ABSTRACT:
The field of organic electronics is an active emerging technology with immense promise for innovative, convenient and high-performance electronics. Breakthrough products employed in commercial technologies include organic light-emitting diodes (OLEDs) used in displays for car radios.1 Organic field effect-transistors (OFETs) are showing promise as their efficiencies are being rapidly improved.2 Organic photovoltaic and fuel cells also employ conducting polymers for a number of applications.3 Two classes of materials are actively investigated for organic electronic applications:
ELECTRONIC POLYMERS: These materials contain an extended π-conjugated organic backbone, giving rise to their unique opto-electrical properties. The inherently (or intrinsically) conductive polymers (ICPs) possess the electrical properties of metals or semiconductors while exhibiting the mechanical properties and processing characteristics of polymers. Applications for ICPs include, electromagnetic-interference (EMI) shielding, conductive layers for OLEDs and OFETs, optically active layers for OLEDs, and anti-corrosion coatings for iron and steel. ICPs include polythiophene, PANI, and PPy. The light emitting polymers (LEPs) possess electronic bandgaps that allow for the emission of visible light. These polymers include PPV, CN-PPV, PFO, and PFE.
INTRODUCTION:
Organic electronics first became a subject of academic interest during the 1950s. Because of their structures constructed of primarily covalent bonds, organic materials can behave as both semiconductors and insulators. Research in such topics described how electrons behaved in various bond structures and solid state. Organic electronic first drew commercial interest when they were observed to be photoconductive. Their applications in materials and controls for LCDs, LEDs, thin film solar cells, and superconductors drew interest from many sectors.
HISTORY:
ORGANIC ELECTRONIC DEVICES:
Organic electronics relies upon a wide variety of different types of electrically active materials. Among these materials, some of the most commonly used are conductors, semiconductors, dielectrics, as well as various luminescent, electrochromic or electrophoretic materials. Some type of supporting material is generally also used.
Many other types materials can also be employed, such as surface active agents, encapsulation materials, dopants, etc.
CONDUCTORS:
Almost all printed devices require some type of electrode. The electrodes may need to satisfy a number of requirements including low resistance, smooth surface, chemical stability, and appropriate work function (the energy required for an electron to escape a solid surface) for
ORGANIC PHOTODIODE FABRICATION:
The OPD was fabricated by multilayer thermal evaporation (Fig. 2(a)). Glass wafers with 30–60 nm thick layer of indium tin oxide (ITO) with sheet resistance of 30–60 X/_ (Delta- Technologies) were patterned by wet etching in a 3: 1 mixture (v/v) of HCl: HNO3 at 55 ◦C for 3min. The patterned ITO glass was sonicated in acetone for 30 min, rinsed with fresh acetone, methanol and de-ionized water, and dried withN2 gas.A100 nm
The field of organic electronics is an active emerging technology with immense promise for innovative, convenient and high-performance electronics. Breakthrough products employed in commercial technologies include organic light-emitting diodes (OLEDs) used in displays for car radios.1 Organic field effect-transistors (OFETs) are showing promise as their efficiencies are being rapidly improved.2 Organic photovoltaic and fuel cells also employ conducting polymers for a number of applications.3 Two classes of materials are actively investigated for organic electronic applications:
ELECTRONIC POLYMERS: These materials contain an extended π-conjugated organic backbone, giving rise to their unique opto-electrical properties. The inherently (or intrinsically) conductive polymers (ICPs) possess the electrical properties of metals or semiconductors while exhibiting the mechanical properties and processing characteristics of polymers. Applications for ICPs include, electromagnetic-interference (EMI) shielding, conductive layers for OLEDs and OFETs, optically active layers for OLEDs, and anti-corrosion coatings for iron and steel. ICPs include polythiophene, PANI, and PPy. The light emitting polymers (LEPs) possess electronic bandgaps that allow for the emission of visible light. These polymers include PPV, CN-PPV, PFO, and PFE.
