl. Phys. Lett., 51, 913(1987)
3 M. A. Baldo, D. F. O’ Brien, Y. You, et al., Highly efficient phosphorescent emission from organic electroluminescent devices, Nature, 395, 151(1998)
4 C. Adachi,Third generation OLED by hyperfluorescence, SID Symposium Digest of Technical Papers, 44, 513(2013)
5 H. Liu, G. Cheng, D. H. Hu, et al., A highly efficient, blue-phosphorescent device based on a wide-bandgap host/FIrpic: rational design of the carbazole and phosphine oxide moieties on tetraphenylsilane, Adv. Funct. Mater, 22, 2830(2012)
6 D. H. Yu, F. C. Zhao, C. C. Han, 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, 24, 509(2012)
7 C. L. Yang, L. P. Zhu, T. X Liu, et al., Using an organic molecule with low triplet energy as a host in a highly efficient blue electrophosphorescent device, Angew. Chem. Int. Ed., 53, 2147(2014)
8 H. Sasabe, J. Takamatsu, T. Motoyama, et al., High-efficiency blue and white organic light-emitting devices incorporating a blue iridium carbene complex, Advanced Materials, 22, 5003(2010)
9 H. H. Chou, C. H. Cheng,A highly efficient universal bipolar host for blue, green, and red phosphorescent OLEDs, Advanced Materials, 22, 2468(2010)
10 Z. M. Hudson, Z. B. Wang; M. G. Helander,et al., N-heterocyclic carbazole-based hosts for simplified single-layer phosphorescent OLEDs with high efficiencies, Adv. Mater, 24, 2922(2012)
11 D. D. Zhang, L. Duan, Y. L. Li, et al., Towards high efficiency and low roll-off orange electrophosphorescent devices by fine tuning singlet and triplet energies of bipolar hosts based on indolocarbazole/1, 3, 5-triazine hybrids, Adv. Funct. Mater., 2014, DOI: 10.1002/ 201303926
12 S. J. Su, C. Cai, J. J. Kido,RGB phosphorescent organic light-emitting diodes by using host materials with heterocyclic cores: effect of nitrogen atom orientations, Chemistry of Materials, 23, 274(2011)
13 E. Mondal, W. Y. Hung, H. C. Dai, et al., Fluorene-based asymmetric bipolar universal hosts for white organic light emitting devices, Adv. Funct. Mater., 24, 3096(2013)
14 H. Huang, Y. X. Wang, B. Pan, , et al., Simple bipolar hosts with high glass transition temperatures based on 1, 8-disubstituted carbazole for efficient blue and green electrophosphorescent devices with “ideal” turn-on voltage, Chem. Eur. J., 19, 1828(2013)
15 K. Wang, F. C. Zhao, C. G. Wang, et al., High-performance red, green, and blue electroluminescent devices based on blue emitters with small singlet–triplet splitting and ambipolar transport property, Adv. Funct. Mater, 23, 2672(2013)
16 D. B. Xia, B. Wang, B. Chen, et al., Self-host blue-emitting iridium dendrimer with carbazole dendrons: nondoped phosphorescent organic light-emitting diodes, Angew. Chem. Int. Ed., 53, 1048(2014)
17 H. Fukagawa, T. Shimizu, H. Hanashima, et al., Highly efficient and stable red phosphorescent organic light-emitting diodes using platinum complexes, Adv. Mater., 24, 5099(2012)
18 Z. M. Hudson, C. Sun, M. G. Helander, et al., Highly efficient blue phosphorescence from triarylboron-functionalized platinum(II) complexes of N-heterocyclic carbenes, J. Am. Chem. Soc., 134, 13930(2012)
