JP6092679B2 - Transistor element - Google Patents

Description

  The present invention particularly relates to a transistor element exhibiting excellent current modulation, and more particularly to a transistor element excellent in driving an organic EL display or the like and excellent in current amplification factor that modulates a large current at a low voltage.

  In recent years, flat TVs and notebook computers have been widely used, and the required performance for display displays such as liquid crystal displays, organic EL displays, and electronic papers is also increasing. Furthermore, with the spread of high-function mobile phones and tablet terminals, display displays are becoming finer, smaller, and thinner. A field effect transistor (FET) is used for driving such display elements. Currently, FETs using silicon, which is an inorganic material, are used, but displays using organic transistor elements have been reported for the purpose of cost reduction, large area, and flexibility. Is expected.

  However, many of them are a combination of an organic field effect transistor (OFET) and a liquid crystal display unit or an electrophoresis cell. OFETs are difficult to obtain a large current due to their structure and low mobility, and few examples have been reported for use in driving elements of organic EL displays that are current-driven devices that require large currents. Therefore, it is desired to develop an organic transistor element that can drive an organic EL display and operates with a large current at a low voltage.

  Currently, in order to obtain a large current using an OFET, it is necessary to shorten the channel length of the transistor element. However, the patterning technology with a view to mass production is to reduce the channel length to several μm or less. difficult. In order to solve this problem, a “vertical transistor structure” that can operate at a low voltage and a large current by flowing a current in the film thickness direction has been studied. In general, the thickness of an element used in a vertical sandwich device is several tens to several hundreds of nanometers, and it is possible to control the film thickness on the order of nm or less with high accuracy. The vertical transistor can easily realize a short channel length of 1 μm or less by setting the channel in the film thickness direction (vertical direction), and a large current may be obtained. So far, such vertical organic transistor elements have been depleted with polymer grid triode vertical transistors using a self-organized network structure of polyaniline film as grit electrodes, and fine striped intermediate electrodes. A static induction transistor (SIT) that controls the current between the source and the drain by modulating the layer width is known.

  In addition, a vertical organic transistor element that exhibits high-performance transistor characteristics by producing a laminated structure of organic semiconductor / metal / organic semiconductor has been proposed (Patent Document 1). In this vertical transistor element, an organic semiconductor layer and a striped intermediate metal electrode are provided between an emitter electrode and a collector electrode. In this organic transistor element, electrons injected from the emitter electrode are transmitted through the intermediate metal electrode, whereby current modulation similar to that of a bipolar transistor is observed, and the intermediate metal electrode acts like a base electrode. It is called an organic transistor (Metal-Base Organic Transistor: hereinafter referred to as MBOT).

  In MBOT, when an output voltage is applied to the emitter electrode and the collector electrode and no voltage is applied between the emitter electrode and the base electrode, almost no current flows, but when a voltage is applied between the emitter electrode and the base electrode, the emitter electrode-collector is applied. A current flows between the electrodes. The current flowing between the emitter electrode and the collector electrode is the collector current, and the current flowing between the base electrode and the collector electrode is the base current. MBOT is a current amplifying element capable of modulating the collector current by the base voltage because the collector current increases abruptly as compared with the base current that increases by the application of the base voltage. The “leakage current” that flows when voltage is applied between the emitter electrode and the collector electrode and no voltage is applied between the emitter electrode and the base electrode is OFF current, and the voltage is applied between the emitter electrode and the base electrode. The current that sometimes flows is the ON current. MBOT is a transistor element in which an OFF current is close to zero and a large ON current can be obtained.

  In addition, as a structure of an organic transistor (MBOT), MBOT has been reported that can be easily formed by stacking an organic semiconductor / metal / organic semiconductor by vacuum deposition on a transparent ITO electrode as a collector electrode (patent) Reference 2). As the organic semiconductor, dimethylperylenetetracarboxylic acid diimide (Me-PTCDI) and fullerene (C60), which are n-type organic semiconductor materials, are used. As the electrode material, Al is used as the base electrode, and Ag is used as the emitter electrode. It has been. This MBOT is capable of large current modulation with improved on / off ratio (ratio of current density of ON current to current density of OFF current) by introducing a dark current suppression layer and heat-treating the base electrode. It becomes a transistor element. Thus, although MBOT is a vertical transistor, it does not require fine patterning of fine grid electrodes and stripe electrodes.

  Further, as an organic transistor element (MBOT), an organic semiconductor layer and a sheet-like base electrode are provided between an emitter electrode and a collector electrode, and an energy barrier layer and a charge transmission promoting layer are provided between the base electrode and the collector electrode. MBOT (Patent Document 3) and MBOT (Patent Document 4) using an organic semiconductor layer made of perylenetetracarboxylic acid diimide having a long-chain alkyl group on the collector electrode side as a collector layer have been proposed, It has been reported that good current modulation characteristics and on / off ratios can be obtained without heat treatment. Furthermore, MBOT in which the organic semiconductor layer of the emitter electrode and the base electrode has a diode structure has been reported as a transistor element having good amplification (Patent Document 5).

  Further, as a vertical transistor, an organic semiconductor layer and a sheet-like base electrode are provided between an emitter electrode and a collector electrode, and N organic semiconductor layers between the emitter electrode and the base electrode and between the collector electrode and the base electrode are provided with N , N′-diphenyl-N, N′-di (1-naphthyl) -1,1′-biphenyl-4,4′-diamine (NPB) / fullerene (C60) heterojunction organic semiconductor layer transmission A conductive metal substrate organic transistor has been reported as a bipolar transistor (Non-patent Document 1).

  In addition, as a vertical transistor, an organic semiconductor layer and a comb-shaped base electrode are provided between an L-shaped emitter electrode and a collector electrode, and the organic semiconductor layer is BTQBT [Bis (1,2,5-thiadiazolo). -P-quinobis (1,3-dithiol)] is reported to exhibit a large current value and ON / OFF ratio despite being a hole transport material (Patent Document 6). .

JP 2003-101104 A JP 2007-258308 A JP 2009-272442 A JP 2010-263144 A International Publication No. 2011/027915 Pamphlet JP 2010-251472 A

J. et al. Hung et al, Organic Electronics, 10, 210 (2009)

  However, polymer grid triode type vertical transistors and electrostatic induction transistors (SIT) are difficult to achieve high performance and mass production due to the difficulty of forming an intermediate electrode. In addition, the organic transistor element (MBOT) described in Patent Documents 1 and 2 may have a high off-state current depending on the film thickness and structure, and the transistor has an organic semiconductor / metal / organic semiconductor stacked structure. Once manufactured, current modulation is not necessarily observed. Therefore, in order to exhibit stable performance, obtain a large current value, a high amplification factor, and a high on / off ratio, it is necessary to provide an oxide layer on the surface of the base electrode by heat treatment to form an off-current suppressing layer. . In addition, the organic transistor element (MBOT) described in the above-mentioned Patent Document 3 amplifies the current without heating the electrode by providing an insulating current transmission promoting layer under the base electrode. However, it is difficult to obtain a large current value, a large amplification factor, and a large on / off ratio sufficient to operate an electronic device, and stable operation as an MBOT with a hole transporting material is difficult. is there.

  Further, in Patent Document 6, current modulation is shown by forming an organic semiconductor layer by BTQBT as a hole transport material, but the materials that can be used are limited, and the synthesis of the material is multi-stage and a large amount of synthesis is possible. It is difficult, and since the electrode shape of the element is a comb shape or an L shape and is complicated, it is difficult to mass-produce stable elements by a simple manufacturing process.

  Non-Patent Document 1 shows a current modulation action as a bipolar transistor element, and thus may be used for a complementary logic circuit or the like, but has a large current value and current sufficient to operate an electronic device. It is difficult to obtain enhancement of the above, and it is difficult to use it as a driving element such as an organic EL.

  Accordingly, an object of the present invention is to solve the above-described problems, and in particular, it can be stably provided by a simple manufacturing process, particularly a process using a coating printing method, and mass production is also possible. It is a structure that can be made possible, and it is possible to provide a transistor element (MBOT) having a large current amplification action and an excellent on / off ratio under a low voltage.

  The above object is achieved by the present invention described below. That is, according to the present invention, a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and a p-type organic semiconductor layer is provided on each of the front and back sides of the base electrode. Provided is a transistor element characterized in that a hole permeation promoting layer is provided between a p-type organic semiconductor layer on the emitter electrode side, and the hole permeation promoting layer is a film having a conductive polymer. .

  The following are mentioned as a preferable form of the transistor element of the present invention described above. The hole permeation promoting layer is a hydrophilic film formed from a material having a conductive polymer. The conductive polymer contains poly (3,4-ethylenedioxythiophene). The energy level of the conductive polymer is larger than the highest occupied molecular orbital of the p-type organic semiconductor layer provided between the base electrode and the emitter electrode. A current transmission promoting layer made of an alkali metal salt is laminated between the hole transmission promoting layer and the base electrode. The film thickness of the hole permeation promoting layer is from 5 nm to 200 nm.

