WO2009099205A1

WO2009099205A1 - Method and apparatus for driving light-emitting device

Info

Publication number: WO2009099205A1
Application number: PCT/JP2009/052092
Authority: WO
Inventors: Takeshi Yamao; Yasuhiro Shimizu; Kohei Terasaki; Shu Hotta
Original assignee: National University Corporation Kyoto Institute Of Technology
Priority date: 2008-02-08
Filing date: 2009-02-06
Publication date: 2009-08-13
Also published as: JPWO2009099205A1; JP5403518B2

Abstract

A light-emitting device (1) comprises a light-emitting layer (10) composed of a semiconductor material (for example, an organic semiconductor), first and second electrodes (12, 13) electrically connected to the light-emitting layer, and a third electrode (15) connected to the light-emitting layer through an insulating layer (14). A direct current voltage (VD-VS) is applied between the first electrode (12) and the second electrode (13), and an alternating current voltage (VG) is applied to the third electrode (15).

Description

Driving method and driving apparatus for light emitting device

The present invention includes a light emitting layer made of a semiconductor material (for example, an organic semiconductor material), two electrodes electrically connected to the light emitting layer, and an electrode connected to the light emitting layer through an insulator layer. The present invention relates to a method and an apparatus for driving a light emitting device.

Organic electroluminescent elements and organic field effect transistors have been studied as organic light emitting devices using organic semiconductor materials for the light emitting layer. For example, regarding an organic field effect transistor, Patent Document 1 discloses that a gate electrode is provided on an insulating support substrate, an insulator layer and an organic light emitting layer are provided thereon, and a source electrode and a drain electrode are provided thereon. An organic field effect transistor is disclosed (see FIG. 28). In order to emit light from such an organic light emitting device, it is necessary to efficiently inject electrons and holes into the light emitting layer and recombine them.

In order to realize efficient recombination, an organic electroluminescent element generally includes a metal having a high work function (anode), an organic semiconductor that easily allows holes to flow (p-type semiconductor), an organic semiconductor as a light emitting material, an electron Is formed with an element structure including an organic semiconductor (n-type semiconductor) and a metal (cathode) having a small work function, and the total thickness of the organic semiconductor is 1 μm or less. Holes are injected into the light emitting layer from the anode and the p-type semiconductor, and electrons are injected into the light emitting layer from the cathode and the n type semiconductor, and light emission is realized by recombining them in the light emitting layer.

On the other hand, in the organic field effect transistor as shown in FIG. 28, the source electrode 12 directly attached to the organic light emitting layer made of a bipolar (or p-type or n-type) organic semiconductor material using both electrons and holes as carriers. And a gate electrode 15 attached to the organic semiconductor material via the insulator layer 14 to induce carriers in the organic light emitting layer 10 made of the organic semiconductor material on the insulator layer side. . Then, a voltage is applied between the source electrode 12 and the drain electrode 13 which is another electrode attached to the organic light emitting layer 10, thereby causing a current to flow between the source electrode 12 and the drain electrode 13. In the case of an ambipolar organic semiconductor, light emission is observed inside the organic light emitting layer 10, and in the case of a p-type semiconductor, light emission is observed on the drain electrode 13 side in the organic light emitting layer 10 (see FIG. 28).

In the organic electroluminescence device, the emission luminance can be controlled by changing the voltage value between the anode and the cathode. Since this element is an element having only two electrodes (bipolar element), if the voltage of the power source is changed in order to adjust the luminance, the current flowing through the power source used for the control also changes at the same time.

On the other hand, an organic field effect transistor is an element having three electrodes (tripolar element), and as long as a constant voltage power source capable of supplying power is connected to the source electrode and the drain electrode, the source electrode and the drain electrode are connected. The current flowing between them can be controlled simply by changing the value of the gate voltage. At this time, no current flows through the gate electrode. That is, in the organic field effect transistor, the power source for controlling the luminance (gate voltage control power source) does not need to be supplied with power, and therefore the organic field effect transistor is suitable for practical use such as a display panel.

However, the conventional driving method of the organic field effect transistor uses a DC power source for the light emission control voltage, and therefore, it is not possible to effectively inject electrons and holes into the organic light emitting layer, and the emission luminance does not increase. was there. As a technique for solving this problem, there is a technique disclosed in Patent Document 2.

In Patent Document 2, a positive potential rectangular wave voltage is applied to one of a source electrode and a drain electrode (second conductor) of an organic field effect transistor with a gate potential (first conductor) as a reference, and the inside of the organic light emitting layer After a certain time has elapsed, a negative rectangular wave voltage is applied to the other of the source electrode and the drain electrode, and electrons are injected into the organic light emitting layer, thereby effectively bringing carriers into the organic light emitting layer. A method of injecting is disclosed.

JP 2004-128469 A JP 2005-328002 A

However, in the method of Patent Document 2, the potentials of the source electrode and the drain electrode are temporally changed with reference to the gate potential. That is, the source electrode and the drain electrode are AC driven. For this reason, separate power supplies for supplying an AC voltage to each of the source electrode and the drain electrode are required. In this case, there is a problem that it is necessary to synchronize the power supplies, the circuit configuration becomes complicated, and a plurality of power supplies are required, so that the circuit scale increases. In particular, in applications such as a display panel that uses a plurality of organic field effect transistors arranged in an array, the method of Patent Document 2 requires more power and causes a problem that the circuit scale increases. This is a practical problem.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a light-emitting device that realizes light emission of a light-emitting device (for example, an organic light-emitting device) with high light emission luminance with an easy circuit configuration. A driving method and a driving apparatus are provided.