19 T. Fleetham, J. Ecton, Z. X. Wang, et al., Single-doped white organic light-emitting device with an external quantum efficiency over 20%, Adv. Mater., 25, 2573(2013)
20 I. Cho, S. H. Kim, J. H. Kim, et al., Highly efficient and stable deep-blue emitting anthracene-derived molecular glass for versatile types of non-doped OLED applications, J. Mater. Chem., 22, 123(2012)
21 K. H. Lee, J. K. Park, J. H. Seo, et al., Efficient deep-blue and white organic light-emitting diodes based on triphenylsilane-substituted anthracene derivatives, J. Mater. Chem., 21, 13640(2011)
22 T. Zhang, D. Liu, Q. Wang, et al., Deep-blue and white organic light-emitting diodes based on novel fluorene-cored derivatives with naphthylanthracene endcaps, J. Mater. Chem., 21, 12969(2011)
23 J. H. Huang, J. H. Su, X. Li, et al., Bipolar anthracene derivatives containing hole- and electron-transporting moieties for highly efficient blue electroluminescence devices, J. Mater. Chem., 21, 2957(2011)
24 K. R. Wee, W. S. Han, J. E. Kim, et al., Asymmetric anthracene-based blue host materials: synthesis and electroluminescence properties of 9-(2-naphthyl)-10-arylanthracenes, J. Mater. Chem., 21, 1115(2011)
25 C. J. Chiang, A. Kimyonok, M. K. Etherington, et al., Ultrahigh efficiency fluorescent single and Bi-layer organic light emitting diodes: the key role of triplet fusion, Adv. Funct. Mater., 23, 739(2013)
26 A. Endo, K. Sato, K. Yoshimura, et al., Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes, Appl. Phys. Lett., 98, 083302(2011)
27 Q. S. Zhang, J. Li, K. Shizu, et al., Design of efficient thermally activated delayed fluorescence materials for pure blue organic light emitting diodes, J. Am. Chem. Soc., 134, 14706(2012)
28 H. Uoyama, K. Goushi, K. Shizu, et al., Highly efficient organic light-emitting diodes from delayed fluorescence, Nature, 492, 234(2012)
29 S. P. Huang, Q. S. Zhang, Y. Shiota, et al., Computational Prediction for Singlet- and Triplet-Transition Energies of Charge-Transfer Compounds, Journal of Chemical Theory and Computation, 9(9), 3872–3877(2013)
30 Q. S. Zhang, B. Li, S. P. Huang, et al., Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence, Nature Photonics, 8, 326(2014)
31 D. D. Zhang, L. Duan, C. Li, et al., High efficiency fluorescent organic light-emitting devices using sensitizing hosts with a small singlet-triplet exchange energy, Adv. Mater. 2014, DOI: 10.1002/adma.201401476.
32 K. Goushi, K. Yoshida, K. Sato, et al., Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion, Nat. Photon., 6, 253(2012)
33 V. Jankus, C. J. Chiang, F. Dias, et al., Deep blue exciplex organic light-emitting diodes with enhanced efficiency; P-type or E-type triplet conversion to singlet excitons? Adv. Mater., 25, 1455(2013)
34 H. Liu, G. Cheng, D. H. Hu, et al., A highly efficient, blue-phosphorescent device based on a wide-bandgap host/FIrpic: rational design of the carbazole and phosphine oxide moieties on tetraphenylsilane, Adv. Funct. Mater, 22, 2830(2012)
35 W. J. Li, Y. Y. Pan, R. Xiao, et al., Employing ~100% Excitons in OLEDs by Utilizing a Fluorescent Molecule with Hybridized Local and Charge-Transfer Excited State, Advanced Functional Materials, 24, 1606(2014)
