KR101183967B1 - Functionally graded Transparent conducting oxide film and method for manufacturing thereof, Anode for Organic light emitting diode and window layer for solar cell using functionally graded transparent conducting oxide film - Google Patents

Abstract

The present invention relates to a gradient function transparent conductive oxide film, an anode for an organic light emitting diode, and a method for manufacturing the same, wherein the transparent conductive oxide film according to the present invention is based on zinc oxide (ZnO), and has a concentration gradient in the thickness direction. Gallium oxide (Ga ₂ O ₃ ) may be deposited and preferably applied to the anode of the organic light emitting diode (OLED).
According to the present invention, the material cost is lower than that of ITO, which is used as a conventional transparent conductive oxide film (TCO), and the process can be simplified as compared with an impurity-doped ZnO-based TCO. In addition, according to the present invention, when used as an electrode included in a flat panel display such as an OLED and a solar cell, preferably the anode of the OLED device, due to the high light transmittance, low resistance, high work function value, etc., the anode and the hole transport layer ( By lowering the injection barrier between the hole transport layers, device efficiency and lifetime extension are achieved.

Description

Functionally graded transparent conducting oxide film and method for manufacturing description, Anode for Organic light emitting diode and window layer for solar cell using functionally graded transparent conducting oxide film}

The present invention relates to an organic light emitting diode anode and a solar cell window layer using a gradient function transparent conductive oxide film, a method of manufacturing the same, and a gradient function transparent conductive oxide film, and more particularly, has a low resistance and high light transmission characteristics. The present invention relates to a transparent conductive oxide film (TCO) and a method of manufacturing the same, which are capable of adjusting the function, and which can be preferably applied to an anode of an organic light emitting diode (OLED) and a window layer of a solar cell.

Transparent conducting oxides (TCO) are functional thin films that transmit electrical light in the visible region and have electrical conductivity, and are widely used as electrode substrates for flat panel displays, touch panels, and solar cells.

TCO materials are key to designing materials to transmit light in the visible range while at the same time having high conductivity. In order to be transparent in the visible region (400 nm to 700 nm wavelength), the electronic energy band gap (electronic energy band-gap) must be 3.1 eV or more, which is the electromagnetic energy of the 400 nm wavelength.

Oxide semiconductors satisfying these characteristics include ZnO (3.3 eV), In ₂ O ₃ (3.7 eV), MgO (3.6 eV), and SnO ₂ (3.6 eV). In general, the TCO has a light transmittance of 80% or more in the visible light region, and as an electrical property, has a resistivity of about 10 ⁻⁴ Ωcm or less.

In order to find a material used for such a TCO, studies of a method of performing doping, alloying, etc. on various materials have been mainly conducted. In particular, In ₂ O ₃ shows lower resistivity than SnO ₂ or ZnO. For this reason, it was commercialized first, and it is still used today, which is Sn doped In ₂ O ₃ .

ITO is currently applied to display electrodes such as LEDs, LCDs, PDPs, and solar cells, and is generally about 10 ^-4 Ωcm and about 10 ^-5 Ωcm at the laboratory level. Has

However, such ITO has a disadvantage that In is expensive as a rare element, and when exposed to hydrogen plasma which is commonly used in a flat panel display manufacturing process, In or Sn is reduced to deteriorate electrical and optical properties. Therefore, development of TCO using materials other than ITO is an important issue at present.

Among these, zinc oxide (ZnO) -based thin films are excellent in electrical conductivity in the infrared and visible light region, excellent in plasma resistance, low temperature process, low raw material price, and ITO transparent conductive thin film. It is getting the spotlight as a substitute material.

However, when ZnO without impurities is exposed to the air for a long time, the change in electrical properties occurs due to the change in the ratio of Zn and O due to the influence of oxygen, and it is not stable in a high temperature atmosphere. Research has been conducted to improve the electrical conductivity by adding impurities such as Ga, B, and P, and to develop ZnO which is stable even in the air. Currently, considerable researches on ZnO TCO having stable electrical properties have been reported (T. Minami, "Transparent conducting oxide semiconductors for transparent electrodes," Semicond Sci Technol, 20:... S35-S44 (2005); GS Heo, S. J Hong, JW Park, IH Lee, BH Choi, JH Lee, S. Y, DC Shin "Decrease in Work Function of Boron Ion-Implanted ZnO Thin Films" J. Nanosci. Nanotechnol . 7, (2007) 4021 et al.).