A driving method of a light emitting device according to the present invention includes a light emitting layer made of a semiconductor material, first and second electrodes electrically connected to the light emitting layer, and a first electrode connected to the light emitting layer through an insulator layer. 3 is a driving method of a light emitting device including three electrodes. In the driving method, a DC voltage is applied between the first electrode and the second electrode, and an AC voltage is applied to the third electrode.

A light emitting device driving apparatus according to the present invention includes a light emitting layer made of a semiconductor material, first and second electrodes electrically connected to the light emitting layer, and a first electrode connected to the light emitting layer via an insulator layer. A driving device for a light-emitting device comprising three electrodes, a first power supply for supplying a DC voltage between the first electrode and the second electrode, and an AC voltage for the third electrode. A second power source to be supplied.

The semiconductor material constituting the light emitting layer is, for example, an organic material. The organic material is preferably a bipolar material (both n-type and p-type semiconductors) having both electrons and holes as carriers. The semiconductor material constituting the light emitting layer may be an amorphous film or a crystalline film. Alternatively, the organic material may be a crystal and both end surfaces thereof form a resonator structure.

The AC voltage applied to the third electrode may be a rectangular wave voltage.

According to the present invention, the light emitting device is driven by simultaneously applying a DC voltage to the source electrode and the drain electrode and applying an AC voltage to the gate voltage. Thereby, efficient injection of electrons and holes into the light emitting layer and efficient recombination of electrons and holes become possible, and high emission intensity can be obtained. In addition, since only the voltage applied to the gate electrode is changed over time without changing the voltage applied to the source electrode and the drain electrode over time, the power supply configuration of the drive circuit of the light emitting device can be facilitated. Increase in scale can be suppressed.

The figure which shows the structural example of the drive circuit which implement | achieves the drive method of the organic field effect transistor which concerns on this invention The figure which showed the waveform of the gate voltage applied to an organic field effect transistor by the drive circuit shown in FIG. 1, a source voltage, and a drain voltage The figure explaining the change of the carrier density corresponding to each voltage application state (a) to (f) shown in FIG. The figure which shows another structure of the drive circuit which implement | achieves the drive method of the organic field effect transistor which concerns on this invention The figure which showed the waveform of the gate voltage, source voltage, and drain voltage which are applied by the drive circuit shown in FIG. The figure which showed the waveform of the rectangular wave voltage applied as a gate voltage Diagram showing the waveforms of the gate voltage, source voltage, and drain voltage when the amplitude of the gate voltage is changed and when the DC voltage is superimposed on the gate voltage Diagram for explaining the comb-shaped electrode of the organic field effect transistor used in the experiment The figure which showed the emission spectrum of the organic field effect transistor which made the vapor deposition film the light emitting layer measured when the alternating voltage was applied as a gate voltage, and when the gate voltage was not applied The figure which showed the emission spectrum of the organic field effect transistor which made the vapor deposition film the light emitting layer measured when the gate voltage of alternating voltage and direct current voltage was applied The figure which showed the emission spectrum of the organic field effect transistor (channel length 0.4 micrometer) which uses the vapor deposition film as a light emitting layer measured with respect to the various frequency of gate voltage The figure which showed the emission spectrum of the organic field effect transistor (channel length 10 micrometers) which uses the vapor deposition film measured for various frequencies of gate voltage as a light emitting layer Diagram showing the emission spectrum of an organic field-effect transistor with the deposited film as the light-emitting layer, measured for various amplitudes of the gate voltage The figure which showed the emission spectrum of the organic field effect transistor which made the vapor deposition film the light emitting layer measured with respect to various values of drain voltage and source voltage The figure which showed the emission spectrum of the organic field effect transistor measured with respect to the intercombination distance of two different types of comb electrodes The figure which showed the mode of light emission of the organic field effect transistor which makes a vapor deposition film the light emitting layer when an alternating voltage is impressed to a gate electrode The figure which showed the emission spectrum of the organic field effect transistor which made the crystalline film the light emitting layer measured with and without applying the AC voltage as the gate voltage The figure which showed the emission spectrum of the organic field effect transistor which made the crystal | crystallization film | membrane measured when the gate voltage of alternating voltage and direct-current voltage was applied the light emitting layer Figure showing the emission spectrum of an organic field-effect transistor with a crystalline layer as the light-emitting layer, measured for various frequencies of the gate voltage Diagram showing the emission spectrum of an organic field-effect transistor with a crystalline film as the light-emitting layer, measured for various amplitudes of the gate voltage Figure showing the emission spectrum of an organic field-effect transistor having a light-emitting layer as a crystal film, measured for various values of drain voltage and source voltage The figure which showed the mode of light emission of the organic field effect transistor which uses a crystalline film as a light emitting layer when an alternating voltage is applied to a gate electrode The figure which showed the mode of light emission of the organic field effect transistor which uses a crystalline film as a light emitting layer when an alternating voltage is applied to a gate electrode A diagram showing how the organic field effect transistor emits light over time when an AC voltage is applied to the gate electrode. Diagram showing emission spectrum when asymmetric voltage is applied to source and drain electrodes A diagram showing the light emission intensity when the AC voltage applied as the gate voltage is a rectangular wave voltage and a sine wave voltage Diagram showing emission intensity and fluorescence spectrum under ultraviolet excitation when the AC voltage applied as the gate voltage is a rectangular wave voltage Diagram showing emission intensity and fluorescence spectrum under ultraviolet excitation when the AC voltage applied as the gate voltage is a rectangular wave voltage The figure for demonstrating the drive method of the conventional organic field effect transistor

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic field effect transistor 10 Organic light emitting layer 12 Source electrode 13 Drain electrode 14 Insulator layer 15

Gate electrode

20, 25

Drive circuit

21, 22, 26 DC power source 23 AC power source 27 AC which outputs AC voltage on which DC voltage is superimposed Power supply 40

Organic material

42, 43 Comb electrode

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1. Configuration FIG. 1 shows an example of the configuration of a drive circuit that realizes the organic field effect transistor drive method according to the present invention.

