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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 13 — Jun. 18, 2012
  • pp: 14564–14572
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Tandem organic light-emitting diodes with KBH4 doped 9,10-bis(3-(pyridin-3-yl)phenyl) anthracene connected to the charge generation layer

Lian Duan, Taiju Tsuboi, Yong Qiu, Yanrui Li, and Guohui Zhang  »View Author Affiliations


Optics Express, Vol. 20, Issue 13, pp. 14564-14572 (2012)
http://dx.doi.org/10.1364/OE.20.014564


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Abstract

Tandem organic light emitting diodes (OLEDs) are ideal for lighting applications due to their low working current density at high brightness. In this work, we have studied an efficient electron transporting layer of KBH4 doped 9,10-bis(3-(pyridin-3-yl)phenyl)anthracene (DPyPA) which is located adjacent to charge generation layer of MoO3/NPB. The excellent transporting property of the DPyPA:KBH4 layer helps the tandem OLED to achieve a lower voltage than the tandem device with the widely used tris-(8-hydroxyquinoline)aluminum:Li. For the tandem white OLED with a fluorescent blue unit and a phosphorescent yellow unit, we’ve achieved a high current efficiency of 75 cd/A, which can be further improved to 120 cd/A by attaching a diffuser layer.

© 2012 OSA

1. Introduction

Organic light-emitting diodes (OLEDs) have been of interest for applications to flat panel display and lighting because of low consumption energy, light-weight, and flexible. To improve the current efficiency (or luminous efficiency), power efficiency, and operational lifetime at high brightnesses required for lighting, tandem structure with a charge generation layer (CGL) has been employed for the OLED devices, where several electroluminescence (EL) units are vertically stacked with interconnecting CGL [1

1. L. S. Liao and K. P. Klubek, “Power efficiency improvement in a tandem organic light-emitting diode,” Appl. Phys. Lett. 92(22), 223311 (2008). [CrossRef]

4

4. T. Matsumoto, T. Nakada, J. Endo, K. Mori, N. Kawamura, A. Yokoi, and J. Kido, “Multiphoton organic EL device having charge generation layer,” SID Symposium Digest of Technical Papers 34, 979–981 (2003).

].

Generally, CGL consists of an n-doped organic semiconductor layer and a p-doped organic semiconductor layer [5

5. M. Terai and T. Tsutsui, “Electric-field-assisted bipolar charge generation from internal charge separation zone composed of doped organic bilayer,” Appl. Phys. Lett. 90(8), 083502 (2007). [CrossRef]

,6

6. M. Ho, T. M. Chen, P. C. Yeh, S. W. Hwang, and C. H. Chen, “Highly efficient p-i-n white organic light emitting devices with tandem structure,” Appl. Phys. Lett. 91(23), 233507 (2007). [CrossRef]

], or consists of an electron accepting layer (EAL) and an electron donating layer (EDL) [7

7. S. Hamwi, J. Meyer, M. Kröger, T. Winkler, M. Witte, T. Riedl, A. Kahn, and W. Kowalsky, “The role of transition metal oxides in charge-generation layers for stacked organic light-emitting diodes,” Adv. Funct. Mater. 20(11), 1762–1766 (2010). [CrossRef]

,8

8. T. Chiba, Y.-J. Pu, R. Miyazaki, K. Nakayama, H. Sasabe, and J. Kido, “Ultra-high efficiency by multiple emission from stacked organic light-emitting devices,” Org. Electron. 12(4), 710–715 (2011). [CrossRef]

]. In CGL which consists of EAL and EDL bilayer, electrons in the HOMO level of the EDL material are injected into the LUMO level of EAL material under an applied voltage, resulting in generation of electron in the EAL and hole in the EDL, followed by the charge separation. As materials of EAL, inorganic metal oxides such as WO3 and MoO3 [7

7. S. Hamwi, J. Meyer, M. Kröger, T. Winkler, M. Witte, T. Riedl, A. Kahn, and W. Kowalsky, “The role of transition metal oxides in charge-generation layers for stacked organic light-emitting diodes,” Adv. Funct. Mater. 20(11), 1762–1766 (2010). [CrossRef]

] and organic compounds such as 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN6) [8

