KR20170105351A - Method for preparation of electron transport layer of solar cell - Google Patents

Abstract

The present invention relates to a manufacturing method of an electron transport layer of a solar cell. According to the present invention, the manufacturing method of an electron transfer layer of a solar cell does not use a high temperature process, and can manufacture an electron transport layer with a small air gap and a uniform thickness. The manufacturing method of an electron transfer layer of a solar cell comprises the following steps: manufacturing a mixture by mixing titanium dioxide particle, titanium alkoxide, and organic acid; coating a substrate with the mixture; and light sintering the substrate coated with the mixture.

Description

[0001] The present invention relates to a method for preparing an electron transport layer of a solar cell,

The present invention provides a method for producing an electron transport layer of a solar cell.

Researches on renewable and clean alternative energy sources such as solar energy, wind power, and hydro power are actively being conducted to solve the global environmental problems caused by the depletion of fossil energy and its use. Of these, there is a great interest in solar cells that change electrical energy directly from sunlight. The term "solar cell" as used herein refers to a cell that generates a current-voltage by utilizing a photovoltaic effect that absorbs light energy from sunlight to generate electrons and holes.

Currently, np diode-type silicon (Si) single crystal based solar cells with a light energy conversion efficiency of more than 20% can be manufactured and used for actual solar power generation. Compound semiconductors such as gallium arsenide (GaAs) There is also solar cell using. However, since such an inorganic semiconductor-based solar cell requires a highly refined material for high efficiency, a large amount of energy is consumed for refining the raw material, and expensive process equipment is required in the process of making single crystal or thin film using raw material And the manufacturing cost of the solar cell can not be reduced. Accordingly, in order to manufacture a solar cell at a low cost, it is necessary to drastically reduce the cost of the core material or the manufacturing process of the solar cell. As an alternative to the inorganic semiconductor-based solar cell, a dye- Solar cells are being actively studied.

Dye-sensitized solar cell (DSSC) was first developed by Professor Michael Gratzel of the Lausanne University of Technology in Switzerland (1991) and introduced to Nature magazine (Vol. 353, p. 737) . The working principle of a dye-sensitized solar cell is as follows. When dye molecules chemically adsorbed on the surface of a porous photocathode absorb solar light, dye molecules generate electron-hole pairs, and electrons are converted into conduction tines of semiconductor oxide used as a porous photocathode Injected and transferred to the transparent conductive film to generate a current. The holes remaining in the dye molecules are transferred to the photocathode by the hole conduction or hole conductive polymer by the oxidation-reduction reaction of the liquid or solid electrolyte, and form a complete solar cell circuit, .

Organic photovoltaics (OPVs), which have been studied extensively since mid-1990, have been used to study organic materials with electron donor (D or often called hole acceptor) characteristics and electron acceptor (A) . When a solar cell made of organic molecules absorbs light, electrons and holes are formed. This is called an exiton. The exciton migrates to the D-A interface and the charge is separated, the electrons are transferred to the electron acceptor, the holes are transferred to the electron donor, and the photocurrent is generated. Since the distance that the exciton generated from the electron donor can travel normally is very short, about 10 nm, the photoconductivity can not be accumulated thickly, and the efficiency of the photoconductivity is low due to low light absorption. In recent years, however, efficiency has greatly increased with the introduction of the so-called bulk heterojunction (BHJ) concept of increasing the surface area at the interface and the development of donor organic materials having a small band gap that is easy to absorb a wide range of solar light, Organic solar cells with efficiency over 8% have been reported (Advanced Materials, 23 (2011) 4636).

In addition, a 9% efficiency has been reported using a material having a hybrid organic perovskite structure instead of a pure inorganic quantum dot in place of a dye in a dye-sensitized solar cell (Scientific Reports 2, 591).

In the electron-hole pairs generated in the solar cell, electrons are injected into the conductive band of the semiconductor oxide and transferred to the transparent conductive film. At this time, TiO ₂ is widely used as the semiconductor oxide. Generally, a Ti precursor is coated on a substrate and sintered at a high temperature to prepare TiO ₂ particles having a crystallinity of several nanometers. The high-temperature sintering method as described above has an advantage in that uniform TiO ₂ coating layer and interconnection between TiO ₂ particles can be made excellent. However, since a high temperature of about 500 ° C. is required for sintering, There is a problem that it can be used. For example, the use of a flexible polymer substrate is inevitably limited.

On the other hand, in order to produce the TiO ₂ coating layer at the lower temperature, TiO ₂ particles are dispersed in a solution, coated on the substrate, and then subjected to heat treatment at a low temperature. However, although the above method has an advantage of not using a high temperature, it is difficult to obtain a uniform TiO ₂ coating layer, and voids are generated in the TiO ₂ coating layer, thereby deteriorating the efficiency of the solar cell.

