JP2006093628A - Organic semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic semiconductor laser device capable of advantageously executing laser oscillation which is generated by current excitation by the suppression of a propagation loss caused by a cathode by forming a hole transportation layer into a thick-film structure, and also, by the maintenance of high hole injection efficiency with the hole transportation layer despite its thick-film structure. <P>SOLUTION: The organic semiconductor laser device is composed of a substrate on which an anode, the hole transportation layer, a laser active layer, an electron transportation layer, and the cathode are successively formed. A triphenylamine tetramer compound is used for the hole transportation layer. Alternatively, the organic semiconductor laser device is composed of a substrate on which the cathode, the electron transportation layer, the laser active layer, the hole transportation layer, and the anode are successively formed. The triphenylamine tetramer compound is used for the hole transportation layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic semiconductor laser device characterized in that a triphenylamine derivative is contained in a hole transport layer.

  In the case of using a group III-V compound, which is an inorganic substance, as a semiconductor layer, a semiconductor laser element or a light emitting diode is reported (for example, refer to Patent Document 1), and a surface emitting semiconductor laser and an edge emitting semiconductor laser are reported. (For example, refer to Patent Document 2). On the other hand, an organic semiconductor laser device using an organic compound includes a substrate, an anode layer, a hole transport layer, a laser active layer, an electron transport layer, and a cathode layer as its structure. The laser active layer may also serve as a hole transport layer or an electron transport layer. In this apparatus, holes are injected from the anode into the laser active layer (light emitting layer) by applying a voltage, and electrons are injected from the cathode into the laser active layer (light emitting layer), so that the laser active layer (light emitting layer) is injected. ), Holes and electrons recombine to emit light, and this light is amplified by being guided through the laser device and emitted as laser light.

  In the field of organic electroluminescent devices, a large number of compound types have been reported so far for each of the light emitting layer, the electron transport layer, and the hole transport layer. When paying attention to the hole transport layer, it has been reported that among many types of compound for hole transport layer, the triphenylamine tetramer compound is excellent in heat resistance (see, for example, Patent Document 3).

JP 2003-304034 A JP 2003-63896 A Japanese Patent No. 3194657

In the conventional organic semiconductor laser structure, the hole transport layer and the electron transport layer cannot be made thick, so that the propagation loss of light due to the electrodes is large, resulting in amplified spontaneous emission (ASE). Therefore, there is a problem that the threshold value (ASE threshold value) for this becomes extremely high. Therefore, in practice, it is extremely difficult to cause ASE oscillation by current excitation from the anode and the cathode.
Therefore, it is indispensable to introduce a thick film layer as a hole transport layer. However, when a thick film device is formed using a normal hole transport material, the driving voltage is remarkably increased and the hole injection efficiency is decreased. Resulting in. Furthermore, in order to cause ASE oscillation by current excitation, current injection of several thousand amperes is necessary. However, under such a large current injection, there is a problem that many hole transport materials are thermally destroyed. is there.

  In the present invention, the hole transport layer has a thick film structure to suppress the propagation loss due to the cathode, and the hole transport layer maintains high hole injection efficiency even with a thick film, thereby enabling laser oscillation by current excitation. An object of the present invention is to provide an organic semiconductor laser device that can be advantageously performed. Another object of the present invention is to provide an organic semiconductor laser device that can withstand thermal destruction caused by injection of a large current and can advantageously perform laser oscillation by current excitation.

  In order to achieve the above object, the present inventors have repeatedly investigated the possibility of a thick hole transport layer, and as a result, by adopting a triphenylamine derivative for the hole transport layer, the hole transport layer can be made 100 nm or more. Even with this thick film, the propagation loss of the anode can be suppressed, and it has been found that a configuration advantageous for laser oscillation by current excitation is possible, and the present invention has been completed.

  That is, the present invention has an anode, a hole transport layer, a laser active layer, an electron transport layer, and a cathode sequentially on a substrate, and an organic semiconductor characterized by using a triphenylamine tetramer compound for the hole transport layer. The present invention is a laser device, and the present invention has a cathode, an electron transport layer, a laser active layer, a hole transport layer, and an anode on a substrate, and a triphenylamine tetramer compound is used for the hole transport layer. This is an organic semiconductor laser device.

  The laser active layer in the present invention can also serve as an electron transport layer, and the laser active layer can also serve as an electron transport layer and a hole transport layer.

