HK1232009B - Hybrid display assembly including a solar cell - Google Patents

Description

Hybrid display assembly including solar cells

Technical Field

The present invention relates to a hybrid display assembly including solar cells. More particularly, the present invention relates to a display assembly including two stacked display devices with solar cells disposed thereunder.

Background Art

The readability of information displayed by a digital display device, such as a liquid crystal display (LCD), is determined primarily by the surface area available for displaying the information. Therefore, for a given display surface area, a compromise must be found between the amount of information required and its size. The larger the size of the displayed information, the better its readability. However, this inevitably limits the amount of information that can be displayed. Conversely, reducing the size of the displayed information increases the amount of information, but this comes at the expense of readability.

To overcome this shortcoming, a second display device has been proposed, positioned below the first. This allows for the first display device to display some information, while the second display device can display some information. By switching between the first and second displays, the information displayed on either the first or second display device can be selectively displayed, enabling the display of larger amounts of information and larger sizes.

A disadvantage of such a display assembly comprising two superimposed display devices is its relatively high power consumption. Such a display assembly is usually intended to be installed in a small portable object with limited power reserve, such as a wristwatch.

Furthermore, the readability of information displayed by a display device, such as a liquid crystal display unit or an organic light-emitting diode display device, is largely dependent on ambient lighting conditions. For some display devices, displayed information can be read well in bright environments but is difficult to read in dark environments. Conversely, other types of display devices provide high-quality display in dim or dark environments but are difficult to read in bright sunlight.

For example, consider a transflective liquid crystal display (LCD) cell—that is, a LCD cell capable of displaying information that is visible during the day by means of reflection and also visible at night by means of transmission through a backlight. Such LCD cells are optimized to provide the best possible reflection of sunlight and, therefore, ensure good readability of the displayed information in bright ambient conditions. However, to achieve the best possible reflection of sunlight, the transmission efficiency of such LCD cells is significantly limited. Consequently, when the backlight is activated to allow the displayed information to be read in dim light, the vast majority of the light emitted by the backlight is lost through absorption. Consequently, energy efficiency is very low. Furthermore, the optical quality of the information displayed by the LCD cell is highly dependent on the viewing angle.

Regarding emissive display devices, such as organic light-emitting diode displays, these devices have optical qualities that are superior to those of liquid crystal display cells because they do not depend on the viewing angle. However, these high-quality emissive display devices do not allow for a reflective operating mode. The information displayed by them is therefore easy to read in dim light or darkness, but becomes difficult to read once viewed outdoors. To overcome this problem, the amount of current supplied to the emissive display device can be increased to ensure a minimum level of readability. However, even under normal conditions of use, these emissive display devices use more electricity than reflective liquid crystal cells. Their power consumption makes it difficult to envision keeping them permanently on, especially when they are incorporated into a small portable object such as a wristwatch, the only source of energy for which is a battery that is typically required to last for more than a year.

Summary of the Invention

It is therefore an object of the present invention to overcome the above-mentioned and other problems by providing a display assembly whose energy requirements can be met even when it is incorporated into a small portable object, such as a wristwatch, whose energy reserves are limited. The present invention also provides a display assembly that operates satisfactorily in both well-lit environments and dark environments.

To this end, the present invention relates to a component for displaying at least one information for a portable object, the display component comprising a first at least partially transparent display device located on the observer side and configured to display at least one first information, and a second at least partially transparent display device and a solar cell arranged in sequence below the first display device for displaying at least one second information, the first and second display devices being capable of switching between an active state in which they display information and a passive state in which they do not display information.

As a result of these features, the present invention provides a display assembly comprising two superimposed display devices, namely a first display device displaying a first information and a second display device displaying a second information. Thus, a portion of the information can be displayed using the first display device and a portion of the information can be displayed using the second display device. By switching between the first and second display devices, it is possible to choose to reveal the information displayed by the first or second display device, which makes it possible to display a larger amount of information and information of a larger size. Furthermore, by teaching that the solar cell is arranged below the two superimposed display devices, the present invention allows such an assembly to be integrated into a small portable object whose electrical energy reserves are necessarily limited. In fact, it has been observed that the amount of light reaching the solar cell via the set of two superimposed display devices is sufficient to provide the amount of electrical energy required for the operation of the two superimposed display devices through the phenomenon of photoelectric conversion. Consequently, little or no electrical energy reserves of the portable object are required for the operation of the two superimposed display devices.

According to a supplementary feature of the present invention, the first display device located on the observer's side is of a reflective type, and the second display device located below the first display device is of an emissive type.