8. T. Chiba, Y.-J. Pu, R. Miyazaki, K. Nakayama, H. Sasabe, and J. Kido, “Ultra-high efficiency by multiple emission from stacked organic light-emitting devices,” Org. Electron. 12(4), 710–715 (2011). [CrossRef]

] have been employed, while hole-transporting materials such as 4, 4’, 4”-tris(N-carbazolyl)-triphenylamine (TCTA) [7

7. S. Hamwi, J. Meyer, M. Kröger, T. Winkler, M. Witte, T. Riedl, A. Kahn, and W. Kowalsky, “The role of transition metal oxides in charge-generation layers for stacked organic light-emitting diodes,” Adv. Funct. Mater. 20(11), 1762–1766 (2010). [CrossRef]

] and N, N’-diphenyl-N, N’-bis(1-naphthyl)-(1,1’-biphenyl)-4, 4’-diamine (NPB) [8

8. T. Chiba, Y.-J. Pu, R. Miyazaki, K. Nakayama, H. Sasabe, and J. Kido, “Ultra-high efficiency by multiple emission from stacked organic light-emitting devices,” Org. Electron. 12(4), 710–715 (2011). [CrossRef]

] has been used as materials of EDL. In this type of tandem OLED, an n-doped electron transporting layer (ETL) is also required to facilitate the electron injection. Although Alq3:Li has been conventionally used [9

9. L. S. Liao, W. K. Slusarek, T. K. Hatwar, M. L. Ricks, and D. L. Comfort, “Tandem organic light-emitting mode using hexaazatriphenylene hexacarbonitrile in the intermediate connector,” Adv. Mater. (Deerfield Beach Fla.) 20(2), 324–329 (2008). [CrossRef]

,10

10. M. Yokoyama, S. H. Su, C. C. Hou, C. T. Wu, and C. H. Kung, “Highly efficient white organic light-emitting diodes with a p-i-n tandem structure,” Jpn. J. Appl. Phys. 50(4), 04DK06 (2011). [CrossRef]

], it is found that performance of the n-doped ETLs can be improved by using an electron-transporting host with higher electron mobility [11

11. M. Y. Chan, S. L. Lai, K. M. Lau, M. K. Fung, C. S. Lee, and S. T. Lee, “Influences of connecting unit architecture on the performance of tandem organic light-emitting devices,” Adv. Funct. Mater. 17(14), 2509–2514 (2007). [CrossRef]

]. In the present study we fabricate the tandem OLEDs with an efficient n-doped ETL with a high mobility host of 9,10-bis(3-(pyridin-3-yl)phenyl)anthracene (DPyPA) and a thermally decomposable n-dopant of KBH4, which is proved effective in reducing the driving voltage in OLEDs [12

12. L. Duan, D. Zhang, Y. Li, G. Zhang, and Y. Qiu, “Improving the performance of OLEDs by using a low-temperature-evaporable n-dopant and a high-mobility electron transport host,” Opt. Express 19(S6Suppl 6), A1265–A1271 (2011). [CrossRef] [PubMed]

].

On the other hand, the external quantum efficiency of OLED is given by internal EL efficiency of the emitting layers multiplied by out-coupling efficiency. The out-coupling efficiency is usually around 20%. To increase the out-coupling efficiency, i.e., to lessen the trapped light inside the OLED layers, several methods have been tried. For example, the ITO is covered by (1) an ordered monolayer of silica microspheres as scattering medium [13

13. T. Yamasaki, K. Sumioka, and T. Tsutsui, “Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium,” Appl. Phys. Lett. 76(10), 1243–1245 (2000). [CrossRef]

], (2) microlens arrays to direct emitted light [14

14. S. Möller and S. R. Forrest, “Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays,” J. Appl. Phys. 91(5), 3324 (2002). [CrossRef]

], (3) a nanoporous film [15

15. H. Peng, Y. L. Ho, X. J. Yu, and H. S. Kwok, “Enhanced coupling of light from organic light emitting diodes using nanoporous films,” J. Appl. Phys. 96(3), 1649–1651 (2004). [CrossRef]