Although the triphenylamine tetramer compound has excellent performance as a carrier transport layer, since the HOMO (highest unoccupied orbital) level is shallow, the molecule between the layer in contact with the triphenylamine tetramer compound May cause interaction. In order to alleviate such intermolecular interaction, it is effective to insert a thin film second hole transport layer, and the hole transport layer of the present invention can be composed of a plurality of hole transport layers. The triphenylamine tetramer compound is used for at least one of the plurality of hole transport layers.

  The laser active layer is in contact with the hole transport layer that receives the supply of holes from the anode and the electron transport layer that receives the supply of electrons from the cathode, and has a higher refractive index than these hole transport layer and hole transport layer. desirable. This configuration has a so-called double heterostructure in which the laser active layer is sandwiched between the electron transport layer and the hole transport layer, and the laser active layer has a higher refractive index than the electron transport layer and the hole transport layer. By doing so, light is confined well in the laser active layer, and the ASE threshold can be lowered. Here, the laser active layer is preferably made of an organic semiconductor material having a larger energy gap between the HOMO level and the LUMO level than the electron transport layer and the hole transport layer. As a result, carriers can be efficiently confined in the light emitting layer, so that the ASE threshold can be further lowered.

As an organic material constituting the electron transport layer, a metal complex such as Alq3 (8-hydroxyquinoline aluminum), PBD (2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4 Oxadiazole triazoles such as -oxadiazole) and TAZ (1,2,4-triazole derivatives), and phenanthrolines such as BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) It can be illustrated.

  An aromatic amine derivative is extremely effective as the organic material constituting the hole transport layer. In the present invention, a triphenylamine tetramer compound is used as an essential organic material constituting the hole transport layer, and a triphenylamine tetramer compound represented by the formula [1] is particularly effective.

(In the formula [Chemical Formula 1], each of R1 to R8 may be the same or different and is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, or a linear or branched group having 1 to 4 carbon atoms. (A represents a single bond, a phenylene group, a 4,4′-biphenylene group, a 1,1-cyclohexylene group, or a 9,9-fluorenylene group.)

[Chemical Formula 1] Specific compounds of the triphenylamine tetramer compound represented by the formula include the following compounds.

Among these compounds, those in which the substituents represented by R1 to R8 are hydrogen atoms are more preferable.

Further, when the second hole transport layer (hole injection / transport material) is inserted between the above triphenylamine tetramer compound layer and the laser active layer, the following triphenylamine derivatives are used. . arylamines such as α-NPD (4,4′-bis [N (1-naphthyl) -N-phenyl-amino] biphenyl and CBP (4,4′-di (N-carbazolyl) biphenyl), and TPD (( N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-biphenyl) -4,4′-diaminine) and the like.

Typical examples of the laser active layer include a laser active layer using a styrylamine derivative as a laser dye (a dopant for a laser active layer) and a phenylcarbazole derivative as a host material, but other materials may also be used. Is possible. Specific examples of styrylamine derivatives used for laser dyes include BSB (1,4-dimethyl-2,5-bis [p- {N-phenyl-N- (m -Tolyl) amino} styl] benzene). Specific examples of the phenylcarbazole derivative used for the host material include CBP represented by the following chemical formula [Chemical Formula 17], mCP represented by the following chemical formula [Chemical Formula 18], and CDBP represented by the following chemical formula [Chemical Formula 19]. Is shown.

  As the laser dye, DCM2 (dicyanomethylenepyran derivative: red) represented by the following chemical formula [Chemical Formula 20], Coumarin 6 represented by the following chemical formula [Chemical Formula 21], and Perylene represented by the following chemical formula [Chemical Formula 22] (Blue).

  The material used for the anode is preferably a transparent electrode such as ITO or IZO that is highly transparent in the visible range with little light propagation loss.

As a material used for the cathode, a transparent electrode such as ITO or IZO, which has high transparency in the visible region with a small light propagation loss, like the anode can be used. Here, in order to improve the efficiency of electron injection from the transparent electrode, it is effective to insert an alkali metal such as Mg, Cs, Li, or Ca or an alkaline earth metal at the interface between the cathode and the electron transport layer.

As the substrate, glass, sapphire, silicon, compound semiconductors (GaAs, InP, etc.), metals (copper, stainless steel, etc.), graphite, diamond, amorphous carbon, etc. can be used. In particular, by using a substrate having excellent thermal conductivity, it is possible to inject a current of the order of 1000 amperes into the organic semiconductor laser active layer without causing breakdown.

  The organic semiconductor laser device of the present invention can generate laser oscillation by light excitation instead of current excitation. That is, the light is amplified in the organic semiconductor laser active layer by entering the pumping laser light from the transparent substrate side or the cathode side. As a result, laser light can be extracted from the end face.

