Efficient Stacked OLED processed by Organic Vapor Phase Deposition (OVPD)

2015 ◽  
Vol 1788 ◽  
pp. 13-18
Author(s):  
M. Brast ◽  
S. Axmann ◽  
M. Slawinski ◽  
M. Weingarten ◽  
F. Lindla ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Voltage Drop ◽  
Hole Transport ◽  
Hole Injection ◽  
Large Area ◽  
Charge Generation ◽  
Light Emitting ◽  
Precise Control ◽  
Organic Vapor Phase Deposition ◽  
P Type

ABSTRACTThe development of efficient large-area organic light emitting diodes (OLED) requires reliable and easily processable charge generation layers (CGL) with low excess voltage drop and high optical transparency. OVPD offers the advantage of a precise control of layer morphology, composition and thickness and is a powerful method for the deposition of advanced OLED designs. In this work, electrical doping of organic semiconductors using OVPD is investigated and applied to stacked OLED utilizing inorganic/organic CGL. The organic p-type dopant NDP-9 of Novaled GmbH is used for doping the hole transport material N,N‘-diphenyl-N,N‘-bis(1-naphthylphenyl)-1,1‘-biphenyl-4,4‘-diamine (α-NPD) in an AIXTRON OVPD tool. A doping concentration of 8 vol.% of NDP-9 in α-NPD is found optimal for hole injection as well as conductivity. This dopant concentration was employed in CGL with the structure: electron transport material/LiF/Al/α-NPD:8 vol.% NDP-9. External quantum efficiencies (EQE) of 15%, 35% and 50% and luminous efficiencies of 37 lm/W, 45 lm/W and 45 lm/W at 1000 cd/m2 are demonstrated for single, double- and triple-unit green phosphorescent OLED, respectively.

P-type Doping of Organic Charge Transport Materials with Tungsten Oxide

2015 ◽  
Vol 1805 ◽  
Author(s):  
X. M. Li ◽  
R. Y. Yang ◽  
X. A. Cao
Keyword(s):  
Doping Level ◽  
Voltage Drop ◽  
Hole Transport ◽  
Transport Layer ◽  
Hole Injection ◽  
Constant Current ◽  
Hole Transport Layer ◽  
Band Bending ◽  
Light Emitting ◽  
P Type

ABSTRACTThe effects of WO3 doping in 4,4’-bis-9-carbozyl biphenyl (CBP) were studied through detailed electrical device characterization. A series of hole-only devices have been fabricated, where the doping level was varied from 10-40mol% and the doped CBP thickness was varied from 5-40 nm. It was found that, to achieve effective doping for improved hole injection and transport, the doping level should be greater than 20mol% and the doped layer should be at least 10 nm thick. It was also found that an energy barrier exists at the doped and undoped CBP interface, resulting in an additional voltage drop. This finding was explained by a large downward shift of the Fermi level in WO3-doped CBP, which causes band bending and depletion at the interface. Finally, simplified green phosphorescent organic light-emitting diodes (OLEDs) with CBP as the hole transport and host material were fabricated. With a WO3-doped hole transport layer, the OLEDs attained brightness above 105 cd/m2 at 20 mA/cm2, and exhibited an improved reliability under constant-current stressing as compared to undoped OLEDs.

scholarly journals Large Area Emission in p-Type Polymer-Based Light-Emitting Field-Effect Transistors by Incorporating Charge Injection Interlayers

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 901
Author(s):  
Gizem Acar ◽  
Muhammad Javaid Iqbal ◽  
Mujeeb Ullah Chaudhry
Keyword(s):  
Field Effect ◽  
Field Effect Transistors ◽  
Charge Injection ◽  
Limiting Factors ◽  
Hole Injection ◽  
Large Area ◽  
Device Structure ◽  
Light Emitting ◽  
Emission Area ◽  
P Type

Organic light-emitting field-effect transistors (LEFETs) provide the possibility of simplifying the display pixilation design as they integrate the drive-transistor and the light emission in a single architecture. However, in p-type LEFETs, simultaneously achieving higher external quantum efficiency (EQE) at higher brightness, larger and stable emission area, and high switching speed are the limiting factors for to realise their applications. Herein, we present a p-type polymer heterostructure-based LEFET architecture with electron and hole injection interlayers to improve the charge injection into the light-emitting layer, which leads to better recombination. This device structure provides access to hole mobility of ~2.1 cm2 V−1 s−1 and EQE of 1.6% at a luminance of 2600 cd m−2. Most importantly, we observed a large area emission under the entire drain electrode, which was spatially stable (emission area is not dependent on the gate voltage and current density). These results show an important advancement in polymer-based LEFET technology toward realizing new digital display applications.

scholarly journals Interlayer Engineering of Flexible and Large Area Red Organic Light Emitting Diodes Based on a N-Annulated Perylene Diimide Dimer

2019 ◽  
Author(s):  
Mohammad Rahmati ◽  
Majid Pahlevani ◽  
Gregory Welch
Keyword(s):  
Red Light ◽  
Ambient Air ◽  
Hole Transport ◽  
Transport Layer ◽  
Hole Injection ◽  
Hole Transport Layer ◽  
Large Area ◽  
Average Roughness ◽  
Light Emitting ◽  
Slot Die

