Patent Application
20070139756
The present invention relates to materials and compositions for forming stable and persistent electrochromic film stacks, and to associated processes for using and making themn
Electrochromic (EC) devices known in the art have a substantial potential between the two electrodes in at least one of the optical states. An electrochromic device is typically controlled or driven by an external circuit that applies an electrical charge when a state change is desired. Depending on circuit design, when the circuit is not actively driving the electrochromic material, the external circuit may present an impedance between the two electrodes from a short to about 20 Mohms. When sufficient potential exists between electrodes, the driving circuit will allow current to drain between electrodes, thereby allowing the electrochromic material to transition from its desired state to an undesirable rest state. Also if diodes (including surface diodes) are used in external circuits then these diodes may be turned on by residual potential in an EC device. If these diodes are turned on, then current will flow, allowing the EC material to transition from its desired state. A typical voltage range to turn on the diodes are between 0.2 to 1V. Since most know EC devices produce more potential than 0.2 volts, these known devices return to an undesired rest state, unless external power is periodically applied. To avoid activating the diodes, an EC device should have a residual voltage in any of its optical states (usable optical range for a particular application) to be less than 0.2V and preferably close to 0 volts.
Briefly, the present invention provides a stable electrochromic stack that is able to persistently hold a desired optical state. The stable electrochromic stack has at least two states. One state may be, for example, a bleached state in which light may readily pass, and the other state may be a colored state that distorts or interferes with the passage of light. Advantageously, the persistent electrochromic stack holds one or both of the optical states without the application of external power. The persistent time period may extend for days, weeks, or years depending on particular constructions, and on application requirements.
In one example, the electrochromic stack is constructed by positioning an electrochromic layer adjacent to an electrolyte layer. Electrodes typically attach to the layers for connection to a powering circuit. When in a first optical state, for example a dark state, the electrolyte is in a highly stable state. Accordingly, there is almost no potential between the electrochromic layer and the electrolyte layer, so the electrochromic stack maintains the first optical state persistently. Upon the application of a voltage, the electrochromic layer (any possibly the electrolyte layer) transition to a second optical state, for example, a bleached state. The electrolyte layer also transitions from its first highly stable state to a second highly stable state. After the voltage is removed, there is almost no potential between the electrochromic layer and the electrolyte layer, because the electrolyte layer is in a highly stable state. Accordingly, the electrochromic stack maintains its second optical state persistently because the electrolyte layer is in a highly stable state
In one example, the stable electrochromic stack is used with an associated optical media, and more particularly, as part of an optical shutter. The optical media has an integrated circuit, which is used to cause the electrochromic stack to transition from a first state to the second state. In one example, an integrated circuit acts as the powering circuit for the electrochromic stack, as well as providing logic and processing functions. The integrated circuit also couples to an RF antenna, enabling the integrated circuit to communicate with an associated RF scanning device. It will be appreciated that many other fields and applications may benefit from a persistent electrochromic stack.
Advantageously, the persistent electrochromic device enables an optical shutter to be positioned on or in an optical disc, and for the shutter to maintain its bleached or colored state. In this way, a darkened shutter may disable access to the disc when the disc is manufactured, and then the disc moved through a distribution chain with confidence that the disc will remain unusable until an authorization event occurs. Upon the authorization event, for example, a consumer purchase, the optical shutter is transitioned to its clear state, and the clear state will be maintained, allowing the consumer to use the disc for years.
Referring now to
For example, stable electrochromic device 10 may be in an initial opaque state as shown in arrangement 25. In arrangement 25, the electrochromic material 14 is opaque and thereby interfering with the passage of light. The interference may include a blocking of all or a substantial portion of the light, a change in refraction, a blurring effect, or another optical effect distorting the passage of light. It will also be appreciated that the electrochromic material may substitute another electro-optic material for affecting other wavelengths, or having other desirable optical effects. Advantageously, when the electrochromic material 14 is in its colored state, the electrolyte 16 is in a stable condition, such as a stable oxidation state. Accordingly, there is almost no potential generated between electrodes 18 and 21. With proper selection of materials, the potential between electrodes and across the electrochromic stack is small enough that even shorting between electrodes will not cause the electrochromic material 14 to immediately transition to its rest state. For example, with proper selection of electrolyte and electrochromic materials, and selection of proper additives, the electrochromic stack will persistently maintain its colored state for several days or weeks, even when electrodes 18 and 21 are shorted. This means that in normal use, where the electrochromic device is typically not shorted, and instead may be constructed to have a relatively large impedance, the electrochromic stack may persistently remain in the darkened state for months, years, or even decades. For purposes of this discussion, a persistent state means that the electrochromic material maintains its desired optical state for a time sufficient for the application. For example, some applications may require that an electrochromic device maintain a darkened state for several months, while other applications may require a few years. It will be appreciated that the teachings of this discussion may be used to select materials, select additives, and adjust processes for meeting a wide range of persistent durations.
When a voltage 28 is applied to the electrodes of the electrochromic stack 10, ions pass between the electrolyte layer 16 and the electrochromic layer 14. As shown in arrangement 35, the electrochromic layer 14 will then transition from its opaque state towards a substantially transparent state. This transition may take anywhere from less than a second to a few seconds. The speed of transition is typically related to the amount of available current. For example, faster transitions may be made with the application of larger current sources. It will also be understood that the amount of electrochromic material to transition also affects speed of transition. For example, a large picture window covered with an electrochromic device would take substantially more current and time to transition than a small optical shutter placed on an optical desk.