The organic semiconductor laser device of the present invention has a thick hole transport layer structure, suppresses propagation loss due to the cathode, and maintains a high hole injection efficiency even if the hole transport layer is thick. An organic semiconductor laser device capable of advantageously performing laser oscillation by excitation can be provided. In addition, since it withstands thermal destruction caused by large current injection, it is possible to provide an organic semiconductor laser device that advantageously performs laser oscillation by current excitation. Furthermore, an organic semiconductor laser device that performs laser oscillation by optical excitation can be provided.
Since the hole transport layer has a thick structure, the generation of pinholes can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a drawing for explaining the configuration of an organic semiconductor laser device according to an embodiment of the present invention. This organic semiconductor laser device includes a transparent substrate, an anode, a hole transport layer, a laser active layer, an electron transport layer, and a cathode. [FIG. 2] is a drawing showing a configuration of an organic semiconductor laser device in which a second electron transport layer is inserted between an electron transport layer (first electron transport layer) and a cathode in the organic semiconductor laser device of the present invention. is there. [FIG. 3] shows the configuration of the organic semiconductor laser device of the present invention in which a second hole transport layer is further inserted between the hole transport layer (first hole transport layer) and the laser active layer. FIG. [FIG. 4] is a reverse structure which supports a cathode on a transparent substrate, and further comprises an electron transport layer, a laser active layer, a hole transport layer, and an anode.

An embodiment of each layer constituting the organic semiconductor laser device of the present invention will be described. The cathode is composed of a laminated structure film of an ultra-thin MgAg layer (for example, a film thickness of 2.5 nm) in contact with the electron transport layer and an ITO transparent conductive film (for example, 20 nm). The anode is made of ITO and has a film thickness of 30 nm, for example. For the substrate, for example, a material having high thermal conductivity such as a sapphire substrate can be used. The organic layer is formed by laminating a hole transport layer, a laser active layer, and an electron transport layer in order from the anode side, and these are all made of an organic semiconductor material. The laser active layer is composed of an organic semiconductor mixture layer using BSB [Chemical Formula 16] as a laser dye and CBP [Chemical Formula 17] as a host material, and has a film thickness of, for example, 70 nm. The content of BSB is, for example, 6% by weight. The electron transport layer constitutes a BCP layer (film thickness 20 nm) that forms the first electron transport layer in contact with the laser active layer, and a second electron transport layer sandwiched between the first electron transport layer and the cathode. It has a laminated structure with Alq3 (for example, a film thickness of 100 nm). See FIG.

The film thickness in the hole transport layer is in the range of 10 to 1000 nm. If the film thickness is thinner than this range, the propagation loss of light due to the electrodes increases and the probability of pinholes also increases, which is not preferable. A more preferable film thickness is in the range of 20 to 300 nm. As a material for the hole transport layer, a triphenylamine tetramer compound [Chemical Formula 1] is used. As shown in FIG. 3, inserting a second hole transport layer such as α-NPD at the interface between the TPT1 layer and the laser active layer is also effective in improving the laser action.

The organic semiconductor laser device has a double hetero structure in which a laser active layer is sandwiched between a hole transport layer and an electron transport layer. The laser active layer needs to have a refractive index n higher than both the hole transport layer and the electron transport layer disposed on both sides thereof. As a result, light is easily confined in the laser active layer (light emitting layer). The refractive index of the light-emitting layer made of CBP: BSB in the embodiment is n = 1.84, the refractive index of the hole transport layer is n = 1.8, and the refraction of the BCP constituting the first electron transport layer The rate is n = 1.7.

  Further, the energy gap between the HOMO level and the LUMO level is the largest in CBP: BSB constituting the laser active layer according to the embodiment, and the hole transport layer adjacent to the laser active layer and the first The energy gap of the electron transport layer is smaller than the energy gap of the laser active layer. As a result, the carrier is easily confined in the laser active layer. That is, the hole transport layer and the first electron transport layer also have a function as a carrier confinement layer.

  According to the organic semiconductor laser device according to this embodiment, since the electron injection electrode such as the ultra-thin MgAg layer and the transparent conductive film are arranged on the organic semiconductor laser active layer, the cathode is constituted by a thick metal film. In comparison, light propagation loss can be remarkably suppressed. In addition, since the ultrathin MgAg layer is formed on the surface of the organic multilayer, the electron injection barrier is relaxed and the organic multilayer can be protected from plasma damage when forming the transparent conductive film. Thereby, the electron injection efficiency from the cathode to the laser active layer can be remarkably increased.