For example, recently, studies on controlling work function by ion implantation of B and P ions into ZnO and AZO (Aluminum doped Zinc Oxide) have been reported. In particular, the literature suggesting that the work function increased by 0.32 eV when B ion was ion-implanted in AZO (SJ Hong, GS Heo, JW Park, IH Lee, BH Choi, JH Lee, S). Y, DC Shin "Work Function Increase of Al-doped ZnO Thin Films by B ⁺ Ion Implantation" J. Nanosci. Nanotechnol. 7, (2007) 4077).

However, the implanted B ⁺ ions are positively charged due to a noticeable (positive charge), by filling an oxygen vacancy striking a negative charge (oxygen vacancy) offset the donor site (donor site), as compared to before the injection the sheet resistance was increased, Al ³⁺ ( Lattice scattering increases due to interstitial intrusion of B ⁺ (0.23Å) ions with a smaller ion radius compared to 0.51Å), Zn ²⁺ (0.72Å), and O ^2- (1.32Å). Seemed. In addition, according to such an ion implantation method, there are problems such as expensive process cost and the use of toxic gas.

In addition, Korean Patent No. 73915 discloses a technique using a magnetron sputtering method for depositing a ZnO buffer layer on a polymer material substrate and depositing a TCO thin film and a thin film including a Ga-doped ZnO thin film thereon. However, even with such a method, the ion implantation method or the like must be separately performed as a doping method for doping Ga to ZnO, which poses a problem for expensive equipment and the environment.

Therefore, there is a need for a technique for manufacturing a thin film made of ZnO and other compounds, which inevitably eliminates impurity doping having the aforementioned problems.

On the other hand, among flat panel displays, interest in organic light emitting diodes (OLEDs) has recently increased, which, unlike LCDs requiring backlights, emits light on their own, making a thinner panel possible, which enables ultra-thin designs and enables each pixel. Because it lights only when light is needed, it has many advantages such as ultra low power design because it can operate at ultra low power (2 ~ 10 V) unlike LED which has to shine backlight light all the time. .

In order to improve the efficiency of the OLED device, it is necessary to increase the recombination ratio of electrons and holes, and in order to reduce the injection barrier of holes, it is necessary to adjust the work function of the TCO. By lowering the hole injection barrier, it is possible to extend the life of the device by reducing the heat generation, which is a fundamental problem of the OLED device. Therefore, there is a need to find a TCO material capable of adjusting the work function.

On the other hand, the solar cell has a PN junction structure consisting of an N-type semiconductor and a P-type semiconductor, the pair of electrons and holes are generated inside the semiconductor of the solar cell by the light from the outside, the pair of electrons and holes is a semiconductor When freely moving inside and entering the electric field generated by PN junction, electrons (-) move to N-type semiconductor and holes (+) move to P-type semiconductor, whereby electrodes are formed on the surface of P-type semiconductor and N-type semiconductor. When the electrons are connected to an external circuit, they act as solar cells.

Such solar cells may be classified into crystalline silicon, amorphous silicon, compound semiconductors, and the like according to their materials.

The crystalline silicon solar cell can obtain a high energy conversion efficiency, but there is a limit to reduce the production cost due to the silicon substrate of about 200㎛, in particular, the supply instability of the silicon raw material is also pointed out as a problem.

Therefore, research on compound semiconductor solar cells as thin film solar cells that can manufacture solar cells using only a low-cost substrate such as glass instead of crystalline silicon solar cells and only a thin layer of about 5 μm has been actively conducted, and especially CIS In the case of (copper, indium, selenium) thin film solar cells, related research is being actively conducted due to the low production cost and the highest energy conversion efficiency among non-silicon solar cells.

The CIS solar cell has a high light absorption coefficient and is chemically stable, which is very excellent in terms of stability and efficiency compared to other thin film solar cells.

The structure of such a CIS solar cell generally includes a substrate, a back electrode, a light absorption layer, a buffer layer, a window layer, and the like. In this case, the window layer is not only a P-type junction with the P-type semiconductor as the N-type semiconductor, but also formed on the front surface of the solar cell to function as a transparent electrode (transparent conductive oxide film), so the light transmittance must be high and the electrical conductivity must be good. In addition, in order to improve the efficiency of the solar cell, the interlayer contact resistance of the window layer must be lowered, and the work function and bandgap adjustment of the window layer are essential.

