JP2015184441A - Electrochromic display device and drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochromic display device composed of a plurality of elements and a drive method of the device, in which coloring states of the elements can be controlled to be uniform.SOLUTION: The electrochromic display device drives a display panel including a first electrode layer, a charge accumulating layer, an electrolyte layer, an electrochromic display layer, a second electrode layer, and a transparent substrate, successively stacked on a substrate. When coloring by an electrochromic effect is induced by applying a predetermined voltage between the first electrode layer and the second electrode layer, refresh driving is carried out, prior to driving charges necessary to real display, by applying a pulse group comprising negative voltage pulses and positive voltage pulses, in which a voltage with the highest absolute value is applied immediately after starting the application and voltages in absolute values are gradually decreased.

Description

  The present invention relates to an electrochromic display panel, and more particularly to an electrochromic display device that emits and decolors by an oxidation-reduction reaction by an electrochemical oxidation reaction and a driving method of the device.

  In recent years, a liquid crystal using a backlight as an information display panel has been mainstream. However, the burden on the eyes is large, and it is not suitable for applications that keep watching for a long time.

  Therefore, as a reflective display device with a small eye load, a display panel having a pair of opposed electrodes and an electrophoretic display layer provided between the electrodes has been proposed as an electrophoretic display device ( For example, see Patent Document 1).

  Since this electrophoretic display device displays characters and images by reflected light, similarly to the printed paper surface, it is suitable for work that keeps the screen viewed for a long time with little load on the eyes. However, since the white reflectance is not sufficiently high, there is a demand for a reflective display device of a high reflection type by another method.

  As one of them, there is an electrochromic display method in which a high reflectance can be expected by using an electrochromic material that emits and decolors by an oxidation-reduction reaction by an electrochemical oxidation reaction. This electrochromic display system has advantages such as low driving voltage and high flexibility, and is expected to be put to practical use.

Japanese Patent Publication No. 50-015115

  Electrochromic (EC) is a reversible change in optical properties due to electrical energy, generally a change in color and color of a substance caused by an electrochemical redox reaction, and a phenomenon that causes a change in the amount of electricity. It is. In other words, in order to change the color tone or color of the electrochromic material, the amount of charge necessary for a certain oxidation-reduction reaction may be given to the coloring electrode.

  The electrochromic element in which the charge is accumulated has a property that the charge is gradually lost with time due to natural discharge such as air discharge or leakage current, and returns to the state before color development. The discharge characteristics depend on the amount of charge remaining at the time of charging, and in the case of an electrochromic display device formed of a plurality of elements, the color development elapsed time is different for each element. There is a problem that the colored state becomes non-uniform because of different discharge times.

  Accordingly, an object of the present invention has been made in view of the above problems, and an electrochromic display device capable of unifying the color development state of each element in a display device formed of a plurality of elements and a driving method of the device. Is to provide.

  In the first aspect of the present invention for solving the above-described problem, a first electrode layer, a charge storage layer, an electrolyte layer, an electrochromic display layer, a second electrode layer, and a transparent substrate are sequentially formed on a substrate. An electrochromic display device for driving a laminated display panel, which is necessary for actual display when a predetermined voltage is applied between the first electrode layer and the second electrode layer to develop electrochromic color. Before driving the amount of charge, a pulse group consisting of a negative voltage pulse and a positive voltage pulse, a voltage having the highest absolute value is applied immediately after application, and refresh driving is performed while gradually decreasing the voltage. An electronic display device.

  In addition, a second aspect of the present invention for solving the above-described problem includes a first electrode layer, a charge storage layer, an electrolyte layer, an electrochromic display layer, a second electrode layer, and a transparent substrate on a substrate. , A method of driving a sequentially laminated display panel, in which when a predetermined voltage is applied between the first electrode layer and the second electrode layer to generate electrochromic color, the charge required for actual display Before driving the quantity, it is a pulse group consisting of a negative voltage pulse and a positive voltage pulse. Immediately after application, a voltage having the highest absolute value is applied, and refresh driving is performed while gradually decreasing the voltage. Is the method.

  In the second aspect, the display panel can be driven by an active matrix driving method or a passive matrix driving method. Further, the display panel can be driven by a segment drive type display panel instead of the matrix drive type.

