ORGANIC ELECTRONICS
What is organic electronics? It’s a branch of electronics that uses organic materials to make circuits and other electronic devices, preferably having an advantage over traditional inorganic materials that we’re all familiar with. It’s a pretty new field, but the possibilities are endless and it has already succeeded in achieving a great deal.
Organic electronics evolved in the 1950s, with the discovery of the first conducting organic molecule by H. Inokuchi and colleagues. From this discovery, it was gathered that organic molecules can be semi-conductors, a term that was commonly reserved for silicon, germanium and other elements like it. Turns out organic semiconductors have a number of advantages over traditional semiconductors. W. Helfrich and W.G. Schneider found that organic molecules can emit light, and this was first observed in a molecule called anthracene. The only downside was this required a high voltage, which made it highly inefficient. Then in the 1980s, three scientists Heeger, MacDiarmid and Shirakawa made the discovery of conductive polymers, for which they received the Nobel Prize in 2000. Some years later, PTCDA, an organic dye molecule that is still used in car paints, was discovered to have semiconducting properties.
The next major milestone was the discovery of Organic Light Emitting Diode(OLED). This device was invented in 1987 by Ching Tang and Steven Van Slyke at Kodak. This device was able to emit light at just 5 volts, and would forever change the display industry.
Organic electronics have a wide range of applications, four of which are discussed in length below — display, photovoltaic and transistor technologies, and biomedicine.
1. Display:
OLED (Organic Light Emitting Diodes) is a ground-breaking technology that was developed by Ching Tang and Steven Van Slyke. OLEDs consist of an organic film that uses the property of phosphorescence to generate their own light instead of using backlight. Phosphorescence is the emission of radiation due to excitation of electrons which lasts for a long period of time. You might have observed this in wristwatches and clock dials that glow in the dark.
The working of an OLED is fairly straightforward. There are two layers in an organic film, the emissive layer and the conductive layer. Holes are present in the boundary between the two layers. The emissive layer emits electrons and recombination of the electrons and holes leads to the generation of photons, which constitutes light.
There are mainly two types of OLEDs — Passive-matrix OLED and Active-matrix OLED. Passive-matrix OLED (PMOLED) have strips of cathode and strips of anode which are arranged perpendicular to each other. The intersections form the pixels where light is emitted. External circuits supply current to selected strips of anode and cathode, determining which pixels get turned on and which remain off. The brightness depends upon the amount of applied current. Their drawback is that they consume a lot of power, and so are found in small screens such as PDAs (Personal Digital Assistant) and MP3 players.
The second type of OLED is Active-matrix OLED (AMOLED). AMOLEDs also have full layers of cathode, organic material and anode, but the anode layer overlays a Thin Film Transistor (TFT) array matrix. The TFT array is the circuitry that determines which pixels get turned on to form the image.
AMOLEDs consume much less power than PMOLEDs as the TFT array requires less power than external circuitry. As a result, they are suitable for large displays like computer monitors, TVs and electronic billboards.
OLEDs have a lot of advantages over LCDs (Liquid Crystal Display). Traditional LCDs have a lot of parts. The liquid crystals in an LCD do not have their own light, so they use a backlight. Then there are reflector sheets to improve brightness, diffuser sheets to break up and distribute the light evenly, a bottom polarizer and a top polarizer, colour filter to create coloured light, and of course the liquid crystals which are the key elements. This increases the thickness of the screen drastically.
Quantum Light Emitting Diodes (QLEDs) are the other competition. They contain polarizers and colour filters. They also need a backlight as the quantum dots can’t emit their own light. The result is that these displays are too thick. OLEDs are sleek, produce more absolute blacks than the QLEDs and works better in dim light as each pixel is individually lit. OLED screens can be extremely thin. LG makes large, foldable displays with amazing picture quality supporting 4K and even 8K. Most display experts and consumers agree that OLED displays are the world’s best smartphone displays. Dynamic AMOLED displays produced by Samsung are one of the best smartphone displays.
2. Photovoltaic applications:
Organic photovoltaic devices are basically organic solar cells. Polymers are typically used as the photovoltaic material. One of the main advantages of using organic material for solar cell manufacture is that the ‘optical absorption coefficient’ of organic molecules is high, so a large amount of light can be absorbed with a small amount of material, usually on the order of hundreds of nanometers. They are also very flexible and much thinner than their silicon counterparts. While current OPV (Organic Photovoltaic) technology boasts conversion efficiencies that exceed 10 percent, reaching even 12 percent, some researchers predict organic solar cells will reach 15–20 percent efficiency. They can also be rolled up and even composted.
While we live in an increasingly electronic world, access to that world is limited. An estimated 1.3 billion people have no access to electricity, with many people relying on kerosene, batteries, or diesel-fueled generators. Because of their cheaper manufacturing costs, organic electronics promise not only to change the way people use technology but also to expand the use of technology to populations without access to on-grid electricity.
The main disadvantage associated with organic photovoltaic cells is the low efficiency compared to inorganic photovoltaic cells such as silicon solar cells. But research is being done to address that problem, and new materials are being discovered every day that could revolutionize the solar energy industry.