Therefore, it is necessary to find a transparent conductive oxide material having a work function and a band gap control and apply the same to a window layer of a CIS solar cell to manufacture a solar cell having a high light transmittance, a low resistance, a work function, and a band gap control. have.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a ZnO-based TCO thin film having excellent optical properties by a simple and economical sputtering deposition method without performing a separate impurity doping process and a method of manufacturing the same. Is in.

In addition, the present invention, in the electrode used in the display device such as OLED and the electrode used in the solar cell, the work function can be adjusted by lowering the injection barrier of the hole, the work function can be adjusted to lower the interlayer resistance It is an object of the present invention to provide an inclined transparent conductive oxide film having electrical reliability and chemical stability.

In order to solve the above problems, the gradient functional transparent conductive oxide film according to the present invention, as shown in Figure 1, ZnO thin film 200 deposited on the transparent substrate 100 and ZnO and Ga ₂ O on the ZnO thin film ₃ includes a gradient thin film 300 formed by simultaneous deposition, and the Ga ₂ O ₃ in the gradient thin film 200 has a concentration gradient in the thickness direction.

As described above, the inclined transparent conductive oxide film according to the present invention includes a ZnO thin film 200 and a ZnO-Ga ₂ O ₃ inclined functional thin film 300, so that no additional doping of impurities is required, and gallium oxide (Ga ₂ O ₃ ) is required. A ZnO-based transparent conductive oxide film obtained by mixing the above can be obtained. That is, a transparent conductive oxide film having excellent optical and electrical properties can be manufactured in a simple process without a doping process such as an ion implantation method.

Here, the transparent substrate 100 used in the present invention is not only glass, but also polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene adipate (PPA), Substrates made of any known transparent resin such as polyisocyanate (PI) can be applied without limitation.

In the present invention, the ZnO thin film 200 deposited as the first layer has excellent electrical conductivity in the infrared and visible light region, excellent durability against plasma, and preserves the characteristics of ZnO that can be processed at low temperature. In order to be applied without other mixed layers. However, when exposed to the atmosphere may change the electrical properties due to the change in the ratio of Zn and O due to oxygen, the inclined thin film 300 was introduced to the surface portion in contact with the atmosphere.

In the present invention, the graded thin film (hereinafter referred to as 'FGTF') 300 is a main thin film structure (ZnO in the present invention) by giving a concentration gradient to a specific functional thin film in the thickness direction. When combined with the above, it means a thin film that gives desired characteristics to the resulting transparent conductive oxide film (TCO).

In the present invention, in order to overcome the instability of the Zn and O due to the change in the electrical properties and the high temperature atmosphere due to the change of the ratio of Zn and O by oxygen, which is considered as a disadvantage of the pure ZnO thin film, while simultaneously depositing gallium oxide (Ga ₂ O ₃ ) It is manufactured in the form of a gradient thin film together with ZnO, and thus the transmittance is improved, and has a low resistance and a high work function, especially when used as an anode, such as OLED, and the hole transport layer (hole transport layer) It was confirmed that a transparent conductive oxide film having a lower injection barrier between) can be obtained.

In addition, gallium oxide (Ga ₂ O ₃ ) is co-deposited in order to overcome the instability of the Zn and O due to the change in the electrical properties and the high temperature atmosphere due to the change of the ratio of Zn and O due to oxygen, which is a disadvantage of the pure ZnO thin film. By manufacturing in the form of inclined thin film together with ZnO, it can have the advantage of controlling the low resistance and work function, and as a result, it can increase the efficiency when used as a window layer of the solar cell through the control of the resistance and work function .

Here, the content ratio of the inclined function thin film 300 to the entire transparent conductive oxide film is about 10 to 40%, preferably 14 to 30%, in the thickness direction from the surface (opposite in contact with the substrate). The best optical properties were shown.

Here, the thickness of the transparent conductive oxide film is preferably formed to 50 to 400nm, preferably 60 to 300nm, so that the gradient function thin film 300 is preferably formed of about 6 to 160nm.

In addition, the transparent conductive oxide film according to the present invention includes a hexagonal wurtizite crystal structure, which corresponds to both the ZnO thin film 200 and the ZnO-Ga ₂ O ₃ gradient function thin film 300, Both have the same structure and are excellent in bonding.

