CH709964A2 - hybrid display assembly including a solar cell. - Google Patents

Abstract

The invention relates to a display unit for at least one piece of information for a portable object, said display unit (1) comprising a first display device (2) at least partially transparent located on the side of an observer ( 4) and which is arranged to display at least a first information, a second at least partially transparent display device (6) arranged to display at least one second information and a solar cell (10) being arranged in this order under the first display device (2), the first and second display devices (2, 6) being capable of switching between an active state in which they display information and a passive state in which they do not display information.

Description

Field of the invention

The present invention relates to a hybrid display assembly comprising a solar cell. More specifically, the present invention relates to such a display assembly comprising two superimposed display devices in which is arranged a solar cell.

Technological background of the invention

The readability of the information displayed by the digital display devices such as liquid crystal display cells is determined in particular by the surface offered by the digital display device for displaying information. For a given display surface, it is necessary to find a compromise between the number and the size of the information that one wishes to display. The larger the information displayed, the better the readability of the information. Nevertheless, the number of information that can be displayed will necessarily be limited. Conversely, if we reduce the size of the information displayed, we can increase their number, but this will be at the expense of readability.

To overcome this drawback, it has already been proposed to have a second display device under a first display device. It is thus possible to display the information partly with the first display device, and partly with the second display device. By switching between the first and the second display device, the information displayed by the first or the second display device can be displayed, which makes it possible to display a larger number of information and according to a more big size.

The disadvantage of such a display assembly comprising two superimposed display devices is its consumption of electrical energy which is quite important. However, such display sets are usually intended to be embedded in portable objects of small dimensions such as wristwatches whose energy reserves are limited.

On the other hand, the readability of the information displayed by the display devices such as liquid crystal display cells or display devices organic electroluminescent diodes is very dependent on ambient light conditions. With some display devices, the information displayed can be read in good conditions in a bright environment, but are difficult to read in a dark environment. Conversely, other categories of display devices provide a good quality display in dim light or dark, but are difficult to read in daylight.

By way of example, consider the liquid crystal display cells of transflective type, that is to say liquid crystal display cells capable of displaying information that will be visible by day thanks to to a phenomenon of reflection, and which will also be visible in the dark by transmission using a backlight device. Such transflective type liquid crystal display cells are optimized to be able to best reflect the sunlight and thus ensure good readability of the information displayed under conditions of high ambient light. However, so that such transflective liquid crystal display cells can best reflect sunlight, their transmission efficiency is greatly limited. Thus, when the backlighting device is activated in order to read the information displayed in the penumbra, a major part of the light emitted by the backlighting device is lost in absorption phenomena. The energy efficiency is therefore bad. In addition, the optical qualities of the information displayed by the liquid crystal cell are strongly dependent on the angle of view.

With regard to the emissive type display devices such as display devices with organic electroluminescent diodes, they have optical qualities that are greater than those of liquid crystal display cells, these optical qualities do not depending in particular not on the angle of view. Nevertheless, these high quality emissive type display devices do not allow operation in reflective mode. The information they display is therefore very readable in the dark or dark, but become difficult to read as soon as they are observed outdoors. To remedy this problem, it is possible to increase the amount of current supplied to the emissive display devices to ensure a minimum of readability. However, even under normal use conditions, these emissive display devices consume more than a reflective type liquid crystal cell. Their power consumption is such that it is difficult to envisage keeping them on permanently, especially when they are embedded in a portable object of small dimensions such as a wristwatch whose only source of energy is a battery of which we usually want it to last at least a year.

Summary of the invention

The present invention aims to remedy the aforementioned problems as well as others by providing a display assembly whose energy requirements can be met even when it is embedded in a portable object of small dimensions such as a wristwatch whose energy reserves are limited. The present invention also provides a display assembly whose operation is satisfactory both in a brightly lit environment and in a dark environment.

For this purpose, the present invention relates to a display assembly of at least one piece of information for a portable object, this display assembly comprising a first at least partially transparent display device located on the side of an observer. and which is arranged to display at least a first piece of information, a second at least partially transparent display device arranged to display at least a second piece of information and a solar cell being arranged in this order under the first display, the first and second display devices being able to switch between an active state in which they display information and a passive state in which they do not display information.