After the transition is complete as shown in arrangement 45, the electrochromic stack once again returns to a stable state. Accordingly, the electrochromic material 14 persistently stays in its substantially transparent state. In a substantially transparent state, an electrochromic material provides little distortion or interference to passing light. With the ion movement caused by the application of voltage during the transition state 35, the electrolyte layer 16 has reacted to another highly stable state. For example, in arrangement 45, the electrolyte layer 16 may have moved to a different but very stable oxidation state. Since the electrolyte material 16 in arrangement 14 is in a highly stable condition, the electrochromic device 10 has almost no tendency to transition to a rest state. This is evidenced by the near-0V potential between electrodes 18 and 21. Accordingly, the substantially transparent state of the electrochromic material 14 may be maintained persistently. As generally described above, this means that the electrochromic material 14 maintains its desirable substantially transparent state for as long as required by the specific application. For example, some applications may require that the electrochromic material remain clear for days or weeks, while other applications may require that the electrochromic material persistently stay bleached for months, years or even decades. Again, it will be appreciated that the teachings of this discussion may be used by one skilled in the art to select appropriate electrolyte and electrochromic materials, and appropriately provide additives or dopants for reaching the required persistent durations.
Advantageously, a stable electrochromic device maintains its desired optical state for a persistent duration. More particularly, this means that an electrical device is enabled to maintain its desired state without continuous, continual, or periodic applications of external voltage. In contrast, known electrical devices require at least some application of external voltage to maintain either a bleached or colored state. Since the known electrical devices require periodic application of external power, their uses have been limited, or have required cumbersome connections to electrical power sources. With a persistent electrochromic stack, many applications are enabled or simplified. For example, electrochromic devices may now be used as optical shutters for optical disks. Such an application is more fully described in co-pending U.S. patent application Ser. No. 11/460,827, filed Jul. 28, 2006, and entitled “Persistent Electro-Optic Devices and Processes for Optical Media”, which is incorporated herein by reference in its entirety. In another example, larger transparent or reflective surfaces may be set to a darkened or bleached state, and that optical state maintained without application of external electricity. For large areas, this saves considerable power, and enables more efficient electronic control of light. It will be understood that this discussion describes an electrochromic device having a fully colored state and a fully bleached state, however more states may be provided. In this way, an intermediate persistent state could be provided which passes partial or blurred light. It will also be understood that electrochromic devices discussed herein have a wide range of applications in military, industrial, automotive, and entertainment fields.
Referring now to
Referring now to
Referring now to
Referring now to
Referring now to
The metal layer may be made very thin, for example 20-50 nm. By reducing the thickness of the metal, reduced optical path effects are generated. This enables better transmission when the metal is in its oxidized state. These metal coatings may also be porous so that the electrolyte intercalates through these pores reducing kinetic considerations. It will be understood that other metal materials may also be used. The electrochromic device 150 is generally a one-way or irreversible process. The electrochromic device 150 may be initially provided in its bleached state as shown in arrangement 175, and then be “one-way” transitioned to its colored state. Alternatively, the electrochromic device may be initially provided in its colored state, and then be “one-way” transitioned to its bleached state. Voltage is applied that transitions the device to its fully bleached state as shown in arrangement 225, and the electrochromic layer permanently changes or reacts to MX. An application oftypical transition voltages would not be effective to return the electrochromic layer to a colored state. However, it will be appreciated that some high voltages may be able to at least partially recolor the electrochromic layer. However under normal operating conditions the device 150 would be considered a one-way, irreversible process.
Referring now to
Referring now to
Referring now to
Referring now to
When it is desired to change the optical state of the electrochromic device, a voltage is applied as shown in block 435. Depending upon the type of reaction intended to occur; the voltage may be applied as a reducing voltage or an oxidizing voltage. The application of voltage causing an ion or current flow that causes the electrochromic layer to transition from its first optical state to a second optical state as shown in block 437. More particularly, electrochromic layer transitions from its bleached state towards a darkening state, or from its colored state towards a more transparent state. At the same time, the electrolyte layer also has a chemical, polymerization, or oxidation/reduction reaction occurring as shown in block 436. After the electrochromic layer has fully transitioned, the voltage is removed as shown in block 440. Accordingly, the electrochromic layer is in its second optical state as shown in block 442, and electrolyte layer has been transitioned to a second highly stable state as shown in block 441. Since the electrolyte layer is in another highly stable state, there is almost no voltage across the electrochromic device. In this way, the electrochromic device holds the second optical state persistently.
As generally described earlier, the electrochromic device may be designed to hold one or both optical states persistently. A convenient measure for the ability to persistently hold an optical state is to measure the time it takes an electrical device to return to a rest (intermediate colored) state upon shorting the device's electrodes. By directly connecting the electrodes together, any potential generated between the electrolyte and electrochromic layers would immediately and spontaneously cause a current or ion flow. For example, known electrochromic devices, when shorted, returned to a rest state almost immediately. Depending on the device construction and materials employed, the rest state may be completely bleached state, completely colored state or somewhere between the two. For a device where the rest state is intermediate of the two extremes, a fully bleached electrochromic device will turn partially opaque within a few seconds, or a darkened electronic device will become translucent within a few seconds. Using the teachings described herein, the stable electrochromic device is able to maintain its bleached or colored states for extended periods of time, even when its conductors are shorted. Of course, when the electrochromic devices are actually used, the electrodes will not be shorted, but will be connected only through substantial or low impedances. For example, typical impedance between electrodes may be thousands, tens ofthousands, or even millions of ohms of resistance or it may be only a few hundred ohms. Accordingly, measuring the time it takes to return to a rest state when electrodes are shorted may be used as a direct indicator of the time period an optical state may be persistently held. Of course, it will be appreciated that in actual use persistent time periods will change depending upon the impedance presented between electrodes. It will also be understood that temperature and other environmental conditions may also affect or change the rate of return to the rest state. For example, higher temperatures tend to drive the electrochromic material towards a rest state more quickly. Of course, this means that elevating the temperature while testing a shorted device also speeds characterizing the devices persistent time period.