36 D. Y. Kondakov, T. D. Pawlik, T. K. Hatwar, et al., Triplet annihilation exceeding spin statistical limit in highly efficient fluorescent organic light-emitting diodes, J. Appl. Phys., 6, 124510(2009)
37 L. Duan, D. Q. Zhang, K. W. Wu, et al., Controlling the recombination zone of white organic light-emitting diodes with extremely long lifetimes, Adv. Funct. Mater., 21, 3540(2011)
38 H. Sasabe, J. Takamatsu, T. Motoyama, et al., High-efficiency blue and white organic light-emitting devices incorporating a blue iridium carbene complex, Adv. Mater., 22, 5003(2010)
39 S. L. Gong, Y. H. Chen, J. J. Luo, et al., Bipolar tetraarylsilanes as universal hosts for blue, green, orange, and white electrophosphorescence with high efficiency and low efficiency roll-off, Advanced Functional Materials, 21, 1168(2011)
40 C. Han, G. H. Xie, H. Xu, 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 , Advanced Materials, 23, 2491(2011)
41 J. Ye, C. J. Zheng, X. M. Ou, et al., Management of singlet and triplet excitons in a single emission layer: A simple approach for high-efficiency fluorescence/phosphorescence hybrid white organic light-emitting device., Adv. Mater., 24, 3410(2012)
42 Q. Wang, C. L. Ho, Y. B Zhao, et al., Reduced efficiency roll-off in highly efficient and color-stable hybrid WOLEDs: The influence of triplet transfer and charge-transport behavior on enhancing device performance, Organic Electronics, 11, 238(2011)
43 C. J. Zheng, J. Wang, J. Ye, et al., Novel efficient blue fluorophors with small singlet-triplet splitting: hosts for highly efficient fluorescence and phosphorescence hybrid WOLEDs with simplified structure, Advanced Materials, 25, 2205(2013)
44 L. J. Zhang, S. J. Hu, J. W. Chen, et al., A Series of Energy-Transfer Copolymers Derived from Fluorene and 4, 7-Dithienylbenzotriazole for High Efficiency Yellow, Orange, and White Light-Emitting Diodes, Advanced Functional Materials, 21, 3760(2011)
45 J. H. Zou, H. Wu, C. S. Lam, et al., Simultaneous optimization of charge-carrier balance and luminous efficacy in highly efficient white polymer light-emitting devices, Advanced Materials, 23, 2976(2011)
46 B. H Zhang, G. P. Tan, C. S. Lamet al., High-efficiency single emissive layer white organic light-emitting diodes based on solution-processed dendritic host and new orange-emitting iridium complex, Advanced Materials, 24, 1873(2012)
47 H. Gorter, M. J. J. Coenen, M. W. L. Slaats, et al., Toward inkjet printing of small molecule organic light emitting diodes, Thin Solid Films, 532, 11(2013)
48 S. Tekoglu, G. Hernandez-Sosa, E. Kluge, et al., Gravure printed flexible small-molecule organic light emitting diodes, Org. Electron., 14, 3493(2013)
49 S. H?fle, M. Bruns, S. Str?ssle, et al., Tungsten oxide buffer layers fabricated in an inert sol-gel process at room-temperature for blue organic light-emitting diodes, Adv. Funct. Mater., 25(30), 4113(2013)
50 Q. Fu, J. S. Chen, C. S. Shi, et al., Room-temperature sol?gel derived molybdenum oxide thin films for efficient and stable solution-processed organic light-emitting diodes, ACS. Appl. Mater. Interfaces, 5, 6024(2013)
