Display device

Abstract

To provide a display device in which display quality can be improved in both of a non-light emission type and a self-luminous type while having a simple structure and control mechanism.SOLUTION: A display device comprises: a display unit; and a lighting control unit that is arranged at a light-emitting surface side of the display unit. In the lighting control unit, the larger the visible light intensity incident from the display unit becomes, the larger the permeability of visible light becomes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The following disclosure relates to a display device.

Background Art

[0002] Display devices are widely used in electronic devices such as televisions, smartphones, tablet terminals, and car navigation systems. In recent years, display devices used are roughly classified into non-emissive display devices that control a light source of a backlight without the display element itself emitting light, such as liquid crystal displays, and self-emissive display devices in which the display element itself, such as an organic EL display, emits light.

[0003] Display devices have problems related to display quality depending on the display format. For example, non-emissive display devices such as liquid crystal displays require a light source such as a backlight because the display element does not emit light, and there is a problem that the contrast is lowered due to light leakage of the light source. In response to this problem, a dual cell in which a liquid crystal panel for dimming is disposed between the backlight and the liquid crystal panel has been proposed (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the dual cell has a problem that the cost increases because it requires a complicated structure and control for performing dimming on a pixel-by-pixel basis. On the one hand, although self-emitting display devices such as organic EL displays can achieve high-contrast displays compared to non-emitting display devices, when displaying the first gradation when the black display is at the 0th gradation (gray scale (GL) = 1), the luminance is too high, and there is a problem that it is difficult to adjust the transmittance change (gamma curve) according to the gradation. For this problem as well, it is conceivable to perform dimming on a pixel-by-pixel basis similar to a dual cell, but it requires a complicated structure and control. Therefore, there is a need for a method to improve the display quality of both non-emitting and self-emitting display devices with a simpler structure and control.

[0006] The present invention has been made in view of the above situation, and an object thereof is to provide a display device that can improve the display quality in both non-emitting and self-emitting types while having a simple structure and control mechanism.

Means for Solving the Problems

[0007] This disclosure is composed of the following Disclosures 1 to 7. Hereinafter, this disclosure will be described in detail. [Disclosure 1] A display device comprising a display unit and a dimming unit disposed on the light-emitting surface side of the display unit, wherein the dimming unit is a display device in which the transmittance of visible light increases as the intensity of visible light incident from the display unit increases. [Disclosure 2] The display device according to Disclosure 1, wherein the display unit is a liquid crystal display having a pair of polarizing plates and a liquid crystal layer sandwiched between the pair of polarizing plates. [Disclosure 3] The display device according to Disclosure 1, wherein the display unit is a self-emitting display. [Disclosure 4] The dimming unit includes a photochromic material layer containing a photochromic material and an ultraviolet front light disposed on the photochromic material layer, wherein the photochromic material is in a state of transmitting visible light when visible light is incident from the display unit, and is in a state of blocking visible light when ultraviolet light is incident from the ultraviolet front light. The display device according to Disclosure 1, 2, or 3. [Disclosure 5] The photochromic material is oriented in a certain direction in the photochromic material layer, The display device according to Disclosure 4, wherein the photochromic material layer has an absorption axis parallel to the polarization axis of the light emitted from the display unit. [Disclosure 6] The light control unit is a normally white type display element including a TFT substrate, The TFT substrate has a drain electrode, a source electrode, and a photoreistor or a photodiode disposed at a position where visible light from the display unit is incident, The photoreistor or the photodiode connects the drain electrode and one of the source electrodes adjacent to the drain electrode, and has a light shielding layer disposed on the photoreistor or the photodiode. The display device according to Disclosure 1, 2, or 3. [Disclosure 7] The light control unit is a normally white type display element including a TFT substrate, The TFT substrate has a semiconductor layer disposed at a position where visible light from the display unit is incident, and a source electrode and a drain electrode connected through the semiconductor layer, and has a light shielding layer disposed on the semiconductor layer. The display device according to Disclosure 1, 2, or 3. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a display device that can improve display quality in both non-emissive type and self-emissive type while having a simple structure and a control mechanism. [Brief Description of the Drawings]

[0009]

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Mode for Carrying Out the Invention

[0010] Hereinafter, a display device according to an embodiment of the present invention will be described. The present invention is not limited to the content described in the following embodiments, and design changes can be appropriately made within the scope that satisfies the configuration of the present invention.