Using the teachings described herein, electrochromic devices have been manufactured and tested to maintain a persistent optical state for weeks, even when electrodes are shorted. For many commercially viable applications, such long term persistence may be desirable. However other commercially viable applications may be enabled with a shorted persistent time period. In this regard, it has been found that devices that are able to maintain a colored or bleached state for more than about eight hours at room temperature with the electrodes shorted have practical commercial application. Another way to test this device would be to increase temperature to about 50° C. or more, and if the device is able to maintain its desired optical state for more that about four hours, then a similar conclusion can be reached. Since transitions occur more rapidly with higher temperatures, when the temperature is about 80° or more, then the same valuable electrochromic device would be expected to maintain its desired optical state for about one hour. It will be understood that other time frames, temperatures, and environmental conditions may be set dependent upon application specific needs.
Referring now to
Referring to
Referring now to
Referring now to
Optical Device:
An optical device may be constructed using thin films or gels or other materials typically layered or otherwise organized in ways that achieve their desired qualities such as rendering the perceptual (optical) medium accessible or non-accessible by blocking, unblocking, reflecting, polarizing, deflecting, focusing, defocusing, changing the spatial or temporal phase magnitude, affecting the spectral response, inducing a wavelength change of, or otherwise disrupting or interfering with a light source. Furthermore the optical device may e.g. be switchable in a repeatable manner between two stable states: an “open” accessible state and a non-accessible “off” state. Additional intermediate states may also be provided.
The optical devices of particular interest are those whose optical properties change in response to electrical signals and in particular electro-optic devices such as electrochromic (EC) devices. Examples of other electrically activated or switchable devices include: liquid crystals, polymer dispersed liquid crystals, dispersed particle systems, cholesteric liquid crystals, polymer stabilized cholesteric texture liquid crystals. Other examples of electro-optic devices which may also be employed use materials that show a change in refractive index (e.g., potassium dihydrogen phosphate (KDP), ferroelectric materials such as lead- lanthanum-zirconium titanate (PLZT), lithium titanate, barium titanate, polyvinylidene fluoride,) and those employing nanocrystal (or quantum dot) structures and particles where transitions are induced by electrical stimulation. Preferred optical devices have multilayer construction with at least two electrically conductive layers. Although the descriptions herein primarily use electro-chromic examples, it will be appreciated that other electro-optic materials may be used.
The materials used in the manufacture of the optical device may be produced or disposed using conventional film/material deposition processes ranging from sputtering, e-beam, and thermal evaporation to chemical vapor deposition or wet chemical deposition such as printing. In another example, one or more of the materials may be disposed using liquid ink-jet processes. These materials form an electro optical film or stack that may be assembled directly onto a target or product or onto a separate substrate, carrier, or tape for integration with a target product. As discussed later, the electrically switchable optical device may also be combined with other devices that switch from an exposure to stimuli other than electrical stimulus such as heat and radiation (including optical radiation).
Electrochromic (EC) Materials Devices and Their Processing
There are several types of known EC materials which may be used for providing selectable optical states. A description of various standard EC materials is given in U.S. Pat. No. 6,493,128. However, these EC materials as constructed using known processes, need on-going power to maintain a desired state, or else they transition to an undesirable rest stated. As described below, EC materials are selected to interact with another material in an EC stack, and when the EC material is in its desired long-term state, the other material is in a highly stable condition. In this way, there is almost no voltage across the EC device, so almost no leakage current is generated. Therefore, the EC material remains in its desired state persistently.
Metal layer 626 may be made out of any metal or a reflective layer which is optically useful, and as long as it is conductive and electrochemically compatible it could be used as an electrode for EC. Other preferred metals are aluminum alloys (including aluminum/titanium alloys), silver and its alloys, gold, rhodium, titanium, nickel, chromium, antimony and its alloys, tantalum and stainless steel. Of these, preferred aluminum alloys are 2000 series (with mainly copper), 5000 series (with mainly magnesium), 6000 series (with mainly magnesium-silicide) and 7000 series (with mainly zinc). The percentage of the alloyed materials is generally in the range of 0.5 to 3 atomic percent. In aluminum/titanium alloys, the percentage of Titanium is in the range of about 0.5 to 50%. There may also be other added alloying elements in lesser quantities such as chromium, lithium, manganese, titanium, zirconium, iron, lead and bismuth. The preferred alloys of silver are with one or more of neodymium, palladium, gold and platinum. The alloying elements in silver are usually added in a range of less than 3 atomic percent. The preferred stainless steels are 316, 304 and 430.
The conductive electrode layer may not be a single reflective layer but rather it may be composed of several metal layers or a combination of metal and transparent conductor layers. Use of multiple layers avoid the corrosion and electrochemical activity issues of the underlying layers while still being able to use their electrical conductive characteristics. A multilayer conductive electrode may be comprised of a transparent conductor (TC) deposited over a metal layer. Examples of preferred transparent conductors are doped tin oxide, doped indium oxide and doped zinc oxide. Tin oxide may be doped with antimony or fluorine, indium is usually doped with tin oxide (Indium-Tin Oxide (ITO)) or with zinc oxide (called IZO). Another transparent conductor is zinc oxide doped with aluminum oxide (AZO). In ITO and IZO, the atomic percent of tin and zinc is rather high, in the range of 5 to 20% for tin, in the range of 15-50% for zinc, whereas in the other cases the dopant concentration is usually less than 5%. The resistivity of these layers should be as small as possible and for optical media applications less than 100 ohms/square is acceptable. Typically these resistances can be achieved in coatings with a thickness of 50nm or more, where a range of about 50 to 200 nm is preferred. Organic conducting layers may also be used which may be formed using conductive polymers, carbon nanotubes and polyhedrals. The thickness of the metal layers is typically less than 50 nm and that of the TC deposited on the metal is less than 200 nm, preferably less than 100 nm. Multiple metallic layers are used where one of the metal layers serves as adhesion promotion layer between the plastic substrate and the next metal. Some of the adhesion promotion metal layers are chromium and titanium in a thickness of about 5-20 nm. The device concepts here can be adopted for depositing them directly onto a target device, or on separate substrates which are then integrated with the target device. For those devices which are formed separately and then integrated, it is preferred that both of the electronically conducting layers of the EC device are transparent.
