Efficiency improvement of flexible phosphorescent organic light emitting diode by inserting a buffer layer

Green and low-cost approach to modify the indium tin oxide anodes in organic light-emitting diodes by electrochemical treatment in NaCl aqueous solution

Efficient single layer RGB phosphorescent organic light-emitting diodes

The organic semiconductor materials which form Self-Assembled Monolayers (SAMs) on Indium Tin Oxide (ITO) surface have been synthesized and used in Organic Light Emitting Diode (OLED) applications. The synthesized molecules are bonded chemically to the hydrophilic and rough ITO surface and formed a new hydrophobic and smother surface of ITO by the effect of SAM formation. The synthesized SAM molecule is 4″, 4″″-[biphenyl-4,4″-diylbis(phenylimino)]dibiphenyl-4-carboxylic acid (MZ-187) that contains carboxylic acid head group to bond to ITO surface. The formation on ITO surface is analyzed by cyclic voltammetry (CV) and atomic force microscopy (AFM). Two configurations, ITO/SAM(MZ-187)/HTL/EML/LiF/Al (MZ187-OLED) and ITO/HTL/EML/LiF/Al (bare-OLED), are fabricated to investigate the effect of SAM layer on the performance of the OLED device. Current–voltage (I–V) characterization of OLED devices are carried out and the luminescence of the devices are measured by integrating sphere under nitrogen gas in a glow box system. The quantum efficiency is calculated to determine how to affects the SAM layers on OLEDs performance. As a consequence, it is determined that the OLED device containing MZ-187 SAM layer, a similar structure with N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), is exhibited a better OLED performance compare to the device without SAM layer.

The seed mediated growth of gold nanoparticles on indium tin oxide (ITO) surfaces is described, which provided a new method for the construction of gold nanoparticles‐modified ITO electrodes even without using conventional linker molecules, such as (3‐mercaptopropyl)trimethoxysilane (MPTMS). In this process, ultra‐small gold seeds were formed and anchored on the ITO surfaces first. When the seeds‐deposited ITO surfaces came into contact with the gold growth solution, the growth of gold nanoparticles occurred. The morphology of the as‐prepared modified surface was found to be strongly dependent upon the substrate. On an MPTMS‐silanized ITO, mostly gold nanospheres were formed (Au/MPTMS/ITO).In contrast, on a bare ITO, some high aspect ratio gold nanorods as well as large amounts of gold nanospheres were grown and directly attached (Au/ITO). The as‐prepared two gold nanoparticles‐modified ITO electrodes exhibited different electrochemical characteristics, attributed to the influence of MPTMS molecules. Compared with Au/MPTMS/ITO, the Au/ITO was more efficient in decreasing the heterogeneous charge transfer resistance and improving the reaction reversibility of [Fe(CN)6]3−/[Fe(CN)6]4− and exhibited more attractive bioelectrocatalytic properties. Due to the block effect of the thiol monolayer, Au/MPTMS/ITO depressed the selectivity for the determination of epinephrine (EP) in the presence of ascorbic acid (AA) while Au/ITO could improve the detection sensitivity and retain the selectivity.

In order to control differentiation of neural cells and guide the developed neurites to targets, polyelectrolyte multilayer (PEM) films were used because of their capability of modulation of electrical charged characteristics, thickness, and stiffness. In this work, we suggested that indium tin oxide (ITO) is an alternative surface to achieve the above-mentioned objectives. A microfluidic system with four culture chambers was developed and each chamber consisted of parallel ITO surfaces for the application of adjustable electrical field. Neural stem/progenitor cells (NSPCs) were respectively cultured on the ITO surfaces with and without PEM film, constructed by alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA). Analyses of cell morphology, cytotoxicity, process outgrowth, differentiated cell types, and neuron functionality were compared between both surfaces. In this study, NSPCs successfully differentiated on ITO surface with electrical stimulation. The optimal electrical potential was found to be 80 mV that could stimulate the longest process, i.e., >300 μm, after 3 days culture. Cell differentiation, process development, and functionality of differentiated neuron on ITO surface were shown to be strongly controlled by the electrical stimulation that can be simply adjusted by external equipment. The electrically adjustable cell differentiation reported here could potentially be applied to neurochip for the study of neural signal transmission in a well-constructed network.

The effect of exciton‐induced degradation of hole transport layers (HTLs) and its influence on efficiency and stability of phosphorescent organic light emitting devices (PhOLEDs) are investigated. In order to be able to isolate and study the effect of excitons on HTLs, UV illumination as a means to expose them to exciton stress is used. Results reveal that exciton stress of only the HTLs can lead to a significant deterioration in the electroluminescence external quantum efficiency and stability of PhOLEDs, revealing the detrimental role of exciton‐induced degradation of HTLs in limiting the device performance. The creation of quenchers in HTLs and the diffusion of excitons from the HTL to the EML appear to play roles in this degradation mechanism. Observations reveal that exciton‐induced degradation of HTLs more strongly impacts PhOLEDs than their fluorescent counterparts, revealing the more critical role that HTLs play in influencing their stability and pointing to the role of triplet excitons in this phenomenon. Observations also suggest that increasing the exciton stability of HTLs or reducing exciton lifetime in them can help increase device stability. The findings uncover a new degradation mode in PhOLEDs and provide key insights for device design for realizing better performance and stability.

