Light-emitting device, photoelectric conversion device, electronic device, lighting device and mobile object

Abstract

To provide a light emitting device that is advantageous for changing the range of current flowing in a light emitting element for a signal voltage input to the light emitting element.SOLUTION: A light emitting device comprises: a plurality of pixels 102 that each have a light emitting element 201, a drive transistor 202, a capacity holding a threshold voltage of the drive transistor, a signal line 108, a first switch connecting the signal line and a control electrode of the drive transistor to each other, and a second switch connecting a first main electrode of the drive transistor and a predetermined node to each other; and a drive circuit that drives the signal line. In a preparation period for holding the threshold voltage, the first switch is turned on and the second switch is turned off, and the drive circuit drives the signal line at a voltage level selected from a plurality of different voltage levels. In a signal writing period for writing a luminance signal value in the light emitting element, the first switch is turned on and the second switch is turned off, and the drive circuit drives the signal line at a voltage according to the luminance signal value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a light-emitting device, for example a light-emitting device having an organic light-emitting element. [Background technology]

[0002] Patent Document 1 discloses a display device equipped with an organic EL element, which has a video display mode and an aging mode in which the maximum brightness is higher than that of the video display mode as display modes. The display device of Patent Document 1 includes a DAC (Digital to Analog Converter) that converts a digital signal indicating brightness into an analog voltage and supplies it to pixels. It discloses that in the aging mode, in order to increase the maximum brightness, the maximum brightness is increased by increasing the number of bits of the digital signal input to the DAC. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-097016 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a method of switching the number of bits of a digital signal to switch the analog voltage supplied to a pixel depending on the mode as in Patent Document 1, the range of brightness is limited to the range of the signal voltage according to the digital signal due to the limited number of bits of the DAC. An object of the present invention is to provide a light-emitting device that is advantageous in changing the range of the current flowing through the light-emitting element relative to the signal voltage input to the light-emitting element. [Means for solving the problem]

[0005] A light emitting device of the present invention includes a plurality of pixels each having a light emitting element, a drive transistor for driving the light emitting element, a capacitance for holding a threshold voltage of the drive transistor, a signal line, a first switch for connecting the signal line to a control electrode of the drive transistor, and a second switch for connecting a first main electrode of the drive transistor to a predetermined node, and a drive circuit for driving the signal line, wherein during a preparation period for holding the threshold voltage in the capacitance, the first switch is controlled to be on and the second switch is controlled to be off, and the drive circuit drives the signal line at a voltage level selected from a plurality of different voltage levels and writes a luminance signal value to the light emitting element, and during a signal writing period, the first switch is controlled to be on and the second switch is controlled to be off, and the drive circuit drives the signal line with a voltage corresponding to the luminance signal value. the plurality of different voltage levels include a first voltage and a second voltage higher than the first voltage, the light emitting element emits light in a first mode in which the first voltage is supplied and the threshold voltage is maintained, or in a second mode in which the second voltage is supplied and the threshold voltage is maintained, and when the signal line is driven with the same voltage as the voltage according to the luminance signal value in the first mode and the second mode during the signal writing period, the light emitting element emits light with a luminance higher in the second mode than in the first mode. The present invention is characterized by the above. Effect of the Invention

[0006] According to the present invention, it is possible to provide a light emitting device that is advantageous in changing the range of the current flowing through the light emitting element relative to the signal voltage input to the light emitting element. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a system schematic diagram of an example of a part of the light emitting device according to the first embodiment. [Diagram 2] FIG. 2 is a circuit diagram of an example of a pixel of the light emitting device according to the first embodiment. [Diagram 3] FIG. 2 is a timing chart of the light emitting device according to the first embodiment. [Figure 4] (A) Electrical characteristics of a pixel in a light-emitting device, (B) light-emitting characteristics of the light-emitting device. [Figure 5(A)] FIG. 3 is a diagram showing electrical characteristics of a pixel of the light emitting device according to the first embodiment. [Figure 5(B)] FIG. 2 is a diagram showing the light emitting characteristics of the light emitting device according to the first embodiment. [Figure 6] 1A is a diagram showing electrical characteristics of a pixel of the light emitting device according to embodiment 1. FIG. [Figure 7]1A is a diagram showing electrical characteristics of a pixel of the light emitting device according to embodiment 1. FIG. [Figure 8] 1A is a diagram showing electrical characteristics of a pixel of the light emitting device according to embodiment 1. FIG. [Figure 9] FIG. 11 is a system schematic diagram of an example of a part of a light emitting device according to a second embodiment. [Figure 10] FIG. 11 is a circuit diagram of an example of a pixel of the light emitting device according to the second embodiment. [Figure 11] FIG. 6 is a timing chart of the light emitting device according to the second embodiment. [Figure 12] 1A is a schematic cross-sectional view showing an example of a pixel of a light emitting device according to an embodiment, and FIG. 1B is a schematic cross-sectional view showing an example of a display device using the light emitting device according to an embodiment. [Figure 13] FIG. 1 is a schematic diagram illustrating an example of a display device. [Figure 14] 1A is a schematic diagram illustrating an example of an imaging device, and FIG. [Figure 15] 1A is a schematic diagram showing an example of a display device, and FIG. 1B is a schematic diagram showing an example of a foldable display device. [Figure 16] 1A is a schematic diagram showing an example of a lighting device, and FIG. 1B is a schematic diagram showing an example of an automobile having a vehicle lamp. [Figure 17] 1A and 1B are schematic diagrams showing an example of a wearable device having an imaging device; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0009] (Embodiment 1) In the following, a case will be described in which a driving transistor is connected to the anode of an organic electroluminescence (EL) element, which is an example of an organic light-emitting element, and all the transistors are P-type transistors, but the light-emitting device of this embodiment is not limited to this. The polarity and conductivity type may all be reversed. In addition, the driving transistor may be a P-type transistor and the other transistors may be N-type transistors, and the supplied potential and connection may be changed appropriately according to the conductivity type and polarity.

[0010] Fig. 1 is a system schematic diagram showing an example of a part of a light emitting device according to this embodiment. The light emitting device 101 shown in Fig. 1 has a pixel array section 103 and a circuit arranged around the pixel array section 103. The pixel array section 103 has a plurality of pixels 102 arranged two-dimensionally in a matrix, and each pixel 102 has an organic light emitting element.

