[20p-W521-1~16] 12.4 Organic light-emitting devices and organic transistors

▼ [20p-W521-4] Horizontal molecular orientation in solution-processed glassy organic thin films based on oligofluorene derivatives

〇(D)Li Zhao¹, Takeshi Komino^1,2,3, Munetomo Inoue¹, Ju-Hyung Kim¹, Jean-Charles Ribierre^1,3, Chihaya Adachi^1,2,3 (1.OPERA, Kyushu University, 2.Education Center for Global Leaders in Molecular System for Devices, Kyushu University, 3.ERATO, JST)

Keywords:Solution-process,Molecular orientation,OLEDs

Horizontal molecular orientation in organic light-emitting diode (OLED) materials has been already reported in a variety of vacuum-deposited glassy thin films. It is now well-established that such a horizontal molecular orientation is essential to improve the light outcoupling efficiency and the overall performance of the light-emitting devices. However, this preferential orientation has not been observed so far in spin-coated glassy organic films. Because of the current need to develop high performance solution-processed OLEDs for low cost and large area applications, control of the molecular orientation in spin-coated glassy organic thin films is a critical issue for improving the OLED performance. Here, we show that the horizontal orientation of light-emitting molecules can be obtained in spin-coated glassy thin films based on a blend of a heptafluorene derivative in a 4,4’- bis(N-carbazolyl)-1,1’-biphenyl (CBP) host. Variable angle spectroscopic ellipsometry and angle dependent photoluminescence measurements are carried out to investigate the molecular orientation in the heptafluorene neat films and in CBP blends. Solution-processed fluorescent OLEDs with horizontally oriented heptafluorene emitters are then fabricated and exhibit deep blue electroluminescence with an external quantum efficiency as high as 5.3 %.