  According to the present invention, an organic transistor element (MBOT: hereinafter simply referred to as a transistor element) having the following excellent characteristics is provided. In the transistor element of the present invention, a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and a p-type organic semiconductor layer (hereinafter simply referred to as an organic semiconductor layer) is provided on each side of the base electrode. ) And a conductive layer between the base electrode and the p-type organic semiconductor layer on the emitter electrode side (hereinafter referred to as “emitter electrode-side organic semiconductor layer”). A hole permeation promoting layer made of a film having a polymer is provided. More preferably, the hole permeation promoting layer characterizing the present invention is a hydrophilic film formed from a conductive polymer, and the conductive polymer contains poly (3,4-ethylenedioxythiophene). It can be mentioned. Since the hole permeation promoting layer can be formed using a water-based ink containing the conductive polymer as described above, its production is simple and a hole permeation promoting layer in a good state can be formed. . Specifically, in the transistor element of the present invention, the organic semiconductor layer is disposed as described above, and a hole permeation promoting layer provided between the base electrode and the emitter electrode side organic semiconductor layer is formed, for example, with a hydrophilic property. Therefore, it is possible to form a smooth surface of the hole permeation promoting layer. For this reason, when an organic semiconductor layer is laminated on this, it is possible to form a laminated structure with small surface irregularities, and as a result, the transistor element of the present invention is capable of high current modulation at low voltage. The effect can be obtained stably.

  The transistor element of the present invention has high performance as described above, and as an element for driving various displays and an organic light emitting transistor element, in particular, an organic EL element driven by large current modulation, an element for driving electronic paper In addition, it is useful as a current amplification element. Transistor elements for driving these elements require contrast between on and off, and are required to have a larger on / off ratio and suppression of dark current. When the on / off ratio is low and the dark current is large, not only cannot it be used as a switching element, but also problems such as the organic EL emitting light when it is off. On the other hand, the transistor element of the present invention exhibits high performance as an amplifying action transistor element and a switching transistor element due to excellent large current modulation characteristics and frequency characteristics in a low voltage region.

The organic transistor element of the present invention exhibits a large current amplification factor, and a large current amplified between the emitter electrode and the collector electrode can be passed only by passing a small current between the emitter electrode and the base electrode. The ratio between the input current and the amplified large current is the current amplification factor _hFE . Therefore, as the current amplification factor increases, a large current can be obtained with a small current, and a large change in current can be detected by a slight change in the input current. As will be described later, the transistor element of the present invention has a current amplification factor of 50 or more, and can be 150 or more. If this current amplification factor is 50 or more, it can be sufficiently used as a switching element or an amplification element, and if it is 100 or more, it can be used as an excellent transistor amplification circuit.

  In addition, the transistor element of the present invention can perform a large current modulation in a low voltage region, can reduce the area occupied by the transistor element in one pixel, and can improve the aperture ratio in the display. By applying, it is possible to achieve a high-performance, high-efficiency display. In addition, the organic semiconductor layer of the transistor element of the present invention can use an organic semiconductor polymer as a forming material, and can use a conductive polymer for a hole transmission layer, and thus can be produced by a simple coating printing method. A transistor element can also be formed on a flexible substrate such as plastic. As a result, a display and a device that are reduced in size, weight, thickness, and thickness can be manufactured. Further, the coating printing method can form a large amount of transistor elements on a large-area substrate, and can reduce the cost and energy consumption.

More specifically, the transistor element provided by the present invention applies a voltage (V _C ) between the emitter electrode 12 and the collector electrode 11 as shown in FIG. The collector current modulated between the emitter electrode 12 and the collector electrode 11 is compared with the base current I _B flowing between the emitter electrode 12 and the base electrode 13 when a voltage (V _B ) is applied between the emitter electrode 12 and the base electrode 13. A current modulation type transistor element in which I _C flows is obtained. More specifically, the current amplification factor of the modulated collector current I _C (collector current I _C / base current I _B) becomes a 50 or more, exhibited very good current modulation, applicability to various applications There is expected.

3A and 3B each illustrate a structure of a transistor element of the present invention. 4A and 4B illustrate a structure of a transistor element manufactured in Examples and Comparative Examples. 4A and 4B illustrate a structure of a transistor element manufactured in Examples and Comparative Examples. 4A and 4B illustrate output characteristics (I _C −V _B curve) of a transistor element of the present invention. 4A and 4B illustrate output characteristics (I _C −V _B curve) of a transistor element of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be carried out without departing from the gist of the present invention.

  First, the organic transistor of the present invention, which has an organic semiconductor layer and a sheet-like base electrode between an emitter electrode and a collector electrode, and an organic semiconductor layer is disposed on each of the front and back sides of the base electrode. The element (MBOT) will be described. In the organic transistor element (MBOT) of the present invention, a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and an organic semiconductor layer is provided on each of the front and back sides of the base electrode, and One feature is that the hole permeation promoting layer 31 provided between the base electrode and the emitter electrode side organic semiconductor layer is a film having a conductive polymer. In the present invention, two organic semiconductor layers arranged between the emitter electrode and the collector electrode with the base electrode sandwiched between the collector electrode side are the collector layer, and the emitter electrode side is the emitter layer. Call it.

  An example of the structure of the transistor element of the present invention is shown in FIG. 1. As shown in FIG. 1, the element of the present invention has a stacked structure of organic semiconductor / electrode / organic semiconductor and can be manufactured by a simple stacking process. It is a possible vertical organic transistor. As shown in FIG. 1, the structure is such that a base electrode is disposed on a substrate (not shown) at a position sandwiched between a collector layer 21 and an emitter layer 22 made of an organic semiconductor, and these two organic semiconductor layers. 13. A hole permeation promoting layer 31 is provided. That is, the transistor element of the present invention illustrated in FIG. 1 has a stacked structure in which a collector electrode 11, a collector layer 21, a base electrode 13, a hole transmission promoting layer 31, an emitter layer 22, and an emitter electrode 12 are stacked in this order on a substrate. It has a structure.

  One of the features of the transistor element of the present invention is that the hole permeation promoting layer 31 is formed as a film having a conductive polymer. As a result of intensive investigations to obtain a transistor element that can be put to practical use, the present inventors have described the above in addition to a unique laminated structure in which an organic semiconductor layer is disposed with the base electrode 13 interposed therebetween. As described above, since the hole permeation promoting layer 31 formed of a material containing a conductive polymer has a smooth surface, the emitter layer 22 formed thereon is also smooth, and a laminated structure that forms a smooth interface. It becomes. As a result, a stable current can be obtained, the leakage current generated by the unevenness can be suppressed, and the off-current can be kept small. Further, the holes are accelerated by the conductive polymer constituting the hole permeation promoting layer 31. The transmittance of the base electrode 13 is increased by increasing the charge moving from the emitter layer 22 to the collector layer 21 via the hole permeation promoting layer 31, and a large current gain can be obtained. It has been found that a large output modulation and current modulation can realize a useful organic transistor element (MBOT) that can operate stably.

As described above, the current flowing through the transistor element of the present invention applies the collector voltage V _C between the emitter electrode 12 and the collector electrode 11, and further the base voltage V _B between the emitter electrode 12 and the base electrode 13. Is applied, the holes injected from the emitter electrode are accelerated by the action of the base voltage V _B , pass through the base electrode, and reach the collector electrode. That is, the base current I _B that flows when the base voltage V _B is applied between the emitter electrode 12 and the base electrode 13 is amplified to the collector current I _C that flows between the emitter electrode and the collector electrode by the application of the base voltage. . Therefore, the transistor element of the present invention can stably obtain a current modulation action similar to that of a bipolar transistor, and can perform large output modulation and current amplification.

  The material for forming the hole permeation promoting layer that characterizes the present invention will be described. The conductive polymer used for forming the hole permeation promoting layer of the transistor of the present invention can be used without any problem as long as it is a material that promotes the permeation of holes, but its conductivity is 1-1000 S / cm. preferable. Further, it is preferable to use a hydrophilic conductive polymer in order to form a favorable hole permeation promoting layer. Examples of such include poly (ethylenedioxythiophene), polyaniline, polypyrrole, polythiophene, polyfluorene, poly (p-phenylene vinylene), polyacetylene, polythienylene vinylene, and modified products thereof. Of these, poly (3,4-ethylenedioxythiophene) and polyaniline are preferable. This point will be described later. These conductive polymers can be used alone or in combination of two or more. In addition, these conductive polymers may be those whose conductivity is increased by doping. As the doping material, halogen, Lewis acid, cationic species, anionic species and the like can be used. For example, preferred dope materials for PEDOT include polystyrene sulfonic acid (hereinafter sometimes abbreviated as PSS), toluene sulfonic acid, and the like. In addition, these conductive polymers may be added to carbon-based conductive materials such as graphene, carbon nanotubes, carbon nanohorns, and graphite, metal-based conductive materials such as gold, copper, silver, and nickel, zinc oxide, It can also be used in combination with a metal oxide conductive material such as tin oxide or indium oxide.

