KR20150135692A - Solar cell comprising buffer layer formed by atomic layer deposition and method of fabricating the same - Google Patents

Abstract

The present invention relates to a solar cell and a manufacturing method thereof. The method includes the following steps: (a) forming a back electrode layer on a substrate; (b) forming a light absorbing layer on the back electrode layer; (c) forming a buffer layer on the light absorbing layer by atomic layer deposition; and (d) forming a front electrode layer on the buffer layer. The method further includes a surface heat-treatment step after the step (b) or the step (c).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a solar cell including a buffer layer formed by atomic layer deposition, and a method of manufacturing the solar cell.

The present invention relates to a solar cell including a buffer layer formed by an atomic layer deposition method and a manufacturing method thereof.

Recently, as a part of the development of new and renewable energy to reduce carbon emissions according to environmental regulations, solar cells that can convert electricity from solar energy into electric energy, which can generate electric power easily, have attracted attention.

Such a solar cell is fabricated using a single crystal or polycrystalline silicon wafer, but monocrystalline silicon is generally used most widely in the field of large-scale power generation systems because of its highest photoelectric conversion efficiency. However, such a monocrystalline silicon is uneconomical because of its complicated manufacturing process and high price.

Accordingly, although a method of manufacturing a solar cell using polycrystalline silicon using a low-grade silicon wafer has been developed although it is relatively inefficient, it is currently being used in power generation systems for residential use. However, this process is also complicated and the price of raw materials is rising due to the recent surge in silicon prices, which limits the cost of manufacturing solar cells.

Accordingly, recently, as a thin film solar cell for overcoming this problem, a method of using amorphous silicon having a multi-junction structure and a method of using a compound semiconductor such as a chalcogenide compound have been developed.

(A) forming a rear electrode layer on a substrate; (b) forming a light absorption layer on the rear electrode layer; (c) forming a buffer layer on the light absorption layer by atomic layer deposition; And (d) forming a front electrode layer on the buffer layer, wherein the step (b) or the step (c) further comprises a surface heat treatment step .

However, the technical problem to be solved by the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

(A) forming a rear electrode layer on a substrate; (b) forming a light absorption layer on the rear electrode layer; (c) forming a buffer layer on the light absorption layer by atomic layer deposition; And (d) forming a front electrode layer on the buffer layer, wherein the step (b) or the step (c) further comprises a surface heat treatment.

After the formation of the buffer layer in the step (c), a transparent resistive layer containing ZnO may be additionally formed on the buffer layer.

The surface heat treatment may be performed under at least one gas atmosphere selected from the group consisting of air, N ₂ , Ar, O ₂ , H ₂ O and H ₂ O ₂ .

The surface heat treatment may be performed at a temperature of 100 ° C to 250 ° C.

The surface heat treatment may be performed for 1 minute to 30 minutes.

After the surface heat treatment, the substrate is cleaned by at least one cleaning solution selected from the group consisting of NH ₄ OH, HNO ₃ , HCl, H ₂ SO ₄ , NH ₄ F, HF, H ₂ O ₂ , CdSO ₄ , KCN and DI- can do.

After the surface heat treatment, one or more of a cleaning gas and a plasma may be supplied and cleaned.

The cleaning gas may be at least one selected from the group consisting of NH ₃ , ClF ₃ , F ₂ , H ₂ O, O ₂ , N ₂ O, NF ₃ and N ₂ .

The plasma is formed by at least one reaction gas selected from the group consisting of Ar, N ₂ , O ₂ , H ₂ O, H ₂ , He, CH ₄ , NH ₃ , CF ₄ , C ₂ H ₂ and C ₃ H ₈ .

The cleaning may be performed at a temperature of from 10 캜 to 120 캜.

The cleaning may be performed for 30 seconds to 5 minutes.

In one embodiment of the present invention, a substrate comprises: a substrate; A rear electrode layer formed on the substrate; A light absorbing layer formed on the rear electrode layer; A buffer layer formed on the light absorption layer by atomic layer deposition; And a front electrode layer formed on the buffer layer, wherein the Na content of the buffer layer is 0.5 at% to 2 at%.