The organic field effect transistor 1 to be driven includes an organic light emitting layer 10, which is formed of an organic semiconductor, and a source electrode 12 and a drain electrode 13 are electrically connected. The organic field effect transistor 1 further includes an insulator layer 14 to which a gate electrode 15 is connected via the insulator layer 14.

The drive circuit 20 that drives the organic field effect transistor 1 includes a DC power supply 21, a DC power supply 22, and an AC power supply 23. The DC power source 21 applies a negative DC voltage (V _s ) to the source electrode 12. The DC power source 22 applies a positive DC voltage V _D to the drain electrode 13. AC power source 23 applies an AC voltage V _G to the gate electrode 15. The voltage applied between the source electrode and the drain electrode mainly contributes to the movement and recombination of carriers in the organic light emitting layer 10, and the voltage applied to the gate electrode 15 is used to inject carriers into the organic light emitting layer 10. Contribute.

2. Driving Principle Hereinafter, the driving principle of the organic field effect transistor according to the present embodiment will be described with reference to FIGS. In the following, the case where the organic light emitting layer 10 is composed of an ambipolar organic semiconductor, which is an organic semiconductor that can flow electrons and holes as carriers, will be described as an example.

FIG. 2 is a diagram showing the time change of the voltage at each

electrode

12, 13, 15 of the organic field effect transistor 1. In FIG. 2, as an example, a DC voltage (hereinafter referred to as “drain voltage”) V _D applied to the drain electrode 13 is +60 V, and a DC voltage (hereinafter referred to as “source voltage”) V _S applied to the source electrode 12 is −60 V. when shows the voltage change when the AC voltage (hereinafter referred to as "gate voltage") the frequency of V _G 20 kHz applied to the gate electrode 15, the amplitude was 100 V. FIG. 3 is a diagram schematically illustrating a change in carrier density in the organic light emitting layer 10 made of an ambipolar organic semiconductor material when the voltage applied to each electrode is changed as shown in FIG.

The driving principle by the driving method of the present embodiment is considered as follows. Hereinafter, the state of the carrier density when the gate voltage V _G is in each of the states (a) to (f) shown in FIG. 2 will be considered.

Condition (a): the gate voltage V _G exceeds the drain voltage, the maximum positive polarity. At this time, electrons are injected and accumulated in the organic light emitting layer 10 from the source electrode 12 side (see FIG. 3A). Electrons flow from the source electrode 12 toward the drain electrode 13 due to the electric field generated by the voltage (V _D −V _S ) between the source electrode 12 and the drain electrode 13.
State (b): The gate voltage V _G is lower than the drain voltage V _D. The injection and accumulation of electrons in the organic light emitting layer 10 decrease, and instead holes are injected from the drain electrode 13 side and start to accumulate (see FIG. 3B). A hole flows toward the source electrode 12 by the electric field between the source electrode 12 and the drain electrode 13. Electrons and holes recombine at the interface to emit light (the same applies to the following light emission locations).
State (c): The gate voltage V _G becomes zero (an intermediate value between the source voltage V _S and the drain voltage V _D ). Thereby, the density of electrons and holes is balanced (see FIG. 3C). At this time, light emission can be observed near the center of the organic light emitting layer 10.
Condition (d): the gate voltage V _G is negative. Thereby, the accumulated amount of holes on the drain electrode 13 side increases, and the accumulated amount of electrons on the source electrode 12 side decreases (see FIG. 3D).
State (e): The gate voltage V _G is lower than the source voltage V _S and is negative and minimum. Thereby, in the organic light emitting layer 10, holes are injected from the drain electrode 13 side and accumulated. A hole flows toward the source electrode 12 by the electric field between the source electrode 12 and the drain electrode 13.
State (f): The gate voltage V _G exceeds the source voltage V _S. Thereby, the accumulation of holes in the organic light emitting layer 10 is reduced, and instead, electrons are injected from the source electrode 12 side and start to be accumulated. Electrons flow toward the drain electrode 13 due to the electric field between the source electrode 12 and the drain electrode 13.

As described above, when a DC voltage is applied between the source electrode 12 and the drain electrode 13 and an AC voltage is applied to the gate electrode 15, when the gate voltage is positive, When electrons are mainly injected from the source electrode 12 and the gate voltage is negative, holes are mainly injected from the drain electrode 13. Thus, it is considered that carriers can be efficiently injected into the organic light emitting layer 10 and can be recombined, so that the light emission efficiency of the organic light emitting layer 10 can be improved.

3. Another Configuration Example FIG. 4 shows another configuration of a drive circuit for an organic field effect transistor. In FIG. 4, a drive circuit 25 for driving the organic field effect transistor 1 includes a DC power source 26 that applies a voltage V _D between the source electrode 12 and the drain electrode 13, and a power source 27 that applies a voltage V _G to the gate electrode 15. Is provided. The power supply 27 supplies a voltage obtained by adding a predetermined DC voltage to the AC voltage.

