WO2015040289A1

WO2015040289A1 - Reflective, photovoltaic display device

Info

Publication number: WO2015040289A1
Application number: PCT/FR2014/000211
Authority: WO
Inventors: Jöel GILBERT
Original assignee: Sunpartner Technologies
Priority date: 2013-09-20
Filing date: 2014-09-19
Publication date: 2015-03-26
Also published as: FR3012628A1; FR3012628B1

Abstract

The invention relates to a device for controlling the luminosity and the transparency of one or more pixels of a display system, wherein each pixel includes a first transmissive rectilinear polariser (1), having a first light-polarisation axis and arranged in front of the pixels in the optical path; a second transflective rectilinear polariser (2), having a second light-polarisation axis and arranged behind the first polariser; a photovoltaic surface (8) arranged behind said second polariser; an optoelectronic means (21a, 21b) capable of modifying the polarisation plane of the light that passes through same, such as to vary the amount of light to pass through the second polariser and to light said photovoltaic surface, as well as the amount of light to be reflected by the second polariser in order to emerge from the pixel; a third polariser (9) and a backlighting light source (10) placed behind said third polariser, such that a portion of the light (13a, 13b) emitted by the backlighting source (10) is polarised by passing through the third polariser (9), and then passes consecutively through said optoelectronic means (21a, 21b) and said first polariser (1).

Description

REFLECTIVE AND PHOTOVOLTAIC DISPLAY DEVICE

The present invention relates to electronic display screens which use reflective pixels illuminated by ambient light and which also produce photovoltaic electricity.

STATE OF THE ART Photovoltaic surfaces are used to produce electricity from ambient light, which makes it possible to supply energy, at least partially, to certain appliances used in our daily life. It is interesting to integrate photovoltaic surfaces in the surface of the electronic screens so as to generate an electric current able to supply electricity to these screens. In the case of screens that are reflective, or transflective, that is both reflective and emissive, there are already devices that include photovoltaic surfaces. These screens emit bright images composed of pixels like LCD, LED, OLED, PLASMA, LASER, and contain surface elements that have the property of reflecting the ambient light in order to increase the brightness of the pixels. The integration of photovoltaic surfaces in this type of screen is generally done by positioning said photovoltaic surfaces between the emitting elements, for example in inter pixel spaces, or on a part of the reflecting surfaces. In the first case the inter pixel spaces are very small, which limits the overall photovoltaic area and therefore the production of electricity. In the second case, there is a decrease in the reflective surface and therefore a decrease in the brightness of the images.

Document JPH 1144884 A also discloses a transflective optical system using two superposed polarizers, as well as a photovoltaic element above which a lighting element is located. As a result, the photovoltaic elements partially obstruct the photovoltaic element from the point of view of the ambient light incident, which reduces the electricity production by the photovoltaic element, even when the polarizers are arranged to let a maximum of incident light energy pass.

PURPOSE OF THE INVENTION

The main purpose of the invention is to overcome the aforementioned drawbacks by making it possible to integrate large photovoltaic surfaces in the reflective surfaces of the reflective or transflective screens, while modifying very little the visual quality of the images produced by this type of screen.

SUMMARY OF THE INVENTION

The term "photovoltaic" is defined here by the property of certain materials, or combination of materials, of transforming a portion of the received light energy into electrical energy, which is the case, for example, for amorphous crystalline silicon. , or organic. These photovoltaic materials are also interconnected, and connected to external components, by electrical connections known to those skilled in the art and not described here.

The term "transflective polarizer" is defined here by a surface that has the property both of polarizing the light that passes through it and of polarizing the light that is reflected by this surface. In general, the polarization planes of the transmitted light and the light reflected by a transflective polarizer are perpendicular. The transflective polarizer is often composed of a network of electrically conductive metal strips, such as for example silver, aluminum, copper, carbon or graphene, these strips being parallel to one another with thicknesses, widths and thicknesses. spacings that are less than the wavelength of visible light, so less than 400 nm.