[0011] The circuits arranged around the pixel array 103 are circuits for controlling each pixel 102, and include a vertical scanning circuit 104 and a signal output circuit 105. In the pixel array 103, a first scanning line 106 and a second scanning line 107 are arranged for each pixel row along the row direction. Also, a signal line 108 is arranged for each pixel column along the column direction.

[0012] The first scanning line 106 and the second scanning line 107 are connected to output terminals of corresponding rows in the vertical scanning circuit 104. Moreover, the signal line 108 is connected to an output terminal of the signal output circuit 105. The vertical scanning circuit 104 supplies a write control signal to the first scanning line 106 and a light emission control signal to the second scanning line 107.

[0013] The signal output circuit 105 includes a drive circuit 109 that outputs a voltage (hereinafter, Vsig) of a luminance signal value corresponding to display data given as a digital value from the outside, or a predetermined voltage selected from a plurality of different voltage levels.

[0014] 2 is a circuit diagram of an example of a pixel included in the light-emitting device of FIG. 1. As shown in FIG. 2, the pixel 102 includes an organic light-emitting element 201, a driving transistor 202, a writing transistor 203, a light-emitting control transistor 204, a first capacitance element 205, and a second capacitance element 206. The organic light-emitting element 201 includes an organic layer including a light-emitting layer between an anode and a cathode. The organic layer may include one or more of a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer, in addition to the light-emitting layer. Here, the total number of transistors and capacitance elements and the combination of the conductivity types of the transistors are merely examples, and are not limited to this configuration.

[0015] Specifically, a main electrode (one of the source and drain (drain in FIG. 2)) of the driving transistor 202 is connected to a first electrode of the organic light-emitting element 201. The other of the main electrodes (the source here) of the driving transistor 202 is connected to one of the source and drain (drain in FIG. 2) of the light-emitting control transistor 204. The other of the light-emitting control transistor 204 (the source here) is connected to a node to which a power supply voltage is supplied. Here, the source of the light-emitting control transistor 204 is connected to a first power supply terminal 207 (hereinafter, Vdd). The light-emitting control transistor 204 can function as a switch that connects the source of the driving transistor 202 to Vdd 207. A second electrode of the organic light-emitting element 201 is connected to a second power supply terminal 208 (hereinafter, Vss). One of the source and drain of the writing transistor 203 is connected to a control electrode (the gate here) of the driving transistor 202, and the other of the source and drain of the writing transistor 203 is connected to a signal line 108. The write transistor 203 can function as a switch that connects the gate of the drive transistor 202 to the signal line 108 .

[0016] The gate of the writing transistor 203 is connected to the first scanning line 106. The gate of the light-emitting control transistor 204 is connected to the second scanning line 107. By driving the first scanning line 106 and the second scanning line 107, a pixel in a predetermined row can be selected.

[0017] The first capacitance element 205 is connected between the gate and one of the source and drain (the source in FIG. 2) of the driving transistor 202. The second capacitance element 206 is connected between one of the source and drain (the source in FIG. 2) of the driving transistor 202 and Vdd 207. Both the first capacitance element 205 and the second capacitance element 206 are connected to the source of the driving transistor 202. The first capacitance element 205 and the second capacitance element 206 may be parasitic capacitances or may be capacitances having a MIM (Metal-Insulator-Metal) structure.

[0018] An outline of the operation during the light emission period when the organic light emitting element 201 emits light will be described below. The driving transistor 202 supplies a current from Vdd 207 to the organic light emitting element 201, causing the organic light emitting element 201 to emit light. More specifically, the driving transistor 202 supplies a current according to the signal voltage of the signal line 108 to the organic light emitting element 201. This causes the organic light emitting element 201 to emit light by being current driven.

[0019] When the organic light emitting element 201 emits light, the writing transistor 203 becomes conductive in response to a writing control signal applied to its gate from the vertical scanning circuit 104 through the first scanning line 106. This causes the writing transistor 203 to write a voltage according to a luminance signal value supplied from the signal output circuit 105 through the signal line 108 to the pixel 102. This written signal voltage is applied to the gate of the driving transistor 202.

[0020] The emission control transistor 204 is turned on in response to an emission control signal applied to the gate from the vertical scanning circuit 104 via the second scanning line 107, thereby allowing current supply from Vdd 207 to the driving transistor 202. This allows the driving transistor 202 to emit light from the organic light emitting element 201. That is, the emission control transistor 204 functions as a transistor that controls whether the organic light emitting element 201 emits light or not. In this way, the switching operation of the emission control transistor 204 enables so-called duty control, which is capable of controlling the ratio of the emission period and non-emission period of the organic light emitting element 201. This duty control can reduce afterimage blurring caused by the pixel 102 emitting light during the emission period in one frame period, and can improve image quality, particularly when displaying moving images.

[0021] When the organic light emitting element 201 emits light, the amount of current flowing through the driving transistor 202 is changed according to the luminance. This charges the capacitance between the first electrode (here, an anode) and the second electrode (here, a cathode) of the organic light emitting element 201 to a predetermined potential, and a current according to the potential difference flows. This causes the organic light emitting element 201 to emit light with a predetermined luminance.

[0022] Due to manufacturing variations, the threshold voltage of the driving transistor 202 may differ for each pixel. When the same Vsig is written to multiple pixels that emit the same light, the amount of current flowing through the driving transistor 202 differs for each pixel, resulting in variation in the amount of light emitted. Therefore, before Vsig is applied to the gate of the driving transistor 202, a so-called threshold correction operation is performed in which the threshold voltage of the driving transistor 202 is held in the capacitance between the gate and source of the driving transistor 202. This threshold correction operation can reduce the variation in the amount of current of the driving transistor 202 in each pixel, thereby achieving uniform light emission.

[0023] The threshold correction operation is performed during a preparation period during a non-light emitting period prior to light emission. The threshold correction operation is outlined as follows. After a current flows to the organic light emitting element 201 via the light emitting control transistor 204 and the driving transistor 202, the light emitting control transistor 204 is turned off. This allows a current to flow to the organic light emitting element 201 until the voltage between the gate and source of the driving transistor 202 becomes statically stable. When the voltage between the gate and source becomes statically stable, the threshold voltage can be held in the capacitance between the gate and source. The threshold correction operation will be described below with reference to the timing diagram shown in FIG. 3.

[0024] Here, the threshold correction operation will be described using as an example one frame including a non-light emitting period and a light emitting period as shown in Fig. 3. The period before time t1 is the light emitting period of the organic light emitting element 201 in the previous frame. During the light emitting period, the light emitting control transistor 204 is in the on state and the writing transistor 203 is in the off state.

