FIELD OF THE INVENTION

This invention relates to electro-optic displays. More specifically, this invention relates to an energy harvesting electro-optic display, that is, a display that can gather energy for functioning by converting light energy into electrical energy.

BACKGROUND OF THE INVENTION

The term “electro-optic”, as applied to a material, a display or a device, is used herein in its conventional meaning in the imaging art to refer to a material having first and second display states differing in at least one optical property, the material being changed from its first to its second display state by application of an electric field to the material. Although the optical property is typically color perceptible to the human eye, it may be another optical property, such as optical transmission, reflectance, luminescence or, in the case of displays intended for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.

Some electro-optic materials are solid in the sense that the materials have solid external surfaces, although the materials may, and often do, have internal liquid- or gas-filled spaces. Such displays using solid electro-optic materials may hereinafter for convenience be referred to as “solid electro-optic displays”. Thus, the term “solid electro-optic displays” includes rotating bichromal member displays, encapsulated electrophoretic displays, microcell electrophoretic displays and encapsulated liquid crystal displays.

The terms “bistable” and “bistability” are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. It is shown in U.S. Pat. No. 7,170,670 that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true of some other types of electro-optic displays. This type of display is properly called “multi-stable” rather than bistable, although for convenience the term “bistable” may be used herein to cover both bistable and multi-stable displays.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type as described, for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791 (although this type of display is often referred to as a “rotating bichromal ball” display, the term “rotating bichromal member” is preferred as more accurate since in some of the patents mentioned above the rotating members are not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) which have two or more sections with differing optical characteristics, and an internal dipole. These bodies are suspended within liquid-filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed by applying an electric field thereto, thus rotating the bodies to various positions and varying which of the sections of the bodies is seen through a viewing surface. This type of electro-optic medium is typically bistable.

Another type of electro-optic display uses an electrochromic medium, for example an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least in part from a semi-conducting metal oxide and a plurality of dye molecules capable of reversible color change attached to the electrode; see, for example O'Regan, B., et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.

Another type of electro-optic display is an electro-wetting display developed by Philips and described in Hayes, R. A., et al., “Video-Speed Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). It is shown in U.S. Pat. No. 7,420,549 that such electro-wetting displays can be made bistable.

One type of electro-optic display, which has been the subject of intense research and development for a number of years, is the particle-based electrophoretic display, in which a plurality of charged particles move by an application of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays.

Encapsulated electrophoretic media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes. In a microcell electrophoretic display, the charged particles and the fluid are not encapsulated within capsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film. As used herein, the term “microcavity electrophoretic display” may be used to cover both encapsulated and microcell electrophoretic displays.

Microcavity electrophoretic displays have been used for numerous applications within devices such as wristwatches, e-book readers, newspapers, mobile phones, and electronic shelf labels. Unlike traditional light-emitting diode (LED) and liquid-crystal displays (LCD), electro-optic displays are highly flexible in the materials they can be constructed from. Numerous material options exist for use as the charged particles, media, electrodes, and the other various components. This unique versatility allows for display constructions that are highly tailored to individual applications.

All electronic devices require an energy source to operate, whether they are tied to an electric grid or powered through an energy storage device such as a battery containing electrochemical cells. Display systems that have large surface areas consume considerable amounts of power, especially display systems of the LCD type. Advancements in display technology, such as the electrophoretic display described above, require much less power when compared to backlit displays such as LCD's. However, even these energy efficient displays need a power source.

Traditional photovoltaic cells and combinations suggested in the art are used to drive active signs. However, these displays require a large surface area of photovoltaic cells placed away from the signage itself, such that the photovoltaic cells do not interfere with the display. Additionally, the large surface area of the photovoltaic cell needed to power the signage can become cumbersome.

Reflective displays, such as electrophoretic displays, operate well in ambient light conditions. However, when ambient light conditions are low, there may not be enough reflected light available for a viewer to effectively see the display. To combat this problem, LEDs or other light sources have been used to provide the necessary reflected light during low ambient light conditions. On the other hand, backlit displays including LCD displays, operate well in low ambient light conditions. However, LCD displays continuously drain power, and as a result, various solutions were developed that can be viewed in the art. For example, Yang et al. (Polarizing Organic Photovoltaics. Adv. Mater., 23: 4193-4198, 2011) discloses a photovoltaic cell that is capable of recycling wasted visible light from the backlight but introduces display distortions due to scattering light. Menéndez-Velázquez et al. (Energy Environ. Sci., 2013, 6, 72-75) and U.S. Patent Application Publication No. 2011/0010911 solved this problem by converting the light to near-infrared (NIR) wavelengths, wherein the light was guided by a wave guide to an edge of the display to be absorbed by the photovoltaic cell.

U.S. Pat. No. 7,327,511 describes variable transmission devices including charged pigment particles that are distributed in a non-polar solvent and encapsulated. These variable transmission devices can be driven to an open state (light-transmissive) with an AC driving voltage whereby the charged pigment particles are driven to the capsule walls. Accordingly, such variable transmission devices are useful for viewing surfaces where it is desirable to alter the light transmissivity at will, such as privacy glass, sunroofs, and windows on buildings.

