Oxide sputtering target, transparent conductive oxide thin film, and solar cell comprising same

Abstract

An oxide sputtering target may include a metal oxide wherein the metal oxide is composed of only In2O3 and GeO2, and the content of GeO2 may be 3 wt% to 5 wt% with respect to the sum of the contents of In atoms, Ge atoms, and O atoms. A transparent conductive oxide thin film may include a metal oxide, in which the metal oxide is composed only of In2O3 and GeO2, and the content of GeO2 may be 3 wt% to 5 wt% with respect to the sum of the contents of In atoms, Ge atoms, and O atoms. A solar cell may have the transparent conductive oxide thin film as a transparent electrode or an electron transport layer, and may be any one of a perovskite solar cell, a silicon solar cell, a silicon / perovskite double-junction solar cell, and a perovskite / perovskite double-junction solar cell.

Description

Technical Field

[0001] The present invention relates to an oxide sputtering target, a transparent conductive oxide thin film, and a solar cell including the same, and more particularly, to an oxide sputtering target, a transparent conductive oxide thin film, and a solar cell based on In, Ge, and O components. Background Art

[0002] A transparent conductive oxide (TCO) thin film is a thin film having characteristics of low resistance and high transmittance, and is particularly widely used in the field of solar cells. The TCO thin film suitable for a solar cell forms a thin film having low resistance, high transmittance, and high mobility, so that light from the sun can be effectively transmitted and enter the solar cell unit, and the photoelectrons generated from the unit can migrate smoothly, thereby improving the efficiency of the solar cell unit.

[0003] The TCO thin film is widely used as an upper electrode and a lower electrode in a solar cell. Recently, in order to overcome the limitations of a single-junction solar cell, a multi-junction solar cell in which two or more solar cells that absorb light in different regions are joined has been proposed, and the TCO thin film is also used as an intermediate layer for joining an upper unit and a lower unit in such a multi-junction solar cell.

[0004] As such a TCO thin film, the most widely used material at present is indium tin oxide (ITO: Indium Tin Oxide) which exhibits excellent electro-optical characteristics. In order for ITO to achieve excellent electro-optical characteristics, a deposition process or a post-heat treatment process at a temperature of 200 °C or higher is required. However, for a solar cell, if ITO used as an upper electrode is deposited at a high temperature, it may cause deformation and damage to the layer deposited in the previous process, and thus this may be one of the reasons for the decrease in the efficiency of the solar cell. In particular, for perovskite which is favored as a next-generation solar cell, since it deteriorates or decomposes at a temperature of 200 °C or higher, in order to use ITO as an upper electrode and an intermediate layer, it must be deposited at a low temperature. However, ITO deposited at a low temperature has a higher resistivity than ITO deposited at a high temperature or subjected to a high-temperature post-heat treatment, and as the resistivity of the electrode increases, the fill factor of the solar cell decreases, resulting in a problem of efficiency decrease.

[0005] Therefore, there is a need for a transparent conductive oxide thin film that has excellent electro-optical characteristics even when deposited at a low temperature. Summary of the Invention

[0006] According to a first aspect of the present invention, an oxide sputtering target can be provided, comprising: a metal oxide, wherein the metal oxide is composed only of In2O3 and GeO2, and the content of GeO2 can be 3 wt% to 5 wt% relative to the sum of the contents of In atoms, Ge atoms and O atoms.

[0007] According to a second aspect of the present invention, a method for forming a transparent conductive oxide film can be provided, comprising the steps of: depositing a transparent conductive oxide film by sputtering the oxide sputtering target.

[0008] According to some embodiments, the step of depositing the film can comprise the steps of: depositing the transparent conductive oxide film by DC (direct current) magnetron sputtering the manufactured oxide sputtering target.

[0009] According to some embodiments, the step of depositing the transparent conductive oxide film can be performed at a temperature of less than 200 °C.

[0010] According to some embodiments, it can further comprise the steps of: after depositing the transparent conductive oxide film, post-heat treating the deposited transparent conductive oxide film at a temperature of less than 200 °C.

[0011] According to a third aspect of the present invention, a transparent conductive oxide film can be provided, comprising: a metal oxide, wherein the metal oxide is composed only of In2O3 and GeO2, and the content of GeO2 can be 2.6 wt% to 5 wt% relative to the sum of the contents of In atoms, Ge atoms and O atoms.

[0012] According to a fourth aspect of the present invention, a solar cell can be provided, having the transparent conductive oxide film according to claim 6 as a transparent electrode or an electron transport layer.

