JP5995250B2 - Manufacturing method of organic semiconductor thin film - Google Patents

Description

  The present invention relates to a method for producing an organic semiconductor thin film.

  Organic electronics using high molecular and low molecular organic semiconductors has attracted attention as a major next-generation technology for producing flat panel displays and electronic paper. In recent years, research and development of organic semiconductor thin film field effect transistors that use switching elements for active matrix in addition to organic electroluminescent diodes that have already been commercialized have made great progress.

  One of the major features of organic electronics is that electronic devices can be manufactured by a solution process that does not require vacuum. For this reason, compared to conventional inorganic semiconductor devices, which require high costs for large-scale vacuum devices and high-temperature devices as the product size increases, solutions (inks) in which organic semiconductors are dissolved in organic solvents at a high concentration ) Printing technology is expected to be able to produce large area flat panel displays and electronic paper at low cost and energy saving.

  As a technique for constructing an organic semiconductor thin film using a printing technique, many researches on a polymer organic semiconductor whose viscosity of a solution is increased have been studied. On the other hand, low molecular weight organic semiconductors that have higher device characteristics than high molecular weight semiconductors are homogeneous because of their low solution viscosity and high molecular weight low molecular weight organic semiconductors. It is difficult to form a layer.

  An ink jet printing method has been proposed as an effective printing technique for handling ink having a relatively low viscosity (see Patent Document 1). The method of producing an organic semiconductor thin film by the ink jet printing method is a method in which a solution (ink) in which an organic semiconductor is dissolved in an organic solvent at a high concentration is dropped from an ink head onto a substrate, followed by evaporation of the organic solvent. The layer is deposited. However, in this method, after the ink is dropped, the organic semiconductor is deposited while causing convection inside the droplet, so that the deposition of the material concentrates on the outer edge of the droplet where the solvent mainly evaporates, and the film thickness of the outer edge is increased. However, only a significantly thick non-uniform thin film can be obtained.

  In order to improve film formation characteristics, a method has been proposed in which a soluble polymer such as poly (α-methylstyrene) is mixed in a solution to suppress convection inside the droplet (see Non-Patent Document 1). It has been reported that the effect of the polymer matrix slows the solvent evaporation rate, and thus has the effect of growing larger microcrystalline grains.

  There has also been reported an attempt to control the convection inside the droplets by mixing different organic solvents to improve the uniformity of the film thickness of the organic semiconductor layer (see Non-Patent Document 2). However, it is sufficient from the viewpoints of deterioration of characteristics by mixing polymers that are not related to conductivity into low molecular organic semiconductors, and controllability and uniformity of the entire film formed by dripping. It can not be said.

  On the other hand, as a method for inkjet printing of low-molecular organic materials, a double-shot inkjet printing method has been proposed for conductive organic materials of molecular compounds composed of two types of molecules, electron donating molecules and electron accepting molecules. (See Patent Documents 2 and 3). In this method, an ink obtained by dissolving an electron-donating molecule at a high concentration and an ink obtained by dissolving an electron-accepting molecule at a high concentration are separately prepared, and the same position on a substrate is obtained from separate ink heads. Then, these are applied and mixed at the same position on the substrate to form a molecular compound thin film on the substrate. It has been reported that the solubility of molecular compounds is much lower than the solubility of individual molecules, and the molecular compounds precipitate before evaporation of the organic solvent, so that a thin film with high film quality and film thickness can be obtained.

  However, the above method is limited to a case where a large difference in solubility between a raw material molecule and a compound can be used in a molecular compound composed of two types of molecules. In the past, high-molecular-weight low molecular organic semiconductors with high device characteristics cannot be used as they are because of the large number of organic materials composed of single-component organic molecules.

JP 2005-518332 A JP 2007-305807 A JP 2008-153318 A

Advanced Materials Vol.21, p. 1166, 2009 Advanced Materials Vol.18, p.229, 2008

  In view of the situation as described above, the present invention, when producing an organic semiconductor thin film composed of a single component organic molecule by a printing method, includes a peripheral portion within a predetermined region, and the film quality and film thickness are uniform. Another object of the present invention is to provide a method for producing a homogeneous organic semiconductor thin film with very few pinholes.