With 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. It is therefore possible to display information partly with the first display device, and partly with the second display device. By switching between the first and the second display device, the information displayed by the first or the second display device can be displayed, which makes it possible to display a larger number of information and according to a more big size. In addition, by teaching to have a solar cell under the two superimposed display devices, the present invention allows the integration of such an assembly in a portable object of small dimensions whose reserves of electrical energy are necessarily limited. Indeed, it has been found that the amount of light that reaches the solar cell through all of the two superimposed display devices is sufficient to provide, by photoelectric conversion phenomenon, the amount of electrical energy required for the operation of the solar cells. two superimposed display devices.

Therefore, the electrical energy reserves of the portable object are little, or not solicited by the operation of the two superimposed display devices.

According to a complementary feature of the invention, the first display device located on the observer's side is of the reflective type, and the second display device disposed under the first display device is of the emissive type.

With these other features, the present invention provides a display assembly for a portable object such as a wristwatch whose operation is optimal regardless of ambient lighting conditions. In broad daylight, the information will preferably be displayed by the reflective display device. Indeed, this reflective display device, using a reflection phenomenon of sunlight to display the information, is energy efficient. It can therefore remain permanently lit and offer good readability of information under conditions of high ambient light. Conversely, in darkness or darkness, the information will preferably be displayed by the emissive display device. Such an emissive display device consumes more electric current than a reflective display device, but the information it displays is visible at night or in the dark with very good optical properties which are in particular totally independent of the light. angle of view.

According to a preferred embodiment of the invention, the first display device comprises a reflective liquid crystal display cell, and the second display device comprises a transparent emissive display cell with organic electroluminescent diodes. .

Brief description of the figures

Other features and advantages of the present invention will emerge more clearly from the detailed description which follows of an embodiment of the display assembly according to the invention, this example being given purely by way of illustration and not by way of example. limiting only in connection with the appended drawing in which: <tb> fig. 1 <SEP> is a schematic sectional view illustrating a display assembly according to the invention in which is arranged a solar cell; <tb> fig. 2 <SEP> is a sectional view of an exemplary embodiment of a display assembly according to the invention, the first display device comprises a reflective liquid crystal display cell, and the second display device display comprises a transparent emissive display cell with organic electroluminescent diodes, a solar cell being arranged under this display assembly, and <tb> figs. 3A to 3D <SEP> schematically illustrate the operating mode of the display assembly illustrated in FIG. 2 depending on whether the liquid crystal display cell and the organic electroluminescent diode display cell are active or passive.

Detailed description of an embodiment of the invention

The present invention proceeds from the general inventive idea of having a solar cell under a set of two superimposed display devices capable of switching between an active state in which they consume electrical energy to display information. , and a passive state in which they do not consume electrical energy and display no information. By using two superimposed display devices, information can be displayed partly with the first display device, and partly with the second display device. By switching between the first and the second display device, the information displayed by the first or the second display device can be displayed as desired, which makes it possible to display a greater number of information and according to a more big size. It was further realized that by placing a solar cell under the two superposed display devices, the solar cell provided, by photoelectric conversion effect, an electric current sufficient to allow the operation of the two superimposed display devices. . It is therefore possible to integrate such a display assembly in a portable object of small dimensions such as a wristwatch whose storage capacity in electrical energy are however limited.

According to a complementary aspect of the invention, the first display device located on the side of the observer is of the reflective type, and the second display device disposed under the first display device is of the emissive type. The operation of the display assembly according to the invention is therefore optimal whatever the ambient lighting conditions. In broad daylight, the information will preferably be displayed by the reflective display device that uses a reflection phenomenon of sunlight to display the information. Conversely, in darkness or darkness, the information will be displayed by the emissive display device which is able to emit light by consuming electrical energy.

FIG. 1 is a schematic sectional view of a display assembly according to the invention. Designated as a whole by the general numerical reference 1, this display assembly comprises a first display device 2 at least partially transparent disposed on the side of an observer 4, and a second display device 6 also at least partially transparent arranged under the first display 2.

Within the meaning of the present invention, the first and second display devices 2, 6 are display devices capable of switching between a state in which they consume electrical energy to display information, and a state of passive in which they do not consume electrical energy and display no information.

