Organic and printed electronics is based on the combination of new materials and cost-effective, large-area production processes that open up new fields of application. Thin, lightweight, flexible and environmentally friendly electronics – that is what organic electronics aims to deliver. Here we present an overview and roadmap of the applications for organic and printed electronics.
This article was written by Dr Klaus Hecker and Dr Stephan Kirchmeyer
OLED lighting
OLED lighting is an example of solid state lighting (SSL), which also includes LED-based lighting and is seen as the most promising approach for future lighting due to lack of hazardous materials, and in a flexible form, with high energy efficiency and long lifetime usage. The LED lighting industry is growing rapidly. OLED lighting continues to make progress both technically and towards commercialization and this technology has grown out of the technical progress made in developing the OLED display industry but has increasingly focused on the specific properties of OLEDs that are relevant to lighting. These lighting products promise novel features in the longer term: large areas, very thin and optionally flexible or in a non-planar form, and variable colour are all feasible. New lighting applications can be expected to take advantage of these properties, for example, embedded lighting or homogeneous area lighting.
While OLED lighting has not yet reached the mass market, limited-release prototypes and commercial products have become available to demonstrate the potential and allow interested users to try out this technology. A number of European and Japanese companies have shown advanced prototype products, and in the USA the Department of Energy has supported OLED lighting development strongly. Though vacuum deposited and solution processed OLEDs are possible, vacuum deposited devices are more efficient and dominate the market, though much development is ongoing in improving solution processed OLEDs. The market is expected to grow, especially if some key challenges such as lowering the production cost and developing reliable and cost-effective encapsulation are met.
Organic photovoltaics (OPV)
Organic photovoltaics (OPV) comprises hybrid systems (e.g., combining titania and dyes) and systems using only organic semiconductors. Flexible dye-sensitized titania and polymer- based OPV modules have been available for some years, and products integrating flexible OPV modules have been commercially available since 2010. These applications target low-power consumer applications, e.g., modules for battery chargers for mobile electronics such as cell phones PV-powered computer keyboards, or a mobile laser pointer shown.
Despite the difficult market for PV in general in the last couple of years and the significant setback of the loss of a key OPV pioneer, both technical and commercial development is continuing. Laboratory scale cells have now reached efficiencies that can compete with thin film silicon, while the number of pilot and small production lines has increased.
OPV exhibits a combination of unique features: lightweight, flexible design with options for colour and semi-transparency, good performance in low and diffuse light, a reduced environmental footprint and customizable formats which allow them to address market niches not in direct competition with crystalline silicon technologies. Short term applications will be mostly in consumer electronic and portable power sources. In the medium term, novel forms of building-integrated OPV will appear. The long term perspective of energy generation remains a driving vision, while new business models are also appearing to address unconventional markets and channels to market.
Flexible displays
Flexible displays are an extension of flat panel displays, which have had tremendous success in replacing conventional displays such as cathode ray tubes (CRTs) for use in computers and televisions and in enabling new products such as laptop and tablet computers, e-readers and smart mobile phones to be produced. Flexible displays can dispense with some key issues of current flat displays, such as the presence of (breakable and relatively heavy) glass and the inability to be bent, rolled or used with other than flat form. The requirements for flexible displays depend strongly on the intended use, e.g., for the flexible displays roadmap we focus on the following key types of use, e.g., information and signage (conformal and lightweight is more important than being bendable or rollable), reading (ruggedness, light weight and optionally bendability or rollability are desired) or entertainment/multimedia (where video rate, colour and resolution are critical in addition to the above factors).
The flexible display market has not developed commercially as quickly as had been hoped, partially due to industry restructuring and competition from tablet computers, but there have also been advances. For example, flexible, roll to roll- produced e-paper-based shelf tags have been commercialized at a Finnish electronics superstore chain, garnering a very positive reception. Plastic Logic announced a new business strategy, enabling the company to move beyond the e-reader market into a variety of new markets and applications, driven by flexible display solutions.