[0025] A new frame starts at time t1. At time t1, the emission control signal 107 transitions from low to high, causing the emission control transistor 204 to turn off. Therefore, no current is supplied from Vdd 207 to the organic light emitting element 201 via the emission control transistor 204 and the drive transistor 202, causing the organic light emitting element 201 to enter a non-emitting state. At time t2, the drive circuit 109 switches the voltage of the signal line 108 from Vsig to a threshold correction voltage (hereinafter, Vofs) that is applied when performing a threshold correction operation.

[0026] At time t3, the write control signal 106 transitions from High to Low, turning on the write transistor 203. As a result, Vofs of the signal line 108 is written to the gate of the drive transistor 202. In addition, since the source voltage of the drive transistor 202 is in a floating state, it is affected by capacitive coupling between the gate and source of the drive transistor 202 and changes.

[0027] At time t4, the emission control signal 107 transitions from High to Low, causing the emission control transistor 204 to turn on. As a result, the source voltage of the drive transistor 202 becomes substantially equal to Vdd 207. The period during which the gate potential of the drive transistor 202 is initialized to Vofs and the source voltage is initialized to Vdd is called a reset period. During the reset period, a current is supplied from Vdd 207 to the organic light emitting element 201 via the emission control transistor 204 and the drive transistor 202, and the anode of the organic light emitting element 201 is charged, thereby increasing the anode potential (hereinafter, Vel). At this time, it is desirable for Vel to be a potential lower than the emission threshold of the organic light emitting element 201, but this is not necessarily the case when the reset period is sufficiently short, since the amount of light emission is also sufficiently small.

[0028] At time t5, the emission control signal 107 transitions from Low to High, causing the emission control transistor 204 to be turned off. The threshold voltage Vth is approximately Vg-Vs when a current starts to flow through the drive transistor 202. When the emission control transistor 204 is turned off, the source voltage (hereinafter, Vs) of the drive transistor 202 changes to Vs=Vofs-Vth, which is the difference voltage between Vofs and the threshold voltage (hereinafter, Vth) of the drive transistor 202, and then becomes stable. At this time, the gate voltage (hereinafter, Vg) of the drive transistor 202 is Vg=Vofs, so that Vth is held in the first capacitance element 205. The preparation period (the period from time t5 to time t6) for performing the threshold correction operation during the non-emission period is called the threshold correction period. Therefore, the emission control transistor 204 and the first capacitance element 205 function as a threshold correction unit that compensates the threshold voltage Vth for the input voltage to the drive transistor 202.

[0029] At time t6, the write control signal 106 transitions from low to high, turning off the write transistor 203. At time t7, the signal voltage of the signal line 108 switches from Vofs to Vsig.

[0030] At time t8, the write control signal 106 transitions from High to Low, turning the write transistor 203 on. As a result, Vsig of the signal line 108 is written to the gate of the drive transistor 202. The period during which the gate voltage of the drive transistor 202 is set to Vsig is the signal write period. In addition, since the gate voltage of the drive transistor 202 changes from a voltage approximately equal to Vofs to Vsig, the source voltage increases due to capacitive coupling between the gate and source of the drive transistor 202. The source voltage Vs of the drive transistor 202 is Vs=Vofs-Vth+ΔVs.

[0031] Here, ΔVs is expressed by the following equation (1) using the capacitance value C1 of the first capacitance element 205, the capacitance value C2 of the second capacitance element 206, the gate-source capacitance of the driving transistor 202, and the source capacitance Cs excluding the source-Vdd capacitance.

[0032] ΔVs=(Vsig-Vofs)·C1 / (Cs+C1+C2) ···(1) At time t9, the write control signal 106 transitions from low to high, turning off the write transistor 203.

[0033] At time t10, the emission control signal 107 transitions from High to Low, turning the emission control transistor 204 on. At this time, the source voltage of the drive transistor 202 becomes a voltage substantially equal to Vdd 207. Then, a current is supplied from Vdd 207 to the organic light emitting element 201 via the emission control transistor 204 and the drive transistor 202. This charges the anode of the organic light emitting element 201, increasing Vel. When Vel reaches a potential equal to or higher than the emission threshold, the organic light emitting element 201 emits light.

[0034] Furthermore, since the source voltage of the driving transistor 202 changes to a voltage substantially equal to Vdd 207, the gate voltage increases due to capacitive coupling between the gate and source of the driving transistor 202. The gate voltage Vg of the driving transistor is Vg=Vsig+ΔVg. Here, ΔVg is expressed by the following equation (2) using the gate capacitance Cg excluding the gate-source capacitance of the driving transistor 202.

[0035] ΔVg=(Vdd-Vs)·C1 / (Cg+C1) ···(2) Here, if Cg is the parasitic capacitance between the gate and drain of the driving transistor 202 and the parasitic capacitance between the gate of the writing transistor 203 and the gate of the driving transistor 202, it is assumed that Cg is sufficiently small compared to C1. If Cg is ignored because it is sufficiently small, then equation (2) can be further expressed by equation (3) using equation (1).

[0036] ΔVg=Vdd-{Vofs-Vth+(Vsig-Vofs)·C1 / (Cs+C1+C2)}···(3) Here, because Vth is held in the first capacitance element 205 by the threshold correction operation from time t5 to time t6, the threshold voltage is cancelled at the gate of the driving transistor 202. Therefore, if the Vsig written to each pixel is the same, the current flowing through the driving transistor 202 can reduce the effect of the variation even if there is a variation in the threshold voltage Vth of the driving transistor 202. Therefore, it is possible to realize uniform light emission between pixels of the same light emission color. Note that the period from time t1 to time t10 is a non-light emission period.

[0037] At time t11, the voltage of the signal line 108 switches from Vsig to Vofs.

[0038] Next, the relationship between the signal voltage (Vsig) that drives the driving transistor 202 and the current flowing through the light emitting element will be described with reference to Fig. 4(A). Fig. 4(A) shows the electrical characteristics of the pixel in Fig. 2. A curve 401 shows the current characteristics of the driving transistor 202 with respect to the voltage Vsig, with the vertical axis being a logarithmic scale. Here, Vsig written to the pixel is V M , V H1 , V L1 The relationship between these magnitudes is V H1 <V M <V L1 At this time, the voltage V M , V H1 , V L1 The current flowing through the P-type driving transistor 202 is I M , I H1 , I L1 It is.