[0011] (Embodiment 1) FIG. 1 shows a schematic diagram of a display device according to Embodiment 1. The display device according to Embodiment 1 includes a display unit 100 and a light control unit 200 disposed on the light-emitting surface side of the display unit 100. The light control unit 200 has a property that the transmittance of visible light increases as the intensity of visible light incident from the display unit 100 increases (hereinafter, visible light is simply referred to as light). By providing such a light control unit 200 on the display unit, strong light emitted from the white-display pixels of the display unit 100 is transmitted, while weak light leaking from the black-display sub-pixels is blocked, so that the contrast of the display device can be enhanced. Further, when compared with mini-LEDs that have improved the contrast problem of ordinary liquid crystal displays, since black is tightened more when the light is weak, halos are less likely to occur. Furthermore, in the display device according to Embodiment 1, since the control of the transmittance is performed by the light from the display unit, the contrast can be enhanced with a simpler structure and a simpler control mechanism compared to dual cells. In this specification, "black display" means a display state in which light from the display unit side is blocked or the display unit does not emit light, and "white display" means a display state in which light from the display unit side is transmitted or the display unit is emitting light, including display states of all colors other than black, not limited to white. Also, "visible light" refers to light with a wavelength of 360 nm to 830 nm.

[0012] FIG. 2 shows a schematic diagram illustrating an example of the display of the display unit and the display of the light control unit in the display device according to Embodiment 1. In the display unit 100 of FIG. 2, it is shown that the sub-pixels represented by oblique lines are white displays, and the sub-pixels represented by gray are black displays. When the display unit 100 is in the display state as shown in the left figure of FIG. 2, in the light control unit 200 of the display device according to Embodiment 1, the light control unit (for example, the sub-pixel of A) on the white-display sub-pixel becomes transparent by light and transmits the light. On the other hand, the light control unit (for example, the sub-pixel of B) on the black-display sub-pixel remains opaque because only weak light that leaks to the extent of light leakage reaches it, so that the light leakage of the black display is greatly reduced, and the contrast of the display device can be enhanced. In this specification, "up" means the direction on the observer side in the thickness direction of the display device, and "down" means the direction opposite to the above "up", which is the direction on the back side of the display device.

[0013] When a non-emissive display such as a liquid crystal display is used in the display unit of the display device according to Embodiment 1 and each of the embodiments described later, the contrast can be increased. On the other hand, even when a self-emissive display such as an organic EL display capable of high-contrast display is used, the display quality can be improved. In the case of an organic EL display, when the first gradation is displayed when the black display is the 0th gradation (gray scale (GL) = 1), the luminance may be too high, and it may be difficult to adjust the transmittance change (gamma curve) according to the gradation. In the display device of the present embodiment, by providing the above-described dimming unit, the luminance at the time of GL = 1 can be suppressed, so that the defect of the gamma curve can be reduced.

[0014] The above display unit can use a display (non-emissive display) that controls the light of the backlight without the display element emitting light or a display (self-emissive display) using a self-emissive element. Examples of the non-emissive display include a liquid crystal display having a pair of polarizing plates and a liquid crystal layer sandwiched between the pair of polarizing plates, electro-wetting, electronic paper, and the like. Examples of the self-emissive display include an organic EL display (OLED), a quantum dot LED display, an LED display, and the like.

[0015] Fig. 3 shows a graph for explaining the transmittance characteristics of the light control section of the display device according to Embodiment 1. The material or element used for the light control section of the present embodiment preferably has a transmittance characteristic of blocking light with low intensity and increasing the transmittance as the light intensity increases. Specifically, it is particularly preferable to have a transmittance characteristic in which the light intensity and the light transmittance are linearly proportional, like the straight line shown by the solid line in Fig. 3. However, a transmittance characteristic in which the transmittance rapidly increases from a certain intensity, like the curve shown by the broken line, is also preferable. Further, as shown by the thick broken line, a material having a transmittance characteristic in which the transmittance rapidly increases from a stage where the light intensity is low is preferably not used from the viewpoint of further blocking light leakage.