Accordingly, the present inventors have made intensive efforts to produce an electron transport layer capable of increasing the efficiency of a solar cell without using high temperature conditions. As a result, it has been found that a mixture of titanium oxide particles, titanium alkoxide, Coating and photo-sintering proceeded, it was confirmed that the above was satisfied, and the present invention was completed.

An object of the present invention is to provide a method of manufacturing an electron transport layer capable of increasing the efficiency of a solar cell without using high temperature conditions.

The present invention also provides a solar cell comprising an electron transport layer produced by the above production method.

In order to solve the above problems, the present invention provides a method for producing an electron transport layer of a solar cell comprising the following steps:

Mixing the titanium oxide particles, the titanium alkoxide, and the organic acid to prepare a mixture (Step 1);

Coating the mixture on a substrate (step 2); And

And photo-sintering the substrate coated with the mixture (step 3).

The electron transport layer of the solar cell to be produced in the present invention means that the photoconductor transmits electrons generated by the absorption of sunlight and electrons in holes and includes titanium oxide particles as a main component.

Conventionally, a titanium precursor was coated on a substrate and then sintered at a high temperature of about 500 ° C to prepare an electron transport layer. However, since a high temperature was used, there were many restrictions such as a substrate type. In order to avoid the use of a high temperature, the electron transport layer is prepared by dispersing the titanium oxide particles in a solvent and coating the dispersion on a substrate. However, it is difficult to obtain an electron transport layer having a small thickness and a uniform thickness.

In the present invention, titanium oxide particles are used, and titanium alkoxide and organic acid are used together to obtain an electron transport layer having a small thickness and a uniform thickness, and the crystallinity of the electron transport layer is enhanced through photo-sintering .

The present invention will now be described in detail.

Titanium oxide particles, titanium Alkoxide , And an organic acid to prepare a mixture (step 1)

The step 1 is a step of preparing a substance to be coated on a substrate, and mixing the titanium oxide particles, the titanium alkoxide, and the organic acid to prepare a mixture.

The solvent of the mixture may be water, a C _1-5 alcohol, or a mixed solvent thereof, preferably ethanol. The titanium oxide particle is not particularly limited as long as it is a titanium oxide particle used for manufacturing an electron transport layer of a solar cell in the conventional low temperature process as a main component constituting the electron transport layer produced in the present invention. Specifically, the diameter of the titanium oxide particles is preferably 5 nm to 20 nm. The amount of the titanium oxide particles to be used can be appropriately adjusted as required, and it is preferable that the titanium oxide particles are contained in the mixture in an amount of 0.01 to 1% by weight or 0.1 to 0.5% by weight.

The titanium alkoxide serves to fill the interconnection between the titanium oxide particles and the voids of the electron transport layer. If only the above-mentioned titanium oxide particles are coated on the substrate and sintered at a high temperature, voids are formed between the titanium oxide particles, which results in a problem that the efficiency of the solar cell is lowered. Therefore, in the present invention, by using titanium alkoxide in addition to the titanium oxide particles, the above problems can be solved.

Specifically, examples of the titanium alkoxide include titanium diisopropoxide bis (acetylacetonate), titanium isopropoxide, titanium butoxide, and the like. The amount of the titanium alkoxide to be used can be appropriately adjusted as needed, and it is preferable that the titanium alkoxide in the mixture is contained in an amount of 20 to 70 mol% or 30 to 60 mol%.

The organic acid acts as a catalyst so that the titanium alkoxide is well connected to the titanium oxide particles. As the organic acid, acetic acid, propionic acid and the like can be used. The amount of the organic acid to be used can be appropriately adjusted as needed, and it is preferable that the amount of the organic acid is more than 0 and 1 mol% or 0.01 to 0.1 mol% in the mixture.

The step 1 can be carried out at room temperature, and there is no limitation on the mixing method. In addition, if necessary, ultrasonic treatment may be simultaneously performed for uniform mixing.

The mixture On the substrate  The coating step (step 2)

Step 2 is a step of coating the mixture prepared in step 1 on a substrate.

The substrate is not particularly limited as long as it is a substrate used in a solar cell and includes at least one material selected from the group consisting of ITO, FTO, ZnO-Ga ₂ O ₃ , ZnO-Al ₂ O ₃ and tin oxide A conductive layer containing at least one material selected from the group consisting of Pt, Au, Ni, Cu, Ag, In, Ru, Pd, Rh, Ir, Os, C and a conductive polymer is formed on a glass substrate or a plastic substrate . Particularly, in the present invention, since a high-temperature condition is not used for manufacturing the electron transport layer, it is possible to use a substrate such as a plastic substrate.

The method of coating is not particularly limited and may be coated by spin coating, dip coating, screen coating, spray coating, electrospinning, or the like. Also, the thickness of the electron transport layer to be manufactured can be controlled by adjusting the coating amount.