[0013] According to some embodiments, the transparent conductive oxide film can be formed as the transparent electrode on a glass substrate.

[0014] According to some embodiments, the solar cell can be any one of a perovskite solar cell, a silicon solar cell, a silicon / perovskite tandem solar cell, and a perovskite / perovskite tandem solar cell.

[0015] According to some embodiments, the transparent conductive film can be an electrode formed on the light incident side based on the light absorption layer.

[0016] According to the above structure, the advantages of the present invention are that it can provide a transparent conductive oxide film with low resistance and excellent transmittance. In particular, it has the advantage that even when sputter deposition is carried out at a relatively low temperature (for example, at room temperature), a transparent conductive oxide film with low resistance and excellent transmittance can be obtained.

[0017] In addition, the advantages of the present invention are that by applying the transparent conductive oxide film having such excellent physical properties to a solar cell (for example, applying it to the upper electrode of a solar cell), a solar cell with excellent energy conversion efficiency can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figures 1 to 9 is a graph showing the results of depositing a transparent conductive oxide film on a glass substrate at room temperature and measuring the optical and electrical properties.

[0019] Figure 1 is a graph showing the light transmittance.

[0020] Figures 2 to 5 is a graph showing the number of transmitted photons of the germanium doping concentration of the transparent conductive oxide film according to each wavelength band.

[0021] Figures 6 to 9 is a graph showing the electrical properties of the transparent conductive oxide film.

[0022] Figures 10 to 15 is a graph showing the physical properties of a solar cell including the transparent conductive oxide film.

[0023] Figure 10 represents a current density-voltage curve.

[0024] Figure 11 is a graph showing the current density according to the germanium doping concentration of the transparent conductive oxide film.

[0025] Figure 12 is a graph showing the open circuit voltage according to the germanium doping concentration of the transparent conductive oxide film.

[0026] Figure 13 is a graph showing the fill factor according to the germanium doping concentration of the transparent conductive oxide film.

[0027] Figure 14 is a graph showing the energy conversion efficiency according to the germanium doping concentration of the transparent conductive oxide film.

[0028] Figure 15 is a graph showing the series resistance, shunt resistance and fill factor according to the germanium doping concentration of the transparent conductive oxide film.

[0029] Figures 16 to 18 It is a graph shown for comparing and examining the physical properties of the transparent conductive oxide film and the physical properties of the solar cell. Figure 16 It shows simultaneously Figure 6 the charge concentration of Figure 15 and the series resistance of Figure 17 It shows simultaneously Figure 7 the mobility of Figure 15 and the series resistance of Figure 18 It shows simultaneously Figure 8 the resistivity of Figure 15 and the series resistance of

[0030] Figure 19 It is a graph showing the reflectance and the number of reflected photons of the transparent conductive oxide film.

[0031] Figure 20 It is a graph showing the reflectance and the number of reflected photons measured after forming a hole transport layer and a perovskite light absorption layer on the transparent conductive oxide film. Detailed implementation mode

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0033]

Manufacturing method of sputtering target

[0034] Such a target can be manufactured by powder metallurgy. For example, after mixing In2O3 powder and GeO2 powder in a manner conforming to the content ratio, it is manufactured by sintering, or after mixing In2O3 powder and GeO2 powder in a manner conforming to the content ratio, it is formed by forming methods such as cold press, slip casting, filter press, cold isostatic press, gel casting, centrifugal sedimentation, gravimetric sedimentation, etc., and then manufactured by sintering.

[0035]

Sputtering target

[0036] According to some embodiments, the oxide sputtering target may be an oxide sputtering target for forming a transparent electrode film for improving the efficiency of a solar cell unit.

[0037] Moreover, the oxide sputtering target according to an embodiment of the present invention may be applied to a magnetron sputtering device. Since magnetron sputtering is generally used for depositing large-area oxide films, the target material according to an embodiment of the present invention may be provided with a plurality of sintered bodies manufactured as described above in a tile shape or a tubular shape.

[0038] In some embodiments, the sputtering target can perform direct current (DC) sputtering due to the conductivity of the target material itself. That is, if the target material according to the present invention is used, a transparent conductive oxide film can be deposited by DC sputtering.