51 S. Feng, L. Duan, L. D. Hou, et al., A comparison study of the organic small molecular thin films prepared by solution process and vacuum deposition: roughness, hydrophilicity, absorption, photoluminescence, density, mobility, and electroluminescence, J. Phys. Chem. C, 115, 14278(2011)
52 L. Li, J. J. Liang, S. Y. Chou, et al., A solution processed flexible nanocomposite electrode with efficient light extraction for organic light emitting diodes, Sci. Rep., 4, 4307(2014)
53 S. Kim, H. J. Kwon, S. Lee, et al., Low-power flexible organic light-emitting diode display device, Adv. Mater., 23, 3511(2011)
54 Z. Yu, X. Niu, Z. Liu, et al., Intrinsically stretchable polymer light-emitting devices using carbon nanotube-polymer composite electrodes, Adv. Mater., 23, 3989(2011)
55 W. Hu, X. Niu ,L. Li,et al., Intrinsically stretchable transparent electrodes based on silver-nanowire-crosslinked-polyacrylate composites, Nanotechnology, 23, 344002(2012)
56 A. Sandstr?m, H. F. Dam, F. C. Krebs, et al., Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating, Nat. Commun., 3, 1002(2012)
57 D. Yokoyama, H. Sasabe, Y. Furukawa, et al., Molecular stacking induced by intermolecular C-H···N hydrogen bonds leading to high carrier mobility in vacuum-deposited organic films, Advanced Functional Materials, 21, 1375(2011)
58 N. Li, P. F. Wang, S. L. Laiet al., Synthesis of multiaryl-substituted pyridine derivatives and applications in non-doped deep-blue OLEDs as electron-transporting layer with high hole-blocking ability, Advanced Materials, 22, 527(2010)
59 S. Y. Kim, W. I. Jeong, C. Mayr, et al., Organic light-emitting diodes with 30% external quantum efficiency based on a horizontally oriented emitter, Advanced Functional Materials, 23, 3896(2013)
60 H. Park, J. Lee, I. Kang, et al., Highly rigid and twisted anthracene derivatives: a strategy for deep blue OLED materials with theoretical limit efficiency, J. Mater. Chem., 22, 2695(2012)
61 H. Y. Li, L. Duan, Y. D. Sun, et al., Study of the hole and electron transport in amorphous 9, 10-Di-(2 '-Naphthyl) anthracene: the first-principles approach, J. Phys. Chem. C, 117, 16336(2013)
62 J. Li, Y. Zhao, H. S. Tan, et al., A stable solution-processed polymer semiconductor with record high-mobility for printed transistors, Scientific Reports, 2, 754(2012)
63 I. Kang, H. J. Yun, D. S. Chung, et al., Record high hole mobility in polymer semiconductors via side-chain engineering, J. Am. Chem. Soc., 135(40), 14896(2013)
64 H. R. Tseng, H. Phan, C. Luo, et al., High-mobility field-effect transistors fabricated with macroscopic aligned semiconducting polymers, Adv. Mater., 2014, DOI: 10.1002/adma.201305084
65 R. Noriega, J. Rivnay, K. Vandewal, et al., A general relationship between disorder, aggregation and charge transport in conjugated polymers, Nat. Mater., 12(11), 1038(2013)
66 R. Noriega, A. Salleo, A. J. Spakowitz,Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers, Proc. Natl. Acad. Sci. USA, 110(41), 16315(2013)
67 H. Y. Li, L. Duan, C. Li, et al., Transient space-charge-perturbed currents in organic materials: A Monte Carlo study, Org. Electron., 15(2), 524(2014)
68 H. Y. Li, L. Duan, D. Q. Zhang, et al., Transient space-charge-perturbed currents of N, N′-diphenyl-N, N′-bis(1-naphthyl)-1, 1′-biphenyl-4, 4′-diamine and N, N′-diphenyl-N, N′-bis(3-methylphenyl)-1, 1′-biphenyl-4, 4′-diamine in diode structures, Appl. Phys. Lett., 104(18), 183301(2014)