[0039] 4B shows the light emission characteristics of the light emitting device of FIG. 1. Curve 402 is a gamma curve. The voltages corresponding to the display data DM, data DH, and minimum display data DL are V M , V H1 , V L1 The current flowing through the driving transistor 202 and the luminance emitted by the organic light emitting element 201 are approximately proportional to each other. M , D H , and D L The luminance is L M , L H1 , L L1 Therefore, the maximum display data D H When a given luminance L H1It reaches the maximum brightness. Next, an explanation will be given about improving the brightness while keeping the range of the display data as it is. According to the above formula (3), ΔVg can change depending on the value of Vofs. Here, let the threshold correction voltages be Vofsa and Vofsb respectively, and assume Vofsa < Vofsb. In this case, the gate voltages Vga and Vgb of the driving transistor during the light-emitting period are Vga = Vsig + ΔVga and Vgb = Vsig + ΔVgb respectively. ΔVga and ΔVgb are represented by the following formulas (4) and (5) using formula (3).

[0040] ΔVga = Vdd - {Vofsa - Vth + (Vsig - Vofsa)·C1 / (Cs + C1 + C2)} ··· (4) ΔVgb = Vdd - {Vofsb - Vth + (Vsig - Vofsb)·C1 / (Cs + C1 + C2)} ··· (5) The potential difference between ΔVgb and ΔVga is represented by the following formula (6) using formulas (4) and (5).

[0041] |ΔVgb - ΔVga| = (Vofsb - Vofsa)·(Cs + C2) / (Cs + C1 + C2) ··· (6) From formula (6), it can be seen that when Vofs is increased, the curve 401 in FIG. 4(A) showing the characteristics can be shifted in the direction in which Vsig increases (right direction in the figure) like the curve 501 shown in FIG. 5(A). The curve 501 shows the current characteristics of the driving transistor 202 with respect to Vsig when Vofs is increased, and the vertical axis is in logarithmic display. The curve 501 showing the signal voltage (Vsig) - current characteristics when Vofs is increased can have a shape approximately shifted along the positive direction of the horizontal axis from the curve 401. When emitting the maximum brightness and the minimum brightness, the Vsig written to the pixel is V H1 and V L1 respectively. The current is obtained by setting the signal voltage to V H2 and V L2 such that V H2 = V H1 and V L2 = V L1In this case, the intersection point is indicated by a black circle on the curve 501. In other words, if the range between the minimum and maximum values ​​of the signal voltage is the same, when Vofs is increased, the signal voltage V H2 , V L2 The current flowing through the driving transistor 202 is I H2 , I L2 and I shown in the curve 401 H1 and I L1 Greater than.

[0042] As described above, in the threshold correction operation, the Vsig vs. drive current characteristics can be changed by selecting Vofsa or Vofsb from among multiple different voltages as the voltage Vofs output by the drive circuit 109 and driving the signal line. Hereinafter, the light-emitting state of the light-emitting device corresponding to the curve 401 will be referred to as the first display mode, and the light-emitting state of the light-emitting device corresponding to the curve 501 will be referred to as the second display mode. Furthermore, the operation of selecting the voltage to be output by the drive circuit from among multiple different voltages can be performed according to an instruction given to the drive circuit 109. The instruction may be given by operating a switch from the outside, or according to an instruction from a control unit (not shown). The control unit may be provided inside or outside the light-emitting device.

[0043] A solid curve 502 in FIG. 5B shows the light emission characteristics of the light emitting device in FIG. 1 in the second display mode according to this embodiment. The curve 502 is a gamma curve. When the signal voltages corresponding to the display data DH and DL are V H2 , V L2 For the display data DH and DL, the luminance is L H2 , L L2 Here, L H2 >L H1 As described above, according to the present embodiment, it is possible to shift the range of the maximum brightness that can be controlled by increasing Vofs. This makes it possible to change the brightness when the signal line 108 is driven with the same signal voltage.

[0044] Next, control on the low luminance side will be described with reference to FIG. 6. A solid curve 601 in FIG. 6(A) shows the voltage vs. current characteristic used in the second display mode according to this embodiment. The signal voltages written to the pixels are V H3 , V L3 And V H3 and V H1 are equal, and V L3 >V L1 Let the signal voltage V H3 , V L3 The current flowing through the driving transistor 202 is I H3 , I L3 In this example, I L3 =I L1 can be done.

[0045] FIG. 6B shows the light emission characteristics of the light emitting device of FIG. 1 in the second display mode according to the present embodiment. 602 is a gamma curve. When the signal voltages corresponding to the display data DH and DL are V H3 , V L3 The luminance for the display data DH and DL is L H3 , L L3 Here, L L3 =L L1 In this example, the signal voltage V L3 By setting the minimum luminance, it is possible to maintain the minimum luminance regardless of the display mode.

[0046] Next, referring to Figures 7 and 8, it will be described how the signal voltage (Vsig) corresponding to the maximum brightness and the minimum brightness and the threshold correction voltage (Vofs) can be controlled in response to the change in brightness experienced by the light-emitting element due to the environmental temperature.

[0047] A curve 401 shown by a two-dot chain line in FIG. 7A indicates the electrical characteristics of the pixel in FIG. 2 and the range of signal voltages used in the first display mode. The curve 401 indicates the signal voltage vs. drive current characteristics when the threshold correction voltage Vofs=Vofsa. The ambient temperature of the light emitting element in the case of the curve 401 is temperature T1. On the other hand, a curve 701 indicates the current characteristics of the drive transistor 202 with respect to the voltage Vsig when the threshold correction voltage Vofs=Vofsa and the ambient temperature is T2. In both cases, the vertical axis of the current characteristics is expressed logarithmically, and T1>T2. This is because the drive transistor 202 is operated in the subthreshold region and the saturation region, and the lower the temperature, the lower the amount of current that flows. In addition, in the curve 701, the signal voltages written to the pixel when emitting the maximum luminance and the minimum luminance are Vsig and Vsig, respectively. H4 , V L4 When the environmental temperature is T2, the voltage V H4 , V L4 The current flowing through the driving transistor 202 is I H4 , I L4 And, I H4 H1 , I L4 L1 It is.