INTRODUCTION:
Organic electronics first became a subject of academic interest during the 1950s. Because of their structures constructed of primarily covalent bonds, organic materials can behave as both semiconductors and insulators. Research in such topics described how electrons behaved in various bond structures and solid state. Organic electronic first drew commercial interest when they were observed to be photoconductive. Their applications in materials and controls for LCDs, LEDs, thin film solar cells, and superconductors drew interest from many sectors.
HISTORY:
- In 1862, Henry Letheby obtained a partly conductive material by anodic oxidation of aniline in sulfuric acid. The material was probably polyaniline.[1] In the 1950s, it was discovered that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens.[2] This finding indicated that organic compounds could carry current.
- Technology for plastic electronics on thin and flexible plastic substrates was developed at Cambridge University’s Cavendish Laboratory in the 1990s. In 2000, Plastic Logic was spun out of Cavendish Laboratory to develop a broad range of products using the plastic electronics technology.
- Conductive polymers are lighter, more flexible, and less expensive than inorganic conductors. This makes them a desirable alternative in many applications. It also creates the possibility of new applications that would be impossible using copper or silicon.
- Organic electronics not only includes organic semiconductors, but also organic dielectrics, conductors and light emitters.
- New applications include smart windows and electronic paper. Conductive polymers are expected to play an important role in the emerging science of molecular computers.
- In general organic conductive polymers have a higher resistance and therefore conduct electricity poorly and inefficiently, as compared to inorganic conductors. Researchers currently are exploring ways of "doping" organic
- semiconductors, like melanin, with relatively small amounts of conductive metals to boost conductivity. However, for many applications, inorganic conductors will remain the only viable option.
ORGANIC ELECTRONIC DEVICES:
- Their material also incidentally demonstrated "negative differential resistance", now a hall-mark of such materials. A contemporary news article in the journal Nature[8] noted this materials "strikingly high conductivity". These researchers further patented batteries, etc. using organic semiconductive materials. Their original "gadget" is now in the Smithsonian's collection of early electronic devices.
- This work, like that of the decade-earlier report of high-conductivity in a polypyrrole,[9] was "too early" [10] and went unrecognized outside of pigment cell research until recently. At the time, few except cancer researchers were interested in the electronic properties of conductive polymers, in theory applicable to the treatment of melanoma.
Organic electronics relies upon a wide variety of different types of electrically active materials. Among these materials, some of the most commonly used are conductors, semiconductors, dielectrics, as well as various luminescent, electrochromic or electrophoretic materials. Some type of supporting material is generally also used.
Many other types materials can also be employed, such as surface active agents, encapsulation materials, dopants, etc.
CONDUCTORS:
Almost all printed devices require some type of electrode. The electrodes may need to satisfy a number of requirements including low resistance, smooth surface, chemical stability, and appropriate work function (the energy required for an electron to escape a solid surface) for
ORGANIC PHOTODIODE FABRICATION:
The OPD was fabricated by multilayer thermal evaporation (Fig. 2(a)). Glass wafers with 30–60 nm thick layer of indium tin oxide (ITO) with sheet resistance of 30–60 X/_ (Delta- Technologies) were patterned by wet etching in a 3: 1 mixture (v/v) of HCl: HNO3 at 55 ◦C for 3min. The patterned ITO glass was sonicated in acetone for 30 min, rinsed with fresh acetone, methanol and de-ionized water, and dried withN2 gas.A100 nm
thick layer of 3,4-polyethylenedioxythiophene (PEDOT from Baytron) was then spin coated on the patterned ITO glass and cured at 93 ◦C for 30 min. Multilayer thermal evaporation was then performed to deposit CuPC/C60/LiF layer by layer up to thicknesses of 20 nm, 60 nm, and 1 nm, respectively.19,20 The 100 nm thick Al strips were evaporated through a shadow mask to form devices in a cross-linked configuration. Fig. 2(b) illustrates the 3 × 2 array of OPDs.
ORGANIC LIGHT-EMITTING DIODE FABRICATION:
The OLED devices were fabricated at Eastman Kodak labs on patterned ITO substrates. After initial cleaning procedures with solvent cleaning and oxygen plasma, successive layers of 10 nm of EB390 (hole injection layer), 10 nm of NPB (hole transport layer), and 15nmof AlQ (electron emitting layer)were deposited using a vacuum evaporator. This is schematically illustrated in Fig. 3(a). A shadow mask was then used to evaporate 1 nm of LiF (to aid electron injection at the cathode) and 100 nm of aluminium (cathode layer). The devices were encapsulated using Kodak’s proprietary encapsulation technology.21 Fig. 3(b) illustrates four discrete pixels on an encapsulated OLED.
