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Fu Q, Chen J, Shi C, Ma D.
ACS Appl Mater Interfaces. 2012 Dec;4(12):6579-86.
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022, People’s Republic of China.
Abstract
The widely used hole-transporting host 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) blended with either a hole-transporting or an electron-transporting small-molecule material as a mixed-host was investigated in the phosphorescent organic light-emitting diodes (OLEDs) fabricated by the low-cost solution-process. The performance of the solution-processed OLEDs was found to be very sensitive to the composition of the mixed-host systems. The incorporation of the hole-transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) into TCTA as the mixed-host was demonstrated to greatly reduce the driving voltage and thus enhance the efficiency due to the improvement of hole injection and transport. On the basis of the mixed-host of TCTA:TAPC, we successfully fabricated low driving voltage and high efficiency blue and white phosphorescent OLEDs. A maximum forward viewing current efficiency of 32.0 cd/A and power efficiency of 25.9 lm/W were obtained in the optimized mixed-host blue OLED, which remained at 29.6 cd/A and 19.1 lm/W at the luminance of 1000 cd/m(2) with a driving voltage as low as 4.9 V. The maximum efficiencies of 37.1 cd/A and 32.1 lm/W were achieved in a single emissive layer white OLED based on the TCTA:TAPC mixed-host. Even at 1000 cd/m(2), the efficiencies still reach 34.2 cd/A and 23.3 lm/W and the driving voltage is only 4.6 V, which is comparable to those reported from the state-of-the-art vacuum-evaporation deposited white OLEDs.
Additional Information
Organic Light Emitting Diodes (OLEDs) fabricated by solution process have always been irreplaceable on the case of the rapid development of the counterparts by vacuum deposition. The solution-processed OLEDs have their own particular application due to their advantages such as low cost, simple fabrication and large-area manufacturability. Moreover, compared to the complicated co-evaporation in vacuum deposited OLEDs, the solution-processed OLEDs are more simple and accurate to fabricate.
To obtain high-efficiency in solution-processed OLEDs, great progress should be made to manipulate the carriers and excitons activated in the devices, especially in the emissive layers based on the multiple components. Host engineering is one of the key factors directly governing the performances of the devices. In this research, the authors expounded on the match of the host and guest together with the variable carriers balance influenced by the carrier mobility of the hosts. They employed a mixed-host system with hole-hole or hole-electron host materials into the emissive layer in the solution-processed OLEDs. It was found that the hole-hole host system is advantageous over the hole-electron host system to confine the carriers and excitons in the emissive layers. The resulting blue and white devices with the hole-hole mixed-host exhibit the outstanding performance. And their efficiencies are comparable to those in the state-of-the-art vacuum deposited devices.
This research is of benefit to the development of low-cost and high-efficiency OLEDs for displays and lighting.