In the context of the present application, the expressions in front of, behind, below, with regard to the relative arrangement of the elements of the device according to the invention, refer to the order in which these elements are reached by the ambient light incident on the face of the device presented to an observer. The subject of the invention is a device for controlling the brightness and transparency of one or more pixels of a display system, wherein each pixel comprises:

a first rectilinear polarizer of transmissive type, having a first axis of polarization of the light and arranged in front of the pixels in the optical path;

a second rectilinear polarizer of transflective type, having a second polarization axis of the light, and disposed behind the first polarizer;

a photovoltaic surface disposed behind said second polarizer;

an optoelectronic means capable of modifying the plane of polarization of the light passing through it, so as to vary firstly the quantity of light that will pass through the second polarizer and illuminate said photovoltaic surface and, secondly, the amount of light light that will be reflected by the second polarizer to come out of the pixel,

- characterized in that it further comprises a third polarizer and a backlighting light source placed behind said third polarizer, so that a portion of the light emitted by the backlighting source is polarized through the third polarizer , then passes successively through said optoelectronic means and said first polarizer.

Positioning a photovoltaic cell under a transflective polarizer makes it possible to create a polarizing surface partly reflective and partly transparent. The proportion of reflected light and the proportion of light transmitted through said transflective polarizer is a function which is controlled by the plane of polarization of the incident light with respect to the polarization axis of said polarizer.

The fraction of light that passes through the transflective polarizer illuminates the photovoltaic surface under said transflective polarizer and the fraction of light that is reflected by the transflective polarizer illuminates the color filter placed above. This device is particularly interesting when it is integrated in the electronic screens composed of reflective pixels or transflective pixels. These screens indeed have pixels that contain surfaces that reflect ambient light, said ambient light having been polarized a first time by its passage through a first polarizer. The plane of polarization of the light that has passed through the first polarizer is then modified by an electrical control on a liquid crystal or more generally on an optoelectronic component through which the light passes. Typically, the light thus polarized is reflected by micro mirrors and again the plane of polarization of the light is modified by its passage through the optoelectronic device such as a liquid crystal, for example, and finally the light passes through the first again. polarizer before leaving the pixel to the observer.

On the other hand, when the light polarized by the first polarizer strikes the transflective polarizer which is arranged in place of the micro mirrors used in the known devices, this polarized light will have a percentage of reflection and a percentage of transmission by the second polarizer which will depend on the plane of polarization of said light.

In an extreme case, when the plane of polarization of the light coming from the first polarizer will be perpendicular to the polarization axis of the transflective polarizer, the reflection by the second polarizer will be 100% and the transmission of 0%. And in another extreme case, when the plane of polarization of the light from the first polarizer will be parallel to the polarization axis of the second transflective polarizer, the reflection by the second polarizer will be 0% and the transmission of 100%.

Intermediate values of the polarization plane of the light will give intermediate values as to the percentages of reflection and transmission of said light through the second transflective polarizer.

In the particular case where the first polarizer and the second polarizer which is transflective have their parallel axes of polarization, and when the liquid crystal is not active and therefore does not modify the plane of polarization of the light, there will be total transmission of ambient light to the photovoltaic surface under the second transflective polarizer.

Conversely, when the liquid crystal modifies by 90 ° the plane of polarization of the light from the first polarizer, then there will be total reflection of the light from the first polarizer, by the second polarizer. In the other particular case where the first polarizer and the second transfiective polarizer have their perpendicular axes of polarization, then the phenomenon of total transmission of light to the photovoltaic surface or the total reflection of the light is reversed.

Therefore, when the liquid crystal is not active and therefore does not modify the plane of polarization of the light, there will be total reflection of the light from the first polarizer and the photovoltaic surface located under the second transfective polarizer will receive no light .

Conversely, when the liquid crystal modifies by 90 ° the plane of polarization of the light coming from the first polarizer, then there will be total transmission of the light from the first polarizer through the second polarizer and to the photovoltaic surface will receive 100% of the light.

In a particular case, the second transfiective polarizer is dichroic, ie it only reflects part of the spectrum of the light it receives and transmits only another part of the spectrum. In this case the second polarizer acts as a color filter, which implies that it replaces the color filters typically associated with this kind of pixels.