As a result of these other features, the present invention provides a display assembly for a portable object, such as a wristwatch, which operates in an optimal manner regardless of the ambient lighting conditions. In strong sunlight, information will preferably be displayed by a reflective display device. In fact, such a reflective display device, which uses the phenomenon of sunlight reflection to display information, is very energy-efficient. Therefore, it can remain permanently on and provide good readability of information under strong ambient light conditions. Conversely, in dim light or darkness, information will preferably be displayed by an emissive display device. Such an emissive display device uses more current than a reflective display device, but the information displayed by it is visible at night or in the dark and has excellent optical properties that are particularly independent of the viewing angle.

According to a preferred embodiment of the present invention, the first display device comprises a reflective liquid crystal display unit, and the second display device comprises a transparent, emissive organic light emitting diode display unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear more clearly from the following detailed description of an embodiment of a display assembly according to the invention, which example is given purely as a non-limiting example with reference to the accompanying drawings, in which:

- FIG1 is a schematic cross-sectional view showing a display assembly according to the present invention with a solar cell disposed thereunder;

FIG2 is a cross-sectional view of an exemplary embodiment of a display assembly according to the present invention, wherein a first display device comprises a reflective liquid crystal display unit, a second display device comprises a transparent, emissive organic light emitting diode display unit, and a solar cell is disposed below the display assembly; and

3A to 3D schematically illustrate the operating modes of the display assembly shown in FIG. 2 according to whether the liquid crystal display unit and the organic light emitting diode display unit are active or passive.

DETAILED DESCRIPTION

The present invention originates from the following general inventive idea: a solar cell is provided below an assembly consisting of two superimposed display devices, the two superimposed display devices being able to switch between an active state in which they consume electrical energy to display information and a passive state in which they do not use electrical energy and do not display any information. Due to the use of two superimposed display devices, it is possible to display part of the information with the first display device and part of the information with the second display device. By switching between the first and the second display device, it is possible to choose to reveal the information displayed by the first or the second display device, which makes it possible to display a larger amount of information and information of a larger size. It was also recognized that by arranging a solar cell below the two superimposed display devices, the solar cell provides, by means of photoelectric conversion, a current sufficient to allow the two superimposed display devices to operate. Therefore, it is possible to integrate such a display assembly into a small portable object such as a wristwatch with limited electrical energy storage capacity.

According to a supplementary aspect of the present invention, the first display device located on the viewer's side is of a reflective type, while the second display device located below the first display device is of an emissive type. Thus, the display assembly according to the present invention operates optimally regardless of ambient lighting conditions. In bright sunlight, information will preferably be displayed by the reflective display device, which utilizes the phenomenon of sunlight reflection to display information. Conversely, in dim or dark conditions, information will be displayed by the emissive display device, which consumes electrical energy to generate light.

1 is a schematic cross-sectional view of a display assembly according to the invention. The display assembly, designated as a whole by the general reference numeral 1, comprises a first, at least partially transparent, display device 2 arranged on the side of an observer 4, and a second, likewise at least partially transparent, display device 6 arranged below the first, at least partially transparent, display device 2.

Within the meaning of the invention, the first display device 2 and the second display device 6 are display devices that can be switched between a state in which they consume electrical energy to display information and a passive state in which they consume no electrical energy and do not display any information.

Preferably, the first display device 2 is bonded to the second display device 6 via a transparent adhesive layer 8. The transparent adhesive layer 8 can be formed of an adhesive film or a liquid acrylic or silicone adhesive. The purpose of the adhesive layer 8 is to prevent stray reflection problems that would occur if the two display devices 2 and 6 were separated by an air layer, which would reduce the optical quality of the display assembly 1 according to the present invention.

Finally, a solar cell 10 capable of providing electrical energy by utilizing a photoelectric conversion phenomenon is disposed below the second display device 6 .

FIG2 is a detailed cross-sectional view of an exemplary embodiment of a display assembly 1 according to the present invention, wherein the first display device 2 includes a reflective liquid crystal display unit 20, the second display device 6 includes an emissive, transparent organic light-emitting diode display unit 60 (hereinafter referred to as a TOLED display unit), and finally, a solar cell 10 is disposed below the display assembly 1.

More specifically, the reflective liquid crystal display unit 20 includes a front substrate 21 disposed on the side of the observer 4 and a rear substrate 22 extending parallel to and away from the front substrate 21. The front substrate 21 and the rear substrate 22 are bonded to each other by a sealing frame 23, which defines a sealed volume 24 for accommodating liquid crystals. The optical properties of the liquid crystals are modified by applying appropriate voltages at specific intersections between transparent electrodes 25a disposed on the lower surface of the front substrate 21 and transparent counter electrodes 25b disposed on the upper surface of the rear substrate 22. The electrodes 25a and the counter electrodes 25b are made of a transparent conductive material, such as indium-zinc oxide or indium-tin oxide (ITO).