  In addition to the materials described above, the hole permeation promoting layer forming material used in the present invention improves adhesion to the base material during film formation and lamination, and imparts smoothness to the film surface. For the purpose, polyvinyl alcohol, hydroxyalkyl cellulose, carboxymethyl cellulose, methyl cellulose, polyalkylene oxide, polyacrylamide, polyacrylic acid, polyacrylamide and derivatives thereof, aqueous urethane resin, aqueous acrylic resin, water-soluble epoxy resin, water-soluble polyester, etc. These water-soluble resins, emulsion solutions, and aqueous dispersions can be used in combination.

  Any of the conductive polymers exemplified above can be used as the material for forming the hole permeation promoting layer used in the present invention. As a particularly preferable conductive polymer, poly (3,4-ethylenedioxythiophene) (hereinafter, And may be abbreviated as PEDOT) or polyaniline. According to the study by the present inventors, for example, a conductive polymer layer formed by PEDOT has excellent stability, high conductivity (for example, 1000 S / cm), hole injectability, and in the visible light region. Because of its low absorption, it can also be used in devices for optical applications. In addition, PEDOT can not only increase conductivity by doping with a doping material such as polystyrene sulfonic acid or paratoluene sulfonic acid, but also can control conductivity by selecting a mixing ratio with the doping species. There is also an advantage. In addition, by taking the block structure and graft structure with other polymers as exemplified above (for example, graft compounds with alkylene oxide), the solubility can be controlled, so smooth hole penetration and good hole transmission promotion Layers can be easily formed.

  As described above, in the transistor element of the present invention, the hole permeation promoting layer is formed as a film of a material having a conductive polymer, thereby realizing a base electrode transmittance with a large hole. The hole permeation promoting layer characterizing the present invention is preferably formed using a water-based ink containing a conductive polymer as described below, for example, because of the ease of forming the layer. . A water-based ink containing a conductive polymer used in this case (hereinafter, also simply referred to as a water-based ink) is a film having a conductive polymer that functions as a hole permeation promoting layer (hereinafter, referred to as a water-based ink) by coating and printing. If a conductive polymer layer) can be formed, it can be used without problems.

  The water-based ink used for forming the hole permeation promoting layer includes, for example, water and an alcohol solvent. In the water-based ink, the conductive polymer exists in a dissolved or dispersed state. As described above, the conductive polymer layer formed with such a water-based ink has a high affinity with water for the conductive polymer used to form the conductive polymer layer. There will be no organic solvent resistance. The hole permeation promoting layer constituting the transistor element of the present invention is formed between the base electrode and the emitter layer. The hole permeation promoting layer is excellent in organic solvent resistance, and will be described below. In addition, there is an advantage that almost no erosion or corrosion of the element that may occur in the emitter layer forming process, which is a subsequent process of forming the hole transmitting layer, occurs. The emitter layer can be formed by a vapor deposition method or the like, but if formed by a coating printing method, its production becomes easy, which is extremely preferable in practice. As will be described later, since the organic semiconductor material used for forming the emitter layer can be dissolved in an organic solvent, the emitter layer can be formed by a coating printing method of the organic semiconductor solution. In this case, since the hole permeation promoting layer (conductive polymer layer) is excellent in organic solvent resistance formed by a hydrophilic material, it was formed in the previous step during coating and printing of the organic semiconductor solution. Since the conductive polymer layer does not dissolve, corrode, swell, or deteriorate, it is possible to form a smooth interface between the hole transmission promoting layer and the emitter electrode side organic semiconductor layer.

  As described above, the hole permeation promoting layer constituting the transistor element of the present invention is preferably formed from a water-based ink containing a conductive polymer. As long as it is not reduced, an organic solvent can be included. The organic solvent used in this case is not limited, but for example, alcohol solvents such as methanol, ethanol, propanol, isopropanol, butanol, amyl alcohol, chloroform, dichloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, Halogen hydrocarbon solvents such as chloronaphthalene, ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as diethyl ether, dioxane and tetrahydrofuran, toluene, xylene and ethylbenzene Aromatic hydrocarbon solvents such as tetrahydrofuran, sulfolane, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, etc. , And the like aprotic polar solvents. These solvents may be used alone or in combination.

  According to the study by the present inventors, in the transistor element of the present invention, the work function of the hole permeation promoting layer made of the material as described above is set to the HOMO (maximum occupied) of the p-type organic semiconductor material used for the emitter layer. By making it larger (noble) than the (orbital) level, it is possible to further promote the transmission of holes and increase the current amplification factor. The difference between the work function of the conductive polymer and the HOMO (highest occupied orbital) level of the p-type organic semiconductor material may be the same level, but is preferably higher by 0.1 eV to 1.5 eV. If the voltage is 0.1 eV to 1.5 eV, the charge can efficiently move from the emitter layer to the hole transmission layer, and can flow from the hole transmission promotion layer through the base electrode to the collector layer. If the work function of the hole permeation promoting layer is made smaller (base) than the HOMO (highest occupied orbital) level of the p-type organic semiconductor material used for the emitter layer, a sufficient hole permeation promoting effect can be obtained. Even if it is configured to be large (noble), if the difference is 1.5 eV or more, not only the hole transfer from the emitter layer to the hole transmission promoting layer becomes difficult, but also the hole transmission promoting layer. It is difficult to transmit holes from the collector layer to the collector layer.

  According to the study by the present inventors, for example, by forming a hole transmission layer using PEDOT [poly (3,4-ethylenedioxythiophene)] or PSS (polystyrene sulfonic acid), the emitter layer is changed to the collector layer. Thus, the current transmittance of holes can be increased, and a large amplification factor can be obtained. Moreover, although the ionization potential measured by the atmospheric photoelectron spectrometer (AC-3: manufactured by Riken Keiki Co., Ltd., the following is also measured) is considered to be a work function, the measured value of PEDOT: PSS is 5.2 eV. However, this is larger than the HOMO of the p-type organic semiconductor layer (for example, the measured value of P3HT is 4.8 eV) and is noble, and it is considered that hole injection easily occurs from the PEDOT: PSS layer. The above P3HT is poly (3-hexyl) thiophene.

  An example is given and demonstrated about the manufacturing method of the transistor element of this invention in which the above-mentioned hole permeation | transmission promotion layer is provided (refer FIG. 1). First, a collector layer 11 made of an organic semiconductor is formed on a substrate (not shown) on which a collector electrode is formed by a printing application method, and then a current transmission promoting layer (not shown) made of lithium fluoride which is an alkali metal salt. A base electrode 13 made of aluminum, and a current transmission facilitating layer (not shown) made of lithium fluoride which is an alkali metal salt are formed by vapor deposition. Next, the hole permeation promoting layer 31 characterizing the present invention is formed by a printing method, and further, an emitter layer 22 made of an organic semiconductor is formed by a printing method, and then a charge injection layer made of molybdenum oxide by an evaporation method, and aluminum. The emitter electrode 12 can be formed to produce the transistor element of the present invention.

  In the transistor element of the present invention, as described above, it is preferable to form a current transmission promotion layer composed of an alkali metal salt layer between the hole transmission promotion layer and the base electrode characterizing the present invention. The reason is as follows. When the conductive polymer that is the material for forming the hole permeation promoting layer has an acidic functional group, or when the doped species has an acidic functional group, the surface of the base electrode formed of metal may be corroded. If corrosion of the surface of the base electrode occurs, the on / off ratio of the manufactured transistor element may be reduced, the element characteristics may be deteriorated, and the drive as the transistor element may be hindered. On the other hand, as described above, if the conductive polymer layer is formed after forming the alkali metal salt, the occurrence of corrosion on the surface of the base electrode is prevented, and the on / off ratio maintaining the smoothness of the surface of the base electrode. The MBOT can be made excellent.

  The thickness of the hole permeation promoting layer that characterizes the present invention is preferably 5 nm to 200 nm, more preferably 10 nm to 100 nm. If the thickness exceeds 200 nm, it is difficult to form a uniform interface, the charge that can be transmitted through the base electrode is reduced, and the ON current of the collector current may be greatly reduced. On the other hand, if the thickness is less than 5 nm, it is difficult to form the hole transmission layer uniformly, and there is a possibility that defects or defects of the hole transmission layer may occur, and it becomes difficult to obtain a stable effect.