], (4) a diffusive layer [16

16. T. Nakamura, N. Tsutsumi, N. Juni, and H. Fujii, “Improvement of coupling-out efficiency in organic electroluminescent devices by addition of a diffusive layer,” J. Appl. Phys. 96(11), 6016 (2004). [CrossRef]

], and (5) a meshed surface fabricated on a poly(dimethyl siloxane) film [17

17. Y. H. Cheng, J. L. Wu, C. H. Cheng, K. C. Syao, and M. C. M. Lee, “Enhanced light outcoupling in a thin film by texturing meshed surfaces,” Appl. Phys. Lett. 90(9), 091102 (2007). [CrossRef]

], in addition to replacement of bulk glass substrate by low-index silica aerogel [18

18. T. Tsutsui, M. Yahiro, H. Yokogawa, K. Kawano, and M. Yokoyama, “Doubling coupling-out efficiency in organic light-emitting devices using a thin silica aerogel layer,” Adv. Mater. (Deerfield Beach Fla.) 13(15), 1149–1152 (2001). [CrossRef]

]. For real applications, a simple out-coupling enhancement method is highly desirable. In this work a commercially available diffuser film is used to improve the out-coupling efficiency. As a result, for the tandem white OLED with a fluorescent blue unit and a phosphorescent yellow unit, the efficiency can be improved from 75 cd/A to 120 cd/A by attaching the diffuser layer. We also studied the voltage-dependent color-shift in the white tandem OLEDs.

2. Experimental

We first fabricated two green tandem OLEDs (type A) to compare the EL performance of OLED with n-type layer of DPyPA:KBH4 with the performance of OLED with ETL of Alq3:Li:
  • OLED-A1: ITO/NPB (90 nm)/Alq3 (30 nm)/Alq3:Li (30 nm)/MoO3 (10 nm)/NPB (80 nm)/Alq3 (30 nm)/ Alq3:Li (30 nm) /Al,
  • OLED-A2: ITO/NPB (90 nm)/Alq3 (30 nm) /DPyPA: 20% KBH4 (30 nm)/MoO3 (10 nm)/NPB (80 nm)/Alq3 (30 nm)/ DPyPA: 20% KBH4 (30 nm) /Al,
where Alq3 is tris-(8-hydroxyquinoline)aluminum, and DPyPA is 9,10-bis(3-(pyridin-3-yl)phenyl)anthracene. These devices consist of two identical EL units with EML of Alq3 connected with CGL of MoO3/NPB. The active area of the devices is 3 × 3mm2.

For the white tandem OLEDs, one is without a diffuser sheet (called OLED-B1), the other is covered with a OEF100A self-adhesive diffuser film from Kimoto LTD (called OLED-B2). OLED-B1 and OLED-B2 have the same emission area of 30 × 60 mm2. They were fabricated by thermally evaporation in an ULVAC Satella evaporation tool and then encapsulated. The thicknesses of the organic layers are monitored by quartz crystal microbalances located inside the vacuum chamber. The non-uniformity of the film thickness is less than 10%.

The current density-voltage-luminance (J-V-L(cd/m2)) characteristics and EL spectra of the OLED devices were measured with a Konica-Minolta CS-1000 spectroradiometer and with a computer controlled programmable Keithley 2400 dc Source Meter. We also measured the angular distribution of the electroluminescence.

3. Results and discussions

As shown in Fig. 1(a)
Fig. 1 (a) Luminance-voltage curves and (b) current efficiency-current density curves of the tandem OLED-A1 with Alq3: Li and OLED-A2 with DPyPA: 20% KBH4.
, green tandem OLED with DPyPA:KBH4 has a lower driving voltage than the control device with Alq3: Li. Although both devices show similar current efficiency at the same current density (Fig. 1(b)), the operational lifetime of the tandem OLED with DPyPA: KBH4 is longer (70 hr when initial luminance becomes 80% intensity) than the lifetime (21 hr) of the control device with Alq3:Li (Fig. 2
Fig. 2 Operational lifetime comparison of the tandem OLED-A1 with Alq3: Li and OLED-A2 with DPyPA: 20% KBH4. I is luminance and I0 is the initial luminance.
), suggesting DPyPA:20% KBH4 is better than Alq3:Li for tandem OLEDs. The improvement in lifetime may be attributed to the higher electrochemical stability of DPyPA than Alq3 [20

