Transparent Electrode Layer Research Articles

On-substrate polymerization of solution-processed, transparent PEDOT:DDQ thin film electrodes with a hydrophobic polymer matrix

Thin conductive, hydrophobic films of poly(3,4-ethylenedioxythiophene) or PEDOT were synthesized on-substrate in the presence of the organic electron acceptor and dehydrogenating agent 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) using a versatile processing procedure. Significant polymerization in the processing solution was delayed by using common aprotic, ethereal solvents with low dielectric constants to prevent solvating the EDOT:DDQ charge transfer complex into radicals. Polymerization was initiated by an increase in concentration upon solvent evaporation during spin coating. A hydrophobic polymer matrix additive of polyvinyl acetate was used to aid in film formation, and a post-treatment rinse with acetonitrile was necessary to obtain a conductive film. Conductivities ranged from 17 to 59 S/cm, where the higher values were achieved at the cost of transparency. A work function of 4.62 eV was determined by UV photoelectron spectroscopy for one film recipe. When comparing conductive AFM results of PEDOT:DDQ to highly conductive, ethylene glycol-treated PEDOT: poly(styrenesulfonate) or PSS, surface currents were orders of magnitude higher for PEDOT:DDQ than for PEDOT:PSS. If optimized further, less acidic and hydrophobic PEDOT:DDQ films have the potential to replace PEDOT:PSS for use as a transparent electrode or charge transport layer in organic solar cells, organic light emitting diodes, touch screens, and other optoelectronic devices.

P‐76: Combined Nanostructured Layers for Display Applications

AbstractOne‐step cost effective process of fabrication of a full inorganic nanostructured transparent conductive electrode and LC alignment layer has been developed. More specifically, the subject comprises a self‐organized nanomesh of a valve metal, concomitant porous oxide layer with various functionality and electrochemical method of their fabrication. The nanomesh film is electrically conductive, optically transparent and flexible. It can be fabricated on a variety of substrates, including flexible and rigid substrates. High effective LC alignment layers based of nanostructured alumina can be fabricated at the same anodization process by special electro‐chemical technique in sulfuric and oxalic acids to form a self ordered nanoporous structure of alumina which has a “vertical” surface area that prevails over the “horizontal” one even though Al film's thickness is small. The possibility to control distances between pores and their sizes during the process of anodizing/etching enables to optimize alignment surface according to the required LC material.

Semiconductor Laser Diode

A semiconductor laser diode having high indium composition ratio and light-emitting property is provided to reduce the deterioration of crystal according to low temperature by minimizing heat damage of high indium composition ratio. A semiconductor laser diode(100) comprises a substrate(101), an n-type clad layer(102), an active layer(104) and a p-type cladding layer(106). A transparent electrode layer(107) is formed on the ridge structure of the p-type cladding layer. N-type and P-contacts are formed in the lower-part of substrate and upper side of the transparent electrode layer. An insulating layer(108) covering the ridge structure and transparent electrode layer is formed on the p-type cladding layer. N-type and p-type cladding layer corresponds to the respective top clad layer.

High-Performance Transparent Conducting Ga-Doped ZnO Films Deposited by RF Magnetron Sputter Deposition

Ga-doped zinc oxide (GZO) films were deposited using rf magnetron sputter deposition and a Ga2O3(5 wt %)-doped ZnO ceramic target under various deposition conditions. The effects of each deposition condition on the electrical, structural, and optical properties of the GZO films were investigated to obtain a transparent conducting oxide (TCO) with a high transmittance and a low resistivity for a-Si:H thin-film solar cells. Resistivity showed a strong dependence on working pressure and rf power. The lowest resistivity of 1.9×10-4 Ω·cm was obtained at an rf power density of 2.47 W/cm2. The highest figure of merit for the use of TCO was achieved in the 800-nm-thick GZO film [ρ=2.1×10-4 Ω·cm, average transmittance (400–800 nm) = 92.1%] deposited at 10 mTorr and an rf power density of 1.85 W/cm2. These results indicate that the high-performance TCO fabricated in this work is suitable for use as a transparent electrode layer for thin-film solar cells.

Enhancement of the photon extraction of green and blue LEDs by patterning the indium tin oxide top layer

The indium tin oxide (ITO) transparent electrode layer on green and blue light-emitting diodes (LEDs) was patterned with various-sized periodic hole arrays, size ranging from 300 nm to 380 nm, using thermal nanoimprint lithography and inductively coupled plasma (ICP) etching processes. The imprinted resin was used as a mask layer and etch resistance of the imprinted resin was adjusted in order to control the tapered and enlarged etch profile of the ITO layer, since the tapered etch profile can improve the light extraction efficiency of the LED by prominent scatterings. Photoluminescence intensity from InGaN multi-quantum wells for the green LED structure showed that up to 4.6 times stronger emission was exhibited with the patterned ITO electrode, compared to the identical sample with an un-patterned blanket ITO electrode layer. An electroluminescence (EL) intensity of a blue LED sample witha patterned ITO electrode layer was increased up to 23% compared to that of the identical sample with an un-patterned blanket ITO electrode layer.