Next, the mechanism when the transparent conductive oxide film according to the present invention is applied to the anode of the OLED will be described. 2 is a cross-sectional view of an OLED to which a transparent conductive oxide film according to the present invention is applied as an anode (TCO), and FIG. 3 is a schematic diagram showing a band diagram of the OLED.

 As shown in FIG. 2, the OLED to which the transparent conductive oxide film according to the present invention is applied has a substrate 10, an anode (Anode) 20, a hole transport layer (HTL) 30, a light emitting layer (EML 40), It comprises an electron transport layer (ETL, 50), the cathode (Cathode, 60), a hole injection layer (HIL) between the anode 20 and the hole transport layer 30, the cathode 60 and the electron transport layer 50 The electron injection layer EIL may be further included therebetween. Here, the transparent conductive oxide film according to the present invention is applied as the anode 20. As will be described later, in the case of the anode 20, the work function value must be increased.

OLED devices manufactured in such a structure emit light through several steps. That is, such a light emitting mechanism is composed of carrier injection, carrier delivery, recombination, and light emission. Holes are injected from the anode and electrons are injected from the cathode.They are moved to the organic Occupied Molecular Obital (HOMO) and the Lower Un-occupied Molecular Obital (LUMO), respectively, and are recombined in the organic layer, which is a light emitting layer, to excite excitons. The excitons are then released to the ground and emit light and heat. Considering this mechanism, in order to improve the mechanism, the injection delivery of the carrier should be easy and for this, the barrier to carrier injection should be small.

Specifically, as shown in FIG. 3, in order to facilitate the injection of the carrier, the energy barriers (ΔE _h and ΔE _e on the drawings) must be crossed at the anode and the cathode, and thus, the organic material layer and the electrode (the anode and the cathode) are optimized. Band diagrams should be provided. In the case of the anode 20, the larger the work function value is advantageous to match the HOMO level of the organic material layer, and in the case of the cathode 60, the smaller the work function value is advantageous to match the LUMO level of the organic material layer.

The gradient function transparent conductive oxide film according to the present invention is applied to the anode 20, and has a large work function as a result of several experiments. As described later, it is determined that the Fermi level is shifted accordingly when Ga ₂ O ₃ is deposited by concentration gradient in the thickness direction.

On the other hand, the inclined transparent conductive oxide film according to the present invention can be used as an electrode included in the window layer of the solar cell. As will be described later, the inclined transparent conductive oxide film can be used as an electrode included in the window layer for a high efficiency solar cell because the band gap and work function can be adjusted in addition to transparency and low resistance.

As such, the inclined transparent conductive oxide film according to the present invention can be used as an electrode included in the window layer of a solar cell, and in this case, between the window layer and the N-type absorbing layer due to high light transmittance, low resistance, and work function control. By lowering the injection barrier, the efficiency of the solar cell is increased.

Next, the manufacturing method of the gradient function transparent conductive oxide film according to the present invention will be described.

Method of manufacturing a gradient function transparent conductive oxide film according to the present invention comprises the step of depositing a ZnO thin film on a transparent substrate and the step of simultaneously depositing ZnO and Ga ₂ O ₃ on the ZnO thin film, the Ga ₂ O ₃ It is characterized in that the deposition while changing the output of the deposition. That is, when simultaneously depositing ZnO and Ga ₂ O ₃ by, for example, sputtering, the output to the ZnO target is fixed and Ga ₂ O ₃ is fixed. The output to the target is deposited while varying, resulting in Ga ₂ O ₃ having a concentration gradient in the thickness direction.

Here, the sputtering method, preferably the magnetron sputtering method, in particular the RF magnetron sputtering method (RF magnetron sputtering) is used as a method of depositing the gradient function transparent conductive oxide film according to the present invention.

The RF magnetron sputtering method is a deposition method generally used when stacking semiconductors. The sputtering apparatus is provided with a magnet installed at the rear or side of the target to remove electrons by heating the electrons causing the radiation in the reaction chamber and the target. Follow. The magnet may be trapped near the target by trapping electrons roaming. At this time, since the ion current is about ten times higher than that of a diode sputter device, the metal film can be deposited more quickly at a lower pressure.

According to the present invention, the material cost is lower than that of ITO, which is used as a conventional transparent conductive oxide film (TCO), and the process can be simplified as compared with an impurity-doped ZnO-based TCO.