In the context of the present invention, any liquid crystal phase can be envisaged, such as twisted nematic (TN), super twisted nematic (STN) or vertical alignment (VA). Likewise, all addressing schemes can be envisaged, such as direct addressing, active matrix addressing or passive matrix multiplexing addressing.

The absorptive polarizer 30 is bonded to the upper surface of the front substrate 21 of the reflective liquid crystal display unit 20 via an adhesive layer 32. The adhesive layer 32 can be formed from an adhesive film or a liquid adhesive layer. The adhesive used to bond the absorptive polarizer 30 to the reflective liquid crystal display unit 20 can be transparent or slightly diffuse, depending on whether specular reflection or diffuse reflection is desired. The absorptive polarizer 30 can be, for example, an iodine-based polarizer or a dye-based polarizer.

Reflective polarizer 34 is bonded to the lower surface of rear substrate 22 of reflective liquid crystal display unit 20 via adhesive layer 36. Adhesive layer 36 can be transparent or slightly diffusive, depending on whether specular or diffuse reflection is desired. Reflective polarizer 34 can be a wire grid polarizer. Alternatively, it can be a polarizer composed of a series of birefringent layers that cause polarized reflection or transmission through constructive or destructive interference, such as a dual brightness enhancement film (DBEF) or APF polarizer sold by a US company.

As will be seen below, in a preferred but not mandatory manner, the reflective liquid crystal display unit 20 is bonded to a transparent TOLED display unit 60, with a circular polarizer 38 interposed therebetween. The TOLED display unit 60 comprises a transparent substrate 61 made of glass or plastic, and an encapsulation cover 62 extending parallel to and away from the transparent substrate 61. The transparent substrate 61 and the encapsulation cover 62 are joined to each other by a sealing frame 63, which defines a sealed volume, isolated from air and moisture, to house the stack of electroluminescent layers, generally designated by reference numeral 64. An upper transparent electrode 65, for example, made of indium-tin oxide or ITO, and a lower transparent electrode 66, for example, made of a metal material such as aluminum or gold, or a metal oxide such as ITO or zinc-indium oxide, form the stack of electroluminescent layers 64 on either side. These electrodes 65, 66, made of a metal material, are slightly reflective. Transparent organic light-emitting diode display units can be implemented using direct addressing, where they display only icons or segments, or passive matrix addressing, where they display dot-matrix displays. In the case of a dot matrix display, active matrix addressing can also be used in combination with transparent thin film transistors (TFTs) that are used to control current and are arranged in display pixels on one side of the substrate 61 of the transparent TOLED display unit 60.

Preferably, a circular polarizer 38 is provided between the reflective liquid crystal display unit 20 and the transparent TOLED display unit 60. The purpose of the circular polarizer 38 is to improve the optical quality of the display assembly 1 by absorbing stray reflections generated by the transparent electrodes 65 and 66. However, in cases where it is desired to save cost or space, such a circular polarizer 38 may not be provided. The circular polarizer 38 includes an absorptive linear polarizer 40 and a quarter-wave plate 42. On the reflective liquid crystal display unit 20 side, the circular polarizer 38 is bonded to the reflective polarizer 34 by means of a transparent adhesive layer 44, while on the transparent TOLED display unit 60 side, the circular polarizer 38 is bonded to the substrate 61 by means of a transparent adhesive layer 46. For reasons that will be described in detail below, the transmission axis of the absorptive polarizer 40 is oriented parallel to the transmission axis of the reflective polarizer 34.

Finally, the solar cell 10 is arranged below the stack formed by the reflective liquid crystal display unit 20 and the transparent TOLED display unit 60 on the side opposite to the observer 4. Preferably, the solar cell 10 is bonded to the lower surface of the encapsulation cover 62 by means of a transparent adhesive layer 46.

3A to 3D , the operating principle of the display assembly 1 according to the present invention will now be examined depending on whether a reflective liquid crystal display unit 20 and a transparent TOLED display unit 60 are used. Purely by way of non-limiting example, it will be assumed that the reflective liquid crystal display unit 20 is a twisted nematic (TN) liquid crystal unit and that the transmission axes of the absorptive polarizer 30 and the reflective polarizer 34 are perpendicular to each other.