In the case of transflective screens, the colored pixels are crossed on the one hand by an artificial light emitted behind the pixels that passes through said pixels from the back to the front, and on the other hand by the ambient light that passes through said pixels first from the front to the back, and then this light is reflected by a mirror surface that redirects the light from the back to the front of the pixels.

In these two cases, the brightness of the pixels is controlled individually by a first polarizer placed in front of the pixel, by a second reflective polarizer and by an optoelectronic device such as a transparent liquid crystal placed between the two polarizers, and which rotates the polarization plane of the light to control the absorption of said light by said polarizers.

Preferably, the second polarizer is transfiective on at least a portion of its surface, and the complementary portion is transparent so as to pass the light from a backlighting means. A photovoltaic surface is positioned below the transflective part. When one of the colors of the pixel is to darken, the corresponding liquid crystal, or equivalent, rotates the polarization plane of the light coming from the front so that a larger portion of this polarized light passes through said transflective polarizer. and is absorbed by the photovoltaic surface.

Conversely, when one of the colors of the pixel has to become lighter, the corresponding liquid crystal rotates the polarization axis of the light coming from the front so that a greater part of this polarized light is reflected by said transflective polarizer and comes out. by the front therefore towards the observer.

Pixel brightness control is also done at the same time by controlling the portion of light that passes through said pixels through those of the surfaces of the second polarizer that are transparent.

At this point, when the pixel has to darken, the liquid crystal rotates the plane of polarization of the light that comes from behind so that a larger portion of this polarized light is absorbed by the polarizer of the front.

Conversely, when the pixel has to clear, the liquid crystal rotates the plane of polarization of the light that comes from behind so that a greater part of this polarized light passes through the polarizer of the front and then out to the observer.

So that the effect of the liquid crystal on the darkening or the lightening of a pixel is identical on its reflective part and on its transparent part, the transparent part constitutes a third polarizer for the backlit light, and its axis of polarization is preferably perpendicular to the second polarizer polarization axis.

It is clear that to achieve other desired optical effects, other combinations are possible with respect to the respective polarizations of the transflective polarizer and the transmissive polarizers (the first and the third), and the example described above does not limit in nothing the scope of the basic device of the invention.

In a particular embodiment, the first polarizer consists of a network of parallel photovoltaic strips whose thicknesses and intervals are less than 400 nm. So the first polarizer will absorb 50% of the ambient light by polarizing photovoltaic cells that will produce additional electricity to the device.

In a particular embodiment, the pixels according to the invention are illuminated by the front on the one hand by the ambient light and on the other hand by lateral illumination on the screen whose emission light is guided and distributed over the entire front surface of the screen propagating in the thickness of a transparent plate disposed in front of said screen. In this particular embodiment, part of the light emitted by the side lighting will therefore be absorbed by the photovoltaic cells and will produce electrical energy that can be stored in a battery and / or that can supply at least some of the lamps of the side lighting.

DETAILED DESCRIPTION OF THE INVENTION The invention is now described in more detail with the aid of the description of the indexed FIGS. 1 to 6.

Figure 1 is a sectional diagram of the various components of the device when it is in total reflection mode.

Figure 2 is a sectional diagram of the various components of the device when it is in total transparency mode.

Figure 3 is a sectional diagram of the various components of the device when it is integrated with a transflective type pixel in total light mode.

Figure 4 is a sectional diagram of the various components of the device when it is integrated with a transflective type pixel in total dark mode.

Figure 5 is a sectional diagram of the device when it is illuminated from the front by a light guided by a transparent plate.

Figure 6 illustrates three examples of integration of the device into electronic display screens. With reference to FIGS. 1 and 2, the reflective type display device is composed of a first polarizer (1), a second polarizer (2) which has the characteristic of being transfective, that is to say which reflects light whose polarization axis is not identical to the polarization axis of said polarizer (2) and allows light to pass whose polarization axis is identical to the axis of polarization of the polarizer, a liquid crystal (21a, 21b) or other electro-optical component capable of modifying the polarization axis of the light (11) which passes through it when an electric voltage is applied across electrodes (5, 6), a color filter (F) in general of red (R), green (V) or blue (B), a transparent substrate (3, 4) for encapsulating these different layers, and a photovoltaic cell (8) positioned under the second transfiective polarizer (2), with respect to the incident light (11).

