An EL device resembles a sandwich in that it is comprised of a light emitting material placed in between two insulating layers. This structure in turn is then placed between two conducting electrodes. A light emitter or phosphor- typically zinc sulfide doped with managese- is placed in between the insulating layers. Aluminum and indium tin oxide (ITO), which is a transparent conductive metal, are used as the electrodes. When the voltage exceeds a well defined threshold, the emitter breaks down and conducts current. The current excites the managnese ions, which give off light.
- Screen printable.
- Thin, flexible and lightweight.
- Print intricate designs.
- Highly resistant to aging and atmospheric effects.
- Perform well under humid conditions.
- Exceptionally low heat generation.
- Resistant to impact and vibration.
- Low power consumption.
- Long life
- Electronic equipment
- Toy and games
- Palm computers
- Remote controls.
How does EL work?
Screen Printing Process Flow
low-cost screen printing process is adopted to manufacture printed RFID tags. Figure below shows the details of the process flow. The flexible printed RFID tag can be read successfully by reader with a reading range greater than 10cm
Application methods are of key consideration for RFID inks and it is, therefore, important to understand the primary printing techniques, which include screen printing, flexography and rotogravure. Screen printing is very well-known application method for conductive inks . Flexography and rotogravure are relatively new for RFID, but very established in the packaging industry.
Screen printing is a porous printing process. Distinct from flexography and rotogravure, the image and the non-image are in the same plane. During printing, the frame is loaded with ink and a squeegee presses the ink through the image parts of stencil and onto the substrate, Screen printing is used for displays, signs, instrument panels, textiles and posters. It is a relatively slow printing process, by comparison. A totally automatic flatbed screen printing machine has an output speed around 1500 impressions per hour. A modification on screen printing is rotary screen printing, where an ink supply and the squeegee are fitted inside a rotary screen cylinder. This process is a competitor for flexography and gravure in both output and costs.
Screen-printed solar cells were first developed in the 1970’s. As such, they are the best established, most mature solar cell fabrication technology, and screen-printed solar cells currently dominate the market for terrestrial photovoltaicmodules. The key advantage of screen-printing is the relative simplicity of the process.
A full aluminium layer printed on the rear on the cell, with subsequent alloying through firing, produces a back surface field (BSF) and improves the cell bulk through gettering. However, the aluminium is expensive and a second print of Al/Ag is required for solderable contact. In most production, the rear contact is simply made using a Al/Ag grid printed in a single step.
Screen-printing has been used on a variety of substrates. The simplicity of the sequence makes screen-printing ideal for poorer quality substrates such as multicrystalline material as well as CZ. The general trend is to move to larger size substrates – up to 15 x 15 cm2 for multicrystalline materials and wafers as thin as 200 µm.
Close up of a screen used for printing the front contact of a solar cell. During printing, metal paste is forced through the wire mesh in unmasked areas. The size of the wire mesh determines the minimum width of the fingers. Finger widths are typically 100 to 200 µm
Close up of a finished screen-printed solar cell. The fingers have a spacing of approximately 3 mm. An extra metal contact strip is soldered to the busbar during encapsulation to lower the cell series resistance.
Front view of a completed screen-printed solar cell. As the cell is manufactured from a multi-crystalline substrate, the different grain orientations can be clearly seen. The square shape of a multi-crystalline substrate simplifies the packing of cells into a module.
Rear view of a finished screen-printed solar cell. The cell can either have a grid from a single print of Al/Ag paste with no BSF, or coverage of aluminum that gives a BSF but requires a second print for solderable contacts.
What Is A Fuel Cell?
In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.
The hydrogen reactions with oxygen result in water and heat.
2H2 + O2 2H2O + heat
A fuel cell is a device that abstracts this chemical energy converting into electrical energy.
Fuel cell has been put to practical application for cars, private use generators, or notebook PCs, as a clean power source of good energy efficiency.
What is screen-printing used for?
In polymer electrolyte fuel cell, the screen-printing is noticed as an excellent technique to past the catalysts onto the positive and negative electrodes.
In solid oxide fuel cell, the positive and negative electrodes are fixed at the both sides of the solid electrolyte. These electrodes work as electron conductor and reaction catalyst.
And these electrodes have to be porous and thin, on the solid electrolyte.
There is no technology better than screen-printing to apply the electrodes thin and evenly on the surface of the electrolyte. The developments of pastes of positive and negative electrodes for screen printing are highly expected.