In view of the above information, there exists a need for novel electro-optic configurations that would expand the usage of electro-optic dynamic displays, creating new display applications.

SUMMARY OF THE INVENTION

In one aspect, the disclosure concerns with an energy harvesting electro-optic display. When viewed from above, i.e., from the viewing side of the display, the energy harvesting electro-optic display includes (a) a first fluorescent light concentrator, comprising a first fluorescent dye and a first light guide plate, the first light guide having a pair of opposed faces configured to propagate light along the length of the first light guide plate between the faces, (b) a first photovoltaic cell at one or both the faces of the first fluorescent light concentrator, (c) a first light-transmissive electrode layer, (d) an electro-optic material layer comprising light-transmissive gaps, (e) a backplane comprising a second electrode layer, (f) a second fluorescent light concentrator comprising a second fluorescent dye and a second light guide plate, the second light guide plate having a pair of opposed faces configured to propagate light along the length of the second light guide plate between the faces, and (g) a second photovoltaic cell at one or both the faces of the second light guide plate. The first fluorescent light concentrator absorbs ultraviolet light incident to the viewing side of the energy harvesting electro-optic display, reemits light of longer wavelength, and directs the remitted light onto the first photovoltaic cell to be converted into electric current or voltage. The second fluorescent light concentrator absorbs light incident to the viewing side of the energy harvesting electro-optic display that traverses the electro-optic material layer, reemits the traversed light, and directs the reemitted light onto the second photovoltaic cell to be converted into electric current or voltage. The generated electric current or voltage is used for the operation of the electro-optic display upon the conversion or is stored in a storage component to be used for the operation of the electro-optic display at a later time.

The energy harvesting electro-optic display may further comprise a third light concentrator and a third photovoltaic cell. The third light concentrator comprises a third light guide plate, the third light guide plate having a pair of opposed faces configured to propagate light along the length of the third light guide plate between the faces. The third photovoltaic cell is located at one or both the faces of the third light concentrator. The third light concentrator is located between the first light concentrator and the electro-optic material layer. The third light concentrator absorbs light that is reflected by the electrophoretic material layer, and directs the absorbed light onto the third photovoltaic cell to be converted into electric current or voltage.

The electro-optic material layer of the energy harvesting electro-optic display may comprise an electrophoretic medium. The electrophoretic medium may be compartmentalized in capsules or microcells and the light-transmissive gaps can separate the capsules or microcells. The capsules or microcells may comprise electrophoretic particles in a non-polar electrophoretic liquid. In the case of an electrophoretic medium that is compartmentalized in capsules, the light-transmissive gaps may be light-transmissive beads, wherein the volume ratio of capsules to light-transmissive beads in the electrophoretic medium is from about 1:20 to about 1:3. The light-transmissive beads may have diameter of from about 10 to about 500 μm. In the case of an electrophoretic medium that is compartmentalized in microcells, the light-transmissive gaps may be the walls of the microcells, wherein the wall thickness of the microcells is from about 3 to about 120 μm. The walls of the microcells may comprise less than 0.2 weight percent of pigment or filler particles.

In another aspect, an energy harvesting electrophoretic display comprises in order from the viewing side: (a) a protective layer, (b) an electrophoretic display component comprising a first light-transmissive electrode layer, an electrophoretic material layer and a backplane comprising a second electrode layer, and (c) a photovoltaic layer comprising a photovoltaic element. The electrophoretic material layer comprises an electrophoretic medium that is compartmentalized in capsules or microcells, wherein the compartments are separated by light-transmissive gaps. The capsules or microcells comprise electrophoretic particles in a non-polar electrophoretic liquid. The photovoltaic element absorbs the portion of the incident light to the energy harvesting electrophoretic display that reaches the photovoltaic element via the electrophoretic display component and converts the absorbed light into electric current or voltage. The generated electric current or voltage is used for the operation of the electrophoretic display upon the conversion or stored in a storage component to be used for the operation of the electrophoretic display at a later time. In the case of electrophoretic material layer comprising capsules, the light-transmissive gaps may be light-transmissive beads. The volume ratio of capsules to light-transmissive beads in the electrophoretic material layer may be from about 1:20 to about 1:3. The light-transmissive beads may have diameter of from about 10 to about 500 μm. In the case of electrophoretic material layer comprising microcells, the light-transmissive gaps may be the walls of the microcells. The wall thickness may be from about 3 to about 120 μm. The walls of the microcells may comprise less than 0.2 weight percent of pigment or filler particles.

It is one advantage of the present invention to allow electrophoretic displays to exist in areas where there are no accessible power grids, or in various low power applications.

It is another advantage of the present invention to provide an electrophoretic display area that becomes capable of generating energy.

It is another advantage of the present invention to provide electrophoretic displays that contain a LGP that guides ambient or generated light to the edge of the display to be absorbed by a photovoltaic layer.

These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings and appended claims.