ORGANIC LIGHT-EMITTING DIODE FABRICATION:
The OLED devices were fabricated at Eastman Kodak labs on patterned ITO substrates. After initial cleaning procedures with solvent cleaning and oxygen plasma, successive layers of 10 nm of EB390 (hole injection layer), 10 nm of NPB (hole transport layer), and 15nmof AlQ (electron emitting layer)were deposited using a vacuum evaporator. This is schematically illustrated in Fig. 3(a). A shadow mask was then used to evaporate 1 nm of LiF (to aid electron injection at the cathode) and 100 nm of aluminium (cathode layer). The devices were encapsulated using Kodak’s proprietary encapsulation technology.21 Fig. 3(b) illustrates four discrete pixels on an encapsulated OLED.
DEVICES AND APPLICATIONS:
Organic electronics can be used to make a variety of types of devices, which can be broadly classified based upon whether they are passive or active devices. Active devices are those which are used to perform functions such as switching, rectification, memory, detection, or light emission. Examples of active devices that can be made with organic electronics are transistors, diodes, OLED’s, sensors, memory, displays, batteries or photovoltaic cells. Some examples of passive devices or components that can be made with organic electronics are conductive traces, antennas, resistors, capacitors, or inductors.
TRANSISTORS:
Among the active devices or components, transistors are probably one of the most important or fundamental. They can be used as the building blocks for many other types of devices, such as logic, displays, sensors, etc. Organic electronic transistors are three terminal, multilayer devices, and generally based upon thin film transistors configurations. They are generally known as organic TFT’s (OTFT),
Organic electronics can be used to make a variety of types of devices, which can be broadly classified based upon whether they are passive or active devices. Active devices are those which are used to perform functions such as switching, rectification, memory, detection, or light emission. Examples of active devices that can be made with organic electronics are transistors, diodes, OLED’s, sensors, memory, displays, batteries or photovoltaic cells. Some examples of passive devices or components that can be made with organic electronics are conductive traces, antennas, resistors, capacitors, or inductors.
TRANSISTORS:
Among the active devices or components, transistors are probably one of the most important or fundamental. They can be used as the building blocks for many other types of devices, such as logic, displays, sensors, etc. Organic electronic transistors are three terminal, multilayer devices, and generally based upon thin film transistors configurations. They are generally known as organic TFT’s (OTFT),
or organic field-effect transistors (OFET). An example of the configuration of a typical OFET is shown in Figure 13. The transistor is basically a switch. Current flow between the source and drain electrode is switched, depending on the voltage present at the gate electrode. In order to optimize the transistor performance, the channel length should be as small as possible (for printed transistors, typically 10–50 μm), and the dielectric as thin as possible without defects (typically a few hundred nm). There should be minimal overlap of the gate electrode with the source and drain electrode. The dielectric/semiconductor surface should be smooth and defect free. It is desirable (but virtually impossible to achieve) to have low resistance ohmic electrical contacts between the semiconductor and the source and drain electrodes.
DISPLAYS:
Some of the main advantages and economic driving forces for printed electronics are the ability to manufacture devices inexpensively, on flexible supports, and over large areas. One area where these forces converge is the opportunity for printing displays. Many of the major companies involved in organic electronics are directing their technology toward the production of displays. Some of the earliest applications of printed organic transistors were for the fabrication of backplanes for flexible displays (Figure 14). Electrophoretic displays (Figure 15) are wellsuited for organic transistors, because they are essentially field (voltage) driven devices, and do not require much current flow to drive them. Furthermore, they are bi-stable, which means that they can retain their state (image) without power. Power is only required when necessary to switch the state of the display. One popular type of electrophoretic display material consists of small spheres which are filled with smaller (white) charged spheres and a colored (black) liquid (Figure 15). Upon application of an appropriate electric field, the charged (white) spheres move either toward the top or the bottom of the liquid. When the (white) spheres are toward the observer, the display looks (white). When the (white) spheres are at the other side (bottom) of the display, the color of the liquid (black) is seen. The spheres and liquid can be made to be any color. The contrast is independent of viewing angle, and significantly better than newsprint. Other types of display materials that are capable of being driven by printed organic transistors are polymer dispersed liquid crystals (PDLC), and electrochromic materials.