<p>Flexible red OLEDs based on a quadruple layer stack in-between electrodes with 160 mm<sup>2</sup> active area were fabricated in ambient air on PET via slot-die coating. For the OLED structure PET/ITO/PEDOT:PSS/PVK/PFO:tPDI<sub>2</sub>N-EH/ZnO/Ag the ink formulations and coating parameters for each layer were systematically evaluated and optimized. The air-stable red-light emitting material tPDI<sub>2</sub>N-EH was successfully utilized as blended homogeneous film with PFO for the emitting layer. The use of an organic hole-transport layer (PVK) and inorganic electron injection layer (ZnO) significantly improved the brightness of the reference device from 4 cd/m<sup>2</sup> to 303 cd/m<sup>2</sup>. Surface analysis using AFM measurements showed that PVK interlayer reduced the surface roughness of the hole injection layer (PEDT:PSS) from 0.45 nm to 0.17 nm, which improved the ability to form uniform emitting layers on top. In addition, the ZnO interlayer improved the average roughness of the device from 1.26 nm to 0.85 nm and reduced the turn-on voltage of the device from 5.0 V to 2.8 V.</p>

scholarly journals Interlayer Engineering of Flexible and Large Area Red Organic Light Emitting Diodes Based on a N-Annulated Perylene Diimide Dimer

2019 ◽  
Author(s):  
Mohammad Rahmati ◽  
Majid Pahlevani ◽  
Gregory Welch
Keyword(s):  
Red Light ◽  
Ambient Air ◽  
Hole Transport ◽  
Transport Layer ◽  
Hole Injection ◽  
Hole Transport Layer ◽  
Large Area ◽  
Average Roughness ◽  
Light Emitting ◽  
Slot Die

<p>Flexible red OLEDs based on a quadruple layer stack in-between electrodes with 160 mm<sup>2</sup> active area were fabricated in ambient air on PET via slot-die coating. For the OLED structure PET/ITO/PEDOT:PSS/PVK/PFO:tPDI<sub>2</sub>N-EH/ZnO/Ag the ink formulations and coating parameters for each layer were systematically evaluated and optimized. The air-stable red-light emitting material tPDI<sub>2</sub>N-EH was successfully utilized as blended homogeneous film with PFO for the emitting layer. The use of an organic hole-transport layer (PVK) and inorganic electron injection layer (ZnO) significantly improved the brightness of the reference device from 4 cd/m<sup>2</sup> to 303 cd/m<sup>2</sup>. Surface analysis using AFM measurements showed that PVK interlayer reduced the surface roughness of the hole injection layer (PEDT:PSS) from 0.45 nm to 0.17 nm, which improved the ability to form uniform emitting layers on top. In addition, the ZnO interlayer improved the average roughness of the device from 1.26 nm to 0.85 nm and reduced the turn-on voltage of the device from 5.0 V to 2.8 V.</p>

scholarly journals Switching from Electron to Hole Transport in Solution-Processed Organic Blend Field-Effect Transistors

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2662
Author(s):  
Julia Fidyk ◽  
Witold Waliszewski ◽  
Piotr Sleczkowski ◽  
Adam Kiersnowski ◽  
Wojciech Pisula ◽  
...  
Keyword(s):  
Thermal Annealing ◽  
Organic Semiconductors ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Hole Transport ◽  
Solution Temperature ◽  
Attractive Alternative ◽  
Large Area ◽  
Light Emitting ◽  
Practical Applications

Organic electronics became an attractive alternative for practical applications in complementary logic circuits due to the unique features of organic semiconductors such as solution processability and ease of large-area manufacturing. Bulk heterojunctions (BHJ), consisting of a blend of two organic semiconductors of different electronic affinities, allow fabrication of a broad range of devices such as light-emitting transistors, light-emitting diodes, photovoltaics, photodetectors, ambipolar transistors and sensors. In this work, the charge carrier transport of BHJ films in field-effect transistors is switched from electron to hole domination upon processing and post-treatment. Low molecular weight n-type N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) was blended with p-type poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) and deposited by spin-coating to form BHJ films. Systematic investigation of the role of rotation speed, solution temperature, and thermal annealing on thin film morphology was performed using atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. It has been determined that upon thermal annealing the BHJ morphology is modified from small interconnected PDI8-CN2 crystals uniformly distributed in the polymer fraction to large planar PDI8-CN2 crystal domains on top of the blend film, leading to the switch from electron to hole transport in field-effect transistors.

The Study of Hole Injection in OLEDs with Ultra-Thin Sol-Gel TiO2 Layer

2011 ◽  
Vol 189-193 ◽  
pp. 42-46
Author(s):  
You Wang Hu ◽  
Xiao Yan Sun ◽  
Jian Duan
Keyword(s):  
Sol Gel ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Transport Layer ◽  
Hole Injection ◽  
Hole Transport Layer ◽  
Carrier Injection ◽  
Light Emitting ◽  
Organic Light ◽  
Pre Treatment

Organic light-emitting diodes (OLEDs) with inserting an ultrathin sol–gel titanium oxide (TiO2) buffer layer between the ITO anode and hole transport layer (HTL) were fabricated. The carrier injection and the device efficiency were affected by surface morphology of TiO2, which was changed by different plasma pre-treatment of ITO. Treated by CF4 plasma, the TiO2 layer is the smoothest, and treated by H2 plasma it is like island. The TiO2 layer like island is favor of carrier injection from the anode, which was attributed to the point discharged.

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