In addition, if necessary, drying may be further performed to remove the solvent used in the mixture coated on the substrate.

Photo-sintering the substrate coated with the mixture (step 3)

The step 3 is a step of photo-sintering the mixture coated on the substrate in the step 2 to form an electron transport layer.

According to the step 2, titanium oxide particles are distributed on the substrate, and titanium alkoxide is mediated between the titanium oxide particles. When light sintering proceeds, the titanium alkoxide reacts with the organic acid catalyst to fill the gaps between the titanium oxide particles.

The light sintering means that light of a wavelength range in which titanium alkoxide can react is irradiated with light having a wavelength of preferably 300 nm to 1000 nm.

The irradiation time is not particularly limited as long as the titanium alkoxide can sufficiently react. For example, irradiation is preferably performed for a time of 80 ms to 100 ms. Further, it is preferable that the irradiation is divided into several times so that the temperature does not rise by the irradiation. In addition, since the light sintering proceeds, a high-temperature condition is not necessary. Specifically, the reaction of step 3 can be performed at a temperature of 100 ° C or less, preferably 70 ° C or less. Also, for the efficiency of the irradiation, the reaction of step 3 is preferably 0 ° C or more, 10 ° C or more, or 20 ° C or more.

Electronics of solar cell Transmission layer

The thickness of the electron transport layer may be adjusted as necessary, and may be controlled by adjusting the amount of the coating of step 2 previously. Preferably, the thickness of the electron transporting layer is 50 nm to 100 nm.

The electron transport layer produced according to the present invention can be applied to a solar cell. The type of the solar cell is not particularly limited and can be applied to a dye-sensitized solar cell, an organic solar cell, and a perovskite solar cell. In particular, the present invention can be applied to a solar cell using a flexible plastic substrate, since a high temperature condition is not applied for the production of an electron transport layer.

The solar cell according to the present invention may have a configuration of a generally used solar cell, except that the electron transport layer produced in the present invention is used. For example, a first electrode, an electron transport layer according to the present invention, a photosensitive layer, a hole transport layer, and a second electrode.

As described above, the method for producing an electron transport layer of a solar cell according to the present invention is characterized in that an electron transport layer having a small thickness and a uniform thickness can be produced without using a high temperature process.

FIG. 1 shows the surface of an electron transport layer produced according to an embodiment of the present invention.
Fig. 2 shows the surface of the electron transport layer produced according to the comparative example of the present invention.
Fig. 3 shows XRD data of the electron transport layer prepared according to Examples and Comparative Examples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. However, the following embodiments are intended to illustrate the invention, but the invention is not limited thereto.

Example

(Step 1)

The end portion of the ITO substrate having a size of 25 mm × 25 mm was etched to partially remove ITO. (Titanium diisopropoxide bis (acetylacetonate)) of 60 mol% and acetic acid of 0.01 mol% was added to a 0.15 wt% TiO ₂ solution using ethanol as a solvent. The solution was coated on ITO substrate to a thickness of 60 nm at 700 rpm for 10 seconds and at 2000 rpm for 60 seconds and heat-treated at 100 DEG C for 30 minutes. Then, the ITO substrate was photo-sintered to form an n-type block TiO ₂ layer. The light sintering was carried out by using a Zenon lamp (Novacentrix, PluseForge 1200) as a light source, irradiating light for 1 ms at 330 V and 0.1 Hz, and resting 20 ms for 81 times in total (total 130 J energy) .

(Step 2)

MAI (methylammonium iodide) and PbI ₂ were dissolved in DMSO at a molar ratio of 1: 1 to prepare a 50 wt% solution. The solution was stirred for 1 hour at 60 ° C and then coated on the block TiO ₂ layer at 500 rpm for 5 seconds, 1000 rpm for 90 seconds, and 5000 rpm for 30 seconds, and dried at 150 ° C for 10 minutes And heat treated to form a light absorbing layer. 30 uL of a solution of 58 mM spiro-OMeTAD (72.3 mg / mL), 188 mM TBP (4-tert-butylpyridine, 28.8 uL) and 29.9 mM LiTFSi (17.5 uL) dissolved in chlorobenzene solution And spin-coated at 6000 rpm for 30 seconds to form a hole transporting layer. Au was vacuum-deposited thereon to form an electrode, thereby manufacturing a solar cell.

Comparative Example  One

Except that titanium diisopropoxide bis (acetylacetonate) and acetic acid were not used and the light sintering was not carried out in the step 1, except that titanium diisopropoxide bis (acetylacetonate) Thereby preparing a solar cell.

Comparative Example  2

Except that titanium diisopropoxide bis (acetylacetonate) (bis (acetylacetonate)) and acetic acid were not used in the above step 1, and a solar cell was prepared.