The transistor element of the present invention may have a structure in which an oxide is formed on the surface of the metal electrode by performing heat treatment in the air after forming the base electrode. The metal oxide layer formed in this case functions as a dark current suppression layer. Therefore, when the transistor element of the present invention is manufactured, if the base electrode is formed of metal and the oxide film of the base electrode is formed on one or both surfaces of the base electrode, the voltage V between the emitter electrode and the base electrode is obtained. _The dark current that flows when _B is not applied is effectively suppressed. The temperature of the heat treatment in the above is preferably in the range of 80 ° C to 300 ° C, and more preferably in the range of 80 ° C to 200 ° C. On the other hand, when the heat treatment temperature exceeds 300 ° C., not only the deterioration of the material, particularly when the substrate is an organic substance, the substrate may be deformed, but the organic semiconductor layer may be deteriorated. This is not preferable.

  In addition, the inventors of the present invention suppress the dark current by forming the hole permeation promoting layer that characterizes the present invention even in the above-described element that does not form the dark current suppressing layer. It was found that a sufficient collector current and amplification factor can be obtained. That is, due to the effect of the hole transmission promoting layer of the organic transistor element (MBOT) of the present invention, a leakage current (also referred to as an off-current or dark current that flows when the switch is turned off) flows between the emitter electrode and the collector electrode. As a result, the on / off ratio can be improved.

  In particular, when an organic transistor element (MBOT) is used as an organic EL drive transistor element, if the dark current is large, the organic EL element emits light when it is OFF, and the contrast when ON and OFF is reduced. The off ratio is desirably 10 or more, and preferably, an on / off ratio of 100 or more is required for the driving transistor element. On the other hand, according to the transistor element of the present invention, an on / off ratio of 100 or more can be achieved.

  In the dark current of the transistor element of the present invention, the hole permeation promoting layer made of a film having a conductive polymer is formed on the base electrode or the current permeation promoting layer made of an alkali metal halide layer. The electrode interface becomes smooth, the voltage concentration on the uneven part is not reduced, the leakage current can be reduced, and the energy level of the hole permeation promoting layer is made lower than the HOMO level of the organic semiconductor. As a result, the current flowing between the emitter electrode and the collector electrode hardly flows at the OFF time. Therefore, an excellent on / off ratio can be obtained by suppressing the dark current that flows when the switch is OFF. As a result, according to the transistor element of the present invention, an excellent on / off ratio and amplification factor can be obtained without forming a dark current suppressing layer (aluminum oxide layer) formed by oxidation of the base electrode.

  As described above, in the transistor element of the present invention, the hole permeation promoting layer is formed of a film having a conductive polymer, which can realize a large base electrode transmittance of holes and a large amplification. An element with a rate is obtained. An example of the transistor element of the present invention is obtained, for example, when the hole permeation promoting layer is formed using a conductive polymer containing poly (3,4-ethylenedioxythiophene). The remarkable effect will be described.

For example, the transistor element of Comparative Example 2 to be described later is regioregular (head-to-tail) -P3HT (regularregular-poly (3-hexylthiophene-2,5-diyl)) (hereinafter, this may be referred to as P3HT). A collector layer (230 nm) made of, a 1.1 nm current transmission promoting layer made of lithium fluoride (LiF), a base electrode layer made of metal aluminum and having an average thickness of 6 nm, a surface oxide film layer (dark current suppressing layer) of the aluminum electrode ), A 2 nm current transmission promoting layer made of lithium fluoride (LiF), an emitter layer (70 nm) made of P3HT, a charge injection layer made of molybdenum oxide layer (4 nm), and an emitter electrode made of aluminum having an average thickness of 50 nm. It has the structure which becomes. In the transistor element having this structure, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the on-current density I _C-ON = −99 mA / cm ² of the collector current I _C , the current The amplification factor h _FE was 20.8.

On the other hand, in addition to the structure of the transistor element described above, the transistor element of Example 6 (described later) having a structure in which a hole transmission promoting layer having a thickness of 30 nm made of the material described above is provided has the following characteristics: It will be greatly improved as follows. That is, in addition to the above structure, using a PEDOT: PSS [poly (ethylenedioxythiophene): polystyrenesulfonic acid] aqueous dispersion containing a conductive polymer between the lithium fluoride layer and the emitter layer on the base electrode. In the transistor element of Example 6 in which the hole transmission promoting layer (30 nm) was formed, the on-current density I _C of the collector current I _C when the collector voltage V _C = −5 V and the base voltage V _B = −3 V were applied. _−ON = −164.8 mA / cm ² , current amplification factor h _FE = 188, collector current is 1.6 times or more and current amplification factor is 9 times or more, compared with the transistor element of Comparative Example 2 described above. It was. As described above, the transistor element of the present invention can obtain a sufficient amplification factor to be used as an amplifying element, and can obtain a current sufficient to drive a current driving element.

  The present inventors consider the above-described principle that the above-described remarkable effect is obtained by the configuration of the present invention as follows. That is, as the mechanism, in the transistor element of the present invention having the above-described configuration, [1] the current amplification factor is increased, and [2] even when the dark current suppression layer formed by heating in the atmosphere is not formed. Since current amplification is obtained, it is considered as follows. First, by forming a conductive polymer layer as a hole transmission promotion layer on the base electrode or the current transmission promotion layer, the uniformity of the interface of the current transmission promotion layer, the conductive polymer layer, and the emitter layer is increased. In addition to this, there is no leakage current caused by the concentration of the electric field in the thick or thin part of the electrode, and in addition to this, the holes are accelerated and transmitted through the base electrode, and the energy level of the conductive polymer and the collector layer This is considered to be because the transmission rate of the charge passing through the base electrode can be greatly improved because the energy difference between the two is large and the holes are accelerated.

  In the transistor element of the present invention having a structure in which a current transmission promoting layer made of an alkali metal salt is laminated between a conductive polymer layer, which is a hole transmission promoting layer characterizing the present invention, and a base electrode, the base electrode is more Transmits efficiently, and a larger amplification factor can be obtained. This is because, in addition to the effect of improving the base electrode permeability of the hole permeation promoting layer described above, the hole that is accelerated in the conductive polymer that is the hole permeation promoting layer is a current permeation promoting layer made of an alkali metal salt as an insulator. This is considered to be due to being blocked by the layer to become hot carriers, passing through the base electrode, and reaching the collector layer.

The current value of the transistor element (MBOT) of the present invention can be greatly amplified even in a low voltage region, and a large current can be obtained, which is extremely useful from this point. In general, the organic EL element is an element that is driven in a low voltage region, and the driving transistor element is required to output a large current at several volts. Organic EL elements can achieve high intensity light emission by increasing the applied voltage, but they can realize high intensity light emission, but they cause deterioration and decomposition of the light emitting element material, shorten the life of the element, and provide stable light emission for a long time. Can not. Therefore, the drive voltage is about 1 to 20V, preferably 10V or less. At this time, the current density value modulated by the transistor element in the low voltage region is not particularly limited, but is preferably 0.1 mA / cm ² to 500 mA / cm ² , more preferably 1 mA / cm ^2. To 200 mA / cm ² is preferable. When used as a light emitting element, if the current density value is less than 0.1 mA / cm ² , sufficient light emission cannot be achieved, and sufficient light emission intensity cannot be obtained. In addition, an element having a current value exceeding 500 mA / cm ² cannot obtain a sufficient on / off ratio, and a problem arises that even when OFF (voltage 0 V), a dark current is generated and light is emitted from the light emitting element. Sometimes.

Next, structures and materials of the transistor element of the present invention other than those described above will be described.
(substrate)
The organic transistor element of the present invention is usually used by being formed on a substrate as described below. The substrate used in this case may be any material that can maintain the shape of the transistor element. For example, inorganic materials such as glass, alumina, quartz, and silicon carbide, metal materials such as aluminum, copper, and gold, polyimide films, and polyester films A plastic substrate such as polyethylene film, polystyrene, polypropylene, polycarbonate, or polymethyl methacrylate can be used. When a plastic substrate is used, a flexible transistor element that is lightweight and excellent in impact resistance can be manufactured. In the case of bottom emission in which light is emitted from the substrate side when used as a light emitting transistor element in which an organic light emitting layer is formed, it is desirable to use a substrate having a high light transmittance such as a plastic film or glass. These substrates may be used alone or in combination. As for the size and shape of the substrate, any device such as a card shape, a film shape, a disk shape, or a chip shape can be used without any problem as long as a transistor element can be formed.

(Organic semiconductor layer)
As described above, the organic transistor element of the present invention is characterized in that the p-type organic semiconductor layer to be formed includes a collector layer 21 provided between the collector electrode and the base electrode, as shown in FIG. And an emitter layer 22 formed between the emitter electrodes. Each of the electrodes and these organic semiconductor layers are stacked such that the collector layer 21 is directly or via a current transmission promotion layer, and the emitter layer 22 is stacked via a hole transmission promotion layer or a hole transmission promotion layer and a current transmission promotion layer. (See FIGS. 1 and 2). Hereinafter, the collector layer and the emitter layer which are organic semiconductor layers will be described.