3. Flexible printed organic transistors:
Transistors are the fundamental building blocks of modern electronic devices, either amplifying signals or operating as switches. Organic Field Effect Transistor (OFET) is a field-effect transistor that contains conductive electrodes, an organic semiconductor and a dielectric. Its speciality is that it uses very little power to patrol very large current and also acts as a very good switch. They are produced by printing circuits using organic dyes on a flexible substrate in large printing presses. Great care is taken not to let any impurities enter the material, as this could adversely affect the conductivity of the material.
The interest in OFET has grown enormously in the past few years. There are many reasons for this. The performance of OFET can compete with that of amorphous silicon. As a result, there is now a greater interest in the industrial usage of OFETs for applications that are currently incompatible with the use of a-Si or other inorganic transistor technologies. One of their main technological attractions is that all the layers of an OFET can be deposited and patterned at room temperature, which makes them ideally suited for the realization of low-cost, large-area electronic functions on flexible substrates. Silicon has to be heated to high temperatures of more than 40⁰C to mold. Despite the advantages, several challenges remain before OFET becomes more widespread in use.
4. Biomedicine:
Another important application of organic electronics is in medicine, in the curing of blindness, through a retinal chip which is inserted in the eye. This registers light signals entering the eye and transforms them into electrical signals that are sent to the brain. Electrodes which are coated with organic dyes transmit electric signals to the receptor cells in the eye. Electrodes are coated by electrolysis to ensure uniform coating.
The compound must be bio-compatible. Finding the right materials and the mixture of compounds is critical. Right now this has allowed patients with blindness to perceive light and dark, the outlines of objects, sometimes even letters and facial expressions. The goal is to have high resolution and good performance. This is a good example of technology and medicine working in tandem to improve people’s lives.
The field of organic electronics will continue to grow in ways not even imaginable today. Some applications have already been realized, like the OLED smartphones, T.V.s and the low-cost solar panels that are installed on rooftops in rural communities. Some like the foldable smartphones are expected to become more common and widespread in the future. Others, like electronic skin that mimics human skin in its tactile sensitivity, will take longer to develop. Still others cannot be even foreseen. The potential applications are varied, spanning across multiple fields- medicine and biomedical research, energy and environment, communications and entertainment, home and office furnishings, clothing and personal accessories, and more.
Organic electronics also has the power to make electronics production, use and disposal more environmentally sustainable. Scientists and engineers are seeking ways to make organic electronics more conservative and energy-efficient than today’s silicon-based electronic world. The benefits of using organic ingredients for electronic manufacture are:
· Unique abilities: Organic materials have unique properties impossible to achieve with silicon-based electronics. Their properties include sensing, bio-compatibility and flexibility. Sensing is the use of electronic devices to sense chemical or biological substances in the environment or on the human body. Scientists envision biosensors that not only detect glucose levels in people with diabetes but also actually dispense the appropriate dose of insulin at the right time. Organic electronic materials are not only more chemically compatible with biological systems than silicon-based devices; they enable a flexibility, stretchability and mechanical ‘softness’ to the substance. Together, these properties create the potential for innovative bio-electronic sensors that can conform to the curvature and moving parts of the human body.
· Energy efficient: As scientists and engineers continue to improve the synthesis and characterization of organic materials for use in electronics, their hope is that the use of such materials will lead to more energy-efficient electronic displays, lights and other electronic devices. For example, we need to make organic solar cells more efficient to be used in places like Northern Europe where nights are long and there are only short spells of sunlight. Engineers are trying to build devices out of organics that last longer, that are recyclable or perhaps even biodegradable. Organic electronic manufacturing methods will also become more energy-efficient, leading to fewer steps and methods for recovering lost heat.
· Less wastage, more safety: The use of organic materials to build electronic devices holds the promise that future electronic manufacturing methods will rely on fewer, safer, and more abundant raw materials. Materials can be saved by relying on less wasteful processes, such as printing, whereby materials are added to structures or devices layer by layer as they are built, in contrast to spin-coating which involves removing materials and disposing of those excess materials. In addition to using fewer materials, chemists are seeking ways to use safer materials. For example, many polymers require carcinogenic solvents, including some solvents not even allowed in the EU printing industry because of their toxicity.
Sustainable Electronics
What do we mean by sustainability? This brings to mind energy-efficiency, waste disposal, recycling etc. Creating more sustainable electronic products is not just about building a more ‘eco-friendly’ solar cell or other devices, but also using more ‘eco-friendly’ manufacturing methods to do so. Sustainability has to be applied at every step of the manufacturing cycle, from raw resources to the disposal of wastes. Organic materials might be able to steer electronics into the future in a more environmentally sustainable way than is possible in today’s electronic world.
Finally ‘sustainable electronics’ implies that electronics itself is long-lasting. The versatile nature of organic electronics, combined with the promise the field holds forth for environmental and social sustainability, points the way to a very long-lived set of technologies.
Conclusion
The field of organic electronics clearly has made tremendous strides over the past few decades, with many devices already on the market and a multitude of prototypes in development. The field will continue to grow, changing the way society interacts with technology, as chemists, physicists, and other scientists and engineers address the research challenges. Multidisciplinary research and training programs that bring together scientists and engineers from different fields of knowledge, as well as from different sectors of activity (i.e., academia, industry, government), will facilitate the collaborative effort needed to meet these challenges.
Bibliography
- Wikipedia
- YouTube
- Organic Electronics for a Better Tomorrow
- HowStuffWorks?
- Lifewire
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