2P026
Cyclometalated organoplatinum(II) complex for yellow and white organic light-emitting devices
Shiu-Lun Lai and Chi-Ming Che*
State Key Laboratory of Synthetic Chemistry, HKU-CAS Joint Laboratory on New Materials,
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Phone: +852-2859-2154, Fax: +852-2915-5176, Email: cmche@hku.hk
1.

INTRODUCTION
Phosphorescent white organic light-emitting device (WOLED) technology is a major focus ofOLED area since the demonstration of devices with practical electroluminescence (EL) efficiency ofover 30 cd A-1 has been reported. Utilization of a simplified WOLED structure with two-color
emission, i.e. blue and yellow (BY), is preferential. However, the success for realizing efficient
BY-based WOLEDs strongly relies on the development of high efficiency key emitters. Herein, a highefficiency WOLED incorporating a newly-synthesized yellow-emitting organoplatinum(II) complex,
HKU-Y-Pt, and a modified composite host for blue FIrpic phosphor that can achieve current
efficiency (C) of 46 cd A-1 is reported.
2.

EXPERIMENTSFig. 1 Chemical structure of (a) HKU-Y-Pt and schematic device architectures of (b) yellow OLEDs(HKU-Y-Pt content, x = 2, 4, 6, 8) and (c) WOLED based on blue emission from FIrpic and yellow emission
from HKU-Y-Pt.

Figure 1(a) shows the chemical structure of HKU-Y-Pt that contains a strong chelating
tetradentate ligand having mixed C, O, and N donor atoms. The strong chelation effect of O^N^C^N
ligand in HKU-Y-Pt contributes to excellent thermal stability with high decomposition temperature of400 °C and good emission efficiency with high photoluminescence (PL) quantum yields of 0.82–0.86
in most of organic solvents. HKU-Y-Pt exhibits a saturated yellow emission with peak maximum at ca.
553 nm and emission lifetimes of 6.6–7.6 μs (shown in Fig. 2). To validate its EL performance, yellow
OLEDs with HKU-Y-Pt as phosphorescent dopant at different concentrations were fabricated basedon the configuration shown in Fig. 1(b). As shown in Fig. 3, a maximum C of 75 cd A-1 was achievedat an optimized concentration of 6%HKU-Y-Pt. In addition, the EL spectra for 6%HKU-Y-Pt device
remain unchanged over a wide range of luminance, exhibiting same EL peak at 568 nm, as shown in(Continued to the next page)the inset of Fig. 3. This corresponds to a saturated yellow emission with CIE of (0.52, 0.47).

Fig. 2 PL spectra of HKU-Y-Pt in different

Fig. 3 c-J characteristics of yellow OLEDs. Inset: ELsolvents. Φ and τ are PL quantum yield andspectra

emission lifetime, respectively.

measured at various luminances.

ofyellowOLEDwith6%HKU-Y-Pt

Figure 4 depicts the EL spectrum of the optimized WOLED based on a modified structure(shown in Fig. 1(c)) incorporating a composite blue host of mCP and UGH2 both doped with8%FIrpic and a single yellow emissive layer 4%HKU-Y-Pt:TCTA. EL spectrum of WOLED
resembles to the summation of two monochromatic emissions from blue FIrpic and yellow HKU-Y-Pt,
corresponding to CIE of (0.34, 0.44). Figure 5 shows the C –current density (J) characteristic ofWOLED, in which a high C of 46 cd A-1 could be realized, much higher than those obtained fromconventional devices utilizing same emitters (~26 cd A-1).

Fig. 4 EL spectra of WOLED, blue OLED andFig. 5 c-J (Inset: Current density – voltage –yellow OLED. Blue OLED: ITO / NPB / mCP /luminance (J-V-L)) characteristic of WOLED.

8%FIrpic:UGH2 / BAlq / LiF / Al.

3.

SUMMARY
To conclude, the present work demonstrates WOLED incorporating a composite blue host and ahighly robust yellow-emitting phosphor HKU-Y-Pt. This provides a simple means for achieving highefficiency of WOLED for lighting and can make advances to bring WOLED closer to practicalapplications.
ACKNOWLEDGEMENTS
This work described in this paper was supported by the Theme-Based Research Scheme(T23-713/11) and the National Basic Research Program of China (No. 2013CB834802).