Abstract
In this article, hybrid white organic light-emitting diodes (WOLEDs) under p-i-n structures have been investigated in terms of power efficiency. By using tris(8-hydroxy quinolinato) aluminum (Alq3) doped with 8-hydroxy-quinolinato lithium (Liq) as an n-type and WHI112 doped with molybdenum trioxide (MoO3) as a p-type, the typical device structure of ITO/WHI112: 20 wt.% MoO3 (55 nm)/HTG-1 (10 nm)/UBH15: 3 wt.% EB502 (10 nm)/EPH31: 3 wt.% EPY01 (25nm)/3TPYMB (10 nm)/Alq3: 33 wt.% Liq (25 nm)/Al (150 nm) was fabricated. It has been found that the p-i-n device based device showed the lowest driving voltage and highest power efficiency among the undoped and n-type devices. At the current density of 20 mA/cm2, the roll-off of the efficiency in the p-i-n device was much smaller than the n-type and the undoped devices. The current and power efficiency of the p-i-n device were maintained with 17.2 cd/A and 5.1 lm/W at 100 mA/cm2, it was reduced to 7.5 % and 21 %, respectively. In contrast, the n-type device exhibited the significant reduction of efficiency (14.4 cd/A and 3.8 lm/W at 80 mA/cm2), it was reduced to 20 % and 39.6 %, respectively. The superior performances of the p-i-n structure based device were attributed to the high hole injection ability of WHI112:MoO3 and high electron mobility of Alq3:Liq, leading to high power efficiency and low driving voltage. A better balance of electrons and holes could contribute to a good current efficiency for the device. These findings strongly indicated that carrier injection ability and balance showed significant affects on the performance of OLED. Keywords: Highly efficient OLEDs, hybrid white OLEDs, p-i-n OLED.
Highlights
Since the discovery of the efficient organic light-emitting diodes (OLEDs) considerable interest has been increased in developing OLEDs with high efficiency, low operating voltage for display applications is concerned [1]
The n-type device exhibited the significant reduction of efficiency (14.4 cd/A and 3.8 lm/W at 80 mA/cm2), it was reduced to 20 % and 39.6 %, respectively
We have demonstrated hybrid white organic light-emitting diode (WOLEDs) devices based on the p-i-n structure with Liq doped into Alq3 as the n-doping layer and MoO3 doped into WHI112 as the p-doping layer
Summary
Since the discovery of the efficient organic light-emitting diodes (OLEDs) considerable interest has been increased in developing OLEDs with high efficiency, low operating voltage for display applications is concerned [1]. Reasonable charge carrier control in the OLED emitting layers (EMLs) is a key factor in OLED low driving voltage and high efficiency structure design. The first approach involves with inserting a thin layer as an anode buffer layer between the indium tin oxide (ITO) and hole transport layer (HTL). This buffer layer reduces the energy barrier and enhancesthe charge injection at the interface and reduces the driving voltage improving the device power efficiency [4-7]. The p-doping of HTL for enhancing the hole injection and lowering the drive voltages in OLEDs has attracted much attention [13]. The p-doping could achieve the ohmic conductivity to minimize the voltage drop across
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