Solid electrolyte itself is a fragile sheet substance that has a thickness of less than 1mm.
Screen-printing has a big potential in the field of fuel cell.
Inexpensive Thin Printable Batteries Developed
For a long time, batteries were bulky and heavy. Now, a new cutting-edge battery is revolutionizing the field. It is thinner than a millimeter, lighter than a gram, and can be produced cost-effectively through a printing process.
The characteristics of the battery differ significantly from those of conventional batteries. The printable version weighs less than one gram on the scales, is not even one millimeter thick and can therefore be integrated into bank cards, for example. The battery contains no mercury and is in this respect environmentally friendly. Its voltage is 1.5 V, which lies within the normal range. By placing several batteries in a row, voltages of 3 V, 4.5 V and 6 V can also be achieved. The new type of battery is composed of different layers: a zinc anode and a manganese cathode, among others. Zinc and manganese react with one another and produce electricity. However, the anode and the cathode layer dissipate gradually during this chemical process. Therefore, the battery is suitable for applications which have a limited life span or a limited power requirement, for instance greeting cards. The batteries are printed using a silk-screen printing method similar to that used for t-shirts and signs. A kind of rubber lip presses the printing paste through a screen onto the substrate.
Screen printed biosensors for detection of nitrates in drinking water
This biosensor showed the capability to detect nitrate residue levels lower than the European legislation one for a long storage stability (> 36 days) representing an applicable and cheap method for the analysis of nitrate ions in water and food samples.
Screen Printed Electrodes
Screen printed electrodes (SPE) were produced in three steps, by screen printing different consecutive layers on transparent polyester films. A first layer of a graphite ink was deposed to define the conducting track and the working electrode, the second one was a silver/silver chloride ink used as reference electrode, while the third layer consisted in an insulating ink, UV polymerizable.
The top reading and writing system for the blind is so simple and ingenious that it is used all over the world, but who invented it? The answer is a certain Louis Braille who lived in the 19th-century France and proved very resourceful after losing his sight at an early age as a result of an accident. Braille consists of a system of six dots. Each of the 63 possible combinations of dots represents a letter, a punctuation mark or a number. Like languages based on the Latin alphabet, Braille is read from left to right.
The Braille alphabet – Blind people read Braille by tracing the pattern of solid black dots with their fingers.
Screen printing Braille is more permanent and can provide more depth to the Braille. Die-punched Braille can get compressed in packing and handling, and the surface will not be as raised as [with] screen printing.
However, what if you have to make a lot of copies of invitations, pamphlets, and so on? A normal text can be photocopied, while a braille text must be printed out with a braille printer as many as you need. Brail printer is not as quick as normal laser printer; because one or some pins pound the paper line by line, it takes very much time to “print” braille.
In addition, since the embossments are made out of paper and therefore easy to be smashed, the readability easily deteriorates.
Screen vs. embossing
There are a variety of factors that impact the decision to go with screen printing effects or embossing effects. These include costs, length of the run, color requirements, customer needs, running speeds, and the type of material being converted.
“Price is key,” This is especially evident in shorter runs compared to the cost of purchasing and waiting for delivery of a die or mag plate.”
What is organic EL display ?
The liquid-crystal display, which you see the most often today, is used for personal computers, cellular phones, and even for TVs etc. these days.
Although the liquid-crystal display has the merit of low power consumption, it does not emit light and thus needs to be lit from the back (backlight), being a stumbling block to miniaturization and weight reduction.
The organic EL display, like the PDP (plasma display panel) etc., itself emits light. The structure is as if a very thin film of organic matter is gotten sandwiched between also very thin electrodes, and to put it in extreme terms, film-type rollable displays can be produced. Also, since it emits light itself, it does not need backlights: this is now the most hoped-for display that has both merits of high picture quality and high-speed imaging.
Switchover to screen-printing
In the previous manufacturing process of organic EL, an adhesive agent to put two thin boards has been applied by a device called dispenser.
Since the dispenser applies an adhesive agent with one stroke, the total applying distance becomes long to manufacture many panels from one sheet of glass at a time and thus takes a lot of time.
That is why they have been considering applying an adhesive agent by means of screen-printing.
Screen-printing is capable of printing in 1/3 of time in comparison to applying by the dispenser; besides it makes no difference in time whether producing 10 pieces from one work piece or 20 pieces.