[0048] 7B shows the light emission characteristics of the light emitting device of FIG. 1 in the first display mode. Curve 402 and curve 702 are gamma curves at environmental temperatures T1 and T2, respectively. In curve 702, the signal voltages corresponding to the display data DH and DL are V H4 , V L4 The luminance for the display data DH and DL is L H4 , L L4 Here, L H4 <L H1 , L L4 <L L1 As the temperature decreases, the maximum and minimum luminances decrease.

[0049] ​​FIG. 8A shows the electrical characteristics and signal voltage range of the pixel in FIG. 2. Curve 801 shows the current characteristics of the drive transistor 202 with respect to the voltage Vsig when the threshold correction voltage Vofs=Vofsc and the environmental temperature is T2, and the vertical axis is a logarithmic scale. Here, Vofsc>Vofsa. The signal voltages written to the pixel when emitting the maximum and minimum luminance are V H5 , V L5 And V H5 =V H4 , V L5 <V L4 The signal voltage V H5 , V L5 The current flowing through the driving transistor 202 is I H5 , I L5 and I H5 =I H1 , I L5 =I L1 can be done.

[0050] 8B shows the light emission characteristics of the light emitting device of FIG. 1 in this example. 802 is a gamma curve at an environmental temperature T2. In 802, the signal voltages corresponding to the display data DH and DL are V H5 , V L5 The luminance for the display data DH and DL is L H5 , L L5 Here, L H5 =L H1 , L L5 =L L1 Even if the temperature drops, the maximum brightness and the minimum brightness can be maintained by appropriately selecting Vofs for driving the signal line during the threshold correction operation. The selection of the voltage level of Vofs may be performed by a control unit having a temperature sensor for detecting the environmental temperature, which controls the drive unit.

[0051] Here, in this embodiment, V H5 and V H4 However, depending on the temperature and the amount of change in maximum brightness, not only the threshold correction voltage Vofs but also V H5For example, if the change in maximum luminance is large, V H5 According to the configuration of this embodiment, it is possible to maintain the maximum luminance and the minimum luminance even when the temperature fluctuates.

[0052] (Embodiment 2) Next, the present embodiment will be described with reference to Fig. 9 to Fig. 11. The present embodiment is an example in which a reset transistor that functions as a switch for connecting the anode of an organic light emitting element 201 to Vss 208 is provided. The following mainly describes the configuration different from the first embodiment.

[0053] Fig. 9 is a system diagram showing an outline of an example of a part of the light emitting device according to this embodiment. As shown in Fig. 9, in the pixel array section 103, a third scanning line 901 is arranged for each pixel row along the row direction. The third scanning line 901 is connected to the output terminal of the corresponding row in the vertical scanning circuit 104, and supplies a reset signal to each pixel 102.

[0054] Fig. 10 is a circuit diagram of an example of a pixel included in the light emitting device of Fig. 9. As shown in Fig. 10, one of the source and drain of a reset transistor 301 (the source in Fig. 10) is connected to one of the source and drain of a drive transistor 202 (the drain here). The other of the reset transistor 301 is connected to Vss 208. The gate of the reset transistor 301 is connected to a third scan line 901. During a non-light emitting period, the reset transistor 301 is turned on to connect the anode of the organic light emitting element 201 to Vss 208, and the organic light emitting element 201 can be put into a non-light emitting state.

[0055] 11 is a timing diagram of the light emitting device according to this embodiment. In FIG. 11, at time t1, the reset signal transitions from High to Low, causing the third scanning line 901 to go High and the reset transistor 301 to go into an ON state. At time t10, the reset signal transitions from Low to High, causing the reset transistor 301 to go into an OFF state. Therefore, during the period from time t1 to t10, the anode potential Vel of the organic light emitting element 201 becomes a voltage substantially equal to Vss208, causing the organic light emitting element 201 to go into a non-emitting state. According to the configuration of this embodiment, a display device with a higher contrast can be realized compared to the first embodiment.

[0056] (pixels) The light emitting device has a plurality of pixels. The pixels may include sub-pixels that emit different colors from each other. The sub-pixels may have, for example, RGB emission colors. This area can be called the light emitting area. The pixel emits light in an area also called the pixel aperture. The pixel aperture can be 15 μm or less, or 5 μm or more. More specifically, it can be 11 μm, 9.5 μm, 7.4 μm, 6.4 μm, etc. The spacing between the sub-pixels can be 10 μm or less, and more specifically, it can be 8 μm, 7.4 μm, 6.4 μm.

[0057] The pixels may be arranged in various ways in a plan view. For example, they may be arranged in a stripe, delta, pentile, or Bayer arrangement. The shape of the subpixels in the plan view may be any shape. For example, they may be rectangular, quadrilateral such as a diamond, or hexagonal. Of course, if the shape is not an exact shape but is close to a rectangle, it is included in the rectangle. The shape of the subpixels and the pixel arrangement may be used in combination.

[0058] (Apparatus to which the light emitting device according to the embodiment is applied) Here, an embodiment of a display device to which the light emitting device 101 according to the above embodiment is applied will be described. First, an outline of the structure of the display device will be described with reference to the schematic cross-sectional views shown in Figures 12(A) and (B). The display device given as an example has an organic light emitting element and a transistor connected to the organic light emitting element. The transistor is an example of an active element, and the transistor may be a thin film transistor (TFT).

[0059] 12A shows an example of a cross section of a pixel, which is a component of the display device according to this embodiment. The pixel includes a subpixel 10. The subpixel 10 is divided into subpixels 10R, 10G, and 10B according to the emission color. The emission color may be distinguished by the wavelength of light emitted from the emission layer, or the light emitted from the subpixel 10 may be selectively transmitted or color-converted by a color filter or the like. Each subpixel 10 has a first electrode 2, which is a reflective electrode, on an interlayer insulating layer 1, an insulating layer 3 covering the edge of the first electrode 2, an organic compound layer 4 covering the first electrode 2 and the insulating layer 3, a second electrode 5, a protective layer 6, and a color filter.

[0060] The interlayer insulating layer 1 may have a transistor and a capacitance element disposed thereunder or inside. The transistor and the first electrode 2 may be electrically connected via a contact hole or the like (not shown). The insulating layer 3 is also called a bank or a pixel separation film. It covers the end of the first electrode 2 and is disposed surrounding the first electrode 2. The portion where the insulating layer 3 is not disposed contacts the organic compound layer 4 and becomes a light-emitting region.