In the example of FIG. 1, a DC voltage having opposite polarity is applied to the source electrode 12 and the drain electrode 13, and an AC voltage is applied to the gate electrode 15. On the other hand, in the example of FIG. 4, a DC voltage (drain voltage) V _D is applied to the drain electrode 13 with reference to the potential of the source electrode 12, and a DC voltage is applied to the gate electrode 15 as an AC voltage. applying a voltage V _G obtained by adding the voltage. Here, the value of the DC voltage added to the AC voltage in the gate voltage V _G is a voltage that is ½ of the drain voltage V _D. With the configuration of FIG. 4, the circuit configuration can be further simplified as compared with the case of FIG. FIG. 5 shows how the voltage applied to each electrode in the configuration of FIG. 4 changes with time. As an example, FIG. 5 shows voltage changes when the source voltage V _S is grounded, the drain voltage V _D is +120 V, the frequency of the gate voltage V _G is 20 kHz, and the amplitude is 100 V.

In the configuration shown in FIG. 1, the AC voltage applied as the gate voltage V _G is a sinusoidal voltage, (not shown) instead rectangular wave voltage and the triangular wave voltage as shown in FIG. 6 of the sinusoidal voltage, Alternatively, a sawtooth wave (not shown) may be applied to the gate electrode 15. Also in the configuration shown in FIG. 4, a rectangular wave voltage, a triangular wave voltage, or a sawtooth wave may be used instead of the sine wave voltage. Even if a rectangular wave voltage, a triangular wave voltage, or a sawtooth wave is used, the same effect as in the case of a sine wave voltage can be obtained. In particular, a rectangular wave voltage has a great effect.

The positional relationship of the gate voltage V _G with respect to the source voltage V _S and the drain voltage V _D may be as shown in FIG. In particular, as shown in FIGS. 7B and 7C, the absolute value of the amplitude of the source voltage V _S and the absolute value of the amplitude of the drain voltage V _D when the gate voltage V _G is used as a reference are made different. May be. That is, the value of the source voltage V _S of the measurement of the center of the amplitude of the gate voltage V _G as a reference, may be different from the value of the drain voltage V _D to the center of the amplitude was measured as a reference gate voltage V _G. That is, both voltages may be asymmetric.

4). Experimental Results A light emission experiment was performed on the actual organic field effect transistor using the above driving method. The experimental results are shown below.

(1) Experiment using vapor deposition film The organic field effect transistor used for the experiment was produced as follows. On a silicon substrate (not shown) on which an oxide film corresponding to an insulator layer is formed, a device substrate on which comb-shaped

electrodes

42 and 43 are formed as shown in FIG. An organic material 40 serving as an organic light emitting layer was deposited by about 250 nm to produce an organic field effect transistor. The silicon substrate below the oxide film is also used as an electrode. As the organic material, BP1T represented by the following chemical formula was used.

The cross-sectional structure near the electrodes is a silicon substrate, a silicon oxide film formed on the silicon substrate, a chromium layer disposed on the silicon oxide film, and a gold layer disposed on the chromium layer. A chromium layer and a gold layer constitute an electrode. The inter-comb (channel length) d of the comb electrode is 0.4 μm or 10 μm, and the comb length (channel width) L is 8 cm. One of the comb-shaped

electrodes

42 and 43 serves as the source electrode of the organic field effect transistor, and the other serves as the drain electrode. The silicon substrate becomes a gate electrode.

(1.1) Confirmation of effectiveness when an AC voltage is applied to the gate electrode FIG. 9 shows that the organic field effect transistor having a channel length of 0.4 μm fabricated as described above has a direct current of −40 V applied to the source electrode. When a DC voltage of 40 V is applied to the drain electrode and an AC voltage with an amplitude of 75.5 V and a frequency of 20 kHz is applied to the gate electrode, and when no gate voltage is applied (that is, when the gate electrode is opened) It is the figure which showed the change of the emission spectrum in). When the AC voltage is applied to the gate electrode, the spectral intensity is much higher, and it can be seen that the driving method of this embodiment contributes to the light emission of the organic field effect transistor.

FIG. 10 is measured when a -30V DC voltage is applied to the source electrode of the organic field effect transistor, a DC voltage of 30V is applied to the drain electrode, and an AC voltage having an amplitude of 40V and a frequency of 20 kHz is applied to the gate electrode. It is the figure which showed the emission spectrum. For comparison, FIG. 10 also shows an emission spectrum when the source electrode is a reference voltage (ground), and a DC voltage of −60 V is applied to the drain electrode and −80 V to the gate electrode. From the figure, it can be confirmed that a higher emission spectrum is obtained when an AC voltage is applied to the gate electrode than when a DC voltage is applied. From this, it can be understood that the driving method of the present embodiment contributes effectively to the light emission of the organic field effect transistor.

(1.2) Frequency dependence of gate voltage in emission spectrum Furthermore, the emission spectrum was measured by changing the frequency of the alternating voltage of the gate electrode. FIG. 11A shows measurement results of an organic field effect transistor having a channel length of 0.4 μm, and FIG. 11B shows measurement results of an organic field effect transistor having a channel length of 10 μm. Specifically, the emission spectrum was measured by changing the frequency of the voltage of the gate electrode to 2 Hz, 20 Hz, 200 Hz, 2 kHz, and 20 kHz with respect to the aforementioned organic field effect transistor. A DC voltage of −30 V was applied to the source electrode, a DC voltage of 30 V was applied to the drain electrode, and an AC voltage with an amplitude of 40 V was applied to the gate electrode. From FIGS. 11A and 11B, it was confirmed that the intensity of the emission spectrum increased as the frequency increased. From this, it can be understood that the application of the alternating voltage to the gate electrode according to the present embodiment effectively contributes to the increase in the light emission intensity of the light emitting transistor. In addition, the emission luminance can be controlled by frequency. In addition, when driving at 200 Hz or higher, light emission from the organic field effect transistor was visually recognized as continuous light.