  The organic semiconductor layer of the transistor element of the present invention is a p-type organic semiconductor layer and is made of a p-type organic semiconductor material. Organic semiconductor materials include materials exhibiting n-type characteristics and materials exhibiting p-type characteristics. In the present invention, organic semiconductors exhibiting p-type characteristics because of the variety of materials and ease of handling in the air. Use materials. Accordingly, the material for forming the organic semiconductor layer can be used without any problem as long as it is a p-type organic semiconductor, and is particularly limited if it is a polymer material (hole transporting material) that functions as a hole transport semiconductor and transports holes. It can be used without.

The p-type semiconductor material for forming the organic semiconductor layer in the present invention is preferably a material that is electrically stable and has an appropriate ionization potential and electron affinity. Any general p-type semiconductor material can be used without particular limitation. For example, metal phthalocyanines (Cu-Pc, Co-Pc, Ni-Pc, etc.), metal-free phthalocyanine, pentacene, naphthalocyanine, indico, thioindigo, Anthracene, quinacridone, oxadiazole, triphenylamine, triazole, imidazole, imidazolone, pyrazoline, tetrahydroimidazole, polythiophene, porphyrin, dinaphthothiophene, diindenoperylene and the like can be mentioned. Particularly preferable materials include phthalocyanines such as metal phthalocyanine and metal-free phthalocyanine, pentacene, dinaphthothienothiophene, diindenoperylene, and derivatives thereof. These derivatives include methyl groups, ethyl groups, butyl groups, 2-ethylhexyl groups, octyl groups, dodecyl groups, octadecyl groups and other alkyl groups, heteroalkyl groups having a hetero group in the alkyl group, amino groups, amide groups. And compounds having a functional group such as a carboxyl group. According to the study of the present invention, by having these functional groups, the solubility in a solvent is increased and a coating printing method becomes possible, and it becomes possible not only to form a smooth semiconductor surface, but also to interact with each other by the functional groups. There is a possibility that charge transferability is improved by the action. Examples of the hole transport material that is a polymer material include thiophene-fluorene copolymer, phenylene-vinylene copolymer, poly (3-hexyl) thiophene, poly (3-octa) thiophene, poly (3-dodecyl) thiophene. And derivatives thereof.

  Examples of the p-type semiconductor polymer material that can be used in the present invention include poly (3-hexyl) thiophene (P3HT). According to the study by the present inventors, by forming a collector layer using poly (3-hexyl) thiophene, a base electrode laminated adjacent to the collector layer, and a current formed as necessary The permeation promoting layer can be a smooth and uniform film. In addition, the ionization potential measured by an atmospheric photoelectron spectrometer (AC-3: manufactured by Riken Keiki Co., Ltd., the same as below) is considered to be HOMO (the highest occupied orbit energy level), and P3HT measurement. Although the value is 4.8 eV, it is considered that charge injection easily occurs from a metal such as gold (Au) or aluminum (Al).

  Particularly preferable p-type semiconductor materials for forming the organic semiconductor layer include poly (3-hexyl) thiophene (P3HT) and poly (2,5-bis (3-dodecylthiophen-2-yl) thieno described above. [3,2, b] thiophene) (hereinafter sometimes referred to as MEH-PPV) and (methoxy-ethyl-hexoxy polyphenylene vinylene) (hereinafter sometimes referred to as MEH-PPV). According to the study of the present invention, by forming an emitter layer using the p-type semiconductor polymer material, an emitter electrode laminated adjacent to the emitter layer, a hole injection layer formed as necessary Can be made smooth and uniform. Moreover, HOMO of P3HT is 4.8 eV, and it is considered that charge injection from gold (Au) and aluminum (Al) occurs easily and in large quantities. Poly (3-hexyl) thiophene (P3HT) is preferably stereoregular poly (3-hexylthiophene), including “head-to-head” and “head-to-tail” stereoregular P3HT, more preferably head-to-tail P3HT. It is. P3HT is a material having a high hole mobility, but its performance may deteriorate due to impurities due to residual catalyst, position-specific defects in the polymer chain, and mixing of low molecular weight components. Although it does not specifically limit, that whose number average molecular weight is 1,000-100,000 is preferable, and what is especially 25,000-60,000 is preferable. The purity is preferably 90% or higher, and more preferably 98% or higher.

  However, as the organic semiconductor layer, a substance other than these may be used as long as it has a property of transporting more holes than electrons. The p-type organic semiconductor layer may have not only a single layer structure used alone, but also a mixed layer composed of two or more components and a laminated structure composed of two or more organic semiconductor layers. As a method for forming the p-type organic semiconductor layer, it can be formed by various coating printing methods using a vapor deposition method, or a solution or dispersion containing these compounds.

The organic semiconductor layer forming the organic semiconductor layer in the present invention desirably has a high charge mobility, and is preferably at least 0.0001 cm ² / V · s. The emitter layer 22 is preferably basically thinner than the collector layer 21, and the emitter layer 22 has a thickness of 1,000 nm or less, preferably about 10 nm to 300 nm. If the thickness of the emitter layer is less than 10 nm, there is a possibility that the current is not sufficiently controlled, and there is a possibility that the yield is lowered due to a problem that the transistor performance deteriorates or the leakage current increases due to the defect. Therefore, it is not preferable. On the other hand, if it exceeds 1,000 nm, the production cost and material cost increase, which is not preferable.

  In the present invention, a particularly preferable method for forming the organic semiconductor layer will be described below by taking a suitable P3HT as an example. The poly (3-hexyl) thiophene (P3HT) used in this case can be used by mixing with other p-type organic semiconductor polymers. However, in order to obtain more sufficient transistor characteristics, from 50% by mass It is preferable that many are included. As a specific method for forming the p-type organic semiconductor layer, a coating solution is prepared by dissolving or dispersing these polymer materials in an organic solvent such as toluene, chloroform, dichloromethane, tetrahydrofuran, dioxane, and the like. Simple methods such as coating or printing the dispersion with a coating apparatus or the like can be mentioned, and the dispersion can be easily formed by these methods.

  In the present invention, the organic solvent used when the organic semiconductor thin film made of the above-described material is formed by a solution coating method or a printing method is not particularly limited as long as a solution having an appropriate concentration can be obtained. It can be used without. For example, halogen hydrocarbon solvents such as chloroform, dichloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, chloronaphthalene, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ester solvents such as ethyl acetate, butyl acetate, diethyl ether, Ether solvents such as dioxane and tetrahydrofuran, aromatic hydrocarbon solvents such as toluene, xylene and ethylbenzene, non-hydrocarbons such as tetrahydrofuran, sulfolane, N, N-dimethylformamide, N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide Examples thereof include a protonic polar solvent. These solvents may be used alone or in combination. These organic semiconductor layers can be formed by spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, die coating, air knife, slide hopper, and extrusion. Examples thereof include a coating method such as the John method, and wet processes such as various printing methods and an ink jet method, which can be appropriately selected and applied according to the characteristics of the material used.

  In the present invention, a poor solvent that does not substantially dissolve the organic semiconductor material alone is added to the organic semiconductor solution used when forming the organic semiconductor thin film made of the above-described material by a solution coating method or a printing method. By doing so, the in-film structure (= aggregation state) of the p-type semiconductor polymer material can be controlled. Examples of poor solvents for P3HT include alcohol solvents, aprotic solvents such as NMP, hydrocarbon solvents, anisolones, etc., but in the case of forming on a hole permeation promoting layer composed of a conductive polymer layer. In addition, it is preferable to add a hydrocarbon solvent that does not dissolve the conductive polymer layer, for example, hexane, and the ON current increases. It is considered that the aggregation inside the film has progressed due to the addition of the poor solvent. However, when it is added twice or more by weight to the good solvent, the aggregation in the solution progresses, and it is uniform and continuous by printing coating. In order to obtain the effect, the mass addition ratio to the good solvent is preferably in the range of good solvent: poor solvent = 10: 1 to good solvent: poor solvent = 10: 10. Within this range, a uniform and smooth curtain can be formed, can be used as an organic semiconductor layer, and a large on-current can be obtained.

(electrode)
Next, electrodes used in the transistor element of the present invention will be described. As the electrodes constituting the transistor element of the present invention, there are a collector electrode 11, an emitter electrode 12, and a base electrode 13. As shown in FIG. 1, the collector electrode 11 is usually provided on a substrate (not shown), The base electrode 13 is provided so as to be embedded between the emitter layer 22 and the collector layer 21 which are p-type organic semiconductor layers, and the emitter electrode 12 is disposed at a position facing the collector electrode 11, the p-type organic semiconductor layer 21, 22 and the base electrode 13 are provided.

The material used for each electrode constituting the transistor element of the present invention is, for example, the collector layer 21 constituting the transistor element of the present invention is a p-type semiconductor layer made of a p-type organic semiconductor polymer. As a forming material, for example, a transparent conductive film such as ITO (indium tin oxide), indium oxide, IZO (indium zinc oxide), SnO ₂ , ZnO, metal such as gold, silver, copper, polyaniline, polypyrrole, poly Examples thereof include conductive polymers such as alkylthiophene derivatives and polysilane derivatives. On the other hand, the material for forming the emitter electrode 12 includes simple metals such as aluminum and silver, magnesium alloys such as Mg—Ag and Mg—In, aluminum alloys such as Al—Li, Al—Ca, and Al—Mg, Li, and Ca. And metals having a small work function such as an alloy of these alkali metals.