20. Y. Sun, L. Duan, D. Zhang, J. Qiao, G. Dong, L. Wang, and Y. Qiu, “A pyridine-containing anthracene derivative with high electron and hole mobilities for highly efficient and stable fluorescent organic light-emitting diodes,” Adv. Funct. Mater. 21(10), 1881–1886 (2011). [CrossRef]

], as well as the lower diffusion rate of potassium than lithium [19

19. Q. Liu, D. Zhang, L. Duan, G. Zhang, L. Wang, Y. Cao, and Y. Qiu, “Thermally decomposable kbh4 as an efficient electron injection material for organic light-emitting diodes,” Jpn. J. Appl. Phys. 48(8), 080205 (2009). [CrossRef]

,21

21. J. H. Lee, M. H. Wu, C. C. Chao, H. L. Chen, and M. K. Leung, “High efficiency and long lifetime OLED based on a metal-doped electron transport layer,” Chem. Phys. Lett. 416(4-6), 234–237 (2005). [CrossRef]

]. After we learned the superiority of DPyPA:20% KBH4 to conventional Alq3:Li, we decided to fabricate white tandem OLEDs with DPyPA:20% KBH4.

The voltage-luminance (V-L) characteristics of OLED-B1 and OLED-B2 are shown in Fig. 3
Fig. 3 The luminance plotted against voltage for OLED-B1 and OLED-B2. The inset of Fig. 3 depicts a type B OLED half covered by the diffuser film at a voltage of 7 V.
. The maximum current efficiencies are 75 cd/A and 120 cd/A for OLED-B1 and OLED-B2, respectively, which were obtained when measured immediately after the fabrication. The efficiency improvement is around 60% by attaching the diffuser film. As is clear from the inset of Fig. 3, the left part is much brighter and also shows a blurring effect at the edge for a type B OLED half covered by a diffuser film.

The EL spectra of OLED-B1 at 5.6 and 9.5 V are shown in Fig. 4
Fig. 4 EL spectra of OLED-B1 at 5.6 and 9.5 V.
. The relative contribution from blue emission increases with increasing voltage. Regarding the color shift, although the electrons and holes generated in CGL are well balanced [8

8. T. Chiba, Y.-J. Pu, R. Miyazaki, K. Nakayama, H. Sasabe, and J. Kido, “Ultra-high efficiency by multiple emission from stacked organic light-emitting devices,” Org. Electron. 12(4), 710–715 (2011). [CrossRef]

], it is proposed that population of electrons transported from the MoO3 of CGL into the ADN:5% BD blue EML through ETL of DPyPA: 20% KBH4 is smaller than population of holes transported from the NPB of CGL into the TCTA:SBFK:13%YD yellow EML at low voltages. However, the blue emission enhances at a higher rate with increasing voltage below 8 V than the yellow emission. This is understood as follows: The carrier mobility increases with increasing the electric field according to the Poole Frenkel law [22

22. W. Brütting, S. Berleb, and A. G. Mückl, “Space-charge limited conduction with a field and temperature dependent mobility in Alq light-emitting devices,” Synth. Met. 122(1), 99–104 (2001). [CrossRef]

24

24. G. Paasch, A. Nesterov, and S. Scheinert, “Simulation of organic light emitting diodes: influence of charges localized near the electrodes,” Synth. Met. 139(2), 425–432 (2003). [CrossRef]

]. It is suggested that the mobility of electrons transporting from CGL to the blue EML increases at higher rate with increasing voltage (i.e., electric field) than the mobility of holes transporting from CGL to the yellow EML. This leads to increase of population of electrons injected into the blue EML at higher rate than population of holes injected into the yellow EML, which improves the charge balance inside the blue EML.