Growth of ZnO:Al films by RF sputtering at room temperature for solar cell applications

Aluminum-doped ZnO (ZnO:Al) films were prepared at room temperature in pure argon ambient on glass substrates by RF magnetron sputtering. The influence of sputtering power, deposition pressure and film thickness on the film properties was investigated. The deposited ZnO:Al films were characterized to examine the electrical, optical, and structural properties for the application of thin copper indium gallium selenide (CIGS) solar cells. The deposition parameters of ZnO:Al films were optimized. The optimized ZnO:Al films showed a strong and sharp (0 0 2) X-ray diffraction peak. The 600–800 nm thick ZnO–Al films showed a high transparency above 85% in the visible range and a sheet resistance low to 10 Ω/□. CIGS solar cells with 1.2 μm thick absorbers were fabricated using bi-layer ZnO films (low resistive and thick ZnO:Al/high resistive and transparent thin i-ZnO) as front contacts. The thin absorber layers were prepared by the low cost technique involving co-sputtering of Cu–Ga alloy and In targets and selenization with Se powders. Efficiencies of the order of 6–7% were achieved for the manufactured thin CIGS solar cells without antireflective films. The results demonstrated that RF sputtered ZnO:Al films are suitable for application in low cost and thin CIGS solar cells as transparent conductive electrode layers.

Characteristics of Al-Doped ZnO Transparent Conductive Oxide Films for Solar Cell Applications

Al-doped ZnO (ZnO:Al) films for transparent electrode applications in dye-sensitized solar cells and thin film solar cells were fabricated and characterized. In order to investigate the effect of crystallinity of the ZnO:Al films to the morphology and optical properties of the etched surface, the ZnO:Al films were deposited with varying substrate temperature by rf magnetron sputtering system and then films’ surface was etched in diluted hydrochloric acid (HCl) solution. Surface morphology of the amorphous ZnO:Al film deposited at room temperature was controllable to have large surface area, but it was not appropriate for transparent electrode layers due to high electrical resistivity. However, the resistivities of the ZnO:Al films deposited at the substrate temperatures of 150 and 300 oC were as low as 1.50×10-3 cm. In addition, the surface morphologies of the films deposited at 150 and 300 oC showed larger surface area for dye-sensitized cells and crater shape for light diffusion through the films, respectively. The surface morphologies and optical properties of the etched ZnO:Al films are attributed to the crystallinity of the as-fabricated films.

Electric Properties of the ITO-ZnSe-CdTe-ZnTe Photo Sensor Cell

In this report, the ITO-ZnSe-CdTe-ZnTe cell was used for a photo sensor. ITO(Indium Tin Oxide) was used on the glass substrates as the transparent electrode, and ZnSe and CdTe layer were prepared by the vacuum deposition on this ITO, and were treated with heat at 560°C. The ZnSe-CdTe sample that CdTe layer was prepared on ITO-ZnSe(0.1μm) substrate has not high-density level at the junction surface, and the CdTe layer with little lattice imperfection can be prepared. In spite of improvement in the crystalline form, this ZnSe-CdTe sample cell has not sufficient electric current response for the light absorption of CdTe layer. In order to increase the electric current response for the light, ZnTe layer was prepared by the vacuum deposition on the ZnSe-CdTe layer, and were treated with heat at 560°C. This ITO-ZnSe-CdTe-ZnTe photo sensor cell has sufficient electric current response for the visible light and near infrared light. It is presumed that the electric filed in the CdTe layer is enough to drive the cell.

Effect of band offset on the open circuit voltage of heterojunction CuIn1−xGaxSe2 solar cells

The reasons behind why the theoretically estimated open circuit voltage (Voc) of CuIn1−xGaxSe2 solar cells with large x values has not been realized are discussed. Typically, the reduction in Voc is estimated only on the basis of the conduction-band offset between the absorber and the window material. The importance of the electron affinity difference between the window and the transparent electrode must also be taken into account. Based upon both of these factors, a material selection guideline is reported for the window and the transparent electrode layers suitable for high-x CuIn1−xGaxSe2 absorber-based solar cells.

Analysis of junction and film properties in high efficiency amorphous silicon solar cells

A systematic investigation of the built-in potential V b , mobility-lifetime product μτ and effective surface recombination velocity S has been made in various amorphous silicon (a-Si) solar cells fabricated with different substrates, deposition systems and processes. A p-i-n junction cell formed on a stainless steel substrate possesses a larger V b by about 0.2 V than that for a cell fabricated on glass coated with a transparent electrode. A limiting factor of the efficiency in the former type of cells is a large S at the n-i interface, which is due to damage during deposition of the transparent electrode (indium tin oxide) layer. Impurity inclusion in the i layer during the p-i-n formation process affects both μτ and S and thereby dominates the efficiency. On the basis of these experimental observations and their analysis, it is suggested how to design and fabricate the a-Si solar cells in order to attain higher efficiency.