On the technology side, many of the key players in the display market have showcased prototypes of OLED-driven flexible displays, including active matrix backplanes driven by new materials like oxide semiconductors. E Ink has also announced flexible active-matrix EPD driven displays, and colour EPD display prototypes with organic TFT backplanes have been shown (Figure 1). While simple signage is already available, we expect flexible commercial e-readers to be available in the near future, followed by trends to larger sizes, higher resolution and full colour and flexible OLEDs.
Printed memory
Printed memory is needed for applications where the user is required to store and process information. If the user wants to change the information stored in the memory after production, a rewritable memory, either write once read many (WORM) or rewritable random-access memory (RAM) is necessary. Furthermore, for many applications without constant power, the memory needs to be non-volatile (NV). ID devices and promotional cards using read-only memory (ROM), WORM or NV-RAM were already hitting the market at the time of the last roadmap and have continued to make headway.
Reference designs for toys using NV-RAM memory have been launched, and applications using printed memory for brand protection (i.e., anti-fraud, anti-counterfeit uses) have also emerged recently. Printed memory will be an important component in future integrated smart systems and technology development is proceeding this way. For example, a recently presented NV-RAM that includes CMOS (Figure 2), showed successful integration of a sensor, a display, memory and transistor logic in December 2012. The future is expected to bring applications of increasingly complex systems, moving from simple gaming and anti-fraud applications into ticketing, display memory and electronic products.
Most organic electronics applications target mobile devices, and here power supply is a key issue. Therefore flexible batteries (Figure 3) are of central importance to leverage this technology. A large variety of thin and evenly printed batteries are commercially available. They are currently available for discontinuous use and will be constantly improved in capacity, enabling continuous use. At this time, non-rechargeable zinc-carbon batteries are predominant for printed batteries, but there is significant development in rechargeable batteries, e.g., based on lithium, as well as research activity on printed miniature supercapacitors, which are a kind of cross between batteries and conventional capacitors. There will be a progression from batteries that use printed parts, through batteries that are fully printed in separate processes, to batteries that are printed as part of an integrated process for printing electronic systems.
There will also be a progression from single charge through rechargeable batteries and from single cells to multicell integration. In the longer term, batteries will also be integrated directly in textiles and packages.
Active devices
Active devices are electronic components which contain a semiconductor or other parts that create “active” feedback on applying electric power. Organic thin film transistors (OTFT) are a basic component for electric switch elements or integrated circuits, and can be used as a single component to amplify a current or combined with other transistor as integrated circuits or logic. The current flow between source and drain electrode is switched, depending on the voltage applied at the gate electrode. They are typically not products by themselves but part of other products like smart objects or integrated systems. Diodes are rectifying devices which allow current to flow at a positive voltage but block it at negative voltages. They are also relevant in devices such as RF tags or energy harvesting systems. In the area of printed/organic circuits (logic), multibit microprocessors have been demonstrated by a number of research labs and companies, as well as logic circuits for RFID tags and organic memory control.
Key factors and challenges for future development and appearance are in more complex products and include scaling laws on thickness, lateral dimensions and charge carrier mobility. Display elements are further active components for system integration, which can convert an electrical signal into optical information. In particular, electrochromic and electroluminescent elements are being included.
Printed passive components
Printed passive components based on printable conductors and dielectrics have been used in electronics manufacturing for some time. Due to the rapid development of printable electronics materials and corresponding processes, such applications are becoming more and more visible on the market. Resistors, capacitors and inductors can also be printed. A special application in this field is a printed code detectable by touch sensors. Printed silver paste is the conductive material mostly used to print conductive tracks, but other metal or carbon pastes, nanocarbon materials, or conductive polymers are seeing increased interest.
A special case of capacitors creating more interest for printed electronics are supercapacitors, which can be used for interim storage of energy, have much higher capacitance than plate capacitors but higher cycle life than batteries, and in the best case essentially consist only of plastic, metal, carbon, water and salt. A range of approaches to printed antenna manufacturing has also been applied, including direct printing, plating, and etch resist printing.
Electroluminescent films (EL)
Electroluminescent films (EL) are available as commercial lighting products used in low intensity lighting such as backlighting, decoration and advertising panels. EL lighting offers a number of key user advantages: bendable, fast prototyping, printable and easy product integration. This type of lighting is focused on illuminating specific objects in order to highlight them or create special effects. It is not concerned with illumination of space. EL is especially useful where complex forms (bending, thin shapes) are involved, limited editions, e.g., in packaging (Figure 4) specific aftermarket and original equipment manufacture (OEM) car models, and for fast product execution, e.g., in advertising or exhibitions.