In FIG3A , both the reflective liquid crystal display unit 20 and the transparent TOLED display unit 60 are turned off. Ambient light, indicated by reference numeral 48, is linearly polarized by the absorptive polarizer 30. Ambient light 48 then undergoes a 90° rotation upon passing through the reflective liquid crystal display unit 20. Because the transmission axis of the reflective polarizer 34 extends perpendicular to the direction of extension of the transmission axis of the absorptive polarizer 30, the reflective polarizer 34 allows ambient light 48 exiting the reflective liquid crystal display unit 20 to pass through unchanged. Ambient light 48 is then circularly polarized by the circular polarizer 38 and transmitted without being absorbed by the absorptive polarizer 40, whose transmission axis is oriented parallel to the transmission axis of the reflective polarizer 34. Finally, ambient light 48 passes through the transparent TOLED display unit 60. A small portion of ambient light 48 is reflected by the upper transparent electrode 65 and the lower transparent electrode 66, reversing the direction of rotation of the circular polarization of the light and causing it to be absorbed upon passing through the circular polarizer 38 again. As for the remaining ambient light 48, this light passes through the transparent TOLED display unit 60 without being changed and is absorbed by the solar cell 10 having a dark or black appearance. Therefore, the display assembly 1 appears black to the observer 4.

In FIG3B , the reflective liquid crystal display unit 20 is deactivated, while the transparent TOLED display unit 60 is activated. Ambient light 48, linearly polarized by the absorptive polarizer 30, undergoes a 90° rotation as it passes through the reflective liquid crystal display unit 20 and is then transmitted unchanged by the reflective polarizer 34. The ambient light 48 is then circularly polarized by the circular polarizer 38, which transmits the light without absorption, given that the transmission axis of the absorptive polarizer 40 is oriented parallel to the transmission axis of the reflective polarizer 34. Finally, the ambient light 48 passes through the transparent TOLED display unit 60. A small portion of the ambient light 48 is then reflected by the upper transparent electrode 65 and the lower transparent electrode 66 of the transparent TOLED display unit 60. Upon reflection, the direction of rotation of the light's circular polarization is reversed, causing it to be absorbed by the circular polarizer 38 when it passes through it again. The remaining ambient light 48 is absorbed by the solar cell 10. In addition, half of the light emitted by the transparent TOLED display unit 60 is absorbed by the absorptive polarizer 40, while the other half of the light, which is linearly polarized, passes through the reflective polarizer 34, the reflective liquid crystal display unit 20, and the absorptive polarizer 30 in sequence and is not absorbed. Therefore, the displayed information glows against a dark background.

In FIG3C , the reflective LC display unit 20 is enabled, while the transparent TOLED display unit 60 is disabled. In the unswitched region of the reflective LC display unit 20, ambient light 48 linearly polarized by the absorptive polarizer 30 undergoes a 90° rotation as it passes through the reflective LC display unit 20 and is then transmitted unchanged by the reflective polarizer 34. The ambient light 48 is then circularly polarized by the circular polarizer 38, which transmits the light without absorption, given that the transmission axis of the absorptive polarizer 40 is oriented parallel to that of the reflective polarizer 34. Finally, the ambient light 48 passes through the transparent TOLED display unit 60. A small portion of the ambient light 48 is reflected by the upper transparent electrode 65 and the lower transparent electrode 66. At this point, the direction of rotation of the circular polarization is reversed, so that when the light passes through the circular polarizer 38 again, it is absorbed by the circular polarizer 38. The remaining ambient light 48 is absorbed by the solar cell 10. Furthermore, in the switched region of the reflective liquid crystal display cell 20, the ambient light 48 is transmitted without being altered, so that the polarization direction of the ambient light 48 is perpendicular to the transmission axis of the reflective polarizer 34 and therefore parallel to the reflection axis of the polarizer 34. Therefore, the ambient light 48 is reflected by the reflective polarizer 34 in the direction of the reflective liquid crystal display cell 20. In the switched region of the reflective liquid crystal display cell 20, the liquid crystal molecules do not alter the polarization direction of the ambient light 48 when the ambient light 48 passes through the reflective liquid crystal display cell 20 again, so that the ambient light 48 is not absorbed by the absorptive polarizer 30 during its return journey, which enables the reflective mode of the display assembly 1.

In FIG3D , both the reflective liquid crystal display unit 20 and the transparent TOLED display unit 60 are enabled. In the switched region of the reflective liquid crystal display unit 20, a portion of the ambient light 48 reflected by the reflective polarizer 34 is not absorbed by the absorptive polarizer 30 and is perceptible to the observer 4, allowing the reflective liquid crystal display unit 20 to display information in reflective mode. The remaining ambient light is absorbed by the solar cell 10. Furthermore, half of the light emitted by the transparent TOLED display unit 60 is absorbed by the circular polarizer 38, while the other half of the light emitted by the transparent TOLED display unit 60 passes through the circular polarizer 38, the liquid crystal display unit 20, and the absorptive polarizer 30 and is not absorbed, making it perceptible to the observer 4.