[0016] Here, specific examples of the effects obtained by using the display device according to Embodiment 1 are shown. When a non-emissive display is used as the display section, an effect of improving the contrast of the display device can be obtained. For example, when a liquid crystal display with a contrast (CR) value of 2000 is used as the display section, and a light control section with a transmittance of 5% for light (0.1 cd / m 2 ) during black display and a transmittance of 50% for light (200 cd / m 2 ) during white display is used, the CR value is improved to 20000. Further, when an emissive display is used as the display section, an effect of reducing the defect of the gamma curve can be obtained. For example, when an organic EL display is used for the display section, the luminance at GL = 1 is 0.01 cd / m 2 in the case of only the display section, whereas by using a similar light control section, the luminance at GL = 1 is reduced to 0.001 cd / m 2 , and the adjustment of the gamma curve becomes easier.

[0017] (Embodiment 2) The display device according to Embodiment 2 has a structure including a photochromic material layer containing a photochromic material and an ultraviolet front light disposed on the photochromic material layer. Further, the photochromic material has a property of being in a state of transmitting visible light when visible light is incident from the display section and being in a state of blocking visible light when ultraviolet light is incident from the ultraviolet front light. Here, FIG. 4 shows a schematic diagram illustrating an example of the display of the display unit and the display of the dimming unit in the display device according to Embodiment 2. In the display unit 100 of FIG. 4, it is shown that the sub-pixels represented by diagonal lines are white displays, and the sub-pixels represented by gray are black displays. When the display unit 100 is in the display state as shown in the left diagram of FIG. 4, in the dimming unit 200 of the display device according to Embodiment 2, the photochromic material (for example, the sub-pixel of A) existing on the white-display sub-pixel becomes transparent by light and transmits the light. On the other hand, the photochromic material on the black-display sub-pixel (for example, the sub-pixel of B) remains opaque because only light with a weak degree of light leakage reaches it. Therefore, the light leakage from the black display of the display unit 100 is greatly reduced by the dimming unit 200, and the contrast of the display device can be enhanced. Further, since the photochromic material layer is irradiated with ultraviolet rays from the ultraviolet front light, when the sub-pixels of the display unit directly below are black displays, that is, when strong light does not hit the photochromic material layer, the photochromic material changes to an opaque state by the ultraviolet rays from the ultraviolet front light and reduces the light leakage until it becomes a white display again. As described above, the display device according to Embodiment 2 can enhance the contrast with a simple structure because it does not require control by a circuit.

[0018] The photochromic material is a material that can switch between a transmission state in which visible light is transmitted and a non-transmission state in which visible light is not transmitted. Preferably, when visible light is incident in the non-transmission state, it switches to the transmission state, and when ultraviolet rays are incident in the transmission state or when the time elapses at room temperature, it has the property of switching to the non-transmission state. Specifically, examples include organic compounds such as diarylethene and inorganic compounds such as TiO2 / Ag nanoparticles.

[0019] The above photochromic material may be oriented such that the photochromic material layer has an absorption axis parallel to the polarization axis of the light emitted from the display unit. By orienting the photochromic material in a certain direction so that the polarization from the display unit coincides with the absorption axis of the photochromic material layer, the luminance in the transmission state can be further increased.

[0020] The above ultraviolet front light only needs to be able to change the above photochromic material from a transmission state to a non-transmission state, and the wavelength and intensity of the irradiated ultraviolet light are appropriately adjusted according to the properties of the above photochromic material. As an example, a UV-C front light can be mentioned. The above ultraviolet front light may irradiate ultraviolet light constantly or irradiate it periodically.