  In addition, as described above, in the present invention, the collector layer is formed of the p-type organic semiconductor polymer by using the print coating method as described above, so that the interface of the collector layer forming the base electrode is smooth. It has become. Therefore, the base electrode 13 provided on the collector layer which is the polymer is also formed in a smooth shape. The base electrode 13 having a uniform and smooth shape has neither a thin part nor a thick part even when a base electrode having a predetermined average thickness is formed, and obtains a stable large current value and a high on / off ratio. Can do.

  Further, in the present invention, an oxide film is formed on the electrode surface by thermal oxidation in air after forming an electrode with aluminum as a base electrode that suppresses dark current at OFF and achieves a high on / off ratio. It is also a preferable form to use a base electrode formed with a film.

The thickness of the base electrode used in the transistor element of the present invention is preferably 0.5 nm to 100 nm, and more preferably 1.0 nm to 50 nm. If the thickness of the base electrode is 100 nm or less, the base electrode can easily transmit electrons accelerated by the base voltage V _B. Note that the base electrode can be used without problems if it is provided with no defects or defects in the semiconductor layer and has no irregularities. However, if it is less than 0.5 nm, a defect occurs and it is difficult to form a uniform electrode layer. This is not preferable because it may not operate as an organic transistor element.

  As a method for forming an electrode used in the transistor element of the present invention, a vacuum process such as vacuum deposition, sputtering, CVD, or a coating method may be used for the collector electrode and the emitter electrode among the above-mentioned electrodes. The thickness of the electrode formed by these methods varies depending on the material used, but is preferably about 1 nm to 1,000 nm, for example. Note that when the thickness is less than 1 nm, the transistor element may not operate. When the thickness exceeds 1,000 nm, both the manufacturing cost and the material cost increase, which is not preferable.

(Current transmission enhancement layer)
In the transistor element of the present invention, it is also preferable to further form a current transmission promoting layer in a laminated state on one or both of the front and back surfaces of the sheet-like base electrode. In addition, as a material for forming the current transmission promoting layer, any material that increases the current passing through the base electrode can be used without any problem. Alkaline metal compounds, alkaline earth compounds, metal oxides, and the like can be used as the material for forming the current transmission promoting layer. Preferred examples of the material include an alkali metal compound and the most preferred compound is lithium fluoride. The current transmission promoting layer can be formed between the base electrode and the emitter layer, or between the base electrode and the collector layer, and the effect is recognized if formed on either one. However, according to the study by the present inventors, by forming on both the front and back surfaces of the base electrode, a greater effect can be obtained, and the ON current of the collector current is greatly increased and the OFF current is decreased.

  In addition, as described above, the hole permeation promoting layer that characterizes the present invention may contain an acidic component as a conductive polymer or a doped material, and when formed directly on the electrode, the electrode corrodes and is stable. May not be able to form a simple element. On the other hand, an electrode that may be generated by forming a hole permeation promoting layer by forming an alkali metal compound layer, for example, a lithium fluoride layer, between the base electrode and the hole permeation promoting layer as a current permeation promoting layer. Therefore, it is possible to efficiently produce an element that can be stably driven.

  The thickness of the current transmission facilitating layer is preferably from 0.1 nm to 100 nm. If the thickness exceeds 100 nm, the material is a dielectric, which acts as an insulator layer, which reduces the charge that can be transmitted through the base electrode and may significantly reduce the ON current of the collector current. . Moreover, it is difficult to form a current transmission promoting layer having a film thickness of less than 0.1 nm uniformly on the collector layer or the base electrode to obtain a stable effect because the thickness is too thin. More preferably, it is 0.3 nm to 50 nm, and further preferably about 0.3 nm to 10 nm.

(Dark current suppression layer)
The transistor element of the present invention may be one in which a dark current suppressing layer is formed as described below, if necessary. As the method, after forming a base electrode, you may heat-process the said base electrode. Furthermore, in the transistor element of the present invention, the base electrode is made of metal, and an oxide film of the base electrode is formed on one or both surfaces of the base electrode, whereby the voltage V _B is generated between the emitter electrode and the base electrode. The dark current that flows when no voltage is applied can be effectively suppressed.

  According to the above-described aspect of the invention, since the dark current suppression layer is provided between the collector electrode and the base electrode, it is possible to effectively suppress the flow of dark current. The on / off ratio can be improved. The transistor element of the present invention thus configured apparently effectively functions as a current modulation type transistor element similar to a bipolar transistor, and is an excellent organic material exhibiting a high on / off ratio, a large collector current, and a current amplification factor. It functions as a transistor element. In the transistor element having the hole permeation promoting layer of the present invention, it is possible to obtain an element having a large on / off ratio even in an element in which the dark current suppressing layer is not formed.

(Hole injection layer)
The transistor element of the present invention may have a hole injection layer formed thereon. The hole injection layer reduces the hole injection barrier from the emitter electrode, increases the hole injection efficiency, and improves the stability. The forming material can be used without any problem if the hole injection efficiency is increased, and examples thereof include phthalocyanines and metal oxides. Preferred metal oxides include zinc oxide, molybdenum oxide, and vanadium oxide. The thickness of the hole injection layer is preferably 0.5 nm to 500 nm, and if it is less than 0.5 nm, the effect is small, and if it is thicker than 500 nm, it functions as an insulator layer and the current is greatly reduced, which is not preferable.

  EXAMPLES Hereinafter, although an Example and comparative example of this invention are given and this invention is demonstrated in detail, this invention is not limited to this.

The transistor elements manufactured in Examples and Comparative Examples were evaluated by the following method. First, the evaluation method will be described.
(Evaluation of transistor elements)
For the manufactured transistor element, an applied voltage (V _C ) was applied between the emitter electrode and the collector electrode, and the base voltage (V _B ) applied between the emitter electrode and the base electrode was modulated in the range of 0V to −5V. The output modulation characteristic is measured by applying a collector voltage (V _C ) between the emitter electrode and the collector electrode, and further applying a base voltage V _B (0 to −3 V) between the emitter electrode and the base electrode. The amount of change (off current, on current) of I _B and collector current I _C was measured. Further, the ratio of the collector current change ΔI _{C to} the base current change ΔI _B , that is, the current amplification factor (h _FE = ΔI _C / ΔI _B ), the on / off ratio (I _C ) which is the ratio of the on-current to the off-current. _-ON / _{IC -OFF} ).

Example 1
[Transistor element]
Regioregular-P3HT [regularregular-Poly (3-hexylthiophene-2,5-diyl)] (P3HT) was dissolved in toluene to prepare a P3HT solution so that the concentration was 25 mg / ml. The obtained P3HT solution was applied and dried on an ITO transparent substrate with a spin coater to form a collector layer (230 nm). A current transmission facilitating layer having an average thickness of 1.1 nm made of lithium fluoride and a base electrode layer having an average thickness of 6 nm made of aluminum are formed by a vacuum deposition method, and thereafter heat treatment at 100 ° C. is performed in an air atmosphere. After 1 hour, an oxide film layer (dark current suppressing layer) was formed on the surface of the aluminum electrode. Next, a current transmission facilitating layer having a thickness of 2.0 nm made of lithium fluoride was formed, and then PEDOT: PSS [trade name CLEVIOS AI4083, manufactured by H.C. Starck, conductivity (catalog value) = 10 ⁻³ S / cm ² )] Using a water dispersion, coating was carried out by a spin coating method, followed by drying to form a hole permeation enhancement layer (30 nm). Further, P3HT was dissolved in toluene, adjusted to a concentration of 10.0 mg / ml, coated by spin coating, and dried to form an emitter layer (50 nm) made of P3HT. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 2 nm, and an emitter electrode made of aluminum having an average thickness of 90 nm is formed by a film deposition means by vacuum deposition. A transistor element of Example 1 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 1 obtained above are as follows when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when not applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the ON current density I _C-ON = −212.2 mA / cm ² of the collector current I _C , V _B = The off-current density I _{C-OFF at} −0 V was −0.04 mA / cm ² , the on / off ratio was 5.4 × 10 ³ , and the current amplification factor h _FE was 150.