The transfiective polarizer (2) preferably has its polarization axis which is perpendicular to that of the first polarizer (1). The ambient light (11) which enters the device is polarized at the passage of the first polarizer (1), then passes through the color filter (F) and the liquid crystal which is either in a neutral state (Figure 1, 21a) so that the polarized incident light (11) is not modified, is entirely reflected on the surface of the second polarizer (2) and comes out of the device (12a), ie the crystal liquid is in an active state (Figure 2, 21b) of so that the polarized incident light (11) is modified and for a portion (14) passes through the second polarizer (2) and for another portion (12b) is reflected on its surface and spring of the device.

The portion of light (14) passing through the second transfiective polarizer (2) illuminates the photovoltaic cell (8) which is placed below. The portion of light (14) received by the photovoltaic cell (8) therefore depends on the state in which the device is positioned, namely either in total light reflective mode (FIG. 1) or in partial dark absorption mode (FIG. 2), or in total dark absorption mode (not shown).

The portion of light (14) received on average by the photovoltaic cell (8) will therefore depend on the average brightness of the images that will be displayed, namely that the more the images will comprise dark pixels and the more light (14) received by the photovoltaic cell (8) will be important.

Figures 3 and 4 illustrate a particular embodiment in which the photovoltaic display device is both transfiective and backlit. It is composed of a first polarizer (1), at least a second transfiective polarizer (2) under which is positioned a photovoltaic cell (8), a third polarizer (9), a liquid crystal (21a, 21b ) placed between the first polarizer (1) and the second transfiective polarizer (2) and a backlight light source (10) placed behind the third polarizer (9), so that the light (13a, 13b) emitted by the source of the backlight (10) is polarized through the third polarizer

(9), then passes through the liquid crystal (21a, 21b), then partially passes through the first polarizer (1) according to its polarization axis and therefore depending on the activation state of the liquid crystal (21a, 21b) .

This backlighting function of the pixel via the first polarizer (1) and the third (9) polarizer is complementary with the reflective lighting function of the pixel via the first polarizer (1) and the second polarizer transfiective (2) which operate according to the principle of Figures 1 and 2 already described above (the substrates, filter and electrodes are not illustrated for the sake of clarity in Figures 3 and 4).

The polarization axes of the three polarizers are preferably positioned so that the polarization axes of the first polarizer (1) and the second polarizer (2) are perpendicular and for the polarization axes of the first polarizer (1) and the third polarizer ( 9) are parallel, so that when the liquid crystal is not active (Figure 3, 21a) the ambient light (11) is reflected (12a) by the second polarizer (2) and the light (13a) emitted by the retro lighting

(10) completely traverses the first polarizer (1), and so that when the liquid crystal is active (Figure 4, 21b) the ambient light (11) is only partially reflected (12b) by the second polarizer (2) and the light (13b) emitted by the backlight (10) only partially crosses the first polarizer (1).

According to this configuration of the three polarizers, the activation of the liquid crystal (21b) causes both the darkening (12b) of the ambient light (11) and the reduction of the light (13b) of the backlight (10). which effectively controls the brightness of the pixel regardless of the ambient brightness.

It should be noted that it is possible to alternatively use a single polarizer and cholesteric LCD pixels, but their speed of reactivity is much lower LCDs used here (about 0.7 seconds for cholesteric, and less than 10 milliseconds for standard LCDs).

Another variant of the reflective and photovoltaic display device consists in replacing the first polarizer (1) by a polarizer which will be reflective on its rear face. In this case the backlighting light which will not cross the first reflective polarizer will be reflected (Figure 4, reference 15) to the second polarizer (2) and partially illuminate the photovoltaic cell (8), which will increase its efficiency.