(1.3) Dependence of gate electrode voltage amplitude on emission spectrum The emission spectrum was measured by changing the amplitude of the AC voltage of the gate electrode. FIG. 12 shows the measurement results of an organic field effect transistor having a channel length of 10 μm. Specifically, the emission spectrum was measured by fixing the frequency of the voltage of the gate electrode at 20 kHz and changing the amplitude to 0 V, 10 V, 20 V, 30 V, and 40 V with respect to the organic field effect transistor described above. A DC voltage of −30 V was applied to the source electrode, and a DC voltage of 30 V was applied to the drain electrode. From FIG. 12, it was confirmed that a larger emission spectrum was obtained when the AC amplitude of the gate electrode was larger, and the luminance could be adjusted by changing the AC voltage amplitude of the gate electrode.

(1.4) Voltage dependence of source and drain electrodes in emission spectrum The emission spectrum was measured by changing the voltage of the source and drain electrodes. FIG. 13 shows the measurement results of an organic field effect transistor having a channel length of 10 μm. Specifically, for the organic field effect transistor described above, the amplitude of the voltage of the gate electrode is fixed at 40 V and the frequency is fixed at 20 kHz, and the voltages of the drain electrode and the source electrode are set to 0 V, 10 V and −10 V, 20 V and − The emission spectrum was measured by changing each of 20V, 30V and -30V. From FIG. 13, it was confirmed that a larger emission spectrum was obtained when the absolute values of the drain and source electrode voltages were large.

(1.5) Inter-comb distance dependency of comb electrodes in emission spectrum Further, the dependency of the emission spectrum on the distance between comb electrodes of the organic field effect transistor was measured. FIG. 14 shows the results of measuring the intensity of the emission spectrum when the distance (channel length) d between the combs of the organic field effect transistor is 0.4 μm and 10 μm. As the inter-comb (channel length) d increases, the light emission intensity decreases. Therefore, it can be understood that a narrow element between the combs is more advantageous for light emission.

(1.6) State of light emission FIG. 15 shows a photograph of light emission by applying an AC voltage to the gate electrode of an organic field effect transistor having a channel length of 10 μm. FIG. 15A is a photograph of an organic field effect transistor before application of a voltage in a bright place, and FIG. 15B is a photograph of an organic field effect transistor emitting light with a dark surrounding.

(2) Experiment Using Crystal Film In addition, an organic field effect transistor using a BP1T crystal shown in Chemical Formula 1 as an organic material 40 to be an organic light emitting layer was manufactured. The substrate used is a device substrate on which the

comb electrodes

42 and 43 shown in FIG. 8 are formed. The cross-sectional structure near the electrode is a silicon substrate, a silicon oxide film formed on the silicon substrate, a titanium layer disposed on the silicon oxide film, and a platinum layer disposed on the titanium layer. The titanium layer, the platinum layer and the silicon substrate constitute an electrode. The inter-comb (channel length) d of the comb-shaped electrode is 10 μm, and the comb length (channel width) L is 8 cm. One of the comb-shaped

electrodes

(2.1) Confirmation of Effectiveness when AC Voltage is Applied to the Gate Electrode FIG. 16 shows a DC voltage of −50V applied to the source electrode and 50V DC applied to the drain electrode of the organic field effect transistor fabricated as described above. The figure which showed the change of the emission spectrum when a voltage is applied and the alternating voltage of amplitude 60V and frequency 20kHz is applied to a gate electrode, and when a gate voltage is not applied (namely, when a gate electrode is open | released) It is. When the AC voltage is applied to the gate electrode, the spectral intensity is much higher, and it can be seen that the driving method of this embodiment contributes to the light emission of the organic field effect transistor.

Further, FIG. 17 is measured when a DC voltage of −50 V is applied to the source electrode of the organic field effect transistor, a DC voltage of 50 V is applied to the drain electrode, and an AC voltage having an amplitude of 60 V and a frequency of 20 kHz is applied to the gate electrode. It is the figure which showed the emission spectrum. For comparison, FIG. 17 also shows an emission spectrum when a source electrode is set to a reference voltage (ground), a DC voltage of −100 V is applied to the drain electrode, and −120 V is applied to the gate electrode. From the figure, it can be confirmed that a higher emission spectrum is obtained when an AC voltage is applied to the gate electrode than when a DC voltage is applied. From this, it can be understood that the driving method of the present embodiment also contributes effectively to the light emission of the organic field effect transistor having the crystal as the organic light emitting layer.

(2.2) Frequency dependence of gate electrode voltage in emission spectrum Furthermore, the emission spectrum was measured by changing the frequency of the AC voltage of the gate electrode. FIG. 18 shows the measurement results. Specifically, the emission spectrum was measured by fixing the voltage amplitude of the gate electrode to 60 V and changing the frequency to 2 Hz, 20 Hz, 200 Hz, 2 kHz, and 20 kHz with respect to the organic field effect transistor described above. A DC voltage of −50 V was applied to the source electrode, and a DC voltage of 50 V was applied to the drain electrode. From FIG. 18, it was confirmed that the intensity of the emission spectrum increased as the frequency increased. From this, it can be understood that the application of the alternating voltage to the gate electrode according to the present embodiment effectively contributes to the increase in the light emission intensity of the light emitting transistor. In addition, the emission luminance can be controlled by frequency.