  In order to change the color tone or color of the electrochromic material, it is necessary to give the coloring electrode a charge amount necessary for a certain oxidation-reduction reaction. The electrochromic element has the maximum reflectance immediately after the necessary amount of charge is applied, and the accumulated charge is lost due to natural discharge such as air discharge or leakage current, and the reflectance decreases with time.

  According to the electrochromic display device and driving method of the present invention, the remaining charge can be made substantially zero before driving the amount of charge necessary for actual display, so that the color uniformity of a plurality of elements can be achieved.

Sectional drawing explaining the layer structure of the back common electrode type electrochromic display apparatus which concerns on one Embodiment of this invention. Sectional drawing explaining the layer structure of the back separation electrode type electrochromic display apparatus which concerns on one Embodiment of this invention. The figure which shows the voltage waveform at the time of the refresh pulse drive of the electrochromic cell The figure which shows the voltage and current waveform used for the drive method of the electrochromic display apparatus which concerns on one Embodiment of this invention. The figure which shows the voltage and current waveform used for the drive method of the electrochromic display apparatus which concerns on one Embodiment of this invention. Example of active matrix driving TFT circuit Measured values due to differences in refresh driving and charging methods

An electrochromic display device and a driving method thereof according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view illustrating a layer structure of a back common electrode type electrochromic display device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a layer structure of a back separation electrode type electrochromic display device according to an embodiment of the present invention.

  In the electrochromic display device of this embodiment, the charge storage layer 5, the electrolyte layer 4, and the electrochromic display layer 3 are sequentially formed on the back substrate 7 on which the back electrode layer 6 (first electrode layer) is formed. The transparent base material 1 which is laminated | stacked and provided the transparent electrode layer (2nd electrode layer) 2 on this electrochromic display layer 3 consists of further laminated | stacked.

  First, the outline of the display principle of an electrochromic display device according to an embodiment of the present invention will be described, and the outline of the present invention will be described.

  In the electrochromic display device shown in FIG. 1, the transparent substrate 1 is for visually observing the color development, and the transparent electrode layer 2 is used as an electrode that causes color development. In order to induce an electrochemical reaction on the transparent electrode layer 2, an electrochromic display layer 3 is applied. For the electrolyte layer 4, a liquid, an inorganic solid, a polymer, a gel, or the like is used. Here, the same amount of charge as the amount of charge consumed in the electrochemical reaction of the coloring electrode is also consumed in the charge storage layer 5 of the back electrode layer 6 which is the counter electrode. Each of these layers is supported by the back substrate 7.

  In the electrochromic display device shown in FIG. 2, the back electrode layer 6 is divided into a plurality of pixel electrodes 6a that can be individually driven. The plurality of pixel electrodes 6 a correspond to the pixels, are connected to the respective switching elements, and can apply a voltage between the transparent electrode layer 2.

  For driving the electrochromic display device, an active matrix driving method, a passive matrix driving method, or the like is employed. In addition, it is possible to drive by the segment system instead of the matrix system. In this embodiment, the display principle of an electrochromic display device will be described using the most common active matrix driving method for displaying an image.

  In order to display an image, the back electrode layer 6 is connected to a power source having a circuit configuration of an active matrix drive system. When a voltage is applied to the back electrode layer 6, a current flows through the electrochromic display layer 3.

  Electrochromic is a reversible change in the color and color of a substance caused by a redox reaction by electrical energy. When the back electrode layer 6 is positive, the charge storage layer 5 loses electrons and is oxidized, and electrons are donated and reduced to the electrochromic display layer 3 in contact with the transparent electrode layer 2 serving as the counter electrode. On the contrary, when the back electrode layer 6 is negative, electrons are donated to the charge storage layer 5 and reduced, and the electrochromic display layer 3 loses electrons and is oxidized.

  As the electrochromic display layer 3 is oxidized / reduced, the absorption wavelength region of visible light appears or moves, and the color changes. In the case where the electrochromic display layer 3 does not absorb visible light and is colorless and transparent, color development due to the reflective material dispersed in the electrolyte layer 4 is observed.

  Since the electrochromic structure is an electrochemical structure, like the battery, the electrochromic structure is a very simple structure in which the electrolyte layer is sandwiched between the pair of electrodes shown in FIG. Since it is a two-electrode type consisting of a cathode and an anode, the same amount of charge as that consumed in the electrochemical reaction of the color developing electrode is consumed even at the counter electrode. That is, the electrochromic structure can be considered as a chargeable / dischargeable secondary battery.