FIG. 5 illustrates a particular embodiment in which a light source (16) is injected into the thickness of a transparent plate (17) which is positioned on the front of a photovoltaic reflective display screen according to FIG. invention. Only three juxtaposed devices having red (R) green (V) and blue (B) color filters have been drawn in this figure. One of the faces of the transparent plate is optically structured, for example by a network of scratches, lenses or prisms (not shown) so as to bring out the light (24) which propagates in the thickness of the plate (17). ) to the front of the screen pixels. This illumination (24) of the pixels by the front face passes through the first polarizer (1), the color filter (R, V, B) and the liquid crystal (21a, 21b, 21c) of each pixel and is more or less reflected ( 12a, 12b) on the surface of the second transflective polarizer (2) as a function of the polarization angle of each light beam (23a, 23b, 23c) resulting from the activity of said liquid crystals (21a, 21b, 21c).

Light not reflected by the second reflective polarizer (2) passes more or less said polarizer (2) according to its polarization plane and then illuminates the photovoltaic cell (8) which is placed behind said polarizer (2). This particular embodiment also shows that a single photovoltaic cell (8) as well as a first single polarizer (1) and a second single transflective polarizer (1) may be common to several pixels, or even mutated for all the pixels. of the display screen, which in this case avoids the many welds necessary to form the electrical assembly of a plurality of photovoltaic cells. FIG. 6 illustrates that the reflective and photovoltaic display device according to the invention can be integrated into any device intended to display an electronic image which will be illuminated by solar ambient light (22) or artificial light, such as for example a mobile telephone (18), an electronic book (19) or a computer (20), or else other examples (not shown): a GPS, a watch, a billboard, a commercial sign, a sign, a television.

We now describe a concrete example of embodiment: the display screen of an electronic book (Figure 6, reference 19) is rectangular, made 15 x 20 cm, and is composed of a multitude of colored reflective pixels and positioned according to an organized mesh network of vertical and horizontal rectilinear lines. Each pixel (Figure 5) is composed of three juxtaposed devices, rectangular size 50 per 100 microns, each of them having a different color filter, red (R), green (V) and blue (B). Each color filter (R, G, B) is encapsulated in a stack of optical layers (FIG. 1) comprising, from below: a photovoltaic surface (8), a transflective rear polarizer (2), a glass substrate (4) ), a rear electrode (6), a crystal liquid (21a), a front electrode (5), a color filter (F), a glass substrate (3) and another polarizer (1) or front polarizer. The bottom polarizer (2) is transreflective and is composed of an array of parallel aluminum strips spaced 250 nm apart which causes the linear polarization parallel to said bands by 50% of the natural light that passes through it and causes the rectilinear polarization at 90 ° of said strips of 50% of the natural light that it reflects. The first polarizer (1) is an organic polarizer that absorbs 50% of the natural light that passes through it. Both polarizers cover the entire surface of the screen and are positioned so that their polarization axes are perpendicular. When the screen is black, completely nonreflective, the photovoltaic cell (Figure 5, reference 8) receives a maximum of ambient light (22) or about 40% of it, the rest of the light not received by the cell (8) being absorbed by the other layers of the device and in particular by the first polarizer (1). When the screen (19) is white, all reflective, the photovoltaic cell (Figure 5, reference 8) receives a minimum of ambient light (22) about 4% of the latter, the rest of the light not received by the cell (8) being largely reflected by the second reflective polarizer (2) and absorbed by the first polarizer (1). The successive display of a multitude of colored images will cause an average transparency of the device for the ambient light which will be of the order of 22%, which corresponds to an average between a maximum transparency of 40% and a minimum transparency of 4. %. This 22% of the ambient light will therefore be received by the photovoltaic cell which will transform this energy into electricity. ADVANTAGES OF THE INVENTION

Ultimately the invention meets the goals set by allowing to integrate in a reflective or transflective display screen a larger photovoltaic surface without changing the visual quality of the images displayed.

Claims

CLAIMS 1 - Device for controlling the brightness and transparency of one or more pixels of a display system, wherein each pixel comprises:

a first rectilinear polarizer (1) of transmissive type, having a first axis of polarization of the light and arranged in front of the pixels in the optical path;

a second rectilinear polarizer (2) of transflective type, having a second axis of polarization of the light, and disposed behind the first polarizer;

a photovoltaic surface (8) disposed behind said second polarizer;

an optoelectronic means (21a, 21b) capable of modifying the plane of polarization of the light passing through it, so as to vary on the one hand the quantity of light that will pass through the second polarizer and illuminate said photovoltaic surface and the other hand the amount of light that will be reflected by the second polarizer to emerge from the pixel,

- characterized in that it further comprises a third polarizer (9) and a backlight light source (10) placed behind said third polarizer, so that a portion of the light (13a, 13b) emitted by the The backlighting source (10) is polarized by passing through the third polarizer (9) and then passes successively through said optoelectronic means (21a, 21b) and said first polarizer (1).