A similar result was also obtained for OLED-B2. Figure 5
Fig. 5 The ratio of the blue 459 nm EL intensity to the yellow 564 nm EL intensity plotted against voltage for OLED-B1 and OLED-B2.
plots the intensity ratio of the blue EL intensity to the yellow EL intensity against voltage. The relative intensity of the blue to yellow increases below about 8 V and becomes almost stable at voltage above 8 V. Therefore, at the high luminance required for lighting (at least 1000 cd/m2), color stability is achieved for both devices (see Figs. 3 and 5). This is consistent with the general concept that the high-energy emitter has a wider gap and requires a higher driving voltage than the low-energy emitter and that the EL spectrum composed of the two emissions become stable at high voltages.

It is worth noting that yellow emission is relatively stronger in OLED-B2 with a diffuser film. Two reasons are conceivable at this moment. One is a wavelength-dependent transparency of the diffuser, the other is an interference effect. We checked the transmittance spectrum of the diffuser. No change was observed for the transmittance in the visible range. Therefore, we measured the angular dependence of the EL spectra for the white tandem OLEDs. For OLED-B1 without a diffuser (Fig. 6(a)
Fig. 6 Angular dependence of the EL spectra of the white tandem OLEDs: (a) for OLED-B1; and (b) for OLED-B2. (c) is the polar plots of emission intensities of the two OLEDs.
), the EL shows a significant reduction of the blue emission and a noticeable reduction of the shoulder of the yellow emission with viewing angles due to microcavity effect. On the other hand, for OLED-B2 with a diffuser film (Fig. 6(b)), the shift in EL spectra with viewing angles is largely reduced. Figure 6(c) shows the polar plots of the emission intensities for the two devices. The incorporation of a diffuser not only increases the emission intensity but also modifies the emission pattern of the tandem OLED (Fig. 6(c)), making it closer to Lambertian distribution. These results indicate that the diffuser would lead to mixing/averaging EL of different angles and redistributing light into different directions, which may in turn change the relative intensity of the yellow emission to that of the blue. This agrees well with the results by Wu et al. in which they attached a diffuser film onto a top-emitting OLEDs [25

25. C.-C. Liu, S.-H. Liu, K.-C. Tien, M.-H. Hsu, H.-W. Chang, C.-K. Chang, C.-J. Yang, and C.-C. Wu, “Microcavity top-emitting organic light-emitting devices integrated with diffusers for simultaneous enhancement of efficiencies and viewing characteristics,” Appl. Phys. Lett. 94(10), 103302 (2009). [CrossRef]

].

The corresponding CIE chromaticity diagrams of the white tandem OLEDs are shown in Fig. 7
Fig. 7 The CIE chromaticity diagram of OLED-B1 and OLED-B2 at various applied voltages.
, which indicates the color change in a direction from yellow into white of CIE (0.33, 0.33) with increasing voltage. The CCT is 3200 K at 7 V and 3400 K at 10 V for OLED-B2. Though such a warm color of OLED-B2 is not suitable for lighting in office and school rooms, it is suitable for lighting in European houses and shops.

4. Conclusions

In summary, we studied an efficient ETL of DPyPA:KBH4 which is located adjacent to a charge generation layer of MoO3/NPB in tandem OLEDs. The excellent transporting property of the DPyPA:KBH4 layer helps the tandem OLED to achieve a lower voltage than the tandem device with the widely used Alq3:Li. For the tandem white OLED with DPyPA:KBH4 layer, which has a fluorescent blue emitting unit and a phosphorescent yellow emitting unit, we achieved a high current efficiency of 75 cd/A. This efficiency was improved to 120 cd/A by attaching a diffuser layer to this OLED.

Acknowledgments

This work was supported by the National Key Basic Research and Development Programme of China (No. 2009CB623604), the National High Technology Research and Development Program of China (No. 2011AA03A110) and the National Natural Science Foundation of China (Grant Nos. 50990060 and 51173096), and also by the Grant-in-Aid for the Scientific Research from the Japan Society for Promotion of Science (Project No. 22560013) and from Research Institute of Advanced Technology, Kyoto Sangyo University.

References and links

1.

L. S. Liao and K. P. Klubek, “Power efficiency improvement in a tandem organic light-emitting diode,” Appl. Phys. Lett. 92(22), 223311 (2008). [CrossRef]

2.

Q. Wang, J. Q. Ding, Z. Q. Zhang, D. G. Ma, Y. X. Cheng, L. X. Wang, and F. S. Wang, “A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer,” J. Appl. Phys. 105(7), 076101 (2009). [CrossRef]

3.