[0061] The organic compound layer 4 has a hole injection layer 41, a hole transport layer 42, a first light emitting layer 43, a second light emitting layer 44, and an electron transport layer 45. The second electrode 5 may be a transparent electrode, a reflective electrode, or a semi-transparent electrode. The protective layer 6 reduces the penetration of moisture into the organic compound layer. Although the protective layer 6 is illustrated as being a single layer, it may be a multi-layer. Each layer may be an inorganic compound layer and an organic compound layer.

[0062] The color filters are divided into 7R, 7G, and 7B according to their colors. The color filters may be formed on a planarization film (not shown). A resin protective layer (not shown) may be provided on the color filters. The color filters may be formed on a protective layer 6. Alternatively, the color filters may be provided on an opposing substrate such as a glass substrate and then bonded to each other.

[0063] The display device 100 will be described with reference to Fig. 12(B). Fig. 12(B) shows an organic light-emitting element 26 and a thin film transistor (TFT) 18 as an example of a transistor. A substrate 11 made of glass, silicon, or the like is provided with an insulating layer 12 on the substrate. An active element 18 such as a TFT is provided on the insulating layer, and a gate electrode 13, a gate insulating film 14, and a semiconductor layer 15 of the TFT 18 are provided. The TFT 18 also has a drain electrode 16 and a source electrode 17. An insulating film 19 is provided on the upper part of the TFT 18. An anode 21 constituting the organic light-emitting element 26 and the source electrode 17 are connected via a contact hole 20 provided in the insulating film.

[0064] The electrical connection between the electrodes (anode, cathode) included in the organic light-emitting element 26 and the electrodes (source electrode and drain electrode) included in the TFT is not limited to the embodiment shown in Fig. 12(B). In other words, it is sufficient that either the anode or the cathode is electrically connected to either the source electrode or the drain electrode of the TFT.

[0065] In the display device 100 of Fig. 12(B), the organic compound layer is illustrated as one layer, but the organic compound layer 22 may be multiple layers. A first protective layer 24 and a second protective layer 25 for reducing deterioration of the organic light-emitting element are provided on the cathode 23. In the display device 100 of Fig. 12(B), a transistor is used as the switching element, but other switching elements may be used instead.

[0066] 12B, the transistor used in the display device 100 is not limited to a transistor using a single crystal silicon wafer, but may be a thin film transistor having an active layer on an insulating surface of a substrate. Examples of the active layer include single crystal silicon, amorphous silicon, non-single crystal silicon such as microcrystalline silicon, and non-single crystal oxide semiconductors such as indium zinc oxide and indium gallium zinc oxide.

[0067] The transistors included in the display device 100 of Fig. 12(B) may be formed in a substrate such as a Si substrate. Here, "formed in a substrate" means that the substrate itself such as a Si substrate is processed to produce the transistors. In other words, having a transistor in a substrate can be seen as the substrate and the transistor being integrally formed.

[0068] The organic light-emitting element of the display device 100 according to this embodiment has its light emission brightness controlled by a TFT, which is an example of a switching element. By providing a plurality of organic light-emitting elements in a plane, an image can be displayed based on the light emission brightness of each element. The switching element according to this embodiment is not limited to a TFT, and may be a transistor formed of low-temperature polysilicon or an active matrix driver formed on a substrate such as a Si substrate. On a substrate can also be within the substrate. Whether to provide a transistor in the substrate or to use a TFT can be selected depending on the size of the display unit. For example, if the size of the display unit is about 0.5 inches, an organic light-emitting element can be provided on a Si substrate.

[0069] Examples in which the light emitting device 101 of this embodiment is applied to a display device, a photoelectric conversion device, an electronic device, a lighting device, a moving object, and a wearable device will be described below with reference to FIGS.

[0070] The light-emitting device 101 according to this embodiment can be used as a component of a display device or a lighting device, and can also be used as an exposure light source for an electrophotographic image forming device, a backlight for a liquid crystal display device, a light-emitting device having a white light source and a color filter, etc.

[0071] The display device according to the present embodiment may be an image information processing device having an image input unit for inputting image information from an area CCD, a linear CCD, a memory card, or the like, an information processing unit for processing the input information, and displaying the input image on a display unit. The display device may be used in a display unit of an imaging device or an inkjet printer, and the display unit may have a touch panel function. The driving method of this touch panel function may be an infrared type, a capacitive type, a resistive film type, or an electromagnetic induction type, and is not particularly limited. The display device may be used in a display unit of a multifunction printer.

[0072] First, an example of a display device using the light-emitting device 101 of this embodiment will be described with reference to FIG. 13. The display device 1000 may have a touch panel 1003, a display panel 1005, a frame 1006, a circuit board 1007, and a battery 1008 between an upper cover 1001 and a lower cover 1009. Flexible printed circuits FPC 1002 and 1004 are connected to the touch panel 1003 and the display panel 1005. Circuit elements such as transistors are mounted on the circuit board 1007. The light-emitting device 101 according to this embodiment can be applied to the display panel 1005. The light-emitting device 101 can be driven by a transistor mounted on the circuit board 1007. The battery 1008 may not be provided if the display device is not a portable device, and it does not need to be provided at this position even if the display device is a portable device.

[0073] The display device according to the present embodiment may have color filters having red, green, and blue colors. The color filters may be arranged in a delta arrangement of the red, green, and blue colors. The display device according to the present embodiment may be used in a display unit of a mobile terminal. In this case, the display device may have both a display function for displaying information and a function for operating the terminal. Examples of the mobile terminal include mobile phones such as smartphones, tablets, and head-mounted displays.

[0074] The display device according to the present embodiment may be used as a display unit of an imaging device having an optical unit with a plurality of lenses and an imaging element that receives light that has passed through the optical unit. The imaging device may have a display unit that displays information acquired by the imaging element. The display unit may be a display unit exposed to the outside of the imaging device, or may be a display unit disposed within a viewfinder. The imaging device may be a digital camera or a digital video camera.

[0075] 14A is a schematic diagram showing an example of an imaging device according to this embodiment. The imaging device 1100 may have a viewfinder 1101, a rear display 1102, an operation unit 1103, and a housing 1104. The light-emitting device 101 according to this embodiment may be applied to the viewfinder 1101. In this case, the light-emitting device 101 may function as a display unit and display not only an image to be captured, but also environmental information, imaging instructions, and the like. The environmental information may include the intensity of external light, the direction of external light, the moving speed of the subject, the possibility that the subject will be blocked by an obstruction, and the like.