[0021] Here, specific examples of the effects of using the display device according to Embodiment 2 are shown. A display device is fabricated, which includes a display unit composed of a liquid crystal display with a contrast (CR) value of 2000, and a dimming unit including a photochromic material layer using diarylethene as the photochromic material and a UV-C front light. When the transmittance of the dimming unit of the obtained display device was measured, the transmittance of the light (0.1 cd / m 2 ) when the display unit is black-displayed is 6%, and the transmittance of the light (200 cd / m 2 ) when the display unit is white-displayed is 36%. The CR value of the display device has been improved to 12000. In addition, a display device was fabricated in the same manner as the above display device except that the photochromic material was oriented so that the absorption axis of the photochromic material layer coincides with the polarization from the display unit. As a result, the transmittance of the light when the display unit is black-displayed is 10%, and the transmittance of the light when the display unit is white-displayed is 60%, which is higher than that of the non-oriented one. However, by making the absorption axis of the photochromic material layer coincide with the polarization of the display unit, the CR value becomes the same as that of the non-oriented one, which is 12000.

[0022] (Embodiment 3) The display device according to Embodiment 3 has a normally white type display element in which the dimming unit includes a TFT substrate. Here, FIG. 5 shows a top view of the dimming unit in the display device according to Embodiment 3, FIG. 6 shows a cross-sectional view in the X-X' direction of FIG. 5, FIG. 7 shows a cross-sectional view in the Y-Y' direction of FIG. 5, and FIG. 8 shows an equivalent circuit diagram of the dimming unit of the display device according to Embodiment 3. As shown in FIGS. 5 to 7, the dimming unit of the display device according to Embodiment 3 has a structure in which a TFT substrate 210 with a gate insulating layer 212, a photoresistor or photodiode 213 (hereinafter also simply referred to as a photoresistor), a semiconductor layer 214, a source electrode 215, a drain electrode 216, a first interlayer insulating layer 217a, a second interlayer insulating layer 217b, a pixel electrode 218, and an alignment film 219 laminated on a gate electrode 211, and a dimming layer 220 composed of a liquid crystal material 221 and a dye 222 is provided between a counter substrate 230 with a counter electrode 232, an overcoat layer 233, a light-shielding layer 234, and a substrate 235 laminated on an alignment film 231. The photoresistor 213 connects the drain electrode 216 and one of the source electrodes 215 adjacent to the drain electrode 216, and is disposed at a position where visible light from the display unit is incident. The light-shielding layer 234 is disposed on the photoresistor 213. Further, the liquid crystal material 221 and the dye 222 transmit visible light when no voltage is applied and block visible light when a voltage is applied, and the basic state (the state in which only the dimming unit is driven) is an opaque state in which a voltage is applied to all sub-pixels. In the dimming unit of FIGS. 5 to 7, guest-host type liquid crystal is used as the dimming layer, but any material may be used as long as the dimming unit is in a transparent state when no voltage is applied and in an opaque state when a voltage is applied. In FIGS. 6 and 7, the voltage when the dimming layer is opaque is set to 5V and the voltage when it is transparent is set to 0V, but these voltages are not limited as long as the dimming unit can be switched between a transparent state and an opaque state.

[0023] As shown in FIGS. 5 to 8, in the dimming unit according to Embodiment 3, the drain electrode 216 and the source electrode 215 are connected by the photoresistor 213. As shown in FIGS. 6 and 7, in the dimming unit according to Embodiment 3, when light from the display unit is incident on the photoresistor 213 in the sub-pixels (left and right sub-pixels) on the white display, the resistance of the photoresistor 213 decreases and current leaks from the drain electrode 216 to the source electrode 215, and the voltage of the drain electrode 216 decreases. As a result, in the sub-pixel where light is incident on the photoresistor 213, no voltage is applied to the dimming layer 220, the dimming unit becomes transparent, and light from the white-displayed display unit is transmitted. The transparent state continues until light no longer hits the photoresistor 213, that is, until the sub-pixels of the display unit directly below become black display. On the other hand, in the sub-pixel (central sub-pixel) on the black display, the light incident on the photoresistor 213 is weak, and the resistance of the photoresistor 213 does not change so much that current leaks, so the voltage-applied state, that is, the opaque state, is maintained, and light leakage from the display unit is greatly reduced, improving the contrast. Note that although the structure of the display device according to Embodiment 3 is more complex than those of Embodiments 1 and 2, since the switching between the transparent state and the opaque state of the dimming layer is performed by the light of the display unit, it is possible to enhance the contrast with a simpler structure and control compared to the dual cell.