DISPLAYS:
Some of the main advantages and economic driving forces for printed electronics are the ability to manufacture devices inexpensively, on flexible supports, and over large areas. One area where these forces converge is the opportunity for printing displays. Many of the major companies involved in organic electronics are directing their technology toward the production of displays. Some of the earliest applications of printed organic transistors were for the fabrication of backplanes for flexible displays (Figure 14). Electrophoretic displays (Figure 15) are wellsuited for organic transistors, because they are essentially field (voltage) driven devices, and do not require much current flow to drive them. Furthermore, they are bi-stable, which means that they can retain their state (image) without power. Power is only required when necessary to switch the state of the display. One popular type of electrophoretic display material consists of small spheres which are filled with smaller (white) charged spheres and a colored (black) liquid (Figure 15). Upon application of an appropriate electric field, the charged (white) spheres move either toward the top or the bottom of the liquid. When the (white) spheres are toward the observer, the display looks (white). When the (white) spheres are at the other side (bottom) of the display, the color of the liquid (black) is seen. The spheres and liquid can be made to be any color. The contrast is independent of viewing angle, and significantly better than newsprint. Other types of display materials that are capable of being driven by printed organic transistors are polymer dispersed liquid crystals (PDLC), and electrochromic materials.
![Picture](/uploads/1/4/6/6/14663784/6883852_orig.png?1)
Electronic-paper display (bottom) and exploded view of the components of a unit cell. Middle and left inset:
rubber-stamped organic transistor. The semiconductor is blue, the gate electrode is gray, and the source/drain electrodes
and related interconnects are gold. Top and right inset: microencapsulated electrophoretic “ink.”
In addition to transistors and backplanes, organic electronic materials are also used to make emissive devices, such as Organic Light Emitting Diodes (OLED’s). It is even possible to integrate organic transistors with OLED’s, and fabricate a completely organic emissive display. In the future, completely printed organic emissive displays having integrated organic circuitry may be possible.
SENSORS AND ACTUATORS:
Another important application of organic electronics is in the diverse area of sensors. Many different stimuli can be sensed using organic electronics, including temperature, pressure, light, and chemical identity.
SENSORS AND ACTUATORS:
Another important application of organic electronics is in the diverse area of sensors. Many different stimuli can be sensed using organic electronics, including temperature, pressure, light, and chemical identity.
These principles have been used to produce a variety of different types of devices, including tamper detecting packaging, data logging pill dispensers, chemical sensors, electronic noses and tongues, photodiodes (Figure 18), light scanners (Figure 18), photovoltaic (solar) cells,
temperature and pressure sensors integrated into an artificial skin (Figure 19), etc. Actuators have also been made using organic electronics. An electronic Braille actuator was recently demonstrated (Figure 20), which provided sufficient stimulus to be read by a blind person.
RFID:
Since the mandates from Wal-Mart and the United States Department of Defense in 2003, there has been immense interest in using printing technologies for RFID. The “Holy Grail” has been described as the 5 cent tag. If RFID tags could be produced for 5 cents, item level tagging would become practical. The potential market for such tags would be in the billions or trillions of tags per year, and has captured the attention of many. It is commonly thought that the only way to reduce the price sufficiently, and produce billions or trillions of tags per year is by printing both the circuitry (using organic materials, see Figure 16), and the antenna, in an integrated process (see Figure 17). Some of the major obstacles to be surmounted for RFID applications are high frequency operation and rectification using organic materials. Operational frequencies as high as 600 kHz have been shown. A polymer based half wave rectifier which can operate at frequencies up to 20 MHz has been demonstrated. At 13.56 MHz (one of the key RFID frequencies) 3V DC was obtained from 15V AC. This demonstrates that rectification at RFID frequencies is possible (although not very efficient) using polymer rectifiers. A working demonstration of an organic based 16 bit RFID tag with a read range of 7.5 cm has recently been shown.