[0039] In some embodiments, the oxide sputtering target may be supported by a back plate or a back tube. The back plate or the back tube can support the oxide sputtering target by being joined to the back surface of the oxide sputtering target. The back plate or the back tube serves to support one or more sintered bodies. For this purpose, the back plate is disposed behind the sintered body, and the back tube is joined to the sintered body inside the tubular sintered body through an adhesive. Such a back plate or back tube can be formed of copper having excellent conductivity and thermal conductivity. Preferably, oxygen-free copper, titanium, or stainless steel can be used. The adhesive sandwiched between the sintered body and the back plate and joining them to each other can be formed of indium, for example. And such an adhesive can be formed in a paste form and coated on the front surface of the back plate. In order to join the sintered body and the back plate, a heating unit such as a hot plate, resistance heating, high frequency, electric coil, or laser can be heated to make the adhesive melt and then cool. At this time, the applied heat can be controlled to 170 ± 10 °C to melt the adhesive.

[0040]

Method for forming a transparent conductive film

[0041]

Transparent Conductive Film

[0042]

Solar Cell

[0043] According to some embodiments, the solar cell may be any one of a perovskite solar cell, a silicon solar cell, a silicon / perovskite tandem solar cell, and a perovskite / perovskite tandem solar cell. The structures of these solar cells are well known in the technical field to which the present invention pertains, and thus the descriptions of these structures are omitted in this specification.

[0044] According to the present invention, as described above, it is possible to provide a transparent conductive oxide film having excellent electro-optical characteristics even during low-temperature deposition without deteriorating the characteristics, and thus it is suitable for a perovskite solar cell having a risk of deterioration or decomposition at a high temperature of 200 °C or higher, and is thus suitable for use as an upper electrode or an intermediate layer.

[0045]

Experimental Results for Transparent Conductive Oxide Films

[0046] Figures 1 to 9 It is a graph showing the results of depositing a transparent conductive oxide film on a glass substrate at room temperature and measuring the optical and electrical characteristics.

[0047] Figure 1 And Table 1 below shows the results obtained by ultraviolet-visible absorption spectroscopy (UV-Vis analysis), ellipsometric measurement, etc., and compares the optical characteristics of the respective components of the transparent conductive oxide film deposited at room temperature. The UV-Vis analysis sample was formed into a film with a thickness of 100 nm at room temperature and post-heat treated at 100 °C in air for 30 minutes after deposition. The ellipsometric measurement sample was formed into a film with a thickness of 50 nm at room temperature and no post-heat treatment was performed after deposition.

[0048]

Table 1

[0049] From the average light transmittance according to the wavelength measured by UV-Vis spectroscopy, as the Ge doping concentration increases, the average light transmittance shows an increasing trend from 80.05% to 82.64%. Since the refractive index of the IGO film is similar to that of glass (1.5 to 1.9) among all the components, the reduction in light transmittance caused by light reflection at the glass and IGO interface is judged to be negligible.

[0050] Figures 2 to 5 It is a graph showing the number of transmitted photons of the germanium doping concentration of the transparent conductive oxide film according to each wavelength band. As the germanium doping concentration increases, the number of photons generally shows an increasing trend.

[0051] From the above results, it can be simply expected that as the germanium doping concentration increases, the current density value of the solar cell element increases, and the characteristics of the solar cell element will be high.

[0052] Figures 6 to 9 And Table 2 below shows the results obtained by Hall Measurement, 4-point probe analysis, etc., and compares the electrical characteristics of the respective components of the transparent conductive oxide film deposited at room temperature. After deposition, it was post-heat treated at 100 °C in air for 30 minutes and formed into a film with a thickness of 100 nm.

[0053]

Table 2

[0054] The conditions required for the transparent electrode of a solar cell are as follows: i) High light transmittance to increase the amount of sunlight incident on the light absorption layer; ii) Low surface resistance to reduce the loss of generated charges; iii) Work function to be well-matched with the charge transfer layer to achieve Ohmic contact with the charge transfer layer. Since all are in the form of a composition mainly composed of In2O3 with a small amount of other substances added, it can be expected that there will be no significant difference in the work function. Therefore, it can be judged that as long as conditions i) and ii) are satisfied.

[0055] The following Table 3 shows the results of the composition analysis (EDS) of the fabricated transparent conductive oxide film. It was deposited at room temperature and formed into a film with a thickness of 50 nm. No post-thermal treatment was performed after deposition.

[0056]

Table 3

[0057] As can be seen from Table 3, there is no significant difference between the composition of the target and the composition of the film. According to some embodiments, the content of GeO2 can be 2.6 wt% to 5 wt% relative to the sum of the contents of In atoms, Ge atoms, and O atoms.

[0058]

Experimental Results for the Fabricated Solar Cells

[0059] The solar cell device structure is formed by stacking a glass substrate / lower transparent electrode / hole transport layer / light absorption layer / electron transport layer / metal electrode, and the IGO transparent electrode is deposited under the perovskite light absorption layer (i.e., on the glass substrate).