(2.3) Dependence of gate voltage amplitude on emission spectrum The emission spectrum was measured by changing the amplitude of the AC voltage of the gate electrode. FIG. 19 shows the measurement results. Specifically, the emission spectrum was measured by fixing the frequency of the voltage of the gate electrode at 20 kHz and changing the amplitude to 0 V, 20 V, 40 V, and 60 V with respect to the organic field effect transistor described above. A DC voltage of −50 V was applied to the source electrode, and a DC voltage of 50 V was applied to the drain electrode. From FIG. 19, it was confirmed that a larger emission spectrum was obtained when the AC amplitude of the gate electrode was larger, and the luminance could be adjusted by changing the AC voltage amplitude of the gate electrode.

(2.4) Dependence of source and drain voltage on emission spectrum The emission spectrum was measured by changing the source and drain voltages. FIG. 20 shows the measurement results. Specifically, for the organic field effect transistor described above, the amplitude of the gate voltage is fixed at 60 V, the frequency is fixed at 20 kHz, and the voltages applied to the drain electrode and the source electrode are 0 V, 10 V and −10 V, 30 V and − The emission spectrum was measured by changing each of 30V, 50V and -50V. From FIG. 20, it was confirmed that a larger emission spectrum was obtained when the absolute values of the drain and source electrode voltages were larger.

FIG. 21 shows a photograph of a state where light is emitted by applying an AC voltage to the gate electrode of the organic field effect transistor. FIG. 21A is a photograph of an organic field effect transistor before voltage application in a bright place, and FIG. 21B is a photograph of an organic field effect transistor that emits light with a dark surrounding.

(3) Experiment Using Other Materials In addition, an organic field effect transistor using an AC5-CF ₃ crystal shown in Chemical Formula 2 as the organic light emitting layer 1 was fabricated. Substrate used was a silicon substrate having an oxide film formed thereon corresponding to the insulator layer, the upper placing the crystals of the AC5-CF _3, the organic electroluminescent prepared by depositing a gold layer over the crystal It is an effect transistor. The gold layer becomes the source and drain electrodes. The silicon substrate becomes a gate electrode.

FIG. 22 shows a photograph of a state where an AC voltage is applied to the gate electrode of the organic field effect transistor to emit light. FIG. 22A is a photograph of an organic field effect transistor before voltage application in a bright place, and FIG. 22B is a photograph of an organic field effect transistor that emits light with a dark surrounding.

In addition, an organic field effect transistor using an AC5-1CF 3-12OMe crystal shown in Chemical Formula ₃ as the organic light emitting layer 1 was fabricated. The substance shown in Chemical Formula 3 is a bipolar material. Substrate used was a silicon substrate having an oxide film formed thereon corresponding to the insulator layer, to form a polymethylmethacrylate layer on the oxide film, further crystals of the AC5-1CF ₃ -12OMe thereon Is an organic field effect transistor in which a gold layer and a magnesium silver layer are formed by vapor deposition from above the crystal. The gold layer becomes the drain electrode and the magnesium silver layer becomes the source electrode. The silicon substrate becomes a gate electrode.

FIG. 23A is measured when a DC voltage of −100 V is applied to the source electrode of the organic field effect transistor, a DC voltage of 100 V is applied to the drain electrode, and an AC voltage having an amplitude of 120 V and a frequency of 500 Hz is applied to the gate electrode. It is the figure which showed the time change of the light emission from the alternating voltage applied to the gate electrode and the organic field effect transistor.

FIG. 23B is a diagram showing the time change of light emission from the organic field effect transistor produced by depositing BP1T shown in Chemical Formula 1 on the device substrate having the comb-shaped electrode shown in FIG. . A DC voltage of −30 V was applied to the source electrode, a DC voltage of 30 V was applied to the drain electrode, and an AC voltage having an amplitude of 80 V and a frequency of 200 Hz was applied to the gate electrode.

FIG. 23 (a) shows that when the bipolar material shown in Chemical formula 3 is used for the organic light emitting layer 1, the intensity is maximized at the maximum value and the minimum value of the AC voltage of the gate electrode at 500 Hz. Indicates that light is emitted. On the other hand, when the p-type material shown in Chemical formula 1 is used for the organic light emitting layer 1, light is emitted at 200 Hz so that the intensity becomes maximum when the gate voltage is minimum. This is because when the organic light emitting layer is a bipolar material, electrons flow when the gate voltage is maximum, and holes flow through the organic light emitting layer when the gate voltage is minimum, whereas the p-type material emits light. In this case, when the gate voltage is the minimum, holes flow through the organic light emitting layer to emit light.

(4) Other experimental data (4.1) Emission spectrum when an asymmetric voltage is applied to the source electrode and the drain electrode The organic light emitting layer 1 on the device substrate on which the comb-shaped electrode as shown in FIG. An organic field effect transistor using an AC5 vapor deposition film shown in Chemical formula 4 was prepared. The inter-comb (channel length) d of the comb-shaped electrode is 0.4 μm, and the comb length (channel width) L is 8 cm. FIG. 24 is a diagram showing an emission spectrum when an asymmetric voltage is applied to the source electrode and the drain electrode. Most examples asymmetry is large, and the emission intensity was measured source voltage V _s 0V, the drain voltage V _D as 140 V. As an example with the smallest asymmetry, emission intensity was measured with a source voltage V _s of −70 V and a drain voltage V _D of 70 V. A sine wave AC voltage having an amplitude of 80 V and a frequency of 2 kHz was applied to the gate electrode as the gate voltage V _G.