In
The ion conductors 628 in
The counterelectrodes 69 may be complimentary to the EC electrodes in terms of optical coloration or may show a little or no optical change upon oxidation and reduction. In conventional EC devices the purpose of the counterelectrodes is to store ions which are injected into or ejected from the EC layer when a voltage is applied across the electrodes 626 and 631. These electrodes are also known as ion-storage electrodes. As an example in an EC device that uses an EC layer that colors upon reduction one may use the counterelectrode as another EC layer that colors upon oxidation. Thus when the ions leave the counterelectrode this layer oxidizes (and hence colors) whereas the EC layer also colors as the ions enter this layer and it reduces. Examples of inorganic counterelectrode (CE) materials that do not change their color upon oxidation and reduction are, e.g., are titanium vanadium oxide and cerium titanium oxide. Generally the thickness of counterelectrodes is in the range of 100 to 500 nm. Each of the layers in the EC device may be a single layer of one material or a composite of multiple materials, or they may comprise of multiple layers of different materials. The counterelectrodes may also be organic and their nature oxidizing or reducing is typically opposite to that of the EC electrode. For example a device using an EC electrode of polyaniline which bleaches from a colored state to a bleached state by reduction, would have a counterelectrode which can oxidize. Some of the organic materials for this purpose may be phenazine and hydroquinone and their derivatives. These materials may be incorporated in a solid device by tying them covalently to a polymeric backbone and/or incorporating them in a thermoplastic or a thermosetting matrix. Preferred matrices are polymers which are described in the ionic conductors above. This may be done to increase the ionic conductivity of the layer for faster switching devices. For example CE materials may be made, e.g., hydroquinones mixed with ion conducting polymers as given above, and vanadium or nickel oxide in Li—Al fluoride Some examples of EC materials made by combining ion conductors and EC materials are polyaniline with polyamps, polymeric quaternary ammonium salts or with sodium salt of polystyrene sodium sulfonate, polyacrilic acid and Nafion®, etc. Another example would be tungsten oxide and molybdenum oxide mixed in Li—Al fluoride.
The mobile ions, e.g., protons, lithium, sodium or silver are introduced in the device by co-depositing these with the EC or the counterelectrode (CE), or as a separate layer which is then intercalated into the EC or the counterelectrode, or by chemical or electrochemical reduction. The various layers in the EC device may be deposited by physical vapor deposition (PVD), chemical vapor deposition (CVD) or by wet chemical processing (spinning, dipping, spraying, ink jet printing including patterning of solutions). PVD includes reactive sputtering of metals, radio-frequency or pulsed DC sputtering of non-conductors (e.g., oxides), thermal, laser and e-beam evaporation. These processes may also be assisted by plasma and ion treatments. Lithium is difficult to co-deposit by sputtering or evaporation of lithium metal due to its high reactivity. A preferred method is to use an alloy of lithium and aluminum for evaporation or sputtering. This results in a preferential removal of lithium from the target, and oxygen in the processing chamber is bound by aluminum. In another alternative tungsten oxide comprising oxide materials may be deposited by sputtering in an argon atmosphere which leads to films in the reduced (or colored) state.
Irreversibility or limited cyclability may be introduced to the point of only allowing the device to change once before it locks in the change permanently by several means. One may use a counterelectrode which does not result in reversible change, e.g., zinc oxide, tin oxide, silica, alumina, etc., when intercalated with protons or lithium or causing irreversible chemical/electrochemical changes. The intercalated ions may be made irreversible with time as they bind or react slowly within the host layer. Since these materials are not known to intercalate these ions, such ions may nevertheless be inserted by applying high voltages, i.e. in excess of 2V and preferably in excess of 2.5V and most preferably in excess of 3V. Most EC devices in this disclosure will operate in the range of 0.8 to 6V. These will be called ion-reactive layers as they react with the ions and then do not release them.
The ion-reactive layers may be formed from organic and organometallic materials. These ion-reactive layers may be used as counterelectrodes or even as irreversible ion traps located between the EC and the ion conductor layer. Silanes, such as epoxy silanes, amino silanes, mercapto silanes, methyl tetraorthosilicate, etc. may be used to form these layers. Silanes may be deposited from about 1% solutions in ethanol or methanol. Water or acids may also be added to pre-hydrolyse them. As an example this layer may be added between the EC layer and the ion conductor or be substituted with the ion conductor or be located between the counterelectrode and the transparent conductor. It was found that when using tungsten oxide as the EC layer, the silane coating allowed the ions to go through to color the EC layer, but was more difficult to bleach. Ion-reactive layers to trap lithium may also be made which comprise of crown ethers. Crown ethers are molecules which have cavities of just the right size to trap ions or molecules. Thus, appropriate crown ether should be one that can trap lithium. A crown ether suitable for trapping lithium has a cavity size of about 0.085 nm such as 15-crown-5 (15C5) available from Sigma Aldrich (Milwaukee, Wis.). To form a layer comprising crown ethers, these crown ethers may be mixed with the silanes or introduced in matrices of polyethylene oxide and/or polypropylene oxide or other ion-conducting polymers described above. In one method polypropylene glycol may be mixed with crown ether and a curing agent based on an epoxy or an isocyanate. This mixture is deposited by spin coating or other method and cured (e.g. cross-linked) into a solid film. In some example constructions, formulations may be made, which are UV cured, by using polypropylene glycols which are terminated by methacrylic or acrylic groups (including epoxy and urethane acrylates), adding UV initiators and curing them after deposition. One may also use alternative formulations which are solidified upon cooling (commonly called hot glue) or those materials which are processed like hot glue to give immediate green strength for handling, but can be further cured by UV or by mechanisms using room-temperature vulcanizates (RTVs). For trapping ions one may also use materials that get reversibly or irreversibly reduced, e.g., peroxides, disulfides, manganates, chromates and dichromates, etc, which may be also put in the matrices as are crown ethers.
