Charge injection and transport properties of an organic light-emitting diode

Juhász, P.; Nevrela, Juraj; Micjan, Michal; Novota, Miroslav; Uhrik, Jan; Stuchlíková, Ł.; Jakabovič, J.; Harmatha, L.; Weis, Martin

doi:10.3762/bjnano.7.5

Cited by 34 publications

(21 citation statements)

References 21 publications

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“…Among the target molecules in ultrasmooth films, Alq 3 and NPD films are semiconductors in an amorphous phase and have been drawing great attention as electron transport layer and hole transport layer in OLED, respectively [ 53 , 54 , 55 ]. To further evaluate the FCPVD method, the quality of the film prepared using the FCPVD method has been examined with fabricated electron transport layer-only devices (EOD, ITO/Alq 3 /Al), hole transport layer-only devices (HOD, ITO/NPD/Al), and heterojunction devices (ITO/NPD/Alq 3 /Al)—which are the basic types of OLEDs—by analyzing the current density–voltage characteristics.…”

Section: Resultsmentioning

confidence: 99%

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

Yoon

Lee

et al. 2021

Materials

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Organic thin films with smooth surfaces are mandated for high-performance organic electronic devices. Abrupt nucleation and aggregation during film formation are two main factors that forbid smooth surfaces. Here, we report a simple fast cooling (FC) adapted physical vapor deposition (FCPVD) method to produce ultrasmooth organic thin films through effectively suppressing the aggregation of adsorbed molecules. We have found that thermal energy control is essential for the spread of molecules on a substrate by diffusion and it prohibits the unwanted nucleation of adsorbed molecules. FCPVD is employed for cooling the horizontal tube-type organic vapor deposition setup to effectively remove thermal energy applied to adsorbed molecules on a substrate. The organic thin films prepared using the FCPVD method have remarkably ultrasmooth surfaces with less than 0.4 nm root mean square (RMS) roughness on various substrates, even in a low vacuum, which is highly comparable to the ones prepared using conventional high-vacuum deposition methods. Our results provide a deeper understanding of the role of thermal energy employed to substrates during organic film growth using the PVD process and pave the way for cost-effective and high-performance organic devices.

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Section: Resultsmentioning

confidence: 99%

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

Yoon

Lee

et al. 2021

Materials

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“…Furthermore, we observed the low charge injection region in Figure 3 b and Figure 4 b, below the voltage 2 V and 10 V, for Devices II and IV, respectively. That current density (J) follows the externally applied voltage (V) linearly, as shown in Equation (2), may be the reason behind this [ 22 ].

where en is the charge density ( e : elementary charge, n : charge carrier density), μ eff is the effective charge mobility, and L the organic film thickness.…”

Section: Resultsmentioning

confidence: 99%

“…

where en is the charge density ( e : elementary charge, n : charge carrier density), μ eff is the effective charge mobility, and L the organic film thickness. It is notable that the effective charge mobility μ eff includes charge trapping phenomenon as follows [ 22 ]:

where μ 0 is trap-free charge mobility, and n mob and n trap are mobile and trapped charge carrier densities, respectively. As shown in Figure 3 b, in the voltage region from 2 to 3 V an abrupt increase of the current is observed.…”

Section: Resultsmentioning

confidence: 99%

An Approach for Measuring the Dielectric Strength of OLED Materials

et al. 2018

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Surface roughness of electrodes plays a key role in the dielectric breakdown of thin-film organic devices. The rate of breakdown will increase when there are stochastic sharp spikes on the surface of electrodes. Additionally, surface having spiking morphology makes the determination of dielectric strength very challenging, specifically when the layer is relatively thin. We demonstrate here a new approach to investigate the dielectric strength of organic thin films for organic light-emitting diodes (OLEDs). The thin films were deposited on a substrate using physical vapor deposition (PVD) under high vacuum. The device architectures used were glass substrate/indium tin oxide (ITO)/organic material/aluminum (Al) and glass substrate/Al/organic material/Al. The dielectric strength of the OLED materials was evaluated from the measured breakdown voltage and layer thickness.

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“…Finally, the last zone has m = 5 between 10 to 15 V is dominated by the trap filling process, and the increases of current causes a gradual filling of the states that represents the rise of the activation energy. After the filling of all interfacial states, the charges are injected over the interfacial barrier, which stands for second charge relaxation [53]. Figure 5b,c shows the luminance measured at 14 V for the IrQ(ppy) 2 :CBP (20%) and IrQ(ppy) 2 :CBP (10%) samples and the photoluminescence on the same sample excited at 405 nm.…”

Section: Current-voltage Characteristics: Electroluminescence Of Irq(mentioning

confidence: 99%

Organometallic Coatings for Electroluminescence Applications

Poloşan

Ciobotaru

2020

Coatings

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Organometallic compounds embedded in thin films are widely used for Organic Light-Emitting Diodes (OLED), but their functionalities are strongly correlated with the intrinsic properties of those films. Controlling the concentration of the organometallics in the active layers influences the OLED performances through the aggregation processes. These aggregations could lead to crystallization processes that significantly modify the efficiency of light emission in the case of electroluminescent devices. For functional devices with organometallic-based thin films, some improvements, such as the optimization of the charge injection, are needed to increase the light output. One dual emitter IrQ(ppy)2 organometallic compound was chosen for the aggregation correlations from a multitude of macromolecular organometallics that exist on the market for OLED applications. The choice of additional layers like conductive polymers or small molecules as host for the active layer may significantly influence the performances of the OLED based on the IrQ(ppy)2 organometallic compound. The use of the CBP small molecule layer may lead to an increase in the electroluminescence versus the applied voltage.

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Charge injection and transport properties of an organic light-emitting diode

Cited by 34 publications

References 21 publications

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

An Approach for Measuring the Dielectric Strength of OLED Materials

Organometallic Coatings for Electroluminescence Applications

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