JP2000305077A - Solar battery laminated type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make unprecedented high power generating efficiency and high display quality compatible with each other by providing a solar battery on the rear side of a liquid crystal display panel comprising a liquid crystal cell and a selective reflection plate which resolves colors for a reflective display and for transmissive power generation. SOLUTION: The solar battery laminated type liquid crystal display device is constructed by arranging a red color polarizing plate 1 on the incident side of a liquid crystal cell 2 and a selective reflection plate 3 which reflects blue or green light or a composition of blue and green light on the outgoing side of the liquid crystal cell 2. Furthermore, a solar battery 5 having characteristics to generate more power with red light than with blue or green light is arranged on the rear side of a liquid crystal display panel 4 so as to attain a construction which reduces lowering of power generating efficiency by diminishing loss due to adsorption of the red light having the utmost contribution to the power generation by the solar battery 5 even when a liquid crystal display mode such as a TN or an STN mode is utilized for the liquid crystal panel 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display which is equipped with a solar cell capable of supplying electric power by photoelectrically converting a part of incident light, and which can be used for accessories, watches, calculators, radios, small portable devices and the like. Related to the device.

[0002]

2. Description of the Related Art In recent years, the power consumption of LSIs used in small portable electronic devices and the like has been reduced, so that conventional storage batteries have been replaced with solar cells as power supplies. In the market today, watches, calculators,
Small portable devices such as radios have been sold.

The configuration of a small portable electronic device incorporating a conventional solar cell will be described below. FIG. 2 shows an external view of the card type calculator. As shown in the figure, a conventional card-type calculator includes a reflective LCD 6, a solar cell unit 7, and a case 8 in a case 8.
An input key unit 9 is provided.

A solar cell section is laminated on the back side of the reflection type LCD of the card type calculator shown in FIG. 2, so that the presence of the solar cell from the front of the electronic equipment cannot be understood from the outside.
A method has been proposed in which a solar cell can be used in the area of a CD.

In the configuration described in Japanese Patent Application Laid-Open No. 62-237429, a solar cell is arranged in place of the reflection plate of the reflection type LCD. Also, Japanese Patent Application Laid-Open No. 60-147720
In the configuration described in Japanese Patent Application Laid-Open Publication No. H10-209, a selective reflection filter and a solar cell are sequentially provided behind a display body layer that performs display in a transparent state and a scattering state.

Japanese Patent Application Laid-Open No. 60-147718 discloses a display element, a solar cell, and a region that transmits at least part of the wavelength of light contributing to power generation of the solar cell, and reflects other wavelength regions. A configuration provided with a colored layer is described. As the coloring means layer, a cholesteric liquid crystal obtained by microscopically encapsulating a cholesteric liquid crystal and applied by dispersing in a binder, or a cholesteric polymer sheet is used.

[0007]

Conventionally, a part of light incident on a liquid crystal display panel is used for display, and a part of the light is transmitted through the liquid crystal display panel to enter a solar cell installed on the back of the liquid crystal display panel. However, the configuration of the solar cell stack type liquid crystal display device that can use the electric power generated by the solar cell has the following disadvantages.

For example, the configuration described in Japanese Patent Application Laid-Open No. 60-147720 uses a scattering type liquid crystal mode which does not require the use of a polarizing plate in a liquid crystal display panel. However, there is no duty driving capability of the scattering type liquid crystal mode, and there is a drawback that the display capacity cannot be increased by simple matrix driving. In addition, if active driving is performed by a TFT or the like, the cost is increased, and it is desirable to realize a method capable of simple matrix driving.

To solve the above problem, Japanese Patent Laid-Open No. 62-237
The method disclosed in Japanese Patent No. 429 uses a liquid crystal mode using two polarizing plates, and thus has a configuration capable of duty driving such as a TN mode or an STN mode. However, since a solar cell is also used as the reflector, the brightness when displaying is darkened.

In order to solve the above problem, Japanese Patent Application Laid-Open No. Sho 60-147
No. 718 discloses a configuration in which a selective reflection layer such as a cholesteric polymer sheet is provided between a display element and a solar cell to provide a function of a reflection plate and improve brightness when displaying. I have. However, when a liquid crystal mode capable of duty driving such as TN mode or STN mode is used for the display element, the power generated by the solar cell is greatly reduced in power generation efficiency as compared with a case where the solar cell and the display element are not stacked. Let it.