  In this way, since the threshold value (ASE threshold value) for causing amplified spontaneous emission (ASE) can be lowered, holes are injected from the anode into the laser active layer, and from the cathode to the laser active layer. By injecting electrons into the laser, laser oscillation can be caused by current excitation. That is, holes injected from the anode are transported to the laser active layer by the hole transport layer, and electrons injected from the cathode are transported to the laser active layer by the electron transport layer. In this laser active layer, recombination of electrons and holes occurs, whereby an excited state is formed and light emission occurs. The emitted light is confined in the laser active layer (light emitting layer) due to the refractive index difference between the laser active layer (light emitting layer) and the hole transport layer and electron transport layer. Amplified and ASE light is emitted from the end face.

  In particular, by applying a triphenylamine tetramer compound as a hole transport layer, the heat resistance is remarkably improved. Therefore, even if a current is injected into the organic semiconductor laser active layer at a high current density, the organic semiconductor laser active layer The thermal destruction of is not caused.

  As described in the following examples, the organic semiconductor laser device of the present invention can generate laser oscillation by light excitation instead of current excitation. That is, the light is amplified in the organic semiconductor laser active layer by entering the pumping laser light from the transparent substrate side or the cathode side. Thereby, a laser beam can be taken out from the end face.

An ITO film (110 nm film thickness) is formed on a glass substrate, a 190 nm film thickness TPT1 is formed as a hole transport layer, a 5 nm α-NPD thin film is formed as a second hole transport layer, and a 50 nm Alq3 thin film is formed as a light emitting layer. Then, an MgAg layer (film thickness: 100 nm) as a cathode and an Ag layer (film thickness: 10 nm) as a cathode were laminated to produce an organic light emitting device. The voltage for applying a current of 1 mA / cm ² to this organic semiconductor device was 5.0V.

[Comparative Example 1]
An ITO film (thickness 110 nm) is formed on a glass substrate, a TPT1 with a thickness of 50 nm is formed as a hole transport layer, a 5 nm α-NPD thin film is formed as a second hole transport layer, and a 50 nm Alq3 thin film is formed as a light emitting layer. Then, an MgAg layer (film thickness: 100 nm) as a cathode and an Ag layer (film thickness: 10 nm) as a cathode were laminated to produce an organic light emitting device. The voltage for applying a current density of 1 mA / cm ² to this organic semiconductor device was 5.0 V as in Example 1 having a TPT1 film thickness of 190 nm. It can be seen that the characteristic that the driving voltage does not increase even when the TPT layer is thick is useful as a hole transport layer in an organic semiconductor laser device.

A glass substrate was used as a transparent substrate, and ITO having a thickness of 30 nm was deposited on the surface as an anode. A hole transport layer, a laser active layer, and an electron transport layer were formed on the ITO anode by a vacuum deposition method. The hole transport layer was TPT1 with a thickness of 20 nm. The laser active layer was prepared by co-evaporation using BSB as a laser dye, CBP as a host material, and 6% by weight of BSB added, and the film thickness was set to 70 nm. BCP with a thickness of 20 nm was deposited as the first electron transport layer, and Alq3 with a thickness of 20 nm was deposited as the second electron transport layer (electron injection layer). Cathode, 3 × ¹⁰ -3 Pa about ultra-thin MgAg layer thickness 2.5nm by vapor deposition in a vacuum of was deposited on the electron transport layer, thereafter, 1 × ¹⁰ -1 in a vacuum of Pa, argon ( A transparent conductive film made of ITO was formed by magnetron sputtering in a gas flow of 11.4 sccm) and oxygen (0.6 sccm). The film thickness was 20 nm. When pumping laser light (nitrogen gas laser: wavelength 337 nm) was incident on this device to perform photoexcitation, an ASE threshold value Eth = 5 μJ / cm ² was obtained. From this ASE threshold value, it can be seen that laser oscillation can be easily generated from the laser active layer.

In the device of Example 1, a 5 nm α-NPD layer was inserted between TPT1 and the laser active layer. Similarly, an optical excitation experiment was performed, and an ASE threshold value Eth = 6 μJ / cm ² was obtained. From this ASE threshold value, it can be seen that laser oscillation can be easily generated from the laser active layer.

