Power efficiency improvement in a tandem organic light-emitting diode

Abstract

When a tandem light-emitting diode (OLED) utilizes unoptimized electroluminescent (EL) units, it is fairly easy to improve the power efficiency of such a device. However, when a tandem OLED utilizes optimized EL units, improved power efficiency can only be achieved if each intermediate connector has excellent carrier injection capabilities along with a negligible voltage drop across it. Four organic intermediate connectors were studied in this work, one of which consisting of a Li-doped 4,7-diphenyl-1,10-phenanthroline layer and a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile layer, exhibits the best power efficiency improvement for tandem OLEDs.

The Advanced Charge Injection Techniques Towards the Fabrication of High-Power Organic Light Emitting Diodes

“…Tandem OLEDs consisting of two light emitting units stacked vertically in series have been demonstrated [40,41]. Compared to the single light emitting unit, the two-unit tandem OLED can provide the prolonged working lifetime and higher luminance but nearly the same power efficiency, because the driving voltage of the tandem OLED is twice that of the single light emitting unit at a given current density.…”

“…It has been recognized that the voltage drop across the interconnected structure is the key to determining the operation voltage of the tandem OLEDs [40]. In order to minimize the series resistance of the interconnected structure, it is of great necessity to reduce the ohmic loss of the current conduction in this structure provided that the energy losses due to the internal charge generation and injections have already been optimized.…”

Efficient Green Phosphorescent OLEDs with Hexaazatrinaphthylene Derivatives as a Hole Injection Layer

“…전이금속 산화물이나 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN)과 같은 HIL은 새로운 개념의 정공주입 메커니즘을 바 탕으로 높은 효율의 OLEDs 소자 결과를 얻을 수 있다는 것을 보여줬 다 [6][7]. 이러한 HIL의 정공주입 메커니즘은 HIL과 HTL 층간의 계면 에서의 전하의 분리 및 HTL의 HOMO 에너지 준위로의 정공 이송, HIL의 LUMO 에너지 준위로의 전자 이송의 단계를 거치는 것으로 이 해되고 있다 [8][9].…”

Inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile crystallization by mixing additives for hole injection layers in organic light-emitting devices

“…[1][2][3] To fabricate highly efficient devices, the incorporation of hole injection layers (HILs) is indispensable because these significantly improve the characteristics of hole injection from the anode to the emitting layer, leading to lower driving voltages and improved charge recombination balance. To date, various HILs have been reported, [4][5][6][7][8][9][10][11][12][13][14][15] and, among these, 1,4,5,8,9, 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) has been employed in HILs (leading to low driving voltage) 4,[16][17][18][19][20][21][22] since the first application of OLED by LG Chemical Ltd. 22 HAT-CN was first reported by Czarnik and co-workers 23 and its characterization has been investigated in various studies. [24][25][26][27][28][29] The most remarkable property of HAT-CN is the extremely deep energy level of its lowest unoccupied molecular orbital.…”