69 H. Y. Li, L. Duan, D. Q. Zhang, et al., Relationship between mobilities from time-of-flight and dark-injection space-charge-limited current measurements for organic semiconductors: A Monte Carlo study, J. Phys. Chem. C, 118(12), 6052(2014)
70 M. Abkowitz, J. S. Facci, M. Stolka, et al., Time-resolved space charge-limited injection in a trap-free glassy polymer, Chem. Phys., 177(3), 783(1993)
71 C. Y. H. Chan, K. K. Tsung, W. H. Choi, et al., Achieving time-of-flight mobilities for amorphous organic semiconductors in a thin film transistor configuration, Org. Electron., 14(5), 1351(2013)
72 H. H. Fong, K.C. Lun, S. K. So,Hole transports in molecularly doped triphenylamine derivative, Chem. Phys. Lett., 353, 407(2002)
73 K. K. Tsung, S. K. So,Carrier trapping and scattering in amorphous organic hole transporter, Appl. Phys. Lett., 92, 103315(2008)
74 B. X. Li, J. S. Chen, Y. B. Zhao, et al., Effects of carrier trapping and scattering on hole transport properties of N, N '-diphenyl-N, N '-bis(1-Naphthyl)-1, 1 '-biphenyl-4, 4 '-diamine thin films, Org. Electron., 12, 974(2011)
75 C. Li, L. Duan, Y. D. Sun, et al., Charge transport in mixed organic disorder semiconductors: trapping, scattering, and effective energetic disorder, J. Phys. Chem. C, 116, 19748(2012)
76 C. Li, L. Duan, H. Y. Li, et al., Universal trap effect in carrier transport of organic disorder semi- conductors: transition from shallow trapping to deep trapping, J. Phys. Chem. C, 118(20), 10651(2014)
77 S. Stankovich, D. A. Dikin, G. H. B. Dommett, et al., Graphene-based composite materials, Nature, 442, 282(2006)
78 K. Vakhshouri, D. R Kozub, C. C Wang, et al., Effect of miscibility and percolation on electron transport in amorphous poly(3-hexylthiophene)/phenyl-c-61-butyric acid methyl ester blends, Phys. Rev. Lett., 108, 026601(2012)
79 C. Li, L. Duan, H. Y. Li, et al., Percolative charge transport in a co-evaporated organic molecular mixture, Org.Electron., 14, 3312(2013)
[1] 赵宁, 焦大, 朱艳坤, 刘德学, 刘增乾, 张哲峰. 天然铠甲高效防护的材料学机理[J]. 材料研究学报, 2022, 36(1): 1-7.
[2] 燕映霖,王娟,王亮亮,卢正欣,任冰,许云华. CTAB浓度和反应液的pH值对水热合成GdVO4: Eu3+荧光粉性能的影响[J]. 材料研究学报, 2015, 29(4): 307-314.
[3] 何珂,薛其坤. 拓扑量子材料与量子反常霍尔效应[J]. 材料研究学报, 2015, 29(3): 161-177.
[4] 张广平,李孟林,吴细毛,李春和,罗雪梅. 尺度对金属材料电阻率影响的研究进展*[J]. 材料研究学报, 2014, 28(2): 81-87.
[5] 冯杰 卢津强 秦兆倩. 超疏水表面抗结冰性能研究进展[J]. 材料研究学报, 2012, 26(4): 337-343.
[6] 杨义 李阁平 吴松全 李玉兰 杨柯. Gum Metal钛合金研究进展[J]. 材料研究学报, 2011, 25(1): 1-6.
[7] 樊国栋 肖国平. Pr3+掺杂对SrAl2O4 : Eu2+、Dy3+磷光体发光性能的影响[J]. 材料研究学报, 2010, 24(4): 343-347.
[8] 彭英才 傅广生. 量子点太阳电池的探索[J]. 材料研究学报, 2009, 23(5): 449-457.
[9] 施政余 李梅 赵燕 路庆华. 润湿性可控智能表面的研究进展[J]. 材料研究学报, 2008, 22(6): 561-571.
[10] 贾玉玺; 原波; 杨俊英; 安立佳 . 树脂传递模塑过程的数学描述和数值模拟进展[J]. 材料研究学报, 2005, 19(5): 449-456.
[11] 彭英才; X.W.Zhao; 傅广生 . 晶粒有序Si基纳米发光材料的自组织化生长[J]. 材料研究学报, 2004, 18(5): 449-460.
[12] 王吉会; 姜晓霞; 李曙; 李诗卓 . 腐蚀磨损过程中材料的环境脆性[J]. 材料研究学报, 2003, 17(5): 454-458.
[13] 胡巧玲; 李晓东; 沈家骢 . 仿生结构材料的研究进展[J]. 材料研究学报, 2003, 17(4): 337-344.
[14] 邱建荣; 钱国栋 . 飞秒激光空间选择性诱导玻璃微结构及应用[J]. 材料研究学报, 2003, 17(1): 1-9.
[15] 张明荣;李培俊;殷之文. 闪烁晶体PbWO_4的研究现状[J]. 材料研究学报, 1998, 12(2): 113-122.