(Example 2)
The same regioregular-P3HT as used in Example 1 was dissolved in toluene to prepare a P3HT solution so that the concentration was 25 mg / ml. The obtained P3HT solution was applied and dried on an ITO transparent substrate with a spin coater to form a collector layer (230 nm). A current transmission facilitating layer having an average thickness of 1.1 nm made of lithium fluoride and a base electrode layer having an average thickness of 6 nm made of aluminum are formed by a vacuum deposition method, and thereafter heat treatment at 100 ° C. is performed in an air atmosphere. After 1 hour, an oxide film layer (dark current suppressing layer) was formed on the surface of the aluminum electrode. Next, a 2.0 nm current transmission facilitating layer made of lithium fluoride was formed, and then coated by spin coating using the same PEDOT: PSS aqueous dispersion as used in Example 1 as the conductive polymer. Then, a hole permeation promoting layer (30 nm) was formed by drying. Furthermore, using a solution of poly (2,5-bis (3-dodecylthiophen-2-yl) thieno [3,2, b] thiophene) (hereinafter sometimes referred to as PBTTTT-C12) in chlorobenzene, 10 mg PBTTT-C12 solution was prepared so as to be / ml. The PBTTT-C12 solution was coated by a spin coating method to form an emitter layer (50 nm) made of PBTTTT-C12. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 2 nm, and an emitter electrode made of aluminum having an average thickness of 90 nm is formed by a film deposition means by vacuum deposition. Thus, a transistor element of Example 2 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 2 obtained above are as follows when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −26.9 mA / cm ² of the collector current I _C , V _B = The off-current density I _C-OFF at 0 V was −0.01 mA / cm ² , the on / off ratio was 2.2 × 10 ³ , and the current amplification factor h _FE was 112.

(Example 3)
The same regioregular-P3HT as used in Example 1 was dissolved in toluene to prepare a P3HT solution so that the concentration was 25 mg / ml. The obtained P3HT solution was applied and dried on an ITO transparent substrate with a spin coater to form a collector layer (230 nm). A current transmission facilitating layer having an average thickness of 1.1 nm made of lithium fluoride and a base electrode layer having an average thickness of 6 nm made of aluminum are formed by a vacuum deposition method, and thereafter heat treatment at 100 ° C. is performed in an air atmosphere. After 1 hour, an oxide film layer (dark current suppressing layer) was formed on the surface of the aluminum electrode. Next, a 2.0 nm current transmission facilitating layer made of lithium fluoride was formed, and then coated by spin coating using the same PEDOT: PSS aqueous dispersion as used in Example 1 as the conductive polymer. Then, a hole permeation promoting layer (30 nm) was formed by drying. Further, a MEH-PPV solution was prepared by using a solution of (methoxy-ethyl-hexoxy polyphenylene vinylene) (hereinafter sometimes referred to as MEH-PPV) in chlorobenzene so as to be 5 mg / ml. The MEH-PPV solution was coated by a spin coating method to form an emitter layer (50 nm) made of MEH-PPV. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 2 nm, and an emitter electrode made of aluminum having an average thickness of 90 nm is formed by a film deposition means by vacuum deposition. Thus, a transistor element of Example 3 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 3 obtained above are as follows when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −120.7 mA / cm ² of the collector current I _C , V _B = The off-current density I _{C-OFF at} −0 V was −0.11 mA / cm ² , the on / off ratio was 1.1 × 10 ³ , and the current amplification factor h _FE was 79.4.

Example 4
[Transistor element]
In the same manner as in Example 1, a collector layer (230 nm) made of P3HT, a current transmission promoting layer made of lithium fluoride with an average thickness of 1.1 nm, and a base electrode layer made of aluminum with an average thickness of 6 nm were vacuum deposited. After that, a heat treatment at 100 ° C. was performed for 1 hour in an air atmosphere to form an oxide film layer (dark current suppressing layer) on the surface of the aluminum electrode. Next, a 2.0 nm current transmission facilitating layer made of lithium fluoride was formed, and then coated by spin coating using the same PEDOT: PSS aqueous dispersion as used in Example 1 as the conductive polymer. Then, a hole permeation promoting layer (30 nm) was formed by drying. Furthermore, P3HT was dissolved in a mixed solvent of toluene and hexane, which is a poor solvent (weight ratio toluene: hexane = 50: 10), and adjusted to a concentration of 8.3 mg / ml. An emitter layer (50 nm) made of P3HT was formed using a P3HT solution (8.3 mg / ml) having a concentration different from that of the solvent used to form the collector layer. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 4 nm, and an emitter electrode made of aluminum having an average thickness of 50 nm is formed by a film deposition means using vacuum deposition. Thus, a transistor element of Example 4 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 4 obtained above are as follows when the collector voltage V _C is applied to −5 V between the emitter electrode and the collector electrode, and further the base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −175.7 mA / cm ² of the collector current I _C , V _B = The off-current density I _{C-OFF at} −0 V was −0.04 mA / cm ² , the on / off ratio was 4.0 × 10 ³ , and the current amplification factor h _FE was 189.

(Example 5)
[Transistor element]
In the same manner as in Example 1, a collector layer (230 nm) made of P3HT, a current transmission promoting layer made of lithium fluoride with an average thickness of 1.1 nm, and an organic semiconductor layer masked with an average thickness of 6 nm made of aluminum A base electrode layer was formed by a vacuum deposition method, and then a heat treatment at 100 ° C. was performed for 1 hour in an air atmosphere to form an oxide film layer (dark current suppressing layer) on the surface of the aluminum electrode. Next, a current transmission facilitating layer having a thickness of 2.0 nm made of lithium fluoride is formed, and then PEDOT: PSS (trade name CLEVIOS PH500, manufactured by H.C. Starck, conductivity (catalog value) = 300 S / cm ² ) aqueous dispersion was used for coating by spin coating, followed by drying to form a hole permeation promoting layer (50 nm). Furthermore, P3HT was dissolved in toluene, and the concentration was adjusted to 10.0 mg / ml. An emitter layer (50 nm) made of P3HT was formed using a P3HT solution having a different concentration from that used to form this collector layer. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 4 nm, and an emitter electrode made of aluminum having an average thickness of 50 nm is formed by a film deposition means using vacuum deposition. Thus, a transistor element of Example 5 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 5 obtained above are as follows when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −225.2 mA / cm ² of the collector current I _C and V _B = The off-current density I _C-OFF at 0 V was −1.86 mA / cm ² , the on / off ratio was 1.2 × 10 ² , and the current amplification factor h _FE was 226.

(Example 6)
[Transistor element]
In the same manner as in Example 1, a collector layer (230 nm) made of P3HT, a current transmission promoting layer made of lithium fluoride with an average thickness of 1.1 nm, and an organic semiconductor layer masked with an average thickness of 6 nm made of aluminum A base electrode layer was formed by a vacuum deposition method, and then a heat treatment at 100 ° C. was performed for 1 hour in an air atmosphere to form an oxide film layer (dark current suppression layer) on the surface of the aluminum electrode. Next, a 2.0 nm current transmission facilitating layer made of lithium fluoride was formed, and then coated by spin coating using the same PEDOT: PSS aqueous dispersion as used in Example 1 as the conductive polymer. Then, a hole permeation promoting layer (30 nm) was formed by drying. Furthermore, P3HT was dissolved in toluene and adjusted to a concentration of 25 mg / ml. An emitter layer (70 nm) made of P3HT was formed using this P3HT solution. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 4 nm, and an emitter electrode made of aluminum having an average thickness of 50 nm is formed by a film deposition means using vacuum deposition. Thus, a transistor element of Example 6 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristics of the transistor element of Example 6 obtained above are as follows: the collector voltage V _C is applied between the emitter electrode and the collector electrode, and the base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −164.8 mA / cm ² of the collector current I _C , V _B = The off-current density I _{C-OFF at} −0 V was −0.05 mA / cm ² , the on / off ratio was 3.3 × 10 ³ , and the current amplification factor h _FE was 188.

(Example 7)
[Transistor element]
In the same manner as in Example 6, a collector layer (230 nm) made of P3HT, a current transmission facilitating layer made of lithium fluoride having an average thickness of 1.1 nm, and a base electrode layer having an average thickness of 6 nm were formed. Thereafter, a 2.0 nm current transmission facilitating layer made of lithium fluoride was formed without performing a heat treatment in the air atmosphere, and then the same PEDOT: PSS as used in Example 1 was used as the conductive polymer. The hole dispersion promoting layer (30 nm) was formed by coating with an aqueous dispersion using a spin coating method and drying. Furthermore, P3HT was dissolved in toluene and adjusted to a concentration of 25 mg / ml. An emitter layer (70 nm) made of P3HT was formed using this P3HT solution. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 4 nm, and an emitter electrode made of aluminum having an average thickness of 50 nm is formed by a film deposition means using vacuum deposition. Thus, a transistor element of Example 7 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristic of the transistor element of Example 7 obtained above is that when the collector voltage V _C is applied between the emitter electrode and the collector electrode by −5 V and the base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the on-current density I _C-ON = −164.3 mA / cm ² of the collector current I _C and V _B = The off-current density I _{C-OFF at} −0 V was −0.06 mA / cm ² , the on / off ratio was 3.0 × 10 ³ , and the current amplification factor h _FE was 58.2.