In addition, according to the present invention, when used as an electrode included in a flat panel display such as an OLED and a solar cell, preferably the anode of the OLED device, due to the high light transmittance, low resistance, high work function value, etc., the anode and the hole transport layer ( By lowering the injection barrier between the hole transport layers, device efficiency and lifetime extension are achieved.

Further, according to the present invention, the inclined transparent conductive oxide film may be used as an electrode included in window layers of various solar cells, and in this case, the window layer and the N-type due to high light transmittance, low resistance, work function control, etc. Lowering the injection barrier between the absorbing layer has the advantage that can improve the efficiency of the solar cell.

1 is a cross-sectional view of an inclination function transparent conductive oxide film according to an embodiment of the present invention.
2 is a cross-sectional view of an OLED to which a transparent conductive oxide film is applied as an anode (TCO) according to the present invention.
3 is a schematic diagram showing a band diagram of the OLED shown in FIG.
Figure 4 is a schematic diagram showing a method of manufacturing a gradient function transparent conductive oxide film by RF magnetron sputtering in the embodiment and comparative example of the present invention
5 is an XRD measurement result for the specimen prepared according to the Example and Comparative Example
6 and 7 are graphs showing SIMS measurement results for checking the specific gravity of Ga in the specimen prepared according to the embodiment of the present invention
8 and 9 are graphs showing the specific resistance measurement results and hole mobility and carrier concentration of the specimens prepared according to Examples and Comparative Examples, respectively.
10 to 13 are graphs showing the results of measuring the transmittances for the specimens prepared according to Examples and Comparative Examples, respectively.
14 is a graph of the results measured using the Kelvin prove system for the evaluation of the work function for the Comparative Example and Example specimens

Hereinafter, presenting various embodiments of the present invention to look at the physical properties of the method for producing a gradient functional transparent conductive oxide film according to the present invention and the gradient functional transparent conductive oxide film (hereinafter referred to as 'tilting function thin film TCO') prepared therefrom Shall be.

Inclination Thin Film TCO of Deposition equipment

The equipment used for the deposition of the TCO thin film slope function is a combination RF magnetron sputtering system (C ombinational RF magnetron sputtering system). Up to four targets can be mounted and eleven specimens with different concentration ratios of each target can be obtained in one deposition. A rotary pump was used to create a low vacuum of 7.0 × 10 ^-3 Torr and a high vacuum of 5.0 × 10 ^-7 Torr or lower using a cryo pump. The power supply used for the equipment was RF power supply (VM 1500 AW, dressler) with frequency of 13.56 MHz and output of 1500 W. In order to efficiently apply the generated RF power, a matching network (1320 200V, CESAR ^TM ) was used. Was used.

Deposition method

A 4 inch target of ZnO (99.99%, high purity Korea) and Ga ₂ O ₃ (99.99%, high purity Korea) was used, and manufactured using an RF magnetron sputtering system on a coning 1737 glass substrate. The coning 1737 glass substrate was ultrasonically cleaned using acetone, ethanol, and deionized water, and dried in a stream of nitrogen. The deposition conditions of TCO were deposited at room temperature with a process pressure of 0.14 pa, Ar gas of 20 sccm (standard cubic centimeters), and a distance of 90 mm between the target and the substrate.

The conditions for manufacturing such a gradient thin film TCO is as shown in Table 1 below, as a comparative example, a thin film consisting of pure ZnO is deposited by fixing the input power of ZnO at 250 W, and the three types of examples are ZnO. After the deposition of the fixed input power of 250W, and then adjusted the input power of Ga ₂ O ₃ to 50W, 75W, 100W co-deposited with ZnO fixed to the input power 250W.

Sample division Pure ZnO A-type B-type C-type target ZnO (99.99%) ZnO (99.99%), Ga ₂ O ₃ (99.99%) input
power ZnO 250 W 250 W 250 W 250 W Ga ₂ O ₃ - 50, 75, 100, 75, 50 W 50, 75, 100 W 100, 75, 50 W division Comparative Examples 1-1 to 1-11 Examples 1-1 to 1-11 Examples 2-1 to 2-11 Examples 3-1 to 3-11

The A-type was deposited by increasing the input power of Ga ₂ O _{3 in the order} of 50 W, 75 W, 100 W, 75 W, 50 W, increasing the concentration toward the surface, and decreasing it. ₂ O ₃ of the input power to 50 W, 75 W, had a concentration of Ga ₂ O ₃ to 100 W sequence deposited in a manner that increases toward the surface, as opposed to type B- C- type Ga ₂ O ₃ of the input power The deposition of Ga ₂ O _{3 in} the order of 100 W, 75 W, 50 W was carried out in such a manner as to decrease toward the surface.