2 - Device according to claim 1, characterized in that the amount of light emerging from the first polarizer (1) is a function of the activation state of said optoelectronic means (21a, 21b).

3 - Device according to claim 1 or claim 2, characterized in that the amount of light passing through the second polarizer (2) varies depending on the plane of polarization of the incident light and the active or passive state of said optoelectronic means (21a, 21b), between a total reflection by the second polarizer when the plane of polarization of the light from the first polarizer is perpendicular to the polarization axis of the transfiective polarizer, and a total transmission when the plane of polarization of the light from the first polarizer is parallel to the polarization axis of the second transfiective polarizer. 4 - Device according to one of the preceding claims, characterized in that the second transfiective polarizer is dichroic and serves as a color filter (F).

5 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that the second polarizer (2) transfiectif is composed of electrically parallel conductive strips, preferably metallic, carbon or graphene, the thicknesses and the intervals between them are less than 400 nm.

6 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that when the first polarizer and the second polarizer have their perpendicular axes of polarization and the optoelectronic means (21) is in a neutral state, the incident light (11) which enters the device is polarized at the passage of the first polarizer (1), then passes through the color filter (F) and the optoelectronic means, then is reflected in full on the surface of the second polarizer (2) and spring of the device (12a).

7 - Reflective and photovoltaic display device according to one of claims 1 to 5, characterized in that when the first polarizer (1) and the second polarizer (2) have their perpendicular axes of polarization and the optoelectronic means (21 ) is in an active state, the polarized incident light (11) is modified and for a part (14) passes through the second polarizer (2) and illuminates the photovoltaic cell (8), and for another part (12b) is reflected in its surface and spring device. 8 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that the second transfiective polarizer (2) contains at least one zone of total transparency through which polarized light passes from the back to the front of the device, said polarized light being emitted by said backlighting means (10) which passes successively through said third polarizer ( 9), said electro-optical device (21) and said first polarizer (1).

9 - Display device according to claim 8, characterized in that the polarization axes of the three polarizers (1, 2, 9) are preferably positioned so that the polarization axes of the first polarizer (1) and the second polarizer ( 2) are perpendicular and that the polarization axes of the first polarizer (1) and the third polarizer (9) are parallel, so that when the optoelectronic means (21) is not active, the ambient light (11) is reflected ( 12a) by the second polarizer (2) and the light (13a) emitted by the backlighting means (10) passes completely through the first polarizer (1), and so that when the optoelectronic means (21) is active, the light ambient (11) is reflected only partially (12b) by the second polarizer (2) and the light (13b) emitted by the backlight (10) only partially crosses the first polarizer (1).

10 - Device according to any one of the preceding claims, characterized in that said electro-optical device (21) is of LCD type ("Liquid

Crystal Display ").

11 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that said first polarizer (1) is reflective on its side facing said second polarizer (2).

12 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that said first polarizer (1) consists of an array of parallel photovoltaic strips whose thicknesses and intervals are less than 400 nm. 13 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that said display device is covered with a transparent plate (17) traversed in its thickness by a light injected by one of its edges, said plate being able to illuminate the front face of the pixels of the device.

14 - Reflective and photovoltaic display device according to claim 13, characterized in that said transparent plate (17) is structured on at least one of its faces by a network of stripes, lenses or prisms so as to redirect the light who travels to the front of the pixels of the device.

15 - Reflective and photovoltaic display device according to one of the preceding claims, characterized in that all or a portion of all its photovoltaic surfaces form a single photovoltaic cell.

16 - Apparatus provided with a display device, especially of the mobile phone type, electronic book, computer, GPS terminal, watch, billboard, commercial sign, sign, television, characterized in that it comprises at least one Reflective and photovoltaic display device according to any one of the preceding claims.