The Na content of the buffer layer may have a peak value at a surface in contact with the light absorbing layer.

The Na content of the buffer layer may decrease rapidly along the thickness direction from the surface in contact with the light absorption layer, and may be increased at the surface contacting the front electrode layer after being maintained constant.

The substrate may be a sodalime glass substrate.

The Na content of the sodalime glass substrate may be 13 at% to 15 at%.

The content of one or more impurities selected from the group consisting of C, H and OH in the buffer layer may be within 3 wt%.

And a transparent resistance layer including ZnO may be additionally provided between the buffer layer and the front electrode layer.

The solar cell according to the present invention can improve the relative efficiency by increasing the open-circuit voltage (V _oc ) by removing the impurities on the surface of the light absorbing layer after forming the light absorbing layer, The shunt resistance R shunt by diffusion of the alkaline compound can be increased to increase the filling factor FF and the relative efficiency.

Further, the solar cell according to the present invention has an advantage that a large area of 4 inches or more can be obtained.

1 is a schematic cross-sectional view of a solar cell including a buffer layer formed by atomic layer deposition according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a solar cell including a buffer layer formed by atomic layer deposition according to another embodiment of the present invention.
3 is a graph showing a Na content profile in a light absorption layer and a buffer layer of a solar cell including a buffer layer formed by atomic layer deposition according to an embodiment of the present invention.
FIG. 4 is a graph showing the open circuit voltage (V _oc ) and relative efficiency of a solar cell including a buffer layer formed by atomic layer deposition according to Examples 1 to 3 and Comparative Example 1.
FIG. 5 is a graph showing a shunt resistance (R shunt), a filling factor (FF) and a relative efficiency of a solar cell including a buffer layer formed by atomic layer deposition according to Examples 4 to 5 and Comparative Example 1. FIG.

The inventors of the present invention confirmed that solar cell performance can be improved finally by adding a step of surface heat treatment and cleaning, thereby completing the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. In the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated.

Hereinafter, the formation of an arbitrary structure in the above-mentioned " upper (or lower) " means not only that an arbitrary structure is formed in contact with the upper (or lower) And the present invention is not limited to the configuration including any other configuration.

Hereinafter, the present invention will be described in detail.

(A) forming a rear electrode layer on a substrate; (b) forming a light absorption layer on the rear electrode layer; (c) forming a buffer layer on the light absorption layer by atomic layer deposition; And (d) forming a front electrode layer on the buffer layer, wherein the step (b) or the step (c) further comprises a surface heat treatment.

In addition, the present invention provides a semiconductor device comprising a substrate; A rear electrode layer formed on the substrate; A light absorbing layer formed on the rear electrode layer; A buffer layer formed on the light absorption layer by atomic layer deposition; And a front electrode layer formed on the buffer layer, wherein the Na content of the buffer layer is 0.5 at% to 2 at%.

1 is a schematic cross-sectional view of a solar cell including a buffer layer formed by atomic layer deposition according to an embodiment of the present invention.

As shown in FIG. 1, a solar cell 1 including a buffer layer formed by atomic layer deposition according to an embodiment of the present invention includes a substrate 10; A rear electrode layer (20) formed on the substrate (10); A light absorbing layer 30 formed on the rear electrode layer 20; A buffer layer 40 formed on the light absorption layer 30 by atomic layer deposition; And a front electrode layer 50 formed on the buffer layer 40. The Na content of the buffer layer 40 is 0.5 at% to 2 at%.

2 is a schematic cross-sectional view of a solar cell including a buffer layer formed by atomic layer deposition according to another embodiment of the present invention.

As shown in FIG. 2, a solar cell 1 including a buffer layer formed by atomic layer deposition according to another embodiment of the present invention includes a substrate 10; A rear electrode layer 20; A light absorbing layer 30; A buffer layer 40; And the front electrode layer 50 are the same as those shown in FIG. 1, but further include a transparent resistance layer 60 including ZnO between the buffer layer 40 and the front electrode layer 50.