The above problem is solved by the following means.
(1) Prepare a first ink obtained by dissolving the organic semiconductor at a high concentration in an organic solvent having a high affinity for the organic semiconductor, and a second ink comprising an organic solvent having a low affinity for the organic semiconductor. A method for producing an organic semiconductor thin film, comprising: a step; and a step of mixing the first and second inks on a substrate.
(2) The method for producing an organic semiconductor thin film according to (1), wherein the first and second inks are ejected simultaneously or alternately from the respective ink heads onto the substrate.
(3) The method for producing an organic semiconductor thin film according to (1) or (2), wherein the organic semiconductor is TIPS pentacene.

  According to the present invention, it is possible to avoid agglomeration at the outer edge of the droplet due to simultaneous evaporation and precipitation of the solvent, so that the organic film has a uniform film quality and film thickness over a wide area of 100 μm or more × 100 μm or more. A semiconductor layer can be manufactured. Thereby, an organic semiconductor device exhibiting excellent device characteristics can be constructed without a vacuum by a printing method. In addition, it can be used in a manufacturing process that is suitable for mass production at low cost with rolls, tows and rolls.

It is a schematic diagram of the double shot inkjet method of the two droplet alternate landing method. It is the measurement result of the film thickness profile of the single component organic-semiconductor thin film formed on the board | substrate by the conventional single shot method (a) and the double shot method (b). It is a polarizing microscope photograph of the single component organic-semiconductor thin film formed on the board | substrate by the conventional single shot method (a) and the double shot method (b, c).

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

  An embodiment using 6,13-bistriisopropylsilyltinylpentacene (hereinafter abbreviated as “TIPS pentacene”), which has been reported to form an organic thin film transistor, as an organic material constituting the organic semiconductor layer will be described.

  Two inkjet heads that use chlorobenzene (CB) as a solvent to dissolve TIPS pentacene at a high concentration and N, N-dimethylformamide (DMF) as a solvent that hardly dissolves TIPS pentacene. A TIPS pentacene thin film was fabricated using an inkjet apparatus having

  The raw materials TIPS pentacene, CB, and DMF are all available at low cost. TIPS pentacene used was purified by recrystallization.

  First, in order to prepare an ink in which an organic semiconductor is dissolved at a high concentration, 31 mg of TIPS pentacene (48.5 μmol: molecular weight 639) is dissolved in 1.3 ml of chlorobenzene (CB) and used as an ink at a concentration of 36.3 mmol / l A solution of pentacene was prepared. The viscosity of each of the obtained inks was 2 to 3 mPa · s, and showed suitable properties as an ink used in the ink jet printing method.

  The ink (A ink) in which the above organic semiconductor is dissolved in an organic solvent and the ink (B ink) consisting only of the organic solvent in which the organic semiconductor is hardly dissolved are landed at the same position by an ink jet apparatus having two ink jet heads. After mixing, an organic semiconductor layer obtained by precipitation of the organic semiconductor before solvent evaporation was formed on the substrate by mixing A ink and B ink.

  Hereinafter, the present invention will be described in more detail based on examples. The solution application device used is an ink jet printing device that can arbitrarily discharge fine droplets of about 100 picoliters for each of the two types of ink in a precise amount and position in a non-contact manner. It is. A ink containing TIPS pentacene and B ink consisting only of a solvent with low affinity were respectively applied to the same positions on the substrate and mixed in a solution state (see FIG. 1).

  In addition, in order to demarcate the droplets deposited by the ink jet method within a certain region, it is useful to use a substrate surface that has been subjected to patterning by hydrophilic treatment and hydrophobic treatment.

  In this example, a p-type silicon wafer coated with a 100 nm thick silicon oxide film was used as a substrate, and a silicon oxide film subjected to hydrophilic / hydrophobic patterning was used.

  For patterning, first, the entire surface of the silicon oxide film is hydrophobized by exposing it to gaseous hexamethyldisilazane (HMDS) all day and night, and then UV / ozone treatment is performed with the mask pattern bonded to the substrate surface. This was carried out by selectively hydrophilizing the unmasked surface region.

  The obtained substrate surface has a contact angle of 2 degrees or less on the hydrophilic surface part for CB, for example, whereas the contact angle is 35 degrees on the hydrophobic surface part, thereby confining the droplets within the hydrophilic pattern. Is possible.