[0024] FIG. 9 shows a schematic diagram showing an example of the display of the display unit and the display of the dimming unit in the display device according to Embodiment 3. In the display unit 100 of FIG. 9, it is shown that the sub-pixels represented by oblique lines are white display and the sub-pixels represented by gray are black display. When the display unit 100 is in the display state as shown in the left figure of FIG. 9, in the sub-pixel of the dimming unit 200 on the white display (for example, the sub-pixel of A), light enters the photoreceptor 213 and the voltage of the drain electrode decreases, so that no voltage is applied to the dimming layer and it becomes a transparent state. On the other hand, in the sub-pixel of the dimming unit 200 on the black display (for example, the sub-pixel of B), since light that can significantly reduce the resistance of the photoreceptor 213 does not reach, the state where a voltage is applied to the dimming layer is maintained and it becomes an opaque state. As a result, light leakage from the display unit 100 in the black display is greatly reduced by the dimming unit, so that the contrast can be improved.

[0025] As described above, the dimming unit in the display device according to Embodiment 3 switches between black display and white display according to the light from the display unit. Therefore, it is necessary to apply a voltage to the entire dimming layer in accordance with the refresh timing of the display unit to set it to a charged state (black display state). Here, FIG. 10 shows a timing chart representing the control of the dimming unit of the display device according to Embodiment 3. In FIG. 10, the voltage change of the sub-pixels (the left and right sub-pixels in FIGS. 5 to 7) where the directly below display unit is in white display is represented. In the gate electrode of the dimming unit of the display device according to Embodiment 3, the voltage is controlled to change from Low to High and then back to Low between the same time as or after the clear signal of the display unit and the same time as or before the start pulse. Also, in the source electrode, the voltage is controlled to change from 0V to a Posi voltage (positive voltage) or a Nega voltage (negative voltage) and then back to 0V between the same time as or after the clear signal of the display unit and the same time as or before the start pulse. At that time, the time when the Posi voltage or the Nega voltage is applied is set to be longer including the time when the gate electrode is High. By performing such control, in the drain electrode, the voltage changes from 0V to a Posi voltage or a Nega voltage (charged state) between the clear signal and the start pulse, that is, during the refresh of the display unit, and the voltage decreases to 0V due to the light from the display unit that becomes white display after the start pulse. Note that when the display unit is in black display, the voltage does not decrease even after the start pulse, and the Posi voltage or the Nega voltage is maintained until the next clear signal is transmitted. Also, the voltage values in FIG. 10 are just examples, and any voltage may be used.

[0026] The above photoresistor and photodiode may be any that can lower the voltage of the drain electrode when light is incident. Examples of the above photoresistor include photoresistors using cadmium sulfide (CdS), amorphous silicon (a-Si), low-temperature polycrystalline silicon (LTPS), etc. Also, examples of the above photodiode include PN-type photodiodes, PIN-type photodiodes, APD-type photodiodes, etc.

[0027] The resistance of the above light resistor only needs to be able to switch the state of the above dimming unit when light hits it, but it is preferably determined to satisfy the following conditions. When the resolution of the above dimming unit is full HD, the time when the voltage becomes almost stable is represented by 5×τ using the RC time constant τ. The RC time constant τ is R×C when the resistance is R and the liquid crystal capacitance is C. Assuming that the above dimming unit is driven at 60 Hz, the stabilization time (5τ) during black display needs to be 1 / 60 s = 16667 μs or more, which is one cycle time, because there must be no leakage of the current of the dimming unit and it must be completely black display. Also, since the RC time constant (5τ) during white display needs to be shorter than the on-time per gate and there must be no leakage of the current of the dimming unit and it must be completely white display (transparent state), 16667 μs / 1080 = 15 μs or less corresponding to the above on-time is required. When calculating the value of the resistance R that satisfies the above stabilization time (5τ) when the above dimming material is a liquid crystal with a liquid crystal capacitance C = 300 fF, the resistance during black display is about 11 GΩ or more, and the resistance during white display is about 10 MΩ or less. Therefore, it is preferable that the resistance value during white display is 1 / 1000 or less of the resistance value during black display for the above light resistor.