On the substrate 10 The rear electrode layer 20  formation

Hereinafter, the step of forming the rear electrode layer 20 on the substrate 10 will be described.

The substrate 10 may be a glass substrate, a ceramic substrate, a metal substrate, a polymer substrate, or the like. For example, as the glass substrate, soda lime glass or high strained pointsoda glass substrate can be used. As the metal substrate, a substrate including stainless steel or titanium can be used. As the substrate, a polyimide substrate can be used.

The substrate 10 may be transparent. The substrate 10 may be rigid or flexible.

In the present invention, after the buffer layer 30 is formed or after the transparent resistive layer 60 including ZnO is formed, a step of performing surface heat treatment and cleaning is added to the buffer layer 30 after the light absorption layer 30 is formed, The substrate 10 is prevented from diffusing Na contained in the substrate 10. The substrate 10 is preferably a sodalime glass substrate, but is not limited thereto. In this case, the soda-lime glass substrate used is composed of 70 to 73 wt% of SiO ₂ , 1 to 2 wt% of Al ₂ O ₃ , 12 to 13 wt% of CaO / MnO and 13 to 15 wt% of Na ₂ O / K ₂ O , And the Na content of the sodalime glass substrate can be maintained at 13 at% to 15 at%.

The rear electrode layer 20 is formed on the substrate 10 and may include a metal such as Mo as a conductive layer.

The rear electrode layer 20 may be a single layer or a plurality of layers of two or more layers. When the back electrode layer 20 is formed of a plurality of layers of two or more layers, the respective layers may be formed of the same metal or may be formed of different metals.

The formation of the rear electrode layer 20 may be performed by one or more known methods selected from the group consisting of sputtering, vacuum evaporation, chemical vapor deposition, atomic layer deposition, ion beam deposition, screen printing, spray dip coating, .

The thickness of the rear electrode layer 20 is preferably 0.1 to 1 占 퐉, more preferably 0.5 占 퐉, but is not limited thereto.

The light absorbing layer 30  formation

Hereinafter, the step of forming the light absorbing layer 30 on the rear electrode layer 20 will be described.

The light absorbing layer 30 is formed by depositing and heat-treating a light absorbing layer material on the rear electrode layer 20.

The light absorption layer 30 may be formed of a material having a light absorption layer such as CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ CGTe), Cu (In, Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS) and CdTe. But is not limited thereto.

The deposition of the light absorbing layer material may be performed by vacuum deposition or may be performed by non-vacuum deposition. Specifically, the deposition of the light absorption layer material may be performed by vacuum deposition, and may be performed by one or more methods selected from the group consisting of sputtering, vacuum evaporation, chemical vapor deposition, atomic layer deposition and ion beam deposition, Deposition is by non-vacuum deposition and may be by one or more methods selected from the group consisting of screen printing, spray dip coating, tape gelling and ink jet.

The heat treatment may occur simultaneously with the deposition of the light absorbing layer material, and may occur after the deposition of the light absorbing layer material.

Also, the heat treatment may be performed in an atmosphere of Se or S, and the heat treatment may be performed at 300 ° C to 600 ° C for 30 minutes to 1 hour.

For example, precursors of Cu, In, Ga and Se are deposited by a sputtering method and selenized by heat treatment using H ₂ Se or H ₂ S gas in a heat treatment chamber to form Cu (In, Ga ) S ₂ (CIGS) chalcogenide-based compound may be formed, or a crucible containing a Cu, In, Ga, or Se source in a solid form may be heated and heat- by evaporation in the atmosphere at the same time it may form the light absorption layer 30 including a Cu (in, Ga) S ₂ (CIGS), a chalcogenide-based compound.

Before the buffer layer 40 is formed by atomic layer deposition, which is one type of dry method, the light absorption layer 30 is exposed to the outside air such as atomic layer deposition (ALD) oxidizing agent, H ₂ O, H ₂ O ₂ , O ₃ , Na contained in the substrate 10 is diffused on the surface of the absorbing layer 40 to form alkali compounds (Na-O