Preferably, the first display device 2 is secured to the second display device 6 by means of a transparent adhesive layer 8. This transparent adhesive layer 8 may be formed of a film adhesive or a layer of acrylic liquid glue or silicone. This adhesive layer 8 is intended to avoid the problems of parasitic reflections that would occur if the two display devices 2, 6 were separated by a layer of air and which would degrade the optical quality of the display assembly 1 according to the invention.

Finally, a solar cell 10 capable of supplying electrical energy by exploiting the photoelectric conversion phenomenon is disposed under the second display device 6.

FIG. 2 is a detailed sectional view of an exemplary embodiment of the display assembly 1 according to the invention in the case where the first display device 2 comprises a reflective liquid crystal display cell 20, and the second display device 6 comprises a transparent emissive display cell 60 with organic electroluminescent diodes which will be referred to in the following as transparent transparency display cell TOLED (Transparent Organic Light Emitting Diode). Finally, the solar cell 10 is disposed under this display assembly 1.

More specifically, the reflective liquid crystal display cell 20 comprises a front substrate 21 disposed on the side of the observer 4 and a rear substrate 22 which extends parallel to and away from the substrate before 21. The substrates front 21 and rear 22 are joined together by a sealing frame 23 which delimits a sealed chamber 24 for the confinement of a liquid crystal whose optical properties are modified by applying a suitable voltage to a crossover point considered between transparent electrodes 25a formed on a lower face of the front substrate 21 and transparent counter-electrodes 25b formed on an upper face of the rear substrate 22. The electrodes 25a and the counter-electrodes 25b are made of a transparent electrically conductive material such as indium-zinc oxide or indium-tin oxide, the latter material being better known as a denomination Anglo-Saxon Indium Tin Oxide or ITO.

In the case of the present invention, all the liquid crystal phases such as helical nematic (Twist Nematic or TN in English terminology), super-nematic helix (Super Twist Nematic or STN in English terminology). ) or else vertically aligned (Vertically Aligned or VA in English terminology) can be envisaged. Similarly, all types of addressing such as direct addressing, addressing by active matrix or multiplex addressing of a passive matrix can be envisaged.

An absorbing polarizer 30 is bonded to an upper face of the front substrate 21 of the reflective liquid crystal display cell 20 by means of an adhesive layer 32. This adhesive layer 32 may be formed of a film adhesive or a layer of liquid glue. The adhesive used to secure the absorbing polarizer 30 on the reflective liquid crystal display cell 20 may be transparent or slightly diffusing depending on whether one seeks to obtain specular or diffuse reflection. As for the absorbing polarizer 30, it may be, for example, of the iodine or dye type.

A reflective polarizer 34 is bonded to a lower face of the rear substrate 22 of the reflective liquid crystal display cell 20 by means of an adhesive layer 36 which may be transparent or slightly diffusing depending on whether one seeks to to obtain specular or diffuse reflection. As for the reflective polarizer 34, it may be of the wire mesh type, better known by its English name Wire Grid Polarizer. It can also be a polarizer composed of a succession of birefringent layers that cause the reflection or the transmission of the polarization by a constructive or destructive interference effect, such as polarizers of the type Dual Brightness Enhancement Film (DBEF) or APF type marketed by the American company 3M®.

As will be seen in detail below, the reflective liquid crystal display cell 20 is, preferably but not mandatory, stuck on the transparent display cell TOLED 60 with the interposition of a circular polarizer 38 This TOLED transparent display cell 60 comprises a transparent substrate 61 made of glass or a plastic material and an encapsulation cover 62 which extends parallel to and away from the transparent substrate 61. The transparent substrate 61 and the cover encapsulation 62 are joined together by a sealing frame 63 which delimits a closed volume protected from air and moisture for the confinement of a stack of electroluminescent layers generally designated by the reference numeral 64. A transparent upper electrode 65 made for example of tin-indium oxide or ITO and a transparent lower electrode 66 made for example of a metallic material such as aluminum or gold or a metal oxide such as ITO or zinc-indium oxide are structured on either side of the stack of electroluminescent layers 64 These electrodes 65, 66, made of a metallic material, are slightly reflective. The organic electroluminescent light-emitting diode display cells are available either with direct addressing in cases where it is simply a question of displaying icons or segments, or with a passive matrix type addressing in the case of a dot matrix display. In the case of a dot matrix display, it may also be necessary to make an active matrix type addressing combined with transparent transistors of the Thin Film Transistor or TFT type intended to control the current and which are formed in the pixels. on the substrate side 61 of the TOLED transparent display cell 60.