As shown in FIG. 24, the emission spectrum increases as the degree of asymmetry increases. In this example, the maximum light intensity is obtained when the source voltage V _s is 0 V and the drain voltage V _D is 140 V. Thus, it can be understood that efficient light emission can be obtained by applying an asymmetric voltage to the source electrode 12 and the drain electrode 13.

The source electrode and the drain electrode, when applying the asymmetrical voltage to the gate voltage V _G, the amount of holes and electrons injected into the organic light-emitting layer in accordance with the asymmetry changes, considered emission spectrum changes.

(4.2) Dependence of Gate Voltage Waveform on Luminous Intensity An organic field effect transistor using the BP1T crystal shown in Chemical Formula 1 as the organic light emitting layer 1 was fabricated. The substrate used is a device substrate on which the

comb electrodes

42 and 43 shown in FIG. 8 are formed. The cross-sectional structure near the electrode is a silicon substrate, a silicon oxide film formed on the silicon substrate, a chromium layer disposed on the silicon oxide film, and a gold layer disposed on the chromium layer. The chromium layer, the gold layer, and the silicon substrate constitute an electrode. Between the comb-shaped electrodes (channel length), one of the comb-shaped

electrodes

42 and 43 is a source electrode of the organic field effect transistor, and the other is a drain electrode. The silicon substrate becomes a gate electrode. FIG. 25 is a diagram showing an emission spectrum of the organic field effect transistor when the AC voltage applied as the gate voltage V _G is a rectangular wave voltage and a sine wave voltage. Specifically, with respect to the organic field effect transistor described above, the amplitude of the gate voltage is fixed at 40 V, the frequency is fixed at 20 kHz, the DC voltage applied to the drain electrode is 30 V, and the DC voltage applied to the source electrode is −30 V. The emission spectrum was measured.

As shown in FIG. 25, the AC voltage applied as the gate voltage V _G is better of the rectangular wave voltage than for the sine wave voltage, it can be seen that emit light more efficiently. This seems to be because the square wave voltage instantaneously switches between positive and negative. That is, when applying a rectangular wave voltage as the gate voltage V _G, since the positive and negative gate voltage V _G is switched rapidly, before the injected holes to reach the source electrode (i.e., injected holes organic light-emitting layer The state is switched to a state where electrons are injected. For this reason, it is considered that recombination of electrons and holes occurs efficiently in the organic light emitting layer, and high light emission intensity can be obtained.

In contrast, the gate voltage V _G be a sine wave voltage, since the switch gradually polarity of the gate voltage V _G, the number of injected holes is believed to reach the source electrode before which contributes to light emission. Therefore, switching the polarity of the gate voltage V _G, when electrons are injected, have become less holes remaining in the organic light-emitting layer, Thus, even when electrons are injected, the electrons and holes in the organic emission layer since the recombination does not occur too high luminous intensity as when the case where the gate voltage V _G is the rectangular wave voltage is considered not obtained.

(4.3) Narrowed emission spectrum when a rectangular wave is applied to the gate voltage An organic field effect transistor using the BP1T crystal shown in Chemical formula 1 as the organic light emitting layer 1 was fabricated. The substrate used was a silicon substrate on which an oxide film corresponding to an insulator layer was formed. An organic layer in which the BP1T crystal was placed thereon, and a gold layer and a magnesium silver layer were formed on the crystal by vapor deposition. It is a field effect transistor. The gold layer becomes the drain electrode and the magnesium silver layer becomes the source electrode. The silicon substrate becomes a gate electrode. The organic material of the organic light-emitting layer 1 of the organic field effect transistor thus fabricated is a crystal, and both end surfaces thereof form a resonator structure. FIG. 26 shows the measurement results for this sample.

The solid line in FIG. 26 is a diagram showing an emission spectrum of an organic field effect transistor in the case of applying a rectangular wave voltage as an alternating voltage of the gate voltage V _G. Specifically, for the organic field effect transistor described above, an emission spectrum is obtained by setting the amplitude of the gate voltage to 120 V, the frequency to 2 kHz, the voltage applied to the drain electrode to 120 V, and the voltage applied to the source electrode to −120 V. It was measured.

The broken line in FIG. 26 is a fluorescence spectrum when the BP1T crystal is excited with ultraviolet rays. As shown in FIG. 26, the narrow lines of luminescence emission spectrum and applying a rectangular wave voltage of the AC voltage as the gate voltage V _G is significantly thinner was observed.

As another sample, an organic field effect transistor using an AC5 crystal shown in Chemical Formula 4 as the organic light emitting layer 1 was fabricated. The substrate used was a silicon substrate on which an oxide film corresponding to an insulator layer was formed. The above-mentioned AC5 crystal was placed on the substrate, and a gold layer and a magnesium silver layer were formed by vapor deposition on the crystal. It is a field effect transistor. The gold layer becomes the drain electrode and the magnesium silver layer becomes the source electrode. The silicon substrate becomes a gate electrode. The organic material of the organic light-emitting layer 1 of the organic field effect transistor thus fabricated is a crystal, and both end surfaces thereof form a resonator structure. FIG. 27 shows the measurement results for this sample.