  As described above, in order to display an image, the back electrode layer 6 in FIG. 1 is connected to a power source having a circuit configuration of an active matrix driving method. When a voltage is applied to the back electrode layer 6, a current flows through the electrochromic display layer 3, which can be said to be equivalent to charging a structurally similar secondary battery.

  While the charged electrochromic element having the secondary battery structure maintains a charge, electrons are donated to the electrochromic display layer 3 and the reduced state is continued.

  The electrochromic display control is to rewrite each element with display data, which can be said to be repeated charging / discharging of the electrochromic element. Rewriting by overwriting means adding and charging each time. In general, secondary batteries have a memory effect that causes a voltage drop when added and recharged. However, rewriting of each electrochromic element is performed irregularly in time, so the charge retention state depends on the display state of the previous screen. Is also irregular.

  Due to this memory effect, there is a problem that the discharge characteristics of each element are not constant and the reflectance becomes non-uniform over time. In order to solve this problem, at the time of rewriting each element, the element charge amount is once set to zero, and refresh driving for recovering the memory effect may be performed.

  3 shows an electrochromic cell having the structure shown in FIG. 1 in terms of 1st (−1.8 V), 2 nd (1.4 V), 3 rd (−1.0 V), 4 th (0.6 V), 5 th (−0). .2V) and a voltage waveform when driven by a pulse having a width of 0.5 seconds. The driving by the pulse group composed of the negative voltage pulse and the positive voltage pulse is refresh driving, and has a recovery function for the memory effect at the time of charging the electrochromic cell. Immediately after application, a voltage having the highest absolute value is applied, and driving is performed while gradually decreasing the voltage. Thereafter, driving is performed with an amount of charge necessary for actual display.

  In the refresh drive according to the driving method of the present invention, a high absolute value voltage is applied immediately after application, and then gradually changed to a lower absolute value voltage. Can be zero. For example, if the refresh waveform is pulse driven with an absolute value constant voltage, charge is supplied not less than after the last pulse drive of the refresh waveform, and residual charges are generated during actual display drive, which is added to the electrochromic device. There is a drawback of charging.

  In this embodiment, the electrochromic display device is pulse-driven while reducing the voltage to which refresh is applied, but the voltage and width (time) of the pulse drive are set based on a value for discharging the charge amount of the electrochromic element. The

Next, active matrix driving will be described.
FIG. 6 is a diagram showing a typical example of a two transistor type (2Tr type) TFT drive circuit. The TFT driving circuit shown in FIG. 6 includes two thin film transistors (TFTs) of a driving TFT 15 and a selection TFT 14, a capacitor 13 therebetween, and an electrochromic element (ECD) 16 connected in series to the driving TFT 15. When the selection voltage Vselect12 turns on the selection TFT 14, the signal voltage Vdata10 is written into the capacitor 13, and at the same time, the drive TFT 15 is turned on. At that time, since the gate voltage Vgs (= signal voltage Vdata−source voltage Vsource) of the selection TFT 14 is determined according to the signal voltage Vdata10, the conductivity of the driving TFT 15 is determined. A current corresponding to the conductivity flows from the power source to the electrochromic element (ECD) 16.

Below, the material and member used for this invention, and its structure are demonstrated.
The electrochromic display layer 3 is formed of an electrochromic material, a supporting electrolyte, a reflective material, and a charge storage material.
As the electrochromic material, general organic compounds and inorganic compounds can be used. Specifically, low molecular organic electrochromic compounds such as viologens, phenothiazines, anthraquinones, styryl spiropyrans, pyrazolines, fluorans, styryl spiropyran dyes, phthalocyanines, polyaniline, polythiophene, polypyrrole, etc. Molecular compounds, titanium oxide, molybdenum oxide, niobium oxide, iridium oxide, vanadium oxide, tungsten oxide, indium oxide, iridium oxide, nickel oxide, Prussian blue, and Prussian blue analogues in which the coordination metal is replaced by other than iron An inorganic electrochromic compound etc. are mentioned. Furthermore, it has been found that leuco dyes, which are generally electricity-donating organic substances, can also be electrically colored and decolored. For example, electron-donating dye precursors such as leucooramines, diarylphthalides, polyarylcarbinols, acylauramines, arylolamines, rhodamine B-lactams, indolines, spiropyrans, and fluorans Is mentioned. Note that a low molecular material may be adsorbed by forming a porous layer of a mineral such as titanium oxide on the electrode layer.