(Comparative Example 1)
[Transistor element having no hole permeation promoting layer]
The same regioregular-P3HT as used in Example 1 was dissolved in chloroform to prepare a P3HT solution so as to have a concentration of 20 mg / ml. The obtained P3HT solution was applied onto an ITO transparent substrate with a spin coater to form a collector layer (250 nm). Next, a 0.6 nm current transmission promoting layer made of lithium fluoride was formed, and a base electrode layer made of aluminum and having an average thickness of 10 nm was formed by vacuum deposition. This was heat-treated in the atmosphere at a temperature of 100 ° C. for 1 hour to form an oxide film layer (dark current suppressing layer) on the surface of the aluminum electrode. Next, a current transmission facilitating layer of 3 nm made of lithium fluoride (LiF) was formed, and then an emitter layer (100 nm) was formed with a spin coater again using the P3HT solution used above. Next, a molybdenum oxide layer is formed by vacuum vapor deposition so as to have an average film pressure of 2 nm, and an emitter electrode made of gold having an average thickness of 30 nm is formed by a film deposition means using vacuum vapor deposition. A transistor element was obtained. The structure of the obtained element is shown in FIG.

  The obtained device did not exhibit the current modulation characteristic of MBOT and did not operate as a transistor device.

(Comparative Example 2)
[Transistor element having no hole permeation promoting layer]
In the same manner as in Example 1, a collector layer (230 nm) made of P3HT, a current transmission promoting layer made of lithium fluoride with an average thickness of 1.1 nm, and an organic semiconductor layer masked with an average thickness of 6 nm made of aluminum A base electrode layer was formed by a vacuum deposition method, and then a heat treatment at 100 ° C. was performed for 1 hour in an air atmosphere to form an oxide film layer (dark current suppression layer) on the surface of the aluminum electrode. Next, a 2.0 nm current transmission promoting layer made of lithium fluoride was formed. Furthermore, P3HT was dissolved in toluene and adjusted to a concentration of 25.0 mg / ml. An emitter layer (70 nm) made of P3HT was formed using this P3HT solution. Next, a molybdenum oxide layer (charge injection layer) is formed by vacuum deposition so as to have an average film pressure of 4 nm, and an emitter electrode made of aluminum having an average thickness of 50 nm is formed by a film deposition means using vacuum deposition. Thus, a transistor element of Comparative Example 2 was obtained. The obtained device exhibited current modulation which is a characteristic of MBOT.

The output characteristic of the transistor element of Comparative Example 2 obtained above is that when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3.0 V are applied, the ON current density I _C-ON = −99.2 mA / cm ² of the collector current I _C , V _B = The off-current density I _{C-OFF at} −0 V was −2.07 mA / cm ² , the on / off ratio was 48, and the current amplification factor h _FE was 20.8.

(Comparative Example 3)
[Transistor element having no hole permeation promoting layer]
The same regioregular-P3HT as used in Example 1 was dissolved in toluene to prepare a P3HT solution so that the concentration was 20 mg / ml. The obtained P3HT solution was applied onto an ITO transparent substrate with a spin coater to form a collector layer (250 nm). Next, a 0.6 nm current transmission facilitating layer made of lithium fluoride (LiF), a base electrode layer made of aluminum having an average thickness of 10 nm, and then heat-treated at 100 ° C. for 1 hour in an atmosphere in the atmosphere, An oxide film layer (dark current suppressing layer) was formed on the surface. Furthermore, a 3 nm current transmission promoting layer made of lithium fluoride (LiF), an emitter layer (100 nm) made of the P3HT solution used above, and a molybdenum oxide layer having an average thickness of 30 nm made of gold and 2 nm by vacuum deposition. A transistor element composed of an emitter electrode was prepared.

The output characteristic of the transistor element of Comparative Example 3 obtained above is that when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, the collector current I _C of the ON current density _{I C-ON = -64mA / cm} 2, the current amplification factor h _FE = 11.4, off-current density at the _{V B = 0V I C-OFF} = -0. It was 001 mA / cm ² and the on / off ratio was 9.3 × 10 ⁴ .

(Comparative Example 4)
[Transistor element having no hole permeation promoting layer]
In the same manner as in Comparative Example 3, a collector layer (250 nm) made of P3HT was formed, a 0.6 nm current transmission facilitating layer made of lithium fluoride (LiF), and a base electrode layer made of aluminum having an average thickness of 10 nm were formed. . The dark current suppression layer was not formed by heating in the atmosphere, and left in the atmosphere for 2 hours. Furthermore, a 3 nm current transmission promoting layer made of lithium fluoride (LiF), an emitter layer (100 nm) made of the P3HT solution used above, and a molybdenum oxide layer having an average thickness of 30 nm made of gold and 2 nm by vacuum deposition. A transistor element composed of an emitter electrode was prepared.

The output characteristic of the transistor element of Comparative Example 4 obtained above is that when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and further, a base voltage V _B is applied between the emitter electrode and the base electrode. The measurement was performed by measuring the amount of change in the collector current I _C and the base current I _B when no voltage was applied (0 to −3 V). As a result, the on-current density I _{C-ON of} the collector current I _C -ON = 16.1 mA / cm ² , the current amplification factor h _FE = 1.3, and the off-current density I _C-OFF = − when V _B = 0V. It was 0.001 mA / cm ² , and the on / off ratio was 2.5 × 10 ⁴ mA / cm ² .

(Evaluation results)
The output characteristics of the transistor element are that when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and when a base voltage V _B is applied between the emitter electrode and the base electrode, and when not applied (0 to -3 V). The amount of change in the collector current IC and the base current IB was measured. The transistor elements of the examples were confirmed to operate as MBOT. The evaluation results are shown in Tables 1 and 2 together with the main results. That is, Table 1 shows the results of Examples 1 to 3 performed by changing the material of the emitter layer. FIG. 4 shows “change in collector current (IC-VB characteristics)” of the transistor element in this case. Table 2 also shows the cases of Examples 6 and 7 in which the dark current suppressing layer was formed by heating the base electrode and elements that were not formed, and Example 6 except that the hole permeation promoting layer was not formed. The result of Comparative Example 2 having the same configuration is shown. FIG. 5 shows “change in collector current (IC-VB characteristics)” of the transistor element.

  From the above comparison, the transistor element of the example of the present invention was formed by forming the hole permeation promoting layer with at least a conductive polymer from the comparison with the element of the comparative example in which the hole permeation promoting layer was not formed. It is considered that the rate increased and an excellent current amplification factor and on / off ratio were obtained.

  Further, according to the study by the present inventors, in the case of the example in which at least the hole permeation promoting layer is formed of a conductive polymer, the hole base electrode transmittance is improved, and in that case, the current permeation promoting layer is formed. It has also been confirmed that this is one of the important factors for the excellent performance of the organic transistor (MBOT).

Furthermore, from the examples, it was confirmed that the transistor element of the present invention can obtain a large current having an on-current density of maximum -225 mA / cm ² (see Example 5). Further, in that case, an element excellent in transistor characteristics having a current amplification factor h _{FE of} 226 could be obtained. Thus, it was confirmed that the transistor element of the present invention can perform large current modulation under a low voltage, has a high current amplification factor, and apparently functions effectively as a current modulation type transistor element similar to a bipolar transistor. .

  The organic transistor element of the present invention is used as a transistor element exhibiting excellent current modulation, more specifically, as a transistor element excellent in driving an organic EL display or the like, and excellent in current amplification factor that modulates a large current at a low voltage. It can be used in various fields.

11: Collector electrode 12: Emitter electrode 13: Base electrode 21: Organic semiconductor layer (emitter layer side)
22: Organic semiconductor layer (collector layer side)
31: Hole permeation promoting layer

Claims (6)

And the emitter electrode, is arranged a sheet-like base electrode between the collector electrode formed on a substrate, and, p-type organic semiconductor layer is provided on each side of the front and back surfaces of the base electrode, further, the base electrode and has holes permeation promoting layer is provided between the p-type organic semiconductor layer of the emitter electrode side, the holes permeation promoting layer Ri film der comprising a conductive polymer, said holes permeation enhancement layer and the between the base electrode, the current penetration enhancing layer consisting of alkali metal salts are stacked, the holes permeation promoting layer transistor element characterized that you have been formed on the said current permeation enhancement layer.   The transistor element according to claim 1, wherein the hole permeation promoting layer is a hydrophilic film formed of a material having a conductive polymer.   The transistor element according to claim 1, wherein the conductive polymer contains poly (3,4-ethylenedioxythiophene). 4. The transistor element according to claim 1, wherein an energy level of the conductive polymer is larger than a highest occupied molecular orbital of a p-type organic semiconductor layer provided between a base electrode and an emitter electrode. . 5. The transistor element according to claim 1, wherein a current transmission promoting layer made of an alkali metal salt is further laminated on the collector electrode side of the base electrode .   The transistor element according to claim 1, wherein the hole transmission promoting layer has a thickness of 5 nm to 200 nm.

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