The reason why the power generation efficiency is greatly reduced is that when a liquid crystal mode such as TN mode or STN mode is used, 50% of the incident light is absorbed by the incident side polarizing plate.

As another problem, when a display element and a solar cell are stacked and light is absorbed by the solar cell to display black, a pattern of cells connected in series of the solar cells can be seen. This appearance of the cell pattern lowers the display quality of the liquid crystal display panel.

As described above, in the prior art, when a liquid crystal mode such as TN mode or STN mode is used for a liquid crystal display panel, a selective reflection layer such as a cholesteric polymer sheet is provided between the liquid crystal display panel and the solar cell. However, even if the brightness is improved by providing the function of a reflector by providing the reflector, the power generation efficiency of the solar cell is greatly reduced. In addition, when the solar cell absorbs light and displays black, the pattern of cells connected in series of the solar cell is visible, and the display quality of the liquid crystal display panel is deteriorated. It has been difficult to stack and use a liquid crystal display panel and a solar cell on a small portable device.

[0014]

In order to solve the above-mentioned problems, in the solar cell stack type liquid crystal display device of the present invention, the configuration of the liquid crystal display panel is at least as follows. The liquid crystal display panel has a configuration in which a liquid crystal cell and a red color polarizing plate are provided on the incident side of the liquid crystal cell, and a selective reflection plate for reflecting blue or green or a combined color of blue and green is provided on the exit side of the liquid crystal cell.
In addition, a solar cell having a characteristic of generating more power with red light than blue or green light is disposed behind the liquid crystal display panel, and even if a liquid crystal mode such as TN mode or STN mode is used for the liquid crystal display panel, the solar cell can be used. The configuration is such that loss due to absorption of red light that contributes most to power generation can be reduced, thereby reducing power generation efficiency.

Further, the selective reflection plate can use a cholesteric film. The cholesteric film selectively reflects blue or green or a combined color of blue and green according to the direction of rotation of circularly polarized light and transmits red light without absorption. Power generation can be performed efficiently.

Further, the selective reflection plate can use a dielectric multilayer mirror. Since the dielectric multilayer mirror reflects blue or green or a combined color of blue and green and transmits red light without absorption, it can efficiently generate power using solar cells while having the function of a reflector of a liquid crystal display panel. .

Further, a hologram is used for the selective reflection plate. Since the hologram reflects blue or green or a combined color of blue and green and transmits red light without absorption,
Power generation by the solar cell can be performed efficiently while having the function of the reflector of the liquid crystal display panel.

Further, in the selective reflection plate, a light diffusion layer is arranged on the surface on which light is incident, and a slight diffusion is given to the selectively reflected light, thereby improving the visibility of display.

Further, the problem of pattern appearance occurring in cells connected in series has been solved by using a single cell for the solar cell. With respect to the power generation voltage drop in a single cell, it was possible to obtain a voltage equivalent to that of cells connected in series by a booster circuit.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of the solar cell multi-layer liquid crystal display device having the above-described configuration, which can reduce a decrease in power generation efficiency even when a liquid crystal mode such as a TN mode or an STN mode is used, will be described.

The basic principle of the present invention is that the spectrum of light contributing to power generation of a solar cell and the spectrum of light used for display on a liquid crystal display panel can be made compatible between the power generation efficiency of the solar cell and the visibility of the liquid crystal display panel. It is to divide by condition.
FIG. 8 shows emission spectra of various light sources. FIG.
Indicates spectral sensitivity characteristics of various solar cells.

In the present invention, in the spectra of various light sources shown in FIG. 8, red light including near-infrared light is hardly used for display on the liquid crystal display panel, and blue and green light are used for display on the liquid crystal display panel. Used to display. Red light including near-infrared light is used for power generation by solar cells. As shown in FIG.
C-Si system and CdS / CdTe from near infrared to red
Since the sensitivity of the solar cell is high, the power generation efficiency can be maintained high. In an a-Si solar cell, it is difficult to use near-infrared light. However, since it has a peak sensitivity at 600 nm, red light can be used for power generation.