[0060] The substances, compositions, and thicknesses used in each layer of the solar cell are as follows: - Lower transparent electrode: IGO, thickness - 100 nm.

[0061] - Hole transport layer: (2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2PACz), ~1 nm.

[0062] - Light absorption layer: Perovskite, detailed composition: (FA 0.6 MA 0.4 )Pb(I 0.6 Br0.4 ) 3 to 380 nm.

[0063] - Electron transport layer: C 60 , 20 nm, bathocuproine (BCP), 5 nm.

[0064] - Metal electrode: Cu, 100 nm.

[0065] The solar cell is fabricated as follows: Wash the IGO substrate successively with glass cleaner, acetone, deionized water (DI water), and ethanol; Place the washed substrate into a UV Ozone Cleaner for treatment; Spin - coat 2PACz on the substrate and then heat - treat it at 100 °C for 10 minutes; Spray the perovskite solution on the substrate coated with 2PACz and add chlorobenzene during the spin - coating process. After spin - coating, heat - treat it at 100 °C for 20 minutes; Deposit C 60 , BCP using a thermal evaporator; Deposit the Cu electrode using a thermal evaporator; Sunlight is incident from the lower side (i.e., through the lower transparent electrode).

[0066] Figures 10 to 15 is a graph showing the physical properties of a solar cell made including a transparent conductive oxide film, Figure 10 showing the current density - voltage curve of the solar cell fabricated in this way. Table 4 below shows the electrical characteristics of the solar cell.

[0067] [Table 4]

[0068] Figure 11 is a graph showing the current density according to the germanium doping concentration of the transparent conductive oxide film, Figure 12 is a graph showing the open - circuit voltage according to the germanium doping concentration of the transparent conductive oxide film, Figure 13 is a graph showing the fill factor according to the germanium doping concentration of the transparent conductive oxide film, Figure 14 is a graph showing the energy conversion efficiency according to the germanium doping concentration of the transparent conductive oxide film, Figure 15 is a graph showing the series resistance, shunt resistance, and fill factor according to the germanium doping concentration of the transparent conductive oxide film.

[0069] Short - circuit current density (Jsc ) and the fill factor (FF) both reach their highest values at 5% IGO. For J sc , referring to Figure 20 , for light with wavelengths from 350 nm to 740 nm, since the number of reflected photons is the least, it is expected that the largest number of photons will be incident on the light absorption layer. Consequently, it is judged that this is because a relatively large amount of photo-charge is generated in the light absorption layer, and it is judged that the FF is due to a better energy band alignment resulting from a reduction in the interface defects between the lower electrode and the hole transport layer or a change in the work function of the lower electrode.

[0070]

Examination of Experimental Results

[0071] In the above text, from Figures 1 to 5 and Table 1, it can be simply expected that as the germanium doping concentration increases, the amount of transmitted photons increases, so the current density value of the device will increase, and the device characteristics will be higher. From the average light transmittance according to the wavelength measured by UV-vis spectroscopy, as the Ge doping concentration increases, the average light transmittance shows an increasing trend from 80.05% to 82.64%. In particular, since the total amount of photons transmitted at 400 nm to 700 nm in the absorption region of the light absorption layer of the wide-bandgap perovskite solar cell (i.e., the front element that converts short-wavelength energy when constructing a tandem solar cell) continuously increases as the Ge doping concentration increases, from the aspect of light transmittance, it can be simply expected that the higher the Ge doping concentration, the more suitable it is as a transparent electrode material.

[0072] Generally, in a semiconductor, as the doping concentration increases, the charge concentration rises, the scattering between charges intensifies, and thus there is a tendency for the charge mobility to decrease. Generally, since the increase in charge concentration is superior to the decrease in mobility, it can be simply expected that the electrical properties will increase as the doping concentration increases.

[0073] However, in a solar cell element, since the lower the resistance of the transparent electrode, the easier the collection of charges, thereby reducing the series resistance value of the element, increasing the fill factor (FF) and increasing the efficiency. However, even if the resistance of the transparent electrode is low, in the case where the resistance is low due to a high charge mobility, only the series resistance of the diode element will decrease, but in the case where the resistance is low due to a high charge concentration, the shunt resistance (i.e., parallel resistance) of the diode element will also decrease, thereby instead reducing the fill factor (FF) and thus reducing the efficiency. In a solar cell element, it is difficult to anticipate what kind of impact the reduction in shunt resistance according to the increase in doping concentration will have.