An area that has seen intense activity recently is that of transparent conductive films. Today, ITO (indium tin oxide) is still the most widely used transparent conductive material, which is used in nearly all optical devices like displays, OLEDs, OPV, EMI shielding and especially in the rapidly increasing market of touch sensor applications. There is a huge market demand for ITO substitutes, as it is quite brittle and relatively expensive, so there is need for alternatives. Numerous flexible and lower cost alternatives are coming into the market. The alternative approaches to transparent conductive films can be based either on new transparent conductive materials or on the patterning of thin metal films (metal mesh) on flexible polymer substrates into high resolution transparent conductive meshes. Some of these approaches have also been introduced to the market recently.
Integrated smart systems (ISS)
Integrated smart systems (ISS) bring together multiple core functionalities to perform complex, automated tasks without the need for external electronic hardware. As organic electronics technology progresses, the applications will become ever more challenging and complex. Typical functionalities that one will expect to see on such systems will be power (batteries, miniaturized fuel cells, PV), input devices (physical, chemical and biological sensors) and output devices (displays, visual, audible or haptic interfaces and wireless communications), with these linked together by sophisticated logic circuits and memory. The addition of various forms of sample processing and fluid handling will also involve the integration of microfluidics into some systems.
Thus, the variety of applications for such systems will be immense, made far greater by their potential deployment into so many new areas of application, from smart textiles to automotive, aeronautical and environmental to health and well-being segments. The component technologies underpinned by the organic electronics field will be essential to the success of such systems.
Sensors
Sensors are the means by which the environment is detected. Many of the characteristic features of organic and printed electronics, such as high throughput parallel production including screen printing, have already been used in the development of printed sensors, and these exist already as standalone products. Future development is related to the integration of sensors with other functionalities into an integrated smart system. Optical and electrical/electrochemical sensor components will be used, and we expect a progression from currently available test strips and physical sensor arrays through disposable test strips and the integration of other functionalities such as control electronics, memory or display readouts in the medium term, to smart buildings and skins in the longer term. The key challenges to be faced are related to the integration of different components
and especially interfacing to printed electronic circuitry.
Smart objects
Smart objects combine multiple electronics components and functions to create innovative integrated systems. A key advantage of organic and printed electronics is the possibility of using low cost production methods to make these smart objects light, flexible, cheap and even disposable. Functional printing allows the integration of different devices such as sensors, transistors, memory, batteries or displays onto one substrate. This integration may be achieved either by one process or by a combination of several separately produced components. Sensor tags, dynamic price display and rewritable RF tags are all examples of applications for smart objects. New products have emerged, such as RF-driven smart object cards and printed electronic systems with rewritable memory. A number of technology developers have demonstrated increasingly complex printed RFID tags as well. The roadmap for smart objects and printed RFID, as a whole, is more complex than for other areas of printed electronics.
However, these products make full use of the cost and scalability advantages inherent in this new set of production methods, and thus, are potentially the most revolutionary. The products will likely not show continuous, step-wise improvement but rather, the emergence of products of greater and greater complexity (i.e., the emergence of entirely new product families) as manufacturing processes improve.
Smart textiles
Smart textiles are fabrics that are able to alter their characteristics to respond to external stimuli (mechanical, electrical, thermal, and chemical). In addition, functionalities such as communication, displays, sensors, or thermal management can be integrated into fabric to enable wearable electronics. By taking advantage of organic and printed electronics, the field of smart textiles can make important technological advances in the future. In the coming years though, the use of standard electronic technology such as Si chips or LEDs may still be required in combination with printed components, and heterogeneous integration will be common until sufficiently high performance and integration can be achieved for organic and printed electronics and logic.
Currently, much of this field is still in the development or prototype stage, with significant effortgoing into areas such as stretch-ability and hybrid integration. The first products are expected to be shown around this year, 2014 (washable textile EL), with evolution to more complex systems and applications such as OLEDs coming later.