[0076] Since the timing suitable for imaging is short, it is better to display information as soon as possible. Therefore, it is preferable to use a light-emitting device using the organic light-emitting element according to the embodiment in a display device. This is because the response speed of an organic light-emitting element is generally faster than that of a liquid crystal display device. A display device using an organic light-emitting element is preferable for use in a device that requires a high display speed.

[0077] The imaging device 1100 has an optical section (not shown). The optical section may have a plurality of lenses. The optical section forms an image of a subject on an imaging element housed in a housing 1104. The focus of the plurality of lenses can be adjusted by adjusting their relative positions. This operation can also be performed automatically. The imaging device may be called a photoelectric conversion device. The photoelectric conversion device may include an imaging method that does not capture images sequentially, but detects the difference from the previous image, cuts out an image from an image that is constantly recorded, and the like.

[0078] FIG. 14B is a schematic diagram showing an example of an electronic device according to this embodiment. The electronic device 1200 has a display unit 1201, an operation unit 1202, and a housing 1203. The light-emitting device 101 can be applied to the display unit 1201. The housing 1203 may have a circuit, a printed circuit board having the circuit, a battery, and a communication unit. The operation unit 1202 may be a button or a touch panel type reaction unit. The operation unit may be a biometric recognition unit that recognizes a fingerprint and performs unlocking or the like. An electronic device having a communication unit can also be called a communication device. The electronic device may further have a camera function by including a lens and an image sensor. An image captured by the camera function is displayed on the display unit. Examples of the electronic device include a smartphone and a notebook computer.

[0079] 15(A) and (B) are schematic diagrams showing an example of a display device using the light emitting device 101 of this embodiment. FIG. 15(A) may be a display device such as a television monitor or a PC monitor. The display device 1300 has a frame 1301 and a display unit 1302. The light emitting device 101 according to this embodiment can be applied to the display unit 1302. The display device 1300 has a base 1303 that supports the frame 1301 and the display unit 1302. The base 1303 is not limited to the form shown in FIG. 15(A). The lower side of the frame 1301 may also serve as the base. The frame 1301 and the display unit 1302 may be curved. The radius of curvature may be 5000 mm or more and 6000 mm or less.

[0080] FIG. 15(B) is a schematic diagram showing another example of a display device using the light-emitting device 101 of this embodiment. The display device 1310 of FIG. 15(B) is configured to be bendable, and is a so-called foldable display device. The display device 1310 has a first display unit 1311, a second display unit 1312, a housing 1313, and a bending point 1314. The light-emitting device 101 according to the embodiment can be applied to the first display unit 1311 and the second display unit 1312. The first display unit 1311 and the second display unit 1312 may be a single display unit without a joint. The first display unit 1311 and the second display unit 1312 can be divided by the bending point 1314. The first display unit 1311 and the second display unit 1312 may display different images, or the first and second display units may display one image.

[0081] FIG. 16(A) is a schematic diagram showing an example of a lighting device using the light-emitting device 101 according to the present embodiment. The lighting device 1400 may have a housing 1401, a light source 1402, a circuit board 1403, an optical film 1404, and a light diffusion unit 1405. The light-emitting device 101 according to the present embodiment can be applied to the light source. The optical filter may be a filter that improves the color rendering of the light source. The light diffusion unit 1405 can effectively diffuse the light of the light source, such as lighting up, and deliver the light to a wide range. The optical filter 1404 and the light diffusion unit 1405 may be provided on the light emission side of the lighting. If necessary, a cover may be provided on the outermost part. Thus, in this specification, the display device is not limited to one that displays an image, but also includes one in which a plurality of light-emitting elements are arranged and used as a light source.

[0082] The lighting device 1400 is, for example, a device that illuminates a room. The lighting device 1400 may emit white light, neutral white light, or any other color from blue to red. It may have a dimming circuit that dims the light. The lighting device 1400 may have a light emitting device 101 applied to a light source 1402 and a power supply circuit connected thereto. The power supply circuit includes a circuit that converts AC voltage to DC voltage and a circuit that adjusts the voltage. Moreover, white has a color temperature of 4200K, and neutral white has a color temperature of 5000K. The lighting device may have a color filter. Moreover, the lighting device according to this embodiment may have a heat dissipation unit. The heat dissipation unit dissipates heat inside the device to the outside of the device, and examples of the heat dissipation unit include metals with high specific heat and liquid silicon.

[0083] FIG. 16(B) is a schematic diagram of an automobile, which is an example of a moving body according to this embodiment. The automobile has a tail lamp, which is an example of a lamp. The automobile 1500 has a tail lamp 1501, and may be configured in such a way that the tail lamp is turned on when the brakes are applied or the like. The light emitting device 101 according to this embodiment can be applied to the tail lamp 1501. The tail lamp may have a protective member for protecting the light emitting device 101. The protective member may be made of any material as long as it has a certain degree of strength and is transparent, but may be made of polycarbonate or the like. A furandicarboxylic acid derivative, an acrylonitrile derivative, or the like may be mixed into the polycarbonate.

[0084] The automobile 1500 may have a body 1503 and a window 1502 attached thereto. The window may be a transparent display as long as it is not a window for checking the front and rear of the automobile. The transparent display may have a light-emitting device having an organic light-emitting element according to this embodiment. In this case, the constituent materials of the electrodes and the like of the organic light-emitting element are made of transparent materials. The moving body according to this embodiment may be a ship, an aircraft, a drone, or the like. The moving body may have a body and a lamp provided on the body. The lamp may emit light to indicate the position of the body. The lamp has an organic light-emitting element according to this embodiment.

[0085] A further application example of the light emitting device 101 of each of the above-mentioned embodiments to a display device will be described with reference to Fig. 17. The light emitting device 101 can be applied to a system that can be worn as a wearable device, such as smart glasses, HMD, or smart contact lenses. An image capturing and display device used in such an application example has an image capturing device capable of photoelectrically converting visible light, and a light emitting device capable of emitting visible light.

[0086] 17(A) will be used to explain glasses 1600 (smart glasses) as an example. An imaging device 1602 such as a CMOS sensor or a SPAD is provided on the front side of a lens 1601 of the glasses 1600. In addition, the display device 101 according to each of the above-mentioned embodiments is provided on the back side of the lens 1601.

[0087] The glasses 1600 further include a control device 1603. The control device 1603 can function as a power source that supplies power to a display device including the image capture device 1602 and the light emitting device 101 according to each embodiment. The control device 1603 can also control the operations of the image capture device 1602 and the light emitting device 101. The lens 1601 has an optical system formed therein for focusing light on the image capture device 1602.