H.-D. Lee, S. J. Lee, K. Y. Lee, B. S. Kim, S. H. Lee, H. D. Bae, and Y. H. Tak, “High Efficiency Tandem Organic Light-Emitting Diodes Using Interconnecting Layer,” Jpn. J. Appl. Phys. 48(8), 082101 (2009). [CrossRef]

4.

T. Matsumoto, T. Nakada, J. Endo, K. Mori, N. Kawamura, A. Yokoi, and J. Kido, “Multiphoton organic EL device having charge generation layer,” SID Symposium Digest of Technical Papers 34, 979–981 (2003).

5.

M. Terai and T. Tsutsui, “Electric-field-assisted bipolar charge generation from internal charge separation zone composed of doped organic bilayer,” Appl. Phys. Lett. 90(8), 083502 (2007). [CrossRef]

6.

M. Ho, T. M. Chen, P. C. Yeh, S. W. Hwang, and C. H. Chen, “Highly efficient p-i-n white organic light emitting devices with tandem structure,” Appl. Phys. Lett. 91(23), 233507 (2007). [CrossRef]

7.

S. Hamwi, J. Meyer, M. Kröger, T. Winkler, M. Witte, T. Riedl, A. Kahn, and W. Kowalsky, “The role of transition metal oxides in charge-generation layers for stacked organic light-emitting diodes,” Adv. Funct. Mater. 20(11), 1762–1766 (2010). [CrossRef]

8.

T. Chiba, Y.-J. Pu, R. Miyazaki, K. Nakayama, H. Sasabe, and J. Kido, “Ultra-high efficiency by multiple emission from stacked organic light-emitting devices,” Org. Electron. 12(4), 710–715 (2011). [CrossRef]

9.

L. S. Liao, W. K. Slusarek, T. K. Hatwar, M. L. Ricks, and D. L. Comfort, “Tandem organic light-emitting mode using hexaazatriphenylene hexacarbonitrile in the intermediate connector,” Adv. Mater. (Deerfield Beach Fla.) 20(2), 324–329 (2008). [CrossRef]

10.

M. Yokoyama, S. H. Su, C. C. Hou, C. T. Wu, and C. H. Kung, “Highly efficient white organic light-emitting diodes with a p-i-n tandem structure,” Jpn. J. Appl. Phys. 50(4), 04DK06 (2011). [CrossRef]

11.

M. Y. Chan, S. L. Lai, K. M. Lau, M. K. Fung, C. S. Lee, and S. T. Lee, “Influences of connecting unit architecture on the performance of tandem organic light-emitting devices,” Adv. Funct. Mater. 17(14), 2509–2514 (2007). [CrossRef]

12.

L. Duan, D. Zhang, Y. Li, G. Zhang, and Y. Qiu, “Improving the performance of OLEDs by using a low-temperature-evaporable n-dopant and a high-mobility electron transport host,” Opt. Express 19(S6Suppl 6), A1265–A1271 (2011). [CrossRef] [PubMed]

13.

T. Yamasaki, K. Sumioka, and T. Tsutsui, “Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium,” Appl. Phys. Lett. 76(10), 1243–1245 (2000). [CrossRef]

14.

S. Möller and S. R. Forrest, “Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays,” J. Appl. Phys. 91(5), 3324 (2002). [CrossRef]

15.

H. Peng, Y. L. Ho, X. J. Yu, and H. S. Kwok, “Enhanced coupling of light from organic light emitting diodes using nanoporous films,” J. Appl. Phys. 96(3), 1649–1651 (2004). [CrossRef]

16.

T. Nakamura, N. Tsutsumi, N. Juni, and H. Fujii, “Improvement of coupling-out efficiency in organic electroluminescent devices by addition of a diffusive layer,” J. Appl. Phys. 96(11), 6016 (2004). [CrossRef]

17.

Y. H. Cheng, J. L. Wu, C. H. Cheng, K. C. Syao, and M. C. M. Lee, “Enhanced light outcoupling in a thin film by texturing meshed surfaces,” Appl. Phys. Lett. 90(9), 091102 (2007). [CrossRef]

18.