[0028] The material of the above dimming layer is preferably one that can make the dimming unit in a transparent state when no voltage is applied and can make the dimming unit in an opaque state when a voltage is applied. Examples of such materials include liquid crystal materials, electronic paper, electro-wetting, etc. Also, when the material of the above dimming layer is a liquid crystal material, the liquid crystal mode is not particularly limited.

[0029] As the above dye, a dye used in a conventional guest-host type liquid crystal can be used, and examples include commonly existing dichroic dyes such as G-472.

[0030] In the dimming unit according to Embodiment 3, a light-shielding layer is formed on the above light resistor or the above photodiode. As shown in FIG. 9, the light shielding layer 234 of the light dimming unit 200 is formed so as to overlap the light shielding layer of the display unit 100, and is also formed on the photoresistor 213 in order to suppress malfunction of the photoresistor 213 due to external light. Therefore, the opening D of the sub-pixel of the light dimming unit 200 is smaller than the opening C of the sub-pixel of the display unit 100.

[0031] For each layer constituting the light dimming unit other than the light dimming layer, the photoresistor, and the photodiode, the same ones as those of the normally white type display element including the conventional TFT substrate can be used.

[0032] Here, a specific example of the effect by using the display device according to Embodiment 3 is shown. When a light dimming unit having the structure shown in FIGS. 5 to 7 was manufactured, the transmittance of light (0.1 cd / m 2 ) when the display unit was black-displayed was 6%, and the transmittance of light (200 cd / m 2 ) when the display unit was white-displayed was 60%. When this light dimming unit was arranged on a liquid crystal display having a CR value of 2000, the CR value became 20000.

[0033] (Embodiment 4) The display device according to Embodiment 4 uses a normally white type display element including a TFT substrate in the light dimming unit in the same manner as in Embodiment 3, but is different in that the portion where current and voltage leak from the drain electrode is the semiconductor layer used in the conventional TFT type display element. Here, FIG. 11 shows a top view of the light dimming unit in the display device according to Embodiment 4, FIG. 12 shows a cross-sectional view in the X-X' direction of FIG. 11, and FIG. 13 shows a cross-sectional view in the Y-Y' direction of FIG. 11. As shown in FIGS. 11 to 13, the dimming unit of the display device according to Embodiment 4 includes a semiconductor layer 214, a gate electrode 211, a gate insulating layer 212, a source electrode 215, a drain electrode 216, a first interlayer insulating layer 217a, a second interlayer insulating layer 217b, a pixel electrode 218, and an alignment film 219 laminated on a TFT substrate 210, and a liquid crystal material 221 horizontally aligned at an azimuth angle of 45° between the TFT substrate 210 and a counter substrate 230 on which a counter electrode 232, an overcoat layer 233, a light shielding layer 234, and a substrate 235 are laminated on the alignment film 231. The dimming unit has a dimming layer 220, and polarizing plates 240 with polarization axes of 0° and 90° are respectively arranged under the TFT substrate and on the counter substrate. Further, the polarizing plates 240 are arranged such that they are cross-nicol and the polarization axes of the dimming layer and the polarization of the display unit match. The semiconductor layer 214 is connected to the source electrode 215 and the drain electrode 216 and is arranged at a position where visible light from the display unit is incident, and the light shielding layer 234 is arranged on the semiconductor layer 214. Further, the liquid crystal material 221 changes its alignment so that the dimming unit is in a transparent state when no voltage is applied and in an opaque state when a voltage is applied. In the basic state (a state where only the dimming unit is driven), all sub-pixels are in an opaque state with a voltage applied. In FIGS. 11 to 13, ECB (Electrically Controlled Birefringence) type liquid crystal is used as the dimming layer. However, any material may be used as long as the light incident when no voltage is applied passes through the upper polarizing plate (transparent state), and the light incident when a voltage is applied does not pass through the upper polarizing plate (opaque state). In FIGS. 11 and 12, the voltage of the dimming layer in the opaque state is set to 5V, and the voltage of the transparent state is set to 0V. However, these voltages are not limited as long as the dimming unit can be switched between the transparent state and the opaque state. Further, the semiconductor layer 214 is not limited to the top gate method as shown in FIG. 13 as long as the light from the display unit is incident thereon.