As shown in FIG. 4, the ZnO target and Ga ₂ O ₃ The deposition was performed by attaching the target to another gun, and for each type of Comparative Example and Example, 11 specimens (44 total) having different concentration ratios can be obtained using different masks.

For convenience, except for the comparative example, it is named 'No. 1' (Examples 1-1, 2-1, 3-1) from 'ZnO rich' near the ZnO target, and 'Ga ₂ near the Ga ₂ O ₃ target. O ₃ rich 'was designated as No. 11 (Examples 1-11, 2-11, and 3-11). In this study, three specimens (# 5, # 7, # 9) at midpoint were selected for each example and comparative example, and the characteristics of these specimens were investigated.

Inclination Thin Film TCO Property evaluation of

1 . XRD Measurement

X-ray diffraction analysis was performed for the structural analysis of the gradient thin film TCO. Samples were 1010 mm and analyzed at 20-70 ° using XRD (X'Pert pro MPD, PANalytical).

2. Depth profile measurement

SIMS (Secondary Ion Mass Spectrometry, CAMECA IMS-6f Magnetic sector SIMS) equipment was used to measure the concentration change according to the depth in the sloped thin film TCO. Oxygen was used as the ion source and the analysis conditions are shown in [Table 2].

Gun O ₂ ⁺ Impact energy 2 KeV Current 70 nA Raster size 200 μm × 200 μm Analysis area 60 μm (Φ) Detected ion Ga ⁺ , O ⁺ , Zn ⁺

3. Hall effect measurement

Hall effect measuring device (7707, Lake Shore) was used to measure the resistivity, carrier concentration, and hole mobility in the thin film. The size of the thin film was prepared in a square shape of 10 × 10 mm, and the thickness value measured by SEM was inputted, and soldered with In at each corner of the sample for ohmic contact, and the thin film and sample holder with In wire. Connected. Measured by applying a current of 1.0 mA and applying a magnetic field at 5 KG. In addition, all the measurements were performed at room temperature.

4. Light transmittance measurement

The optical properties of the thin films were measured using a UV-Vis-NIR Spectrophotometer (Hitach, U-1400). The transmittance was measured in the 800 nm region.

5. Work function measurement

The work function change associated with the energy barrier between the organic layer and the electrode was measured by the Kelvin prove system (KT6500, McAllister Technical Services). The standard sample was ITO, and the distance between the probe and the specimen was 5 nm or less in order to reduce external resistance, and analyzed at room temperature.

Measurement result

1. XRD Characteristics

Pure ZnO (Comparative Example) and ZnO-Ga ₂ O ₃ Inclination Function Thin Film (Example) The results of XRD analysis were reviewed to observe the crystallization. FIG. 5 (a) shows the XRD measurement results for the thin film of pure ZnO. In the fifth specimen (Comparative Examples 1-5 and Z 5) from the ZnO target, a wide amorphous phase and a hexagonal wurtzite phase (002) were observed. A peak was observed, and the intensity of the (002) peak increased with distance to the specimens of Comparative Examples 1-7 and 1-9. In addition, the A-type of FIG. 5 (b), the B-type of (c), and the C-type FGTF thin film of (d), in which Ga ₂ O ₃ was added, also exhibited the same tendency as pure ZnO. Accordingly, it can be seen that the farther away from the ZnO target, that is, the ZnO crystal phase is more developed than the amorphous phase on each of the nine specimens.

2. Changes in concentration according to the depth of the gradient thin film TCO

Corresponding to pure ZnO, the results of SIMS measurements for checking the specific gravity of Ga according to the depth of three types of gradient thin films were examined. As shown in FIG. 6, in Examples 1-7, 2-7, and 3-7 specimens, Ga ₂ O ₃ was deposited about 60 nm from the surface of about 400 nm in total, and about 14-16% of the total thickness of the film was inclined. A thin film made of a functional thin film, and as shown in FIG. 7, in Examples 1-9, 2-9, and 3-9 specimens, the thickness of Ga ₂ O ₃ was deposited about 65 nm from the surface of the entire about 260 nm so that the entire thin film. It was confirmed that about 24 to 26% of the thickness was made of the inclined thin film. As the distance from the ZnO target decreases, the overall thin film thickness decreases, and as the deposition amount of Ga ₂ O ₃ increases, the proportion of the inclined functional thin film in the overall thin film increases.