  As a method for forming the electrochromic display layer 3, the electrochromic material described above is used directly or mixed with a binder to form a paint, and screen printing, microgravure coater, kiss coater, comma coater, die coater, bar coater, spin coater, etc. A typical coating technique can be used.

Examples of the supporting salt include inorganic ion salts such as alkali metal salts and alkaline earth metal salts, quaternary ammonium salts, acids and alkalis. Further specific examples of the supporting salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ COO, KCl, NaClO ₃ , NaCl, NaBF ₄ , NaSCN, KBF ₄ , Mg (ClO _{4) 2, Mg (BF 4} ) 2 and the like.

  As the reflective material dispersed in the electrolyte layer 4, examples of the white material include magnesium oxide, barium sulfate, and titanium oxide. Examples of the black material include carbon black made of carbon such as lamp black and bone black, and titanium black powder made of an inorganic material. Furthermore, for a blue material, cobalt aluminate, cobalt chrome blue, phthalocyanines, and for a red material, anthraquinone, an azo compound, and the like can be given. In order to disperse the reflective material in the electrolyte layer 4, the viscosity of the electrolyte layer 4 may be increased by dissolving a polymer material such as an acrylic resin or a urethane resin in the electrolyte layer 4. Alternatively, a dispersant or a surfactant may be added to the electrolyte layer 4.

  As the charge storage material, the same material as the electrochromic material described above can be used. However, a stable material that is unlikely to react with other compounds in both oxidized and reduced forms such as Prussian blue and ferrocene is preferable.

  As the transparent substrate 1, polyethylene terephthalate (PET), polycarbonate, polyimide, polyethylene naphthalate, polyethersulfone, acrylic resin, polyvinyl chloride or other plastic film, glass, or the like can be used. What can be used as the transparent electrode material is a conductive oxide having transparency such as indium oxide, tin oxide and zinc oxide such as ITO. Conventional methods such as vapor deposition, sputtering, and CVD can be used to form the transparent electrode layer 2.

  For the back substrate 7 on which the back electrode layer 6 is formed, an active matrix type electrode plate in which thin transistors using amorphous silicon or polycrystalline silicon, which are generally employed for driving a liquid crystal panel, are arranged. Alternatively, a large-scale active matrix drive is possible by arranging a large number of electrodes in a grid pattern on the front surface of the printed circuit board on the back substrate 7 on which the back electrode layer 6 is formed, and laying wiring on the back surface through through holes for each electrode. A simple electrode plate may be used.

  A dispersion obtained by dispersing 1.0 mol / l of a water-soluble Prussian blue dispersion as an electrochromic material on a 20 mm × 20 mm transparent electrode substrate on which an indium tin oxide electrode was deposited on glass was applied at 100 ° C. A front electrode substrate having a coating film of about 0.3 μm was obtained by drying for 5 minutes.

  As the back substrate, the prepared Prussian blue dispersion was applied by a spin coater in the same manner as the front electrode substrate to obtain a back electrode substrate using Prussian blue as a charge retention layer.

  Furthermore, 0.1 M potassium hexafluorophosphate, PMMA (Wako Pure Chemicals), and titanium oxide (R-830, manufactured by Ishihara Sangyo) were dispersed as electrolytes in propylene carbonate to prepare an electrolytic solution.

A dam was formed by applying a UV curable resin (TB3026E, manufactured by ThreeBond) mixed with beads having a diameter of about 100 μm to the ends of the front electrode substrate and the back electrode substrate with a dispenser. Subsequently, the dam was filled with the above-prepared electrolytic solution, and was adhered by irradiation with light of 500 mJ / cm ² (420 nm).

  As shown in the upper part of FIG. 4 between the completed front and rear substrates, -1.8V, 1.4V, -1.0V, 0.6V, and -0.2V (each 0.5 seconds) are applied as refresh waveforms. After driving 5 times, when 1.8V was applied for 4 seconds to promote a color change from blue to transparent, the pixel was almost completely oxidized and turned transparent after about 1 second, and the electrolyte was titanium oxide. Therefore, it was observed as a white pixel. The charge / discharge current at that time is shown in the lower part of FIG.