Preferably, a circular polarizer 38 is disposed between the reflective liquid crystal display cell 20 and the transparent display cell TOLED 60. This circular polarizer 38 is intended to improve the optical qualities of the assembly. 1 by absorbing the spurious reflections produced by the transparent electrodes 65 and 66. It is however possible to do without this circular polarizer 38 if it is desired to save money or gain space. This circular polarizer 38 comprises an absorbent linear polarizer 40 and a quarter wave plate 42. On the side of the reflective liquid crystal display cell 20, the circular polarizer 38 is glued to the reflective polarizer 34 by means of a layer transparent adhesive 44, and the side of the transparent display cell TOLED 60, the circular polarizer 38 is bonded to the substrate 61 by means of a transparent adhesive layer 46. For reasons which will be detailed below, the axis transmission of the absorbing polarizer 40 is oriented parallel to the transmission axis of the reflective polarizer 34.

Finally, the solar cell 10 is disposed under the stack formed by the reflective liquid crystal display cell 20 and the transparent display cell TOLED 60, on the opposite side to the observer 4. Preferably, the solar cell 10 is secured on the underside of the encapsulation cap 62 by means of a transparent adhesive layer 46.

We now examine in conjunction with Figs. 3A to 3D the principles of operation of the display assembly 1 according to the invention according to whether the reflective liquid crystal display cell 20 and the transparent display cell TOLED 60 are in use or not. It will be assumed, by way of illustrative and nonlimiting example only, that the reflective liquid crystal display cell 20 is a helical or TN nematic liquid crystal cell and that the transmission axes of the absorbing polarizer 30 and the reflective polarizer 34 are perpendicular ..

In FIG. 3A, the reflective liquid crystal display cell 20 and the TOLED transparent display cell 60 are both turned off. The ambient light, denoted by the reference numeral 48, is polarized linearly by the absorbing polarizer 30. The ambient light 48 is then rotated through 90 ° as it passes through the reflective liquid crystal display cell 20. As the axis the reflective polarizer 34 extends in a direction perpendicular to the direction in which the transmission axis of the absorbing polarizer 30 extends, the reflective polarizer 34 passes, without modification, the ambient light 48 which escapes from the cell reflective liquid crystal display 20. The ambient light 48 is then circularly polarized by the circular polarizer 38 and is transmitted without absorption by the absorbing polarizer 40 whose transmission axis is oriented parallel to the transmission axis of the reflective polarizer Finally, the ambient light 48 passes through the transparent display cell TOLED 60. A small portion of the ambient light 48 is reflected on the transparent upper and lower electrodes 65 and 66, so that its direction of rotation of the circular polarization is reversed and is absorbed as it passes through the circular polarizer 38 again. As for the rest of the ambient light 48, it passes through the transparent display cell TOLED 60 without modification and is absorbed by the solar cell 10 which has a dark or black appearance. The display unit 1 thus appears black in view of the observer 4.

In FIG. 3B, the reflective liquid crystal display cell 20 is deactivated, while the transparent display unit TOLED 60 is activated. Ambient light 48, linearly polarized by the absorbing polarizer 30, rotates 90 ° as it passes through the reflective liquid crystal display cell 20, and is transmitted without modification by the reflective polarizer 34. The ambient light 48 is then circularly polarized by the circular polarizer 38 which transmits it without absorption since the transmission axis of the absorbing polarizer 40 is oriented parallel to the transmission axis of the reflective polarizer 34. Finally, the ambient light 48 enters the transmission cell. TOLED 60 transparent display. A small fraction of the ambient light 48 is then reflected by the transparent upper and lower electrodes 65, 66 of the transparent display cell TOLED 60. At the moment of reflection, the direction of rotation of the polarization circular light reverses so that when the light crosses again the polarizes ur circular 38, it is absorbed by the latter. As for the rest of the ambient light 48, it is absorbed by the solar cell 10. On the other hand, half of the light emitted by the transparent display cell TOLED 60 is absorbed by the absorbing polarizer 40, while the Another half of the light, linearly polarized, passes successively through the reflective polarizer 34, the reflective liquid crystal display cell 20 and the absorbing polarizer 30 without being absorbed. The displayed information appears in clear on a dark background.