3. Hall effect characteristics of sloped thin film TCO

In order to evaluate the electrical characteristics, the results of the measurement by each type by Hall effect measurement system were reviewed. FIG. 8 shows the results of the specific resistance measurement. In pure ZnO 5 and 7 specimens (Comparative Examples 1-5 and 1-7), the specific resistance values were 8.36 × 10 ⁻² Ωcm and 3.34 × 10 ⁻² Ωcm, respectively. Burn specimens (Comparative Examples 1-9) exceeded the limits of the measuring equipment and measurement was impossible. However, unlike the pure ZnO, in Example 3 in which the inclined functional thin film was formed on the surface by Ga ₂ O ₃ , in the 9th specimen, the A-type (Example 1-9) was 2.02 × 10 ⁻³ Ωcm, B-type. Is 2.55 × 10 ^-3 Ωcm and C-type is 2.4 × 10 ^-3 Ωcm, which shows the lowest resistivity value, and among them, the lowest resistivity value is 2.02 × 10 ^-3 Ωcm in Example 1-9. It was.

9 shows hole mobility and carrier concentration, and Comparative Examples 1-5 and 1-7 were 10.28 cm 2 / Vs and 7.89 cm 2 / Vs, respectively, and the hole mobility and 7.27 × 10 ¹⁸ cm ^-3 , 2.37 × 10 ¹⁹ cm, respectively. ^Although the carrier concentration value of ^-3 was shown, the specific resistance value of the specimen of Comparative Example 1-9 could not be obtained and thus the hole mobility and the carrier concentration value could not be obtained.

Ga ₂ O ₃ in the case of the functionally gradient exemplary TCO thin film has a ratio of Ga ₂ O ₃ low Example 1-5, specimens added with a concentration gradient, in the case of 9.76 cm² / Vs, in Example 2-5, specimens 9.95 cm² / Vs, Example 3-5 specimens were lowered to 7.29 cm² / Vs, but the specimens of Example 1-9 were 23.58 cm² / Vs and Example 2-9 was gradually added to specimen No. 9 having a high Ga ₂ O ₃ ratio. The hole mobility was increased to 25.07 cm 2 / Vs and Example 3-9 specimens to 20.83 cm 2 / Vs.

In addition, exemplary carrier density in the specimen No. 5 Example 1-5 specimen is 2.03 × 10 ¹⁹ cm ^-3, in Example 2-5, specimens were 1.54 × 10 ¹⁹ cm ^-3, in Example 3-5 specimen is 1.02 × 10 ¹⁹ cm ^{- It} was shown to be low as ³ , 1.31 × 10 ²⁰ cm ^{-3 in} Example 1-9, 9.76 × 10 ¹⁹ cm ^{-3 in} Example 2-9, 1.25 × in Example 3-9 10 ²⁰ cm ^-3 was high.

Carrier concentration increase is determined by Ga ₂ O ₃ acting as a negative donor of ZnO and a change in the concentration of oxygen vacancy associated with the carrier concentration.

4. Optical Characteristics of Inclination Thin Film TCO

10 to 13 are the results of measuring the transmittance in order to evaluate the optical properties for pure ZnO and three types of example specimens, respectively. Pure ZnO and three types of gradient thin film TCO showed an average light transmittance of more than 80%.

As shown in FIG. 10, the pure ZnO thin film showed a band gap of about 3.04 eV in Comparative Example 1-5 and about 2.4 eV in Comparative Example 1-9. In Comparative Examples and Examples, a blue shift was observed toward the specimen No. 5, which is closer to the ZnO target as a whole, that is, when ZnO was relatively contained, which is shown in the XRD pattern of FIG. 5. As described above, it is considered that a large number of amorphous phases have irregular atomic arrangements, which results in a large mean free pace and a wide band gap due to the large potential of atoms compared to crystalline.