Highly efficient two component phosphorescent organic light-emitting diodes based on direct hole injection into dopant and gradient doping

Dependence of surface morphology on molecular structure and its influence on the properties of OLEDs

A conducting polymer polyaniline (PANI) with nanostructure was synthesized on indium tin oxide (ITO) glass. The effect of electrical stimulation on the proliferation and the length of neurites of PC 12 cells was investigated. The dynamic protein adsorption on PANI and ITO surfaces in a cell culture medium was also compared with and without electrical stimulation. The adsorbed proteins were characterized using SDS-PAGE. A PANI coating on ITO surface was shown with 30-50 nm spherical nanostructure. The number of PC 12 cells was significantly greater on the PANI/ITO surface than on ITO and plate surfaces after cell seeding for 24 and 36 h. This result confirmed that the PANI coating is nontoxic to PC 12 cells. The electrical stimulation for 1, 2, and 4 h significantly enhanced the cell numbers for both PANI and ITO conducting surfaces. Moreover, the application of electrical stimulation also improved the neurite outgrowth of PC 12 cells, and the number of PC 12 cells with longer neurite lengths increased obviously under electrical stimulation for the PANI surface. From the mechanism, the adsorption of DMEM proteins was found to be enhanced by electrical stimulation for both PANI/ITO and ITO surfaces. A new band 2 (around 37 kDa) was observed from the collected adsorbed proteins when PC 12 cells were cultured on these surfaces, and culturing PC 12 cells also seemed to increase the amount of band 1 (around 90 kDa). When immersing PANI/ITO and ITO surfaces in a DMEM medium without a cell culture, the number of band 3 (around 70 kDa) and band 4 (around 45 kDa) proteins decreased compared to that of PC 12 cell cultured surfaces. These results are valuable for the design and improvement of the material performance for neural regeneration.

Kinetics of Colloidal Deposition and Release of Polystyrene Latex Particles in the Presence of Adsorbed β-Lactoglobulin Studied Using a Flow Cell

A two-step patterning process was developed based on nanosphere lithography and plasma etching to fabricate an array of electrodes with two different gold ring structures: the arrays of Au micro-ring electrode (Au-MRE) and Au covered with polystyrene micro-ring electrode (Au-PS-MRE). The Au-MRE structure was fabricated by etching a monolayer ofpolystyrene (PS) spheres on indium tin oxide (ITO) surface to generate PS rings on ITO glass. PS rings served as a mask in secondary etching for blocking an interaction of oxygen plasma and ITO surface to create a ring-patterned ITO surface. Then, the PS residue was removed and gold was deposited. The site-selective electrodeposition of gold was carried out and an array of a gold ring structure was formed on the ITO glass. The Au-PS-MRE structure was fabricated by keeping the PS residue from second etching before deposition of gold. The Au-PS-MRE microelectrode was studied by using hexacyanoferrate as an electrochemical probewhere it displayed steady state current in cyclic voltammetry. The respective calibration plots were acquired at a working potential of 0.31V and 0.12V (vs. Ag/AgCl) for oxidation and reduction reaction, respectively. The sensitivity is as high as 163.4-220.7 μA·mM-1·mm-2 which is larger by a factor of 95-132 compared to a conventional gold film macroelectrode. The detection limit (at a signal-to-noise ratio of 3) is 2.2μM. This approach thus yields relatively effective and low-cost fabrication without resorting to high resolution instruments. Conceivably, the technique may be used to produce microelectrode arrays on a large scale. Graphical abstract Schematic presentation of a novel fabrication process of micro-ring electrode arrays. Two-step patterning based on nanosphere lithography leads to electrodes with great electrochemical performance. Direct deposition metal in the presence of polystyrene (PS) mask induces the formation of a new structure with arrays of gold covered with PS microring on the indium tin oxide (ITO) coated glass. The microelectrode-like behavior has been achieved using this fabrication process.

Stability is an essential issue in the application of organic light-emitting devices (OLEDs). We have investigated the indium tin oxide (ITO) surface for operated and unoperated OLEDs using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The device structure consists of ITO/phenyl-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag with NPB thickness varied from 0 to 300 Å. The ITO surface was exposed by removing the organic and metal layers with dichloromethane, an organic solvent in which NPB and Alq3 are highly soluble. Electroluminescence characterization demonstrates that the NPB layer substantially enhanced the stability. XPS analysis shows that for the device made without NPB and after 90 h of operation, there exists an insoluble organic material on the ITO surface. This organic material is not observed on the ITO of unoperated devices. Lateral force AFM also shows a striking difference between the ITO surface of devices with and without NPB after operation. The XPS and AFM results suggest that the organic residue is the degradation product of Alq3 that acts as quenching sites at the ITO/Alq3 interface, which contribute to the early failure of the single-layer devices.

Tin sensitization and silver activation on indium tin oxide surfaces

We investigated the influence of different indium tin oxide (ITO) surface treatments on the performance of organic solar cells with different device architectures. Two types of devices (CuPc in contact with ITO treated with different treatments and C60 in contact with ITO treated with different treatments) were fabricated. The surfaces of CuPc and C60 layers deposited on ITO substrates treated with different surface treatments were examined using atomic force microscopy. The devices were characterized by measuring current-voltage characteristics in the dark and under AM1 illumination. We found that a one order of magnitude improvement in the AM1 power conversion efficiency for ITO/CuPc/C60/Al cells can be achieved for optimal ITO surface treatment, while ITO/C60/CuPc/Cu devices exhibit less sensitivity to surface treatments. Moreover, these devices exhibit better performance compared to ITO/CuPc/C60/Al devices. The observed differences in sensitivity to surface treatments were attributed to difference in the dependence of the film surface on ITO surface morphology for CuPc and C60.

Effects of inductively coupled plasma treatment using O 2, CF 4, and CH 4 on the characteristics of organic light emitting diodes