  In the refresh drive in which the voltage is gradually lowered, in the process of decreasing the supply energy, there is no excess charge when the zero potential is applied after sending the refresh last pulse, and almost all charges are discharged. As a result, there is no residual charge when performing actual display charging, and additional charging to the electrochromic element can be prevented.

  Here, when the above-described cell was refreshed and charged with the waveform of FIG. 4 from the state where the charge amount was 0, the potential difference between the front electrode substrate and the back electrode substrate after 30 seconds was 1.04V. Further, when the above-described cell was refreshed and charged with the waveform of FIG. 4 from the state where the charge amount was full, the potential difference between the front electrode substrate and the back electrode substrate after 30 seconds was 1.10V. The voltage difference 0.06V between the two potential differences is a discharge variation depending on the amount of cell charge before charging, and the smaller the variation, the smaller the variation in reflectance. FIG. 7 shows the measured voltage after 30 seconds of charging with reduced voltage refresh and charging without refresh according to the present invention.

Comparative Example 1

  As shown in the upper part of FIG. 5 between the front and rear substrates completed in the same manner as in Example 1, the application of ± 1.8 V as a refresh waveform is driven 5 times at 0.5 second intervals, and then 1.8 V is applied. Was applied for 4 seconds to promote a color change from blue to transparent, and after about 1 second, the pixel was almost completely oxidized and changed to transparent, and was observed as a white pixel by the titanium oxide of the electrolytic solution. The charging / discharging current at that time is shown in the lower part of FIG.

As shown in FIG. 5, in refresh driving with a voltage having a constant absolute value, it can be seen that a slight amount of charge remains when the potential is set to zero potential after sending the last refresh pulse.
Similarly to the measurement described above, when the above cell is refreshed and charged with the waveform of FIG. 5 from the state of zero charge, the potential difference between the front electrode substrate and the back electrode substrate after 30 seconds is 1.03 V. became. Further, when the above cell is refreshed and charged with the waveform of FIG. 5 from the state where the charge amount is full, the potential difference between the front electrode substrate and the back electrode substrate after 30 seconds becomes 1.14 V, and the voltage between the two potential differences The difference was 0.11V. FIG. 7 shows the measured voltage value after 30 seconds of charging with constant voltage refresh. As is clear from FIG. 7, even in constant voltage refresh, the voltage difference is smaller than that in charging without refreshing, but reduced voltage refresh charging has the smallest voltage difference and the variation in reflectance is small.

  The present invention can be used for various applications as well as an electrochemical device having a conventional electrolytic solution. The electrochromic element that controls the color by voltage application can be applied to a display element, a light control element, and the like.

DESCRIPTION OF SYMBOLS 1 ... Transparent base material 2 ... Transparent electrode layer (1st electrode layer)
3 ... Electrochromic display layer 4 ... Electrolyte layer 5 ... Charge storage layer 6 ... Back electrode layer (second electrode layer)
6a ... Pixel electrode 7 ... Back substrate 10 ... Signal voltage Vdata
11… Source voltage Vsource
12 ... Selection voltage Vselect
13 ... Capacitor 14 ... Selection TFT
15… Driving TFT
16 ... Electrochromic device (ECD)

Claims (5)

An electrochromic display device for driving a display panel in which a first electrode layer, a charge storage layer, an electrolyte layer, an electrochromic display layer, a second electrode layer, and a transparent substrate are sequentially laminated on a substrate. And
When applying a predetermined voltage between the first electrode layer and the second electrode layer to develop electrochromic color, before driving the amount of charge required for actual display, a negative voltage pulse and a positive voltage pulse An electrochromic display device, wherein a voltage having the highest absolute value is applied immediately after application of the pulse group, and refresh driving is performed while gradually decreasing the voltage. A method for driving a display panel in which a first electrode layer, a charge storage layer, an electrolyte layer, an electrochromic display layer, a second electrode layer, and a transparent substrate are sequentially laminated on a substrate,
When applying a predetermined voltage between the first electrode layer and the second electrode layer to develop electrochromic color, before driving the amount of charge required for actual display, a negative voltage pulse and a positive voltage pulse A driving method in which a voltage having the highest absolute value is applied immediately after application, and refresh driving is performed while gradually decreasing the voltage.   The driving method according to claim 2, wherein the display panel is driven by an active matrix driving method.   The driving method according to claim 2, wherein the display panel is driven by a passive matrix driving method.   The driving method according to claim 2, wherein the display panel is driven by a segment driving method.

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