In the present invention, for separating the spectrum of light contributing to power generation of the solar cell and the spectrum of light used for display on the liquid crystal display panel, a red color polarizing plate and blue or green or blue and green Is realized by a selective reflection plate that reflects the composite color of. FIG. 5 shows the spectral transmittance of the red color polarizing plate used in the present invention. The red color polarizing plate has a transmittance of about 90% or more because it does not have uniaxial absorption as a polarizing plate for red light of 600 nm or more and near infrared light.

The selective reflection plate selectively reflects blue or green or a combined color of blue and green, and transmits red light from near-infrared light without absorbing it. Therefore, red light from near-infrared light can be efficiently incident on the solar cell by the red color polarizing plate and the selective reflection plate. FIG. 6 is an example showing the transmittances of blue and red when green is selectively reflected.

The light of blue or green or a combined color of blue and green selectively reflected by the selective reflection plate is used for display on a liquid crystal display panel.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a basic configuration of a solar cell stack type liquid crystal display device. The red color polarizing plate 1 has an elliptically polarizing plate integrated with a retardation plate and a transparent adhesive bonded to a liquid crystal cell 2. The liquid crystal cell 2 has a general reflection type LCD.
An STN mode liquid crystal layer was manufactured by a known method in a gap in which a patterned transparent electrode was formed in two opposing transparent substrates used in Example 1. As a liquid crystal mode to be used, a TN liquid crystal mode or a ferroelectric liquid crystal mode may be used in addition to the STN liquid crystal. Further, it may be used in combination with an active element such as MIM or TFT.

A selective reflection film of a cholesteric polymer that selectively reflects green is adhered to the liquid crystal cell 2 on the selective reflection plate 3 with a transparent adhesive. Sumitomo 3M Limited's DBEF (Dual Brig) that selectively reflects green instead of cholesteric polymer selective reflection film
HT Enhancement Film) may be used.

A light diffusion layer is provided between the selective reflection plate 3 and the liquid crystal cell 2. As the light diffusion layer, a transparent adhesive having a diffusibility may be used, or IDS-21 of Dai Nippon Printing Co., Ltd. may be attached.

Further, instead of the elliptically polarizing plate integrated with the retardation plate used for the red color polarizing plate 1 and the transparent adhesive, the red color polarizing plate 1 is used alone and the retardation plate is connected to the liquid crystal cell 2. The same effect can be obtained even when used between the selective reflection plates 3. A solar cell 5 is provided behind a liquid crystal display panel 4 which is basically composed of a red color polarizing plate 1, a liquid crystal cell 2, and a selective reflection plate 3, and a retardation plate and a light diffusion layer are provided by the red color polarizing plate 1.
It is sufficient if it is between the and the selective reflection plate 3.

As the solar cell 5, an amorphous Si solar cell was used. In addition to amorphous Si solar cells, monocrystalline Si solar cells, polycrystalline Si solar cells, CdS / Cu2S
A solar cell, a CdS / CdTe solar cell, a GaAs-based solar cell, or the like may be used.

The optical characteristics of the solar cell stack type liquid crystal display device having the above-described basic configuration, which achieve both high power generation efficiency and display quality, which have not been achieved in the past, will be described below. FIG. 3 shows a liquid crystal cell 2
FIG. 3 is a diagram for explaining optical characteristics when no voltage is applied to FIG. The incident light will be described separately for incident light 10 of blue (B) and green (G) and red (R) 11 including near infrared.

The blue (B) and green (G) incident light 10 is uniaxially absorbed by the red color polarizing plate 1 and becomes blue (B) and green (G) linearly polarized light 12. When the red color polarizing plate 1 is integrated with the retardation plate, it becomes elliptically polarized light (linearly polarized light is shown in the figure). In this state, about 4 of the incident light
The light intensity is about 0%.

Further, blue (B) and green (G) linearly polarized light 1
2 changes the polarization state in the liquid crystal cell 2 and turns into blue (B) and green (G) circularly polarized light 14. In this state, the light intensity hardly changes. The blue (B) and green (G) circularly polarized lights 14 are separated from the cholesteric polymer selective reflection film having a selective reflection wavelength into the green right circularly polarized light, which is the selective reflection plate 3, with almost no loss, and are reflected as reflected light. It becomes circularly polarized light 15 of green (G) and circularly polarized light 17 of blue (B) as transmitted light.