It goes without saying that the present invention is not limited to the embodiments just described, and that those skilled in the art may envision various simple modifications and variations without departing from the scope of the present invention as defined by the claims appended to this patent application. In particular, it should be understood that the statement that ambient light passes through the reflective liquid crystal display unit or the transparent TOLED display unit unchanged is not strictly accurate. In fact, when ambient light passes through these display units, minor stray light reflections always occur. However, these stray reflections are negligible within the scope of the present invention. It should also be understood from the foregoing that the statement that "transparent" electrodes are not strictly accurate either. In fact, despite being made of transparent conductive material, these electrodes are always slightly reflective. The reflective liquid crystal display unit is selected from the group consisting of a twisted nematic liquid crystal display unit, a super twisted nematic liquid crystal display unit, and a vertical alignment liquid crystal display unit. The reflective liquid crystal display unit may be a bistable display unit. As a variant, the second display device includes a light-emitting display unit that is configured to switch between an active state in which it emits light to display information and a passive state in which it does not emit any light.

Parts List :

1 Display Components

2. First display device

4 Observers

6 Second display device

8 Adhesive layer

10. Solar Cells

20 reflective liquid crystal display unit

21 Front base plate

22 rear substrate

23 Sealing frame

24 Sealed volume

25a Transparent electrode

25b Transparent counter electrode

30 Absorption Polarizer

32 adhesive layer

34 Reflective Polarizer

36 Adhesive layer

38 Circular Polarizer

40 Absorption Linear Polarizer

42 Quarter Wave Plate

44 transparent adhesive layer

46 transparent adhesive layer

48 Ambient Light

60 TOLED display units

61 substrate

62 package cover

63 Sealing frame

64 Stack of electroluminescent layers

65 Upper transparent electrode

66 Lower transparent electrode

Claims (10)

1. A display assembly for displaying at least one piece of information for a portable object, the display assembly (1) comprising a first display device (2) located on the side of an observer (4) and configured to display at least one piece of first information and at least partially transparent, and a second display device (6) configured to display at least one piece of second information and at least partially transparent, and a solar cell (10) sequentially disposed below the first display device (2), the first display device (2) and the second display device (6) being capable of switching between an active state of displaying information and a passive state of not displaying information. The first display device (2) located on the side of the observer (4) is of the reflective type, while the second display device (6) located below the first display device (2) is of the emission type. The first display device (2) includes a reflective liquid crystal display unit (20), which is configured to switch between an active state in which the reflective liquid crystal display unit reflects and displays information and a passive state in which the reflective liquid crystal display unit is transparent and does not display any information. The second display device (6) includes a light-emitting display unit, which is configured to switch between an active state in which the light-emitting display unit emits light to display information and a passive state in which the light-emitting display unit does not emit any light. The reflective liquid crystal display unit (20) is characterized in that it is selected from the group consisting of: twisted nematic liquid crystal display units, super-twisted nematic liquid crystal display units and vertically aligned liquid crystal display units. 2. The display assembly according to claim 1, wherein the first display device (2) is bonded to the second display device (6) by means of an adhesive layer (8). 3. The display assembly according to claim 2, wherein the adhesive layer (8) is formed of an adhesive film or a liquid adhesive layer. 4. The display assembly according to claim 1, wherein the reflective liquid crystal display unit (20) is disposed between the absorptive polarizer (30) located on the side of the observer (4) and the reflective polarizer (34) located below the reflective liquid crystal display unit (20). 5. The display component according to claim 4, characterized in that a circular polarizer (38) is provided between the reflective liquid crystal display unit (20) and the second display device (6). 6. The display component according to claim 5, wherein the circular polarizer (38) comprises an absorption line polarizer (40) and a quarter-wave plate (42). 7. The display assembly according to claim 6, wherein the absorption line polarizer (40) has a transmission axis parallel to the transmission axis of the reflective polarizer (34). 8. The display component according to any one of claims 1 to 7, wherein the reflective liquid crystal display unit (20) is bistable. 9. The display component according to any one of claims 1 to 7, wherein the second display device (6) comprises a transparent organic light-emitting diode (TOLED) display unit (60). 10. The display assembly according to claim 9, wherein the transparent organic light-emitting diode (TOLED) display unit (60) comprises a stack (64) of electroluminescent layers, and an upper transparent electrode (65) and a lower transparent electrode (66) are formed on both sides of the stack.