Since the mandates from Wal-Mart and the United States Department of Defense in 2003, there has been immense interest in using printing technologies for RFID. The “Holy Grail” has been described as the 5 cent tag. If RFID tags could be produced for 5 cents, item level tagging would become practical. The potential market for such tags would be in the billions or trillions of tags per year, and has captured the attention of many. It is commonly thought that the only way to reduce the price sufficiently, and produce billions or trillions of tags per year is by printing both the circuitry (using organic materials, see Figure 16), and the antenna, in an integrated process (see Figure 17). Some of the major obstacles to be surmounted for RFID applications are high frequency operation and rectification using organic materials. Operational frequencies as high as 600 kHz have been shown. A polymer based half wave rectifier which can operate at frequencies up to 20 MHz has been demonstrated. At 13.56 MHz (one of the key RFID frequencies) 3V DC was obtained from 15V AC. This demonstrates that rectification at RFID frequencies is possible (although not very efficient) using polymer rectifiers. A working demonstration of an organic based 16 bit RFID tag with a read range of 7.5 cm has recently been shown.
COMPARISON OF ORGANIC:
ADVANTAGES:
CONCLUSIONS:
In this work, a LOC device for high-sensitivity fluorescence detection using an integrated OLED excitation source and OPD detector has been demonstrated. A novel, low-cost crosspolarization scheme was used to filter leakage excitation light. This approach substantially reduces the background signal due to the leakage excitation light on the optical intensity detector, thereby significantly enhancing the signal-to-noise ratio. The assembled system can be used for any dye, even if the emission and the excitation signals overlap in wavelength. Using this approach, we demonstrated detection of Rhodamine 6G and fluorescein dyes at concentrations as low as 100 nM and 10 lM, respectively, which is a substantial improvement over the previously published reports using organic electronics. The approach also enables detection of multiple dyes with the same device, which opens the possibility of integrated highsensitivity disposable microfluidic LOCs with organic excitation and detection devices for low-cost fluorescence-based analysis. Such a platform for both organic electronics and microfluidic systems is compatible, robust, and inexpensive. Integration of the detection system into the microfluidic LOCs makes the system portable and feasible for point-of-care medical diagnostics or on-site environmental analysis.
- They are also biodegradable (being made from carbon).
- This opens the door to many exciting and advanced new applications that would be impossible using copper or silicon.
- Conductive polymers have high resistance and therefore are not good conductors of electricity.
- Because of poor electronic behavior (lower mobility), they have much smaller bandwidths.
- Shorter lifetimes and are much more dependant on stable environment conditions than inorganic electronics would be.
- Displays:
- (OLED) Organic Light Emitting Diodes
- RFID :
- Organic Nano-Radio Frequency Identification Devices
- Solar cells
- Smart Textiles
- Lab on a chip
- Portable compact screens
- Skin Cancer treatment.
CONCLUSIONS:
In this work, a LOC device for high-sensitivity fluorescence detection using an integrated OLED excitation source and OPD detector has been demonstrated. A novel, low-cost crosspolarization scheme was used to filter leakage excitation light. This approach substantially reduces the background signal due to the leakage excitation light on the optical intensity detector, thereby significantly enhancing the signal-to-noise ratio. The assembled system can be used for any dye, even if the emission and the excitation signals overlap in wavelength. Using this approach, we demonstrated detection of Rhodamine 6G and fluorescein dyes at concentrations as low as 100 nM and 10 lM, respectively, which is a substantial improvement over the previously published reports using organic electronics. The approach also enables detection of multiple dyes with the same device, which opens the possibility of integrated highsensitivity disposable microfluidic LOCs with organic excitation and detection devices for low-cost fluorescence-based analysis. Such a platform for both organic electronics and microfluidic systems is compatible, robust, and inexpensive. Integration of the detection system into the microfluidic LOCs makes the system portable and feasible for point-of-care medical diagnostics or on-site environmental analysis.