[0074] Comparison Figures 6 to 9 And the electrical property results of the thin films in Table 2, it can be simply expected that all thin films except 1% have similar resistance values of 6 - 7×10 -4 Ω•cm, and have a surface resistance value of about 150 Ω / □. The thin films of 3%, 5%, and 11% have a lower charge concentration and a higher charge mobility, thus it is expected that the light scattering generated by charges will be reduced and a higher light transmittance will be presented, so they are most suitable for the transparent electrode.

[0075] However, unexpectedly, the finally fabricated solar cells show different results. As Figure 15 shown, the lowest series resistance, the highest shunt resistance, and the highest fill factor are presented in the range where the Ge doping concentration is from 3 wt% to 5 wt%. In addition, as Figure 11 shown, the current density also shows the highest value in the range where the Ge doping concentration is from 3 wt% to 5 wt%. Although the amount of photons transmitted through the transparent electrode increases as the doping concentration increases, as Figure 20 shown, it is analyzed that the reason why the current density is the highest in the range of 3 wt% to 5 wt% is that the photons reflected at the interface between the perovskite thin film and the transparent electrode are reduced. As Figure 19 shown, only in the measurement results after depositing the thin film on the substrate, it shows that the number of reflected photons is the lowest when the Ge doping concentration is 7%, but unexpectedly, as Figure 20As shown, in the measurement results after forming the perovskite light absorption layer, it shows that the number of reflected photons is the lowest when the Ge doping concentration is 5%, and lower at 3% than at 7%. That is, this result means that in addition to the transmittance of the transparent electrode itself, light reflection in the interface generated when a light absorption layer (such as a wide-bandgap perovskite) is coated on the transparent electrode also plays a very important role. Therefore, according to some embodiments, the transparent conductive film can be an electrode formed on the light incident side with reference to the light absorption layer. That is, in a solar cell where sunlight enters from the lower side (i.e., through the lower transparent electrode), the transparent conductive film can be used as the lower transparent electrode, and in a solar cell where sunlight enters from the upper side (i.e., through the upper transparent electrode), the transparent conductive film can be used as the upper transparent electrode.

[0076] In summary, due to the low series resistance, high shunt resistance, the resulting high fill factor, and the high current density resulting from the high photon incidence rate into the light absorption layer, as shown in Table 4, the highest energy conversion efficiency is shown in the range where the Ge doping concentration is from 3 wt% to 5 wt%. It can be seen from this that the transparent conductive oxide film with a Ge doping concentration of 3 wt% to 5 wt% contributes to a solar cell with the best efficiency.

Claims

1. An oxide sputtering target, characterized in that, Comprising: A metal oxide, wherein the metal oxide is composed only of In2O3 and GeO2, and the content of GeO2 is 3% to 5% by weight relative to the sum of the contents of In atoms, Ge atoms and O atoms.

2. A method for forming a transparent conductive oxide film, characterized in that, Comprising the following steps: Depositing a transparent conductive oxide film by sputtering the oxide sputtering target according to claim 1.

3. The method for forming a transparent conductive oxide film according to claim 2, characterized in that: The step of depositing the film comprises the following steps: depositing the transparent conductive oxide film by the oxide sputtering target manufactured by DC magnetron sputtering.

4. The method for forming a transparent conductive oxide film according to claim 2, characterized in that: The step of depositing the transparent conductive oxide film is carried out at a temperature lower than 200 °C.

5. The method for forming a transparent conductive oxide film according to claim 4, wherein, Further comprising the following steps: After depositing the transparent conductive oxide film, post-heat-treating the deposited transparent conductive oxide film at a temperature lower than 200 °C.

6. A transparent conductive oxide film, characterized in that, Comprising: A metal oxide, wherein the metal oxide is composed only of In2O3 and GeO2, and the content of GeO2 is 2.6% to 5% by weight relative to the sum of the contents of In atoms, Ge atoms and O atoms.

7. A solar cell having the transparent conductive oxide film according to claim 6 as a transparent electrode or an electron transport layer.

8. The solar cell according to claim 7, characterized in that: The transparent conductive oxide film is formed as the transparent electrode on a glass substrate.

9. The solar cell according to claim 7, characterized in that: The solar cell is any one of a perovskite solar cell, a silicon solar cell, a silicon / perovskite tandem solar cell and a perovskite / perovskite tandem solar cell.

10. The solar cell according to claim 7, characterized in that: The transparent conductive film is an electrode formed on the light incident side with respect to the light absorption layer.

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