The green (G) circularly polarized light 15 is diffused by a light diffusion layer between the selective reflection plate 3 and the liquid crystal cell 2 to realize a bright state of the display device. The blue (B) circularly polarized light 17 is absorbed by the solar cell 5 and contributes to power generation.

On the other hand, red (R) 11 containing near-infrared light of incident light
Is red (R) 13 which is not uniaxially absorbed by the red color polarizing plate 1 and contains near-infrared light which is not polarized. Further, the red (R) 13 containing near-infrared light becomes the red (R) 16 containing near-infrared light that is not polarized and does not change its polarization state in the liquid crystal cell 2.
In this state, the light intensity hardly changes. The red (R) 16 containing near-infrared light passes through the cholesteric polymer selective reflection film as the selective reflection plate 3 with almost no loss,
Red (R) 18 including near infrared. Red (R) including near infrared
Numeral 18 is absorbed by the solar cell 5 and contributes to power generation.

Here, the red color polarizing plate 1 and the liquid crystal cell 2
When the selective reflection plate 3 is arranged to reduce the Fresnel reflection without passing through the air layer, the red (R) 11 including the near infrared of the incident light becomes 90% even when reaching the red (R) 18 including the near infrared. Light intensity is obtained. This is because the red color polarizing plate 1 eliminates uniaxial absorption and eliminates reflection on the selective reflection plate 3, which contributes to a large amount of power.

Similarly, FIG. 4 is a view for explaining the optical characteristics when a voltage is applied to the liquid crystal cell 2. The incident light will be described by dividing it into incident light 10 of blue (B) and green (G) and red (R) 11 including near-infrared rays.

The counterclockwise circularly polarized light 19 of blue (B) and green (G) transmitted through the liquid crystal cell 2 when a voltage is applied is converted into a cholesteric polymer having a selective reflection wavelength in green right circularly polarized light as the selective reflection plate 3. The light is transmitted through the selective reflection film with almost no loss, becomes the counterclockwise circularly polarized light 20 of blue (B) and green (G), is absorbed by the solar cell 5, and contributes to power generation.

As compared with FIG. 3, the power generation efficiency is higher because the green (G) wavelength component contributes to power generation. The display is a black display since there is no reflected light. On the other hand, red (R) 11 including the near infrared of the incident light contributes to power generation as in FIG.

The reason that the green (G) wavelength component can contribute to power generation is due to the circular dichroism of the cholesteric polymer selective reflection film. When a dielectric mirror that selectively reflects the same green color or a hologram of the Lippmann system is used for the selective reflection plate 3, the wavelength component of green (G) cannot contribute to power generation.

The solar cell stack type liquid crystal display device thus manufactured was observed under the conditions of 200 lx fluorescent lamp illumination.
Then, in the region where the selection voltage was applied, the incident white light was absorbed by the solar cell and appeared black. In the region where the non-selection voltage was applied, the incident white light was selectively reflected and scattered and observed in green.

Next, the power generation capacity of the solar cell stack type liquid crystal display was verified. For the power generation capacity of solar cells alone,
In the region where the selection voltage is applied, 60% is shown, and in the region where the non-selection voltage is applied, 45% is shown. However, in a normal display, the entire power is not turned on, and the power generation amount fluctuates depending on the area ratio of the ON display.

Next, the solar cell stack type liquid crystal display device of the present invention was mounted on a digital timepiece. The area of the display section has been increased, and the display has become easier to see. In addition, the lack of darkened solar cells from the front panel eliminated the clunkiness in design. Furthermore, when the polarization transmission axis of the red color polarizing plate is changed to be used for normally black display, the cell pattern of the solar cell appears. No green digital display on black background can be realized. The voltage obtained from a single cell solar cell is on the order of 0.6 volts. The digital clock can be operated by converting the voltage to 1.5 volts with a booster circuit.

The selection color of the selective reflection plate 3 is not limited to green,
Blue or a combination of blue and green may be used. FIG. 9 is a chart showing the relationship between the selected color, the display, and the power generation efficiency. FIG.
FIG. 9 shows the relationship between selected colors, display and power generation efficiency when a cholesteric polymer selective reflection film is used in FIG.
(B) shows the relationship between the selected color, the display, and the power generation efficiency when a dielectric mirror or a Lippmann hologram is used.

