The new chemistry of printed electronics

Printed and potentially printed electronics and electrics is conveniently referred to as printed electronics or rather misleadingly plastic or organic electronics. Since this is the future of lighting, signage, electronic displays, sensors, batteries for electronics and even photovoltaics (solar cells), few dispute that it will rise to the order of $300 billion dollars in twenty years from now. IDTechEx has closely analysed this huge new opportunity for the fine chemicals, electronics and process industries. As shown below, even the growth in the next four years is startling enough to attract companies of all sizes, particularly as there are many unsolved technical problems that can lead to premium priced products for those that are successful.

 

 

 

Today the printed electronics business largely consists of applications such as screen, flexo and gravure printed silver for RFID antennas and membrane keyboards and carbon and metal for printed heaters and sensors. Transparent electrodes, antistatic and RF shielding are increasingly printed in indium tin oxide ITO, polyanilene or polythiophene and screen printed ac electroluminescent displays on polyester film employ copper doped zinc sulfide and ITO.

 

 

Few elements have been involved but that is now changing with the first sales of printed Organic Light Emitting Diode displays, a variety of screen printed and thin film manganese dioxide zinc, lithium ion and lithium polymer batteries, ink jet printed copper indium gallium diselenide CIGS photovoltaics and Dye Sensitised Solar Cells DSSC - the latter based on titanium dioxide with ruthenium based organic dye. Specially developed ink jet printing has now overtaken screen as the favoured manufacturing technology for printed electronics today but no one printing technology will ever do everything.

Things have now become really exciting with a huge range of new chemicals, nanotechnology and printing technology brought to bear and sophisticated thin film deposition techniques other than printing being tailored to play a part. Totally new product concepts emerge from the cloak of invisibility to edible electronics, stretchable electronics and electronics as art. Disposable labels and other human interfaces will employ far more of the human senses to give almost unlimited information, entertainment, brand enhancement and brand protection.

In order to meet the widening variety of needs for all printed and potentially printed electronics, not least in flexible, low cost form, a rapidly increasing number of elements are being brought to bear. Oxides, amorphous mixtures, alloys and organics are particularly in evidence.

 

 

Below is an illustration of some of the most promising elements currently being employed by about 2000 organisations - double the number two years ago - in research and production of printed and potentially printed devices. Those used as elements are shown red and those used as compounds and dopants are shown brown and each arrow refers to most of the highlighted elements of the periodic group, the vertical column, in question.

 

 

Printed alternating current (ac) electroluminescent displays are exhibiting better colors and longer life as the chemistry improves but they will be overtaken by the even faster growing electrophoretic displays employing titanium dioxide, carbon and organics to give exceptionally low power and good viewing in sunshine. This is seen in the Esquire magazine giveaway in September 2008 and the various e-books and e-labels newly on the market.

 

Organic Light Emitting Diodes, OLEDs have the potential to replace today's TV and phone screens and to provide ubiquitous "wallpaper" lighting and even disposable electronic displays showing moving color images on packaging. The first OLED television displays have exceptionally vibrant colors, narrow viewing angle and lack of pixilation when the camera is panned. However, OLEDs are a tough business to be in and those developing OLED lighting tend to be different companies from those pursuing OLED displays, because the requirements are so different. Although over 200 organisations started to develop OLEDs we now have attrition with several leaving the business in frustration every year because it is so tough to meet the required price and performance points.

The leaders in OLED materials are investing huge amounts of money to get on top of the fragile chemistry. Although versions sandwiched in glass are selling well, profits are elusive. The advent of mass produced, flexible, low cost OLEDs, particularly wide area types with long life, keeps slipping further into the future. Yet these are the largest potential OLED market because they enable many exciting new product concepts. To extend life and improve electronic and optical performance, an ever widening choice of elements is being employed by those in for the long haul. Fine chemical companies concerned with inorganic materials are among those coming to assist the device makers.

 

 

In research and development, OLEDs now variously employ such materials as B, Al and Ti oxides and nitrides as barrier layers against water and oxygen, Al, Cu, Ag and indium tin oxide as conductors, Ca or Mg cathodes and CoFe nanodots, Ir and Eu in light emitting layers, for example. The organic chemistry is also highly sophisticated with both organic and inorganic dopants in complex organic hosts and different light emitting principles brought to bear. Each layer of the device is a challenge, just as it is with printed transistors being developed by over 360 organisations.

A fairly recent development by materials supplier Merck and others is phosphorescent (triplet) technology for OLEDs. This offers the prospect of exceptionally high efficiency (a factor of 3-4 times over fluorescents usually employed) while, except for a difficult blue challenge, maintaining color purity and long lifetime for red and green. This promising triplet approach has been shown to be capable of being adapted for printing using solution processes. Phosphorescent OLEDs, such as those employing iridium based dyes, have been developed by Pacific Northwest National Laboratory in the USA and others. It has used organic phosphine oxides as electron transport materials. These materials address the critical issue of achieving high quantum efficiency (photons generated per electron injected into an OLED device) at low voltages.

 

 

One class of new OLED materials developed at PNNL is based on organic phosphine oxide compounds while another is based on organic phosphine sulfides. In addition to OLEDS, these materials have the potential to be used in other devices, including photovoltaic cells and thin-film transistors. It is not unusual for an advance in materials for one device to be applicable to others. Another example of this is Kovio printed nanosilicon transistors opening up a new advance in photovoltaics.

Consider barrier layers for flexible OLEDs. They need to be better than those used for any other device. We mean 10-6 grams per square meter per day of water and 10-5 cc per square meter per day of oxygen. Few currently believe that the requirements of life, flexibility, large area, low cost and volume manufacture have been met. Developers such as Vitex, Appliflex and 3M in the USA and IMRE in Singapore use alternating metal oxide or nitride and polymer layers, examples of the inorganic layers being the oxides of boron, aluminium and titanium and there is interest in binding up the undesirables, not just preventing them from getting through. Not one of the developers of barrier layers is able to use printing as yet and samples are very hard to come by, according to various interested parties that IDTechEx has interviewed in the preparation of this article.

The largest conference on the subject will again be Printed Electronics USA, San Jose December 3-4 www.idtechex.com/peUSA. It is expected to double in size this year, given the growth of this new industry.

 

 

Speakers from Pfizer, Kraft, Northrop Grumman, Nokia and Goldman Sachs will verify the huge market pull for this technology. Sessions will cover analyst forecasts and trends, healthcare and bionic man, electronics as art, signage, human interface, radical new printed electronic products, improving traditional electronics, stretchable electronics, invisible electronics and flexible lighting and its applications.

 

All appropriate materials will be covered including the new metamaterials, nanorods, quantum dots and semiconducting, conducting, light emitting, electrolyte and barrier materials whether inorganic, organic or increasingly composite.

 

Environmental and scarcity issues will be covered and all aspects of manufacture. Over 100 exhibitors include BASF, Sun Chemical, Plextronics, HC Starck, Soligie, OTB Engineering/ Pixdro, Northfield Automation Systems, Optomec and InkTec. Unidym, selling printable carbon nanotubes, and Blue Spark Technologies, selling printed batteries, will exhibit and there will be many visits to local centers of excellence as well as optional masterclasses and an investment summit. Lecturers will cover latest breakthroughs such as the electronic contact lens, skin- like electronics, printed lighting for skin treatment, wireless body monitoring, nanotube radio paper, morphing electronics and the formidable resource of new chemistry to make it all happen.