A glass substrate was used as the transparent substrate, and ITO having a thickness of 110 nm was deposited on the surface as an anode. A hole transport layer, a laser active layer, and an electron transport layer were formed on the ITO anode by a vacuum deposition method. The hole transport layer was TPT1 with a thickness of 200 nm. The laser active layer was prepared by co-evaporation using BSB as a laser dye, CBP as a host material, and 6% by weight of BSB added, and the film thickness was set to 70 nm. BCP with a thickness of 20 nm was deposited as the first electron transport layer, and Alq3 with a thickness of 20 nm was deposited as the second electron transport layer (electron injection layer). As the cathode, an ultra-thin MgAg layer having a thickness of 2.5 nm was deposited on the electron transport layer by vapor deposition in a vacuum of about 3 × 10 −3 Pa, and then argon (11. A transparent conductive film made of ITO was formed by magnetron sputtering in a gas flow of 4 sccm) and oxygen (0.6 sccm). The film thickness was 20 nm. When pumping laser light (nitrogen gas laser: wavelength 337 nm) was incident on this device to perform photoexcitation, an ASE threshold value Eth = 5 μJ / cm ² was obtained. From this ASE threshold value, it can be seen that laser oscillation can be easily generated from the laser active layer.

  The organic semiconductor laser device of the present invention can provide an organic semiconductor laser device that can advantageously perform laser oscillation by current excitation and an organic semiconductor laser device that performs laser oscillation by optical excitation. Since the hole transport layer has a thick film structure, the generation of pinholes can be suppressed and the yield can be improved.

It is a figure which shows the organic-semiconductor laser apparatus prescribed | regulated to Claim 1. It is a figure which shows the organic-semiconductor laser apparatus prescribed | regulated to Claim 11. It is a figure which shows the organic-semiconductor laser apparatus which added Claim 11 to Claim 5. It is a figure which shows the organic-semiconductor laser apparatus prescribed | regulated to Claim 2. It is a figure which shows the specific aspect of an organic-semiconductor laser apparatus.

Claims (15)

  An organic semiconductor laser device comprising an anode, a hole transport layer, a laser active layer, an electron transport layer, and a cathode in order on a substrate, and a triphenylamine tetramer compound being used for the hole transport layer.   An organic semiconductor laser device comprising a cathode, an electron transport layer, a laser active layer, a hole transport layer, and an anode on a substrate, and using a triphenylamine tetramer compound for the hole transport layer.   The organic semiconductor laser device according to claim 1, wherein the laser active layer also serves as an electron transport layer.   The organic semiconductor laser device according to any one of claims 1 to 3, wherein the laser active layer serves as both an electron transport layer and a hole transport layer. The above-described hole transport layer is composed of a plurality of hole transport layers, and a triphenylamine tetramer compound is used for at least one layer of the plurality of hole transport layers. The organic semiconductor laser device described in 1. The film thickness of the hole transport layer described above, or the total film thickness of the plurality of hole transport layers in a case where the film is composed of a plurality of hole transport layers is 10 to 1000 nm. 3. The organic semiconductor laser device according to any one of claims 5 and 5. The film thickness of the hole transport layer described above, or the total film thickness of the plurality of hole transport layers in the case of being composed of a plurality of hole transport layers is 20 to 300 nm. 3. The organic semiconductor laser device according to any one of claims 5 to 6. The triphenylamine tetramer compound used for the hole transport layer described above has a structure represented by the formula [Chemical Formula 1], any one of claims 1 to 3 and claims 5 to 7. An organic semiconductor laser device according to any one of the above items.

(In the formula [Chemical Formula 1], each of R1 to R8 may be the same or different and is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, or a linear or branched group having 1 to 4 carbon atoms. (A represents a single bond, a phenylene group, a 4,4′-biphenylene group, a 1,1-cyclohexylene group, or a 9,9-fluorenylene group.)   The substituent of the triphenylamine tetramer compound represented by the formula [Chemical Formula 1] used in the hole transport layer is R1 = R2 = R3 = R4 = R5 = R6 = R7 = R8 = hydrogen atom. The organic semiconductor laser device according to any one of claims 1 to 3, and 5 to 8.   The organic semiconductor laser device according to any one of claims 1 to 3, and 5 to 7, wherein the hole transport layer has a trap level of 0.30 eV or less.   11. The organic semiconductor laser device according to claim 1, wherein the electron transport layer includes a plurality of electron transport layers. 11.   The refractive index of the laser active layer described above is larger than the refractive index of the hole transport layer and the refractive index of the electron transport layer, any one of claims 1 to 3 and claims 5 to 11. The organic semiconductor laser device according to Item.   The energy gap between the HOMO level and the LUMO level in the laser active layer is larger than the energy gap between the HOMO level and the LUMO level in the hole transport layer and between the HOMO level and the LUMO level in the electron transport layer. The organic semiconductor laser device according to any one of claims 1 to 3, and 5 to 12.   14. The organic semiconductor laser device according to claim 1, wherein the organic semiconductor laser device is of a waveguide emission type. 14. The organic semiconductor laser device according to claim 1, wherein the organic semiconductor laser device is a surface emitting type.

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