  In the ink application by the ink jet method, first, the head 1 filled with the A ink is moved to the position of the substrate surface portion 7 where the surface of the substrate 10 has been subjected to a hydrophilic treatment, and 30 drops of A ink are ejected from the opening 3. After landing on the head, the head 2 filled with the B ink is quickly moved to the position where the A ink has landed, and 45 drops of B ink are ejected from the opening 4, and the A ink and the B ink on the substrate. A droplet 9 was obtained.

  The A ink and B ink are mixed in a rectangular hydrophilic region of 200 μm × 800 μm formed in advance. First, the organic semiconductor layer is deposited after a few seconds, and then the solvent is evaporated and dried within a few minutes, and the thickness is 260 nm. About an organic semiconductor thin film was formed. As shown in FIG. 2B, the film thickness profile is compared with the film thickness profile obtained by depositing and drying only the A ink by the single shot method without using the B ink (FIG. 2A). The film thickness was uniform over the entire region.

  FIG. 3 shows a polarizing microscope photograph of a single component organic semiconductor thin film formed on a substrate by the conventional single shot method (a) and double shot method (b, c). (B) and (c) are the results of observing the same thin film with crossed Nicols at different polarization angles.

  3B and 3C, it can be seen that the organic semiconductor thin film having high crystallinity is obtained by the double shot method according to the present invention.

  In addition, said Example is for making an understanding of this invention easy to the last, and is not limited to this Example. That is, modifications and other aspects based on the technical idea of the present invention are naturally included in the present invention.

  For example, as an organic semiconductor, the results relating to TIPS pentacene were exemplified, but other organic semiconductors having high solubility in one kind of organic solvent and almost no solubility in another kind of organic solvent may be used. Good. Moreover, it is good also as an organic molecule which selectively improved the solubility to a certain organic solvent by substituting with an alkyl group or a substituent equivalent to it.

  Further, although CB is exemplified as a solvent having a high affinity for organic semiconductors and DMF is exemplified as a solvent having a low affinity, other solvents may be used as long as they are excellent in the solubility of organic low molecules. The same effect can be obtained as long as they are mixed without being separated from each other.

  For example, as the solution application apparatus, the case of an ink jet apparatus has been exemplified, but two liquids may be applied by a dispenser.

  In the embodiment, the B ink is dropped after the A ink is dropped, but the same result can be obtained when the A ink is dropped after the B ink is dropped or when the A ink is dropped simultaneously.

DESCRIPTION OF SYMBOLS 1 Ink (A ink) head by the solution which dissolved organic semiconductor to high concentration 2 Ink (B ink) head by the organic solvent which does not dissolve organic semiconductor 3 A ink head opening 4 B ink head opening Part 5: Flying A ink droplet 6 Flying B ink droplet 7 Substrate surface part 8 with hydrophilic treatment on the surface Substrate surface part 9 with hydrophobic treatment on the surface After landing on the substrate surface, hydrophilic treatment Ink accumulated on the surface of the applied substrate 10

Claims (6)

  Preparing a first ink obtained by dissolving the organic semiconductor in a high concentration in an organic solvent having a high affinity for the organic semiconductor, and a second ink comprising an organic solvent having a low affinity for the organic semiconductor; A step of ejecting the first and second inks from the respective ink heads onto the substrate and mixing the first and second inks on the substrate; and an organic semiconductor layer is deposited in the mixed droplets And then forming the organic semiconductor film by evaporating the solvent in the droplets. An organic semiconductor thin film manufacturing method using an ink jet apparatus.   The method for producing an organic semiconductor thin film according to claim 1, wherein the second ink is ejected after the first ink is ejected.   The method for producing an organic semiconductor thin film according to claim 1, wherein the first ink is ejected after the second ink is ejected.   The method for producing an organic semiconductor thin film according to claim 1, wherein the first ink and the second ink are simultaneously ejected.   The method for producing an organic semiconductor thin film according to claim 1, wherein the organic semiconductor is TIPS pentacene. The organic solvent having a high affinity for the organic semiconductor is chlorobenzene,
6. The method for producing an organic semiconductor thin film according to claim 5, wherein the organic solvent having a low affinity for the organic semiconductor is N, N-dimethylformamide.