[0034] As shown in FIGS. 11 to 13, in the dimming unit according to Embodiment 4, in the sub-pixels (left and right sub-pixels) on the white display, when light from the display unit is incident on the semiconductor layer 214, the off-resistance of the semiconductor layer 214 decreases and current leaks from the drain electrode 216 to the source electrode 215, causing the voltage of the drain electrode 216 to decrease. As a result, in the sub-pixel where light is incident on the semiconductor layer 214, no voltage is applied to the dimming layer 220, the dimming unit becomes transparent, and light from the white-displaying display unit is transmitted. The transparent state continues until light no longer hits the semiconductor layer 214, that is, until the sub-pixel of the directly underlying display unit becomes black-displayed. On the other hand, in the sub-pixel (central sub-pixel) on the black display, the light incident on the semiconductor layer 214 is weak, and the off-resistance of the semiconductor layer 214 does not change enough for current to leak. Therefore, the voltage-applied state, that is, the opaque state of the dimming unit, is maintained, significantly reducing light leakage from the display unit and improving the contrast. Note that, similar to Embodiment 3, in the display device according to Embodiment 4, the switching between the transparent state and the opaque state of the dimming unit is performed by the light of the display unit. Therefore, it is possible to enhance the contrast with much simpler control compared to a dual cell. Also, since Embodiment 4 does not use a photoreceptor compared to Embodiment 3, it has the advantage of a simpler structure.

[0035] FIG. 14 shows a schematic diagram illustrating an example of the display of the display unit and the display of the dimming unit in the display device according to Embodiment 4. In the display unit 100 of FIG. 14, the sub-pixels represented by diagonal lines are white-displayed, and the sub-pixels represented in gray are black-displayed. When the display unit 100 is in the display state as shown in the left figure of FIG. 14, in the sub-pixel of the dimming unit 200 on the white display (for example, the sub-pixel of A), light enters the semiconductor layer 214 and the voltage of the drain electrode decreases, so that no voltage is applied to the dimming layer and it becomes a transparent state. On the other hand, in the sub-pixel of the dimming unit 200 on the black display (for example, the sub-pixel of B), since light that can significantly reduce the resistance of the semiconductor layer 214 does not reach, the state where a voltage is applied to the dimming layer is maintained and it becomes an opaque state. As a result, light leakage from the display unit 100 in the black display is greatly reduced by the dimming unit, so that the contrast can be improved.

[0036] The control of the dimming unit in the display device according to Embodiment 4 is the same as that in Embodiment 3. As described above, by performing voltage control as shown in the timing chart of FIG. 10, the dimming unit can be switched to the basic state during the refresh of the display unit.

[0037] The material of the semiconductor layer is not particularly limited as long as it is a semiconductor that can absorb visible light such as amorphous silicon (a-Si) and low-temperature polycrystalline silicon (LTPS) and can form a TFT structure.

[0038] The resistance of the semiconductor layer is the same as that in Embodiment 3. For example, when the dimming material is a liquid crystal with a liquid crystal capacitance of 300 fF and the dimming unit is Full HD driven at 60 Hz, if the resistance during black display is 20 GΩ or more and the resistance during white display is 10 MΩ or less, the transmittance of the dimming unit can be switched according to the display state of the display unit. It is preferable that the resistance value during white display is 1 / 1000 or less of the resistance value during black display for the semiconductor layer.