Comparative Example  3

A solar cell was manufactured in the same manner as in the above example except that the light sintering was not carried out in the step 1.

Comparative Example  4

The end portion of the FTO substrate having a size of 25 mm × 25 mm was etched to partially remove the FTO. A solution of 0.1 M [(CH ₃ ) ₂ CHO) ₂ Ti (C ₅ H ₇ O ₂ ) ₂ ] 1-butanol was coated on the FTO substrate to a thickness of 40 nm at 700 rpm for 10 seconds and 2000 rpm for 60 seconds And sintered at 500 ° C for 15 minutes to form an n-type block TiO ₂ layer. Then, a solar cell was prepared in the same manner as in step 2 of the above example.

Experimental Example  1: Electronic Transfer layer  Surface observation

The surface of the electron transport layer prepared in the above Example and Comparative Example 1 was confirmed by an SEM image. The results are shown in Fig. 1 (Example) and Fig. 2 (Comparative Example 1).

As shown in FIG. 1, in the case of the embodiment according to the present invention, voids were not substantially generated, whereas in Comparative Example 1 in which titanium alkoxide and organic acid were not used as shown in FIG. 2, there was. From these results, it can be confirmed that when the titanium alkoxide and the organic acid are used and the light sintering is proceeded as in the present invention, the voids formed between the titanium oxide particles can be sufficiently filled.

Experimental Example  2: XRD  Data Analysis

XRD data were measured to confirm the crystallinity of the electron transport layer prepared in the above Examples, Comparative Examples 1 and 4, and the results are shown in FIG.

Comparing the results of the example of FIG. 3 and the results of Comparative Example 1, it was confirmed that crystallinity increases through light sintering. In addition, the degree of crystallinity of the examples was substantially the same as that of Comparative Example 4 which was subjected to the high-temperature sintering treatment, and it was confirmed that crystallinity was sufficiently obtained through light sintering.

Experimental Example  3: Characterization of solar cell

The characteristics of each solar cell were evaluated using the solar cells prepared in the above-described Examples and Comparative Examples, and the results are shown in Table 1 below.

JSC (mA / cm ² ) Voc (V) FF PCE (%) Example 22.36 1.085 0.69 16.75 Comparative Example 1 23.90 0.719 0.50 8.68 Comparative Example 2 23.61 0.762 0.53 9.58 Comparative Example 3 25.17 0.824 0.62 12.79 Comparative Example 4 21.55 1.118 0.71 17.10

As shown in Table 1, in comparison with Comparative Examples 1 and 2 in which light sintering did not proceed, it was confirmed that the photoconversion efficiency was remarkably high in the example according to the present invention. Also, it was confirmed that the photo-conversion efficiency was remarkably higher than that of Comparative Example 3 in which the photo-sintering proceeded but no titanium alkoxide and organic acid were used. In addition, it can be confirmed that the embodiment according to the present invention exhibits a light conversion efficiency equivalent to that of Comparative Example 4 produced by the high-temperature sintering method, and is also usefully applied to a plastic substrate to which the conventional high-temperature sintering method can not be applied I can confirm that I can do it.

Claims (10)

Mixing the titanium oxide particles, the titanium alkoxide, and the organic acid to prepare a mixture;
Coating the mixture on a substrate; And
And photo-sintering the substrate coated with the mixture.
A method for manufacturing an electron transport layer of a solar cell.
The method according to claim 1,
Wherein the titanium oxide particles have a diameter of 5 nm to 20 nm.
Gt;
The method according to claim 1,
Wherein said titanium alkoxide is titanium diisopropoxide bis (acetylacetonate), titanium isopropoxide, or titanium butoxide.
Gt;
The method according to claim 1,
Wherein the organic acid is acetic acid or propionic acid.
Gt;
The method according to claim 1,
Wherein the content of the titanium alkoxide in the mixture is 20 to 70 mol%
Gt;
The method according to claim 1,
Wherein the content of the organic acid in the mixture is more than 0 and 1 mol%
Gt;
The method according to claim 1,
Wherein the substrate is a glass substrate containing at least one material selected from the group consisting of _{ITO, FTO, ZnO-Ga 2} O 3, ZnO-Al 2 O 3 and tin oxide; Or a conductive layer comprising at least one material selected from the group consisting of Pt, Au, Ni, Cu, Ag, In, Ru, Pd, Rh, Ir, Os, C and conductive polymers.
Gt;
The method according to claim 1,
Wherein the light sintering is performed by irradiating light having a wavelength of 300 nm to 1000 nm onto the substrate,
Gt;
The method according to claim 1,
Characterized in that the light sintering is performed for a time of 80 ms to 100 ms.
Gt;
The method according to claim 1,
Wherein the thickness of the hole transporting layer of the solar cell is 50 nm to 100 nm.
Gt;

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