In FIG. 3C, the reflective liquid crystal display cell 20 is activated, while the transparent display cell TOLED 60 is off. In the areas of the reflective liquid crystal display cell 20 which are not switched, the ambient light 48, linearly polarized by the absorbing polarizer 30, rotates 90 ° as it passes through the crystal display cell. reflective liquid 20 and then transmitted without modification by the reflective polarizer 34. The ambient light 48 is then circularly polarized by the circular polarizer 38 which transmits it without absorption since the transmission axis of the absorbing polarizer 40 is oriented parallel to the The transmission axis of the reflective polarizer 34. Finally, the ambient light 48 enters the transparent display cell TOLED 60. A small fraction of the ambient light 48 is reflected by the transparent upper and lower electrodes 65 and 66. At this time there, the direction of rotation of the circular polarization is reversed, so that when the light passes through again the circular polarizer 38, it is absorbed by the latter. The remainder of the ambient light 48 is absorbed by the solar cell 10.

On the other hand, in the zones of the reflective liquid crystal display cell 20 which are switched, the ambient light 48 is transmitted without modification, so that the direction of polarization of the ambient light 48 is found perpendicular. to the transmission axis of the reflective polarizer 34 and therefore parallel to the axis of reflection of the same polarizer 34. Therefore, the ambient light 48 is reflected by the reflective polarizer 34 towards the liquid crystal display cell In the areas of the reflective liquid crystal display cell 20 that are switched, the liquid crystal molecules do not change the direction of polarization of the ambient light 48 as it passes through the cell once again. reflective liquid crystal display 20, so that the ambient light 48 is not absorbed by the absorbing polarizer 30 during its return journey, which i makes it possible to carry out the reflective display mode of the display assembly 1.

In FIG. 3D, the reflective liquid crystal display cell 20 and the TOLED transparent display cell 60 are both enabled. In the areas of the reflective liquid crystal display cell 20 that are switched, the fraction of the ambient light 48 reflected by the reflective polarizer 34 is not absorbed by the absorbing polarizer 30 and is perceptible by the observer 4, which allows the reflective liquid crystal display cell 20 to display the information in reflective mode. As for the remainder of the ambient light, it is absorbed by the solar cell 10. On the other hand, half of the light emitted by the transparent display cell TOLED 60 is absorbed by circular polarizer 38, while the other half light emitted by the transparent display unit TOLED 60 passes through the circular polarizer 38, the liquid crystal display cell 20 and the absorbing polarizer 30 without being absorbed, so that it is perceptible by the observer 4.

It goes without saying that the present invention is not limited to the embodiments which have just been described and that various modifications and simple variants can be envisaged by those skilled in the art without departing from the scope of the invention. as defined by the claims appended to this patent application. It will be understood in particular that to say that the ambient light passes through without modification the reflective liquid crystal display cell or the transparent display cell TOLED without modification is somewhat an abuse of language. Indeed, when the ambient light passes through these display cells, there always occurs minimal phenomena of parasitic reflection of the light. These parasitic reflections are nevertheless quite negligible in the context of the present invention. It will also be understood from what has been said above that speaking of "transparent" electrodes is also somewhat of an abuse of language. Indeed, although made of a transparent electrically conductive material, these electrodes are still very slightly reflective. The reflective liquid crystal display cell is selected from the group consisting of helical nematic-type liquid crystal display cells, helical super-nematic type liquid crystal display cells, and display cells. liquid crystal type vertical alignment. The reflective liquid crystal display cell may be a bistable display cell. Alternatively, the second display device comprises an electroluminescent display cell arranged to switch between an active state in which it emits light to display information and a passive state in which it emits no light.