T. Tsutsui, M. Yahiro, H. Yokogawa, K. Kawano, and M. Yokoyama, “Doubling coupling-out efficiency in organic light-emitting devices using a thin silica aerogel layer,” Adv. Mater. (Deerfield Beach Fla.) 13(15), 1149–1152 (2001). [CrossRef]

19.

Q. Liu, D. Zhang, L. Duan, G. Zhang, L. Wang, Y. Cao, and Y. Qiu, “Thermally decomposable kbh4 as an efficient electron injection material for organic light-emitting diodes,” Jpn. J. Appl. Phys. 48(8), 080205 (2009). [CrossRef]

20.

Y. Sun, L. Duan, D. Zhang, J. Qiao, G. Dong, L. Wang, and Y. Qiu, “A pyridine-containing anthracene derivative with high electron and hole mobilities for highly efficient and stable fluorescent organic light-emitting diodes,” Adv. Funct. Mater. 21(10), 1881–1886 (2011). [CrossRef]

21.

J. H. Lee, M. H. Wu, C. C. Chao, H. L. Chen, and M. K. Leung, “High efficiency and long lifetime OLED based on a metal-doped electron transport layer,” Chem. Phys. Lett. 416(4-6), 234–237 (2005). [CrossRef]

22.

W. Brütting, S. Berleb, and A. G. Mückl, “Space-charge limited conduction with a field and temperature dependent mobility in Alq light-emitting devices,” Synth. Met. 122(1), 99–104 (2001). [CrossRef]

23.

T. Tsuboi, S.-W. Liu, M.-F. Wu, and C.-T. Chen, “Spectroscopic and electrical characteristics of highly efficient tetraphenylsilane-carbazole organic compound as host material for blue organic light emitting diodes,” Org. Electron. 10(7), 1372–1377 (2009). [CrossRef]

24.

G. Paasch, A. Nesterov, and S. Scheinert, “Simulation of organic light emitting diodes: influence of charges localized near the electrodes,” Synth. Met. 139(2), 425–432 (2003). [CrossRef]

25.

C.-C. Liu, S.-H. Liu, K.-C. Tien, M.-H. Hsu, H.-W. Chang, C.-K. Chang, C.-J. Yang, and C.-C. Wu, “Microcavity top-emitting organic light-emitting devices integrated with diffusers for simultaneous enhancement of efficiencies and viewing characteristics,” Appl. Phys. Lett. 94(10), 103302 (2009). [CrossRef]

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(230.4170) Optical devices : Multilayers

ToC Category:
Light-Emitting Diodes

History
Original Manuscript: October 25, 2011
Revised Manuscript: December 22, 2011
Manuscript Accepted: January 3, 2012
Published: June 14, 2012

Citation
Lian Duan, Taiju Tsuboi, Yong Qiu, Yanrui Li, and Guohui Zhang, "Tandem organic light-emitting diodes with KBH4 doped 9,10-bis(3-(pyridin-3-yl)phenyl) anthracene connected to the charge generation layer," Opt. Express 20, 14564-14572 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-13-14564


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References

  1. L. S. Liao and K. P. Klubek, “Power efficiency improvement in a tandem organic light-emitting diode,” Appl. Phys. Lett.92(22), 223311 (2008). [CrossRef]
  2. Q. Wang, J. Q. Ding, Z. Q. Zhang, D. G. Ma, Y. X. Cheng, L. X. Wang, and F. S. Wang, “A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer,” J. Appl. Phys.105(7), 076101 (2009). [CrossRef]
  3. H.-D. Lee, S. J. Lee, K. Y. Lee, B. S. Kim, S. H. Lee, H. D. Bae, and Y. H. Tak, “High Efficiency Tandem Organic Light-Emitting Diodes Using Interconnecting Layer,” Jpn. J. Appl. Phys.48(8), 082101 (2009). [CrossRef]
  4. T. Matsumoto, T. Nakada, J. Endo, K. Mori, N. Kawamura, A. Yokoi, and J. Kido, “Multiphoton organic EL device having charge generation layer,” SID Symposium Digest of Technical Papers 34, 979–981 (2003).
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