The development of an electrochromic device which is stable in both the dark and bleached form requires a fine tuning of the half cell potentials of redox species. The bleached oxidizing agent and reducing agent must result in a cell potential of less than of equal to zero. This can generally be calculated using the Nernst equation. However, in the search for a device which is stable in both the bleached and dark state the cell potential for the reverse reaction must also be less than or equal to zero. Such a set of oxidizing agent and reducing agents is required for such as system.
An alternative approach to this system is to select either the oxidizing agent or reducing agent to undergo an irreversible reaction. This will prevent any possibility for the establishment of a galvanic cell upon electrochemical switching. This will of course produce a single use electrochemical device. Simple examples would include chemical species which converted to gasses or are precipitated upon undergoing the redox reaction. In an electrochromic device such reactions are not practical, other systems must be considered. Systems which undergo a chemical change through the addition or removal of an electron are desirable. Such systems may undergo dimerization or polymerization, add a ligand or undergo a significant structural change.
Electrochemical polymerizations are generally employed to produce conducting polymers. However, use of the monomers as the reducing agent in an electrochemical cell should produce an irreversible electrochemical device. Pyrroles, thiophenes, anilines and furans have all been shown to undergo electrochemical polymerization. The oxidizing potential of the monomer can be controlled by relative electronegativity of the monomer. Careful selection of the monomer will enable development of an electrolytic cell where there is no possibility of forming a galvanic cell after a potential has been applied
Other possibilities involve a chemical change such as the formation of bonds in the thiol to disulfide conversion. Others would involve a geometric change in a metal complex, such as a tetrahedral to octahedral change in geometry. Many examples of complexes which undergo such changes are know, examples include Cu(I)→Cu(II) and Co(II)→Co(III). In inorganic chemistry other systems where a change in the coordination sphere occurs on oxidation or reduction. Examples include species where oxide ligands leave or enter the coordination sphere such as MnO2→Mn2+, VO2+→VO2+.
Electronic leakage through the device can be controlled by the choice of ion conductor, one such choice is use of ionic layers in between the EC and the inorganic ion conductor or as a replacement of the ion conductor. Examples of ionic layers being poly(sodium 4 styrene sulfonate) and poly(lithium 4 styrene sulfonate), polyamps, Nafion™ and ionomers (e.g., Surlyn® from Dupont (Wilmington, Del.)). These materials are generally described in U.S. Pat. No. 6,178,034. For EC devices where they are activated to a bleached state, and it is desired that this state be maintained for a limited time (few hours to a few days or even weeks), reversible type EC devices are preferred. These devices can be made to revert back to a more colored state by manipulating the ion-conductor so that it has a finite electronic conductivity. Alternatively, the two electrodes may also be joined by a high resistance element in excess of about 100,000 ohms to tune the desired amount of “open state” time. Typically, a thinner ion conductor will have lower electronic resistance, thus more leakage current. Also the microstructure of the ion conductor may be manipulated, e.g., a given ion conductor when deposited in a more dense form will have lower ionic conductivity if the other parameters are held constant. Even with devices with no driving potential, color may be lost because of oxidation, particularly for those layers where coloration occurs in reduced state. Processing conditions, e.g., sputtering or evaporation under high pressures leads to higher porosity, use of elevated temperatures and use of ion-assisted deposition reduces porosity. One may also use materials which are colored in oxidized state, and these can be bleached, but over time revert back to the colored state due to oxygen diffusion in the product, an example of such EC material is polyaniline. It is preferred to encapsulate the EC devices with barrier layers so that permeation of oxygen and water is significantly reduced. Further, these materials may also lend to increased surface hardness. Several of these coatings are listed in other section where hard coats are discussed. Preferred permeation of oxygen or water through these layers at room temperature should be less than 3×10−5 ml/cm2-day-atmosphere and less than 8×10−5 g/cm2-day at 90% relative humidity respectively. When EC layers, ion conductors and the counterelectrodes are deposited by physical vapor deposition, it is preferred that they have sufficiently open structures for ions to go through and have low stresses. For example, EC coating porosity is dependent on the ion to be transported. For example, the lithium ion (Li+) has a size of 0.076 nm and O2− has a size of 0.145 nm (and O2 is about 0.17 nm). The channel size should preferably be greater than about three times the ion diameter. Typically low density or more porous structures are produced at higher vapor pressures (keeping the other factors constant). Pressures in the range of 10−3 to 5×10−5 torr are generally preferred. The pressures are usually controlled by using oxygen, nitrogen and/or argon. A method to deposit organic layers or inorganic layers from liquid precursors is by printing of which a preferred approach is by using ink-jet printing techniques, or any other printing techniques including screen printing, offset and gravure printing methods. Several companies offer capabilities of ink jet printing on rigid substrates such as Litrex (Pleasanton, Calif.), Dimatix (Santa Clara, Calif.) and Microfab Technologies (Plano, Tex.). A combination of processes may be used to deposit multilayer devices, i.e., some by printing and the others by PVD or CVD. PVD is mainly used for metals and inorganic materials. However, increasing use of printing including ink-jet printing is being done for these materials. Typically nano-sized particles of metals or inorganic particles is dispersed in a liquid medium and used as ink. The particle sizes are generally less than 100 nm and more in the range of 5 to 20 nm. As an example formation of such particles in liquid phase are described in U.S. Pat. No. 6,322,901 and published US patent application 20050107478. Liquids comprising nano-particles of inorganic transparent conductors (such as ITO and IZO) and metals can be used for printing. For example Cabot (Billerica, Mass.), ULVAC Technologies Inc (Methuen, Mass.) and Harima (Japan) have nano-metal pastes (e.g., gold, silver, copper, etc) for printing. Also, the RF antennas as described later may also be printed (e.g., using ink jet printers) using these inks on the same substrates as the EC devices.