The solid line in FIG. 27 is a diagram showing an emission spectrum of an organic field effect transistor in the case of applying a rectangular wave voltage as an alternating voltage of the gate voltage V _G. Specifically, for the organic field effect transistor described above, the emission spectrum is obtained by setting the amplitude of the gate voltage to 100 V, the frequency to 20 kHz, the voltage applied to the drain electrode to 70 V, and the voltage applied to the source electrode to -70 V. It was measured.

The broken line in FIG. 27 is a fluorescence spectrum when an AC5 crystal is excited by ultraviolet rays. As shown in FIG. 27, the narrow lines of luminescence emission spectrum and applying a rectangular wave voltage of the AC voltage as the gate voltage V _G is significantly thinner was observed.

As described above, applying a rectangular wave voltage as an alternating voltage of the gate voltage V _G it is found to be effective in a narrow line of light emission.

5. Summary As described above, in this embodiment, when the organic field effect transistor is driven, an AC voltage is applied to the gate electrode 15 while a DC voltage is applied to the source electrode 12 and the drain electrode 13. As a result, electrons and holes are efficiently injected into the organic light emitting layer 10 from each of the source electrode 12 and the drain electrode 13, so that recombination of these carriers is more likely to occur, and high emission intensity can be obtained. it can.

Furthermore, in this embodiment, the potential of the gate electrode 15 is changed with time in a state where the potential of the source electrode 12 and the drain electrode 13 is kept constant without changing with time. With this configuration, it is only necessary to prepare an AC power source only for the gate electrode 15, and there is no need to provide an AC power source for each of the source electrode and the drain electrode as in Patent Document 2, and between the two AC power sources. Since there is no need to synchronize, the configuration of the power supply circuit can be facilitated, and an increase in circuit scale can be suppressed. This is particularly beneficial in an application such as a display panel in which a plurality of organic field effect transistors are arranged in an array, because an increase in device scale can be suppressed. In Patent Document 2, it is necessary to control both the source voltage and the drain voltage with time, and it is necessary to control the source voltage and the drain voltage in order to control the light emission luminance. There was a problem that became complicated. On the other hand, in the method of the present embodiment, only the gate voltage is changed with time, so that only the gate voltage may be appropriately controlled when controlling the light emission luminance. Becomes easy.

Needless to say, the technical idea shown in the present embodiment can be applied not only when the light emitting layer is made of an organic material but also when the light emitting layer is made of an inorganic material.

Although the present invention has been described with respect to particular embodiments, many other variations, modifications, and other uses will be apparent to those skilled in the art. Accordingly, the invention is not limited to the specific disclosure herein, but can be limited only by the scope of the appended claims. This application relates to a Japanese patent application, Japanese Patent Application No. 2008-029318 (submitted on February 8, 2008), the contents of which are incorporated herein by reference.

Claims

A light emitting device comprising: a light emitting layer made of a semiconductor material; first and second electrodes electrically connected to the light emitting layer; and a third electrode connected to the light emitting layer through an insulator layer. Driving method,
Applying a DC voltage between the first electrode and the second electrode, and applying an AC voltage to the third electrode;
A method for driving a light-emitting device.
The method for driving a light emitting device according to claim 1, wherein an amplitude value of the AC voltage is larger than ½ of the DC voltage value.
A first DC voltage is applied to the first electrode, a second DC voltage having a polarity different from that of the first DC voltage is applied to the second electrode, and the third electrode 2. The method of driving a light emitting device according to claim 1, wherein an alternating voltage is applied to the light emitting device.
A first DC voltage is applied to the second electrode with the potential of the first electrode as a reference potential, and an AC voltage is superimposed on the second DC voltage with respect to the third electrode. The method of driving a light emitting device according to claim 1, wherein a voltage is applied.
The method for driving a light-emitting device according to claim 1, wherein the semiconductor material is an organic material.
6. The method for driving a light emitting device according to claim 5, wherein the organic material is a bipolar material using both electrons and holes as carriers.
5. The method for driving a light emitting device according to claim 1, wherein the AC voltage applied to the third electrode is a rectangular wave voltage.
6. The method of driving a light emitting device according to claim 5, wherein the organic material is a crystal and both end faces form a resonator structure.
A light emitting device comprising: a light emitting layer made of a semiconductor material; first and second electrodes electrically connected to the light emitting layer; and a third electrode connected to the light emitting layer through an insulator layer. Drive device
A first power source for supplying a DC voltage between the first electrode and the second electrode;
And a second power source for supplying an AC voltage to the third electrode.
10. The drive device for a light emitting device according to claim 9, wherein an amplitude value of the AC voltage is larger than ½ of the DC voltage value.
The first power source includes a DC power source that applies a first DC voltage to the first electrode, and a second DC voltage that is different in polarity from the first DC voltage with respect to the second electrode. The drive device of the light-emitting device according to claim 9, further comprising:
The first power supply applies a first DC voltage to the second electrode with the potential of the first electrode as a reference potential,
The second power supply is configured to apply a voltage obtained by superimposing an AC voltage on a second DC voltage to the third electrode using the potential of the first electrode as a reference potential. The drive device of the light-emitting device of 9.
13. The light emitting device driving apparatus according to claim 9, wherein the semiconductor material is an organic material.
14. The drive device for a light emitting device according to claim 13, wherein the organic material is a bipolar material using both electrons and holes as carriers.
The drive device for a light-emitting device according to any one of claims 9 to 12, wherein the AC voltage applied to the third electrode is a rectangular wave voltage.
14. The drive device for a light emitting device according to claim 13, wherein the organic material is a crystal and both end faces form a resonator structure.