[0088] Another pair of glasses 1610 (smart glasses) will be described as an example with reference to FIG. 17(B). The glasses 1610 have a control device 1612, and the control device 1612 is equipped with an imaging device corresponding to the imaging device 1602 and a light emitting device 101. The lens 1611 is formed with an imaging device in the control device 1612 and an optical system for projecting light emitted from the light emitting device 101, and an image is projected onto the lens 1611. The control device 1612 functions as a power source that supplies power to the imaging device and the light emitting device 101, and can control the operation of the imaging device and the light emitting device 101. The control device may have a line of sight detection unit that detects the line of sight of the wearer. Infrared light may be used to detect the line of sight. The infrared light emission unit emits infrared light toward the eyeball of a user gazing at a displayed image. An imaging unit having a light receiving element detects the reflected light of the emitted infrared light from the eyeball, thereby obtaining an image of the eyeball. In this case, by providing a portion that reduces the incidence of light from the infrared light emitting portion to the display portion in a plan view, it is possible to reduce the deterioration of image quality.

[0089] The user's gaze with respect to the displayed image is detected from an image of the eyeball obtained by capturing infrared light. Any method can be applied to gaze detection using an image of the eyeball. As an example, a gaze detection method based on a Purkinje image produced by reflection of irradiated light on the cornea can be used. More specifically, a gaze detection process based on a pupil-corneal reflex method is performed. Using the pupil-corneal reflex method, a gaze vector representing the direction (rotation angle) of the eyeball is calculated based on the image of the pupil and the Purkinje image contained in the image of the eyeball, thereby detecting the user's gaze.

[0090] A display device including the light-emitting device 101 according to the embodiment may have an imaging device having a light receiving element, and may control an image to be displayed based on the line-of-sight information of a user from the imaging device. Specifically, a first field of view area to which a user gazes and a second field of view area other than the first field of view area may be determined based on the line-of-sight information. The first field of view area and the second field of view area may be determined by a control device of the display device, or may be received and used based on the determination by an external control device. In the display area of ​​the display device, the display resolution of the first field of view area may be controlled to be higher than the display resolution of the second field of view area. In other words, the resolution of the second field of view area may be lower than that of the first field of view area.

[0091] The display area includes a first display area and a second display area different from the first display area, and a high priority area is determined from the first display area and the second display area based on line-of-sight information. The first field of view area and the second field of view area may be determined by a control device of the display device, or may be determined by an external control device and used. The resolution of the high priority area may be controlled to be higher than the resolution of areas other than the high priority area. In other words, the resolution of an area with a relatively low priority may be lowered.

[0092] AI may be used to determine the first field of view area or the area with high priority. The AI ​​may be a model configured to estimate the angle of the line of sight and the distance to an object at the end of the line of sight from the image of the eyeball, using the image of the eyeball and the direction in which the eyeball in the image was actually looking as teacher data. The AI ​​program may be included in the display device, the imaging device, or an external device. When the external device determines the area, information is transmitted to the display device via communication.

[0093] When controlling display based on gaze detection, the present invention can also be applied to smart glasses that further include an imaging device for capturing images of the outside world. The smart glasses can display captured external information in real time. In addition, the smart glasses can detect instructions based on gaze and control the displayed external information.

[0094] As described above, by using a device using the organic light-emitting element according to this embodiment, it is possible to achieve a display with good image quality and stability even over a long period of time.

[0095] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0096] 402: Gamma curve in the first display mode, 502: Gamma curve in the second display mode, DH: Maximum value of the display data, DL: Minimum value of the display data, LH2: Luminance corresponding to the display data DH, LL2: Luminance corresponding to the display data DL

Claims

1. a plurality of pixels each including a light-emitting element, a drive transistor for driving the light-emitting element, a capacitance for holding a threshold voltage of the drive transistor, a signal line, a first switch for connecting the signal line and a control electrode of the drive transistor, and a second switch for connecting a first main electrode of the drive transistor and a predetermined node; A light emitting device comprising: during a preparation period for holding the threshold voltage in the capacitance, the first switch is controlled to be on and the second switch is controlled to be off, and the drive circuit drives the signal line at a voltage level selected from a plurality of different voltage levels; a luminance signal value is written to the light-emitting element, the first switch is controlled to be on and the second switch is controlled to be off during a signal writing period, and the drive circuit drives the signal line with a voltage corresponding to the luminance signal value; the plurality of different voltage levels includes a first voltage and a second voltage greater than the first voltage; the light-emitting element emits light in a first mode in which the first voltage is supplied and the threshold voltage is maintained, or in a second mode in which the second voltage is supplied and the threshold voltage is maintained, A light-emitting device characterized in that, when the signal line is driven with the same voltage corresponding to the brightness signal value in the first mode and the second mode during the signal writing period, the light-emitting element emits light with a higher brightness in the second mode than in the first mode.

2. the first voltage is less than the second voltage; 2 . The light emitting device according to claim 1 , wherein the light emitting element emits light with a lower luminance in the first mode than in the second mode for the same luminance signal value.

3. 3. The light emitting device according to claim 1, wherein the selected voltage level is selected from the plurality of different voltage levels depending on an environmental temperature of the light emitting element.

4. 4. The light emitting device according to claim 3, wherein a higher voltage level is selected from among the plurality of different voltage levels when the environmental temperature is lower than a predetermined temperature.

5. 5. The light emitting device according to claim 1, further comprising a third switch connected between the anode and cathode of the light emitting element.

6. 6. The light emitting device according to claim 1, further comprising a control unit, wherein the drive circuit selects a voltage from among the plurality of different voltage levels in response to an instruction from the control unit.

7. A photoelectric conversion device comprising: an optical section having a plurality of lenses; an imaging element that receives light that has passed through the optical section; and a display section that displays an image captured by the imaging element, the display section comprising a light-emitting device according to any one of claims 1 to 6.

8. 7. An electronic device comprising: a display unit having the light-emitting device according to claim 1; a housing in which the display unit is provided; and a communication unit provided in the housing for communicating with an external device.

9. 7. An illumination device comprising: a light source having the light emitting device according to claim 1; and a light diffusing portion or an optical film that transmits light emitted by the light source.

10. A moving body comprising: a lighting fixture having the light-emitting device according to claim 1; and a body on which the lighting fixture is provided.

Images