Transparent conducting oxides may be deposited by a number of methods. Preferred methods are those where these oxides may be deposited at high rates to keep up with rates similar to metal deposition in optical media to balance the throughput and minimize the number of discs going through the process at any given time. It is preferred that each layer of the conductive oxide or any other layer in the conductive stack is deposited at about less than 15 seconds, and more preferably in less than 5 seconds, and two to three seconds being most preferable. These are deposition times only and not the period for evacuation through load-lock ,etc. Further, since a substrate may be made out of plastic (for example polycarbonate), it is preferred that the substrate temperature is at least 10 C below the glass transition temperature of the plastic material. For polycarbonate substrate a preferred range is below 130 C, and more preferably below 110 C, and most preferably below 100 C. One preferred method is to use Pulsed DC sputtering for high flux and simultaneous use of an auxiliary oxygen plasma when using an alloy target of the component metals (e.g., indium-tin or indium zinc, etc). The auxiliary plasma can be generated by radio frequency (e.g., 13.56 MHz) or by the use of microwaves. An example of pulsed DC power supply is Pinnacle Plus available from Advanced Energy (Fort Collins, Colo.). A ceramic target may also be used but one has to be careful about the thermal loading. To get high flux in a small area where the coating is to be deposited, hollow cathodes may be used rather than planar cathodes. The material is sputtered through an inner diameter of the target tube and the atoms exit from the end of this tube. This type of system also has high coating efficiency as very little material ends outside the desired coating zone. An important parameter is to achieve a high flux of ions with energy closer to about 20 eV/ion so that dense crystalline films are formed without being disturbed too much from the kinetic energy of the arriving ions.
For the access control, security, and theft protection, the most desirable EC device could maintain its colored and bleached state without having an appreciable potential in either state. This means voltages in any state of coloration should be lower than 0.5V and preferably less than 0.1V and most preferably zero volts. Thus these devices will have low or no internal driving potential which may lead to stable optical characteristics when stored for long periods of time. It is best to have devices exhibit this characteristic at all temperatures to which the target device is to be subjected to.
One may also make the device in
There are other types of EC materials that may also be used where the metal layer itself participates in an EC reaction in going from transparent to reflective or vice versa. U.S. Patent Publication 20040021921 describes examples of these EC devices. Antimony/bismuth and silver-antimony, copper-antimony and antimony layers are preferred metals for this application where the metallic (reflective) state goes to a transparent state when injected with lithium. Further, the preferred range of antimony concentration (atomic %) in these alloys is from about 40% to about 90%.
In one example, the stable electrochromic device is integrated on to an optical media. However, it will be understood that other fields of application exist, for example, in the automotive, medical, entertainment, security fields. It will be understood that specific processes, materials, and optical characteristics may be selected according to application requirements. Optical disc devices may be constructed as shown in
One may also invert the layers for the device 655 as shown in
Another example optical device uses at least two electrodes with a polymer comprising electrolyte in between. Preferably these are two of the metal layers used for data layers. If the data layers are the two halves of the disc as shown in
Al→Al+3+3e− and Al+33OH−→Al(OH)3
The change to Aluminum hydroxide causes loss in reflection. The oxidation reaction in the electrolyte in acidic medium (pH lower than 7) leads to the following balancing reaction where hydrogen will escape through the package
2H+2e−→H2
and in basic medium (pH higher than 7) may lead to the following balancing reaction in the electrolyte
O2+2H2O+2e−→4OH−
Other redox additives may also be added to the electrolyte which will lead to alternative balancing reactions. The electrolyte will also comprise polymeric, monomeric or oligomeric components (e.g., acrylates and methacrylates including urethane and epoxy acrylates). The layers are typically put down from a liquid or a vapor precursor. Solid layers are obtained by polymerization of the material in the layer or evaporation of a solvent. The curing or polymerization may be done by radiation (UV, microwave, etc.) and or heat. Depending on the mechanism of cure appropriate initiators may also be added as commonly known in the art. One may also use alternative polymeric formulations as a matrix which are solidified upon cooling (commonly called hot glue) or those materials which are processed like hot glue to give immediate green strength for handling, but can be further cured by UV or by mechanisms using room-temperature vulcanizates (RTVs).
In the above description it was assumed that the EC is located between the two halves of the DVD. Another highly preferred location is outside of the DVD on the read-out side (see
A set of four EC devices were fabricated on a conductive tin oxide coated glass by depositing coatings using physical vapor deposition (PVD). This was a five layer device similar to the one shown in
Another set of devices was fabricated as in Example 1. however, in this case the counterelectrode was 120 nm thick nickel oxide. At 650 nm, this device in colored state was 2.6% transmitting and in the bleached state the transmission was 15.1%. The colored state transmission at 405 nm was 6.9% and 22.6% when bleached. This device could be reversed.