[0039] The material of the light control layer only needs to be able to make the light control part transparent when no voltage is applied and make the light control part opaque when a voltage is applied. Examples of such materials include liquid crystal materials, electronic paper, electro-wetting, etc. Further, when the material of the light control layer is a liquid crystal material, the liquid crystal mode is not particularly limited. Examples of liquid crystal modes other than the above ECB include TN (Twisted Nematic), VA (Vertical Alignment), FFS (Field Fringe Switching), etc.

[0040] In the light control part according to Embodiment 4, a light shielding layer is formed on the semiconductor layer. As shown in FIG. 14, the light shielding layer 234 of the light control part 200 is formed so as to overlap with the light shielding layer of the display part 100, but is also formed on the semiconductor layer 214 in order to suppress malfunction of the semiconductor layer 214 due to external light. As a result, the opening D of the sub-pixel of the light control part 200 becomes smaller than the opening C of the sub-pixel of the display part 100.

[0041] For the layers constituting the light control part other than the above light control layer, those similar to the normal white type display element provided with a conventional TFT substrate can be used.

[0042] Here, a specific example of the effect by using the display device according to Embodiment 4 is shown. When a light control part having the structure shown in FIGS. 11 to 13 was manufactured, the transmittance of light (0.1 cd / m 2 ) when the display part was black display was 0.08%, and the transmittance of light (200 cd / m 2 ) when the display part was white display was 80%. When this light control part was arranged on a liquid crystal display with a CR value of 2000, the CR value exceeded 1000000.

Explanation of Reference Numerals

[0043] 100: Display part 200: Light control part 210: TFT substrate 211: Gate electrode 212: Gate insulating layer 213: Light resistor or photodiode 214: Semiconductor layer 215: Source electrode 216: Drain electrode 217a: First interlayer insulating layer 217b: Second interlayer insulating layer 218: Pixel electrode 219: Alignment film 220: Light control layer 221: Liquid crystal material 222: Dye 230: Counter substrate 231: Alignment film 232: Counter electrode 233: Overcoat layer 234: Light shielding layer 235: Substrate A: Light control part, photochromic material or sub-pixel of light control part on white display sub-pixel B: Light control part, photochromic material or sub-pixel of light control part on black display sub-pixel C: Opening of sub-pixel of display part D: Opening of sub-pixel of light control part

Claims

1. A display device comprising a display unit and a light control unit disposed on the light emitting surface side of the display unit. The light control unit is a display device in which the transmittance of visible light increases as the intensity of visible light incident from the display unit increases.

2. The display device according to claim 1, wherein the display unit is a liquid crystal display having a pair of polarizing plates and a liquid crystal layer sandwiched between the pair of polarizing plates.

3. The display device according to claim 1, wherein the display unit is a self-emitting display.

4. The light control unit includes a photochromic material layer containing a photochromic material and an ultraviolet front light disposed on the photochromic material layer. The photochromic material is in a state of transmitting visible light when visible light is incident from the display unit, and is in a state of blocking visible light when ultraviolet light is incident from the ultraviolet front light. The display device according to claim 1.

5. The photochromic material is oriented in a certain direction in the photochromic material layer. The display device according to claim 4, wherein the photochromic material layer has an absorption axis parallel to the polarization axis of the light emitted from the display unit.

6. The light control unit is a normally white type display element including a TFT substrate. The TFT substrate has a drain electrode, a source electrode, and a photoresistor or a photodiode disposed at a position where visible light from the display unit is incident. The photoresistor or the photodiode connects the drain electrode and one of the source electrodes adjacent to the drain electrode. The photoresistor or the photodiode has a light shielding layer disposed thereon. The display device according to claim 1.

7. The dimming unit is a normally white display element including a TFT substrate, The TFT substrate has a semiconductor layer disposed at a position where visible light from the display unit is incident, and a source electrode and a drain electrode connected through the semiconductor layer, and has a light-shielding layer disposed on the semiconductor layer, The display device according to claim 1.

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