[0045]

As described above, the present invention relates to a red color polarizer having no uniaxial absorption in the near-infrared to red wavelength region and a liquid crystal cell of a liquid crystal mode capable of duty driving such as STN mode and TN mode. By adopting a configuration in which a solar cell is provided behind a liquid crystal display panel consisting of a reflective display and a selective reflector that separates colors for transmission power generation, it has achieved both unprecedented high power generation efficiency and display quality. .

Further, the power generation efficiency was further improved by matching the wavelength range from near infrared to red, which has high spectral sensitivity of the solar cell, with the wavelength range having no uniaxial absorption of the polarizing plate. In addition, by using the circular dichroism of the cholesteric polymer selective reflection film as the selective reflection plate, the selectively transmitted light was used for power generation, and the power generation efficiency was further improved.

In addition, when the solar cell absorbs light and displays black, the problem that the pattern of cells connected in series in order to obtain a voltage of 1.5 volts from the solar cell can be seen is solved. By converting the voltage of 0.6 volts obtained from the solar cell to 1.5 volts by a booster circuit, the cell pattern was not seen and the display quality of the liquid crystal display panel was improved.

As described above, the solar cell multi-layer liquid crystal display device of the present invention maintains a high photovoltaic power even when using a liquid crystal mode capable of duty driving such as STN mode and TN mode, and furthermore, the solar cell The pattern has no visual appearance, and has a display capability with excellent aesthetic potential. Therefore, when used as watches, other displays for portable electronic devices, and decorative articles, it is effective in differentiating the design, operability, and display capability of the front of the electronic device, which have not existed before.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a basic configuration of the present invention.

FIG. 2 is an external view of an example of a card-type calculator incorporating a conventional solar cell.

FIG. 3 is a diagram illustrating optical characteristics when no voltage is applied to the solar cell multi-layer liquid crystal display device of the present invention.

FIG. 4 is a diagram illustrating optical characteristics when a voltage is applied to the solar cell multi-layer liquid crystal display device of the present invention.

FIG. 5 shows a spectral transmittance of a red color polarizing plate used in the present invention.

FIG. 6 is an example showing the transmittance of blue and red when the solar cell multi-layer liquid crystal display device of the present invention selectively reflects green.

FIG. 7 is an example of the spectral sensitivity of a solar cell used in a solar cell stack type liquid crystal display device of the present invention.

FIG. 8 shows emission spectra of various light sources.

FIG. 9 is a table showing a relationship between a selected color, display, and power generation efficiency.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 red color polarizing plate 2 liquid crystal cell 3 selective reflection plate 4 liquid crystal display panel 5 solar cell 6 reflective LCD 7 solar cell unit 8 case 9 input key unit 10 incident light 11 red (R) including near infrared of incident light 12 Linearly polarized light of blue (B) and green (G) 13 Red (R) including near-infrared which is not polarized 14 Circularly polarized light of blue (B) and green (G) 15 Circle of green (G) as reflected light Polarization 16 Red (R) including near-infrared light 17 Blue (B) as transmitted light 18 Red (R) including infrared light 19 Circularly polarized counterclockwise transmitted blue (B) and green (G) 20 Blue (B) ) And green (G) counterclockwise circularly polarized light

Claims (7)

[Claims] 1. A solar cell stack type liquid crystal display device in which a solar cell is installed on the back of a liquid crystal display panel, a red color polarizing plate provided on the front side of the liquid crystal display panel, and the back side of the liquid crystal display panel. And a selective reflection plate provided in the solar cell stacked liquid crystal display, wherein the selective reflection plate has a characteristic of reflecting blue, green, or a combined color of blue and green. apparatus. 2. The solar cell stack type liquid crystal display device according to claim 1, wherein the solar cell has a characteristic of generating more power with red light than blue or green light. 3. The solar cell multi-layer liquid crystal display device according to claim 1, wherein the selective reflection plate is a cholesteric film. 4. The solar cell multi-layer liquid crystal display device according to claim 1, wherein said selective reflection plate is a dielectric multilayer mirror. 5. The solar cell stack type liquid crystal display device according to claim 1, wherein said selective reflection plate is a hologram. 6. The solar cell stack type liquid crystal display device according to claim 1, wherein the selective reflection plate has a light diffusion layer disposed on a surface on which light is incident. 7. The solar cell stack type liquid crystal display device according to claim 1, wherein the solar cell is a single cell.