5. Work function of gradient thin film TCO

14 is a result measured using the Kelvin prove system to evaluate the work function for the comparative example and the example specimens. The work function of pure ZnO was found to be 4.17 eV in Comparative Examples 1-5, 4.13 eV in Comparative Examples 1-7, and 4.21 eV in Comparative Examples 1-9, and in Examples where Ga ₂ O ₃ was added It can be seen that this value increases compared to pure ZnO. Among them, the highest sample was 4.39 eV in Example 3-9, and showed a large difference of 0.18 eV compared to the maximum value of pure ZnO.

As described above, the work function of the example specimen in which Ga ₂ O ₃ is gradient-concentrated as compared to pure ZnO is increased due to the movement of the Fermi level as described above. The Fermi level of pure ZnO is determined in position depending on temperature and donor density.

In this experiment, since it proceeds at room temperature, the Fermi level is determined by the donor density, and zinc ions or oxygen vacancies present in the TCO are preferentially filled with the doping material. As a result of the addition of Ga ₂ O ₃ , the oxygen vacancies (defects) or Zn vacancies (defects) and other defects that existed on the surface of the ZnO surface are completely compensated at the surface, and thus the work of the donor density and the Fermi level decreases. It is determined that the function value is increased.

It has been described above in detail with reference to preferred examples and comparative examples of the present invention. However, the scope of the present invention is not limited to the above embodiments, but may be embodied in various forms of embodiments within the scope of the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

100: transparent substrate 200: ZnO thin film (200)
300: ZnO-Ga ₂ O ₃ inclined functional thin film

Claims (8)

In a transparent conductive oxide film formed on a transparent substrate,
A ZnO thin film deposited on the transparent substrate; And a gradient function thin film formed by simultaneously depositing ZnO and Ga ₂ O ₃ on the ZnO thin film,
Ga ₂ O ₃ in the gradient function thin film has a concentration gradient in the thickness direction,
The inclined function thin film is inclined function transparent conductive oxide film, characterized in that contained in the thickness ratio of 10 to 40% from the surface with respect to the thickness of the entire transparent conductive oxide film.
delete The method according to claim 1,
The thickness of the transparent conductive oxide film is a gradient transparent conductive oxide film, characterized in that 50 to 400nm.
The method according to claim 1,
The transparent conductive oxide film is an inclined transparent conductive oxide film, characterized in that it comprises a hexagonal wurtzite crystal structure.
In an organic light emitting diode formed by stacking a substrate, an anode, a hole transport layer, a light emitting layer, an electron transport layer, a cathode in order,
The anode is formed of a transparent conductive oxide film,
The transparent conductive oxide film is a ZnO thin film deposited on the substrate; And a gradient function thin film formed by simultaneously depositing ZnO and Ga ₂ O ₃ on the ZnO thin film,
Ga ₂ O ₃ in the gradient function thin film has a concentration gradient in the thickness direction,
The inclined function thin film is an organic light emitting diode, characterized in that contained in a thickness ratio of 10 to 40% from the surface with respect to the thickness of the entire transparent conductive oxide film.
In a solar cell formed by sequentially stacking a substrate, a back electrode, a light absorption layer, a buffer layer, and a window layer serving as a transparent electrode,
The window layer is composed of a transparent conductive oxide film,
The transparent conductive oxide film is a ZnO thin film deposited on the buffer layer; And a gradient function thin film formed by simultaneously depositing ZnO and Ga ₂ O ₃ on the ZnO thin film,
Ga ₂ O ₃ in the gradient function thin film has a concentration gradient in the thickness direction,
The gradient function thin film is a solar cell, characterized in that included in the thickness ratio of 10 to 40% from the surface with respect to the thickness of the entire transparent conductive oxide film.
Depositing a ZnO thin film on a transparent substrate; And
And simultaneously depositing ZnO and Ga ₂ O ₃ on the ZnO thin film to form a gradient thin film.
By depositing the Ga ₂ O ₃ by varying the output during deposition, Ga ₂ O ₃ in the gradient function thin film has a concentration gradient in the thickness direction, the gradient function thin film is 10 to 10 from the surface with respect to the thickness of the entire transparent conductive oxide film Method for producing a gradient transparent conductive oxide film characterized in that it is included in a thickness ratio of 40%.
The method of claim 7,
And depositing the ZnO thin film and the ZnO-Ga ₂ O ₃ mixed thin film by using a magnetron sputtering method.

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