Nomenclature

[0037] <tb> Display Set <SEP> 1 <tb> First display device <SEP> 2 <Tb> Observer <September> 4 <tb> Second display device <SEP> 6 <tb> Adhesive layer <SEP> 8 <tb> Solar cell <SEP> 10 <tb> Reflective liquid crystal display cell <SEP> 20 <tb> Substrate before <SEP> 21 <tb> Rear Substrate <SEP> 22 <tb> Sealing framework <SEP> 23 <tb> Watertight enclosure <SEP> 24 <tb> Transparent electrodes <SEP> 25a <tb> Transparent counter electrodes <SEP> 25b <tb> Absorbent polarizer <SEP> 30 <tb> Adhesive layer <SEP> 32 <tb> Reflective polarizer <SEP> 34 <tb> Adhesive layer <SEP> 36 <tb> Circular Polarizer <SEP> 38 <tb> Absorbent Linear Polarizer <SEP> 40 <tb> Quarter Wave Blade <SEP> 42 <tb> Transparent Adhesive Layer <SEP> 44 <tb> Transparent Adhesive Layer <SEP> 46 <tb> Ambient light <SEP> 48 <tb> TOLED Transparent Display Cell <SEP> 60 <Tb> Substrate <September> 61 <tb> Encapsulation cover <SEP> 62 <tb> Sealing framework <SEP> 63 <tb> Stacking of electroluminescent layers <SEP> 64 <tb> Transparent Upper Electrode <SEP> 65 <tb> Transparent lower electrode <SEP> 66

Claims (13)

A set of display of at least one information for a portable object, said display assembly (1) comprising a first at least partially transparent display device (2) located on the side of an observer (4) and which is arranged to display at least a first information, a second at least partially transparent display device (6) arranged to display at least one second information and a solar cell (10) being arranged in this order under the first device display (2), the first and second display devices (2, 6) being capable of switching between an active state in which they display information and a passive state in which they do not display information. 2. Display assembly according to claim 1, characterized in that the first display device (2) is glued to the second display device (6) by means of an adhesive layer (8). 3. Display assembly according to claim 2, characterized in that the adhesive layer (8) is formed of a film adhesive or a layer of liquid glue. Display unit according to one of Claims 1 to 3, characterized in that the first display device (2) situated on the observer (4) side is of the reflective type, and in that the second display device (6) arranged under the first display device (2) is of emissive type. 5. Display assembly according to claim 4, characterized in that the first display device (2) comprises a reflective liquid crystal display cell (20) arranged to switch between an active state in which it is reflective and displays information, and a passive state in which it is transparent and does not display information, and in that the second display device (6) comprises an electroluminescent display cell arranged to switch between an active state in which it emits light to display information and a passive state in which it emits no light. Display assembly according to claim 5, characterized in that the reflective liquid crystal display cell (20) is arranged between an absorbing polarizer (30) located on the observer (4) side and a reflective polarizer. (34) placed under the reflective liquid crystal display cell (20). Display assembly according to claim 6, characterized in that a circular polarizer (38) is arranged between the reflective liquid crystal display cell (20) and the transparent display cell TOLED (60). 8. Display assembly according to claim 7, characterized in that the circular polarizer (38) comprises an absorbent linear polarizer (40) and a quarter wave plate (42). 9. Display assembly according to claim 8, characterized in that the absorbing linear polarizer (40) has a transmission axis which is parallel to a transmission axis of the reflective polarizer (34). 10. Display assembly according to any one of claims 5 to 9, characterized in that the reflective liquid crystal display cell (20) is selected from the group formed by the liquid crystal display cells type helical nematic, helical super-nematic type liquid crystal display cells and vertical alignment type liquid crystal display cells. Display assembly according to claim 10, characterized in that the reflective liquid crystal display cell (20) is bistable. 12. Display assembly according to any one of claims 5 to 11, characterized in that the second display device (6) comprises a transparent display cell TOLED (60) with organic electroluminescent diodes arranged to switch between a an active state in which it emits light to display information and a passive state in which it emits no light. 13. Display assembly according to claim 12, characterized in that the transparent display unit TOLED (60) comprises a stack of electroluminescent layers (64) on either side of which are structured a transparent top electrode (65). and a transparent lower electrode (66).