PA was deposited on ITO coated glass. The coating was deposited from a solution comprising formic acid and ascorbic acid. The coated substrate was heated to 70° C. for 15 minutes to remove the volatile products and solidify the coating. The 300 nm thick coatings were colorless as produced and were electrochromic as shown in
Two type of coatings, Indium tin oxide (with about 0.1 as tin to indium atomic ratio) and indium-zinc oxide (with about 0.3 zinc to indium ratio). These coatings were deposited on glass without heating. These coatings were deposited by sputter coating process in a thickness of about 100 nm at temperatures lower than 100 C. The resistivity of ITO was 45 ohms/square and of the IZO 60 ohms/square. Their optical transmission spectra are shown in
A tungsten oxide coating on ITO (12 Ω/sq) was prepared from a precursor solution. The precursor solution was prepared from 3 grams of peroxotungstic ester (PTE) dissolved in 30 mls of ethanol. The solution was spin coated at 1000 rpm onto ITO and cured under humid conditions to 135° C. The WO3 coating had a thickness of 250 nm. This coating was chemically reduced to a colored state by subjecting this to dilute sulfuric acid and indium metal.
A UV curable solid electrolyte was prepared by mixing 3.75 g of poly(propylene glycol) diacrylate with 1.25 g of poly(propylene glycol) acrylate and 0.2 g of the UV initiator Irgacure 500 (supplied by Ciba Speciality Chemicals Corp. White plains, N.Y.). To enhance the ionic conductivity of the mixture 0.77 g of 1-Butyl-1-methylpyrrolyidium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]-methanesulfonamide ionic liquid and 0.16 g of lithium trifluoromethanesulfonate. A thin coating of the mixture was cured to a solid film by exposing this for 5 seconds in a Xenon strobe light curing system (Model 550 from Electro-lite Corporation (Danbury, Conn.)).
A cationically cured cathodic layer was made using the following:
A UV curable solid electrolyte was prepared by mixing 3.75 g of poly(propylene glycol) diacrylate (Mol wt. 540) with 1.25 g of poly(propylene glycol) acrylate (Mol wt 475) and 0.5 g of dipentaerythriol pentaacrylate ester and 10 g of amine modified acrylate oligomer, acrylic ester. 0.4 g of the UV initiator Irgacure was added. 0.06 g of glycidoxypropyltriethoxysilane was added as an adhesion promoter. To enhance the ionic conductivity of the mixture 0.246 g of 1-Butyl-1-methylpyrrolyidium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]-methanesulfonamide salt and 0.046 g of lithium trifluoromethanesulfonate salt were added. The redox species ferrocene was added in a concentration of 0.282 g. This mixture was spin coated on glass and cured for 5 seconds in a Xenon strobe light curing system (Model 550 from Electro-lite Corporation (Danbury, Conn.)). The film thickness was 9 μm
A thin layer of the ion conducting material describe in Example 8 above was spin coated at 1000 rpm onto tungsten oxide as described in Example 5, but without the reduction step. The ion conducting layer was cured under UV to give a solid layer 9 microns thick. On top of this layer was deposited 50 nm of gold by a sputtering process to complete the stack and form the top electrode. The cell had an initial reflectivity of 68% at 650 nm and when colored by applying 3.5 volts had a reflectivity of 31%.
A solid state electrochromic device was constructed using a tungsten oxide coating as described in Example 5 above except the WO3 was cured at 250° C. and the coating was reduced in a three electrode configuration using 0.1M lithium trifluoromethanesulfonate and 0.05M ferrocene in propylene carbonate as the electrolyte. The reference electrode was a silver wire. The reduced WO3 on ITO was laminated with another ITO coated substrate through use of the ion conducting layer as described in Example 6. This bonding layer was cured under UV and had a thickness of around 30 μm. The initial transmission of the cell at 650 nm was 55% and when bleached at 3.5 Volts at room temperature its transmission increased to 80%. This cell in the bleached state along with another cell in the colored state (50% T at 650 nm) were stored at room temperature for three days without applying any electrical power. Both the cells did not show any optical change. To see if elevated temperature storage would accelerate a change in optical properties, both of these cells were then subjected to 85° C. for six days without power application. Again no change in optical properties was observed with no change in its optical transmission. This shows that in both cases the optical states were maintained without applying any electrical power.
An electrochromic device was prepared as described in example 10 above except that the WO3 layer was cured at 135° C. and reduced with protons using dilute sulfuric acid and indium metal. The cell at 650 nm had a transmission of 3% and when bleached at 4.0 volts had a transmission of 78%. This cell was placed in the bleach state at 85° C. for six days with no change in transmission or physical appearance of the cell.
An electrochromic device 740 was made by depositing thin layers as shown in
A device was made using two pieces of glass with ITO coatings. On one of these a polyaniline coating in a thickness of 700 nm was deposited on a spin coater at 200 rpm as described in Example 3. This was assembled in a cell with a liquid electrolyte comprising of propylene carbonate to the ionic liquid in a ratio of 4:1 and 0.25 molar hydroquinone. The ionic liquid was 1-Butyl-1-methylpyrrolyidium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]-methanesulfonamide and the other side being ITO on coated glass In principle the cell resembled
Several DVDs were coated with polyaniline solutions (see example 3) by spraying through a mask to create a pattern as shown in
A polyaniline coating was deposited by spin coating a solution (0.6 g of polyaniline (emeraldine base, 50,000 mol wt) in 20 ml of 88% formic acid) on an ITO coated glass substrate. The coating is dried in an air circulated oven at 80 C. The color of the coating as deposited is deep green and after the drying process it is deep blue. The coating thickness was about 300 nm. Doping with hydroquinone was achieved by soaking the polyaniline coating in a solution of 0.25M hydroquinone in 80vol% propylene carbonate and 20vol % ionic liquid at 80° C. for 5 minutes and then washed with ethanol. After doping, the polyaniline changed from deep blue to pale yellow. The coating had an active cyclic voltametry (CV) response and could be colored and bleached. CV was conducted in 0.1M lithium triflate solution in acetonitrile while using a stainless steel counter electrode and silver as pseudo-reference electrode. At a scan rate of 20 mV/s, the electrode was colored at −0.56V versus silver wire and the optical modulation was recorded as shown below.
The modulation of hydroquinone doped polyaniline was surprisingly high at 405 nm. Thus this was deemed as a suitable material at all the three wavelengths of interest. Further, this material had good thermal stability in both (colored and bleached states) as shown in the next table where the transmission change was recorded for both states by subjecting them to an air circulated oven at 80 C No change in colored state at 650 and 405 nm was observed for a period of two hours. In the bleached state the transmission at 650 nm decreased from about 66 to about 40% and at 405 nm this changed from 54 to 50%. It appeared that the change at the end of two hours was leveling off Derivatives of hydroquinone and their mixtures with hydroquinone were also found suitable to give large range at both 405 and 650 nm. For example in a separate experiment the following results were obtained.
A doped HQ containing polyaniline was prepared as in Example 16 on an ITO coated glass substrate and then incorporated in the device. Polyaniline was bleached when incorporated in the device. ITO conductivity was about 15 ohms/square. The substrate size was about 2 cm×2 cm and the area coated with polyaniline was about 0.75 sq cm. A layer of UV curable electrolyte with the following composition was coated on top of doped polyaniline:
After coating with electrolyte another ITO coated glass of similar size, with a slight offset was lowered on top of the electrolyte with ITO touching this layer. The sandwich was then subjected to UV radiation for cure. The thickness of the electrolyte layer was about 1.5 microns. When a voltage of 2.75V was applied with polyaniline electrode being positive, the cell colored. The cell bleached when a reverse potential of 2.75V was applied. This is shown in
For devices to work properly it is important that all layers must have good interface adhesion for proper transport of ions and electrons. We found that to improve the adhesion of polyanilne with other layers, particularly ion conducting layers deposited over it, that it is preferable to modify the polyaniline coating solution by adding ion-conducting material to it. For example addition of polymers with acid containing moieties, such as polyacrylic acid (PAA), Nafion® (Dupont, Wilmington, Del.), or polystyrene sulfonic acid was useful. The ion-conducting material coatings on top of modified polyaniline showed superior wetting during the coating operation. Further, the polymer added to polyaniline may be the same as the ion conducting layer or be a different one. The concentration of modifying polymer was preferably 50% of polyaniline by weight. A more preferred concentration was 10% or less.
To make irreversible devices with no potential in the colored and the bleached states it was decided to couple non-reversible chemical reactions which were induced electrochemically. In these devices the expected reaction upon the application of bleach potential was electrochemical bleaching of the EC layer while a non-reversible polymerization was initiated of the thiophene. The devices were constructed with polyaniline (with 10% polyacrylic acid (molecular weight 2000) by weight ). The coatings were deposited on ITO coated glass by spin coating from 88% formic acid solutions. The thiophene was dissolved in a polyelectrolyte (PSS (polystyrene sulfonic acid), Nafion™ or PSSNa (polystyrene sulfonic acid; sodium salt)). The nafion solution was prepared in lower alcohols, the PSS and PSSNa solutions were prepared in water:ethanol 50:50. This was coated on a second ITO coated substrate, and these were assembled into a device by bringing the two coated substrates together and sandwiching an electrolyte. Initial experiments were carried out using liquid electrolytes which comprised of 0.1 molar lithium triflate in propylene carbonate.
Devices are constructed with polyaniline coatings with similar compositions and process as in Example 18. The reductants are metal salts which are dissolved in a polyelectrolyte (PSS (polystyrene sulfonic acid), Nafion™ or PSSNa (polystyrene sulfonic acid; sodium salt)) in an aqueous solution comprising ethanol and water and coated on top of the polyaniline layer. To make a coating solution, Ig of vanadyl sulfate was added to 2 g of polyacrylic acid and 8 ml of water. Then 0.1 ml of this was added to 0.5 ml ethanol and 0.5 ml of polystyrenesulfonic acid (18 wt % in water) to make the coating solution. The device was constructed where polyaniline was 300 nm thick, electrolyte was 2.9 microns thick and the top electrode was gold in a thickness of 60 nm. The device had an initial reflection of 8% which changed to about 27% when a potential of 2.8V (polyaniline being negative) was applied. This device exhibited stable states when shorted in bleached and color mode. The device had no measurable potential across the terminals in either of the optical states. Another device was constructed where cobalt chloride was used instead of vanadyl sulfate. This also showed stable optical characteristics in both states and the device changed from about 7% reflectivity to 18% reflectivity when bleached at 2.8V.
Several polyaniline coatings were deposited in the pattern and position as shown in
Two DVD-9 were coated with passive truncated diamond-shaped shutters, one in the open state and one in the closed state. The device stacks consisted of physical vapor deposited layers of ITO/WO3(Li)/Li/AlF4/ITO as shown by the photograph in
While particular preferred and alternative embodiments of the present intention have been disclosed, it will be appreciated that many various modifications and extensions of the above described technology may be implemented using the teaching of this invention. All such modifications and extensions are intended to be included within the true spirit and scope of the appended claims.
This application claims priority to U.S. patent application Ser. No. 60/703,673, filed Jul. 29, 2005, and entitled “Devices for Optical Media”, and to U.S. patent application Ser. No. 60/720,986, filed Sep. 27, 2005, and entitled “Devices and Processes for Optical Media”, both of which are incorporated by reference as if set forth in their entirety. This application is also related to U.S. patent application Ser. No. 11/460,827, filed Jul. 28, 2006, and entitled, “Persistent Electro-Optic Devices and Processes for Optical Media”, which is also incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60703673 | Jul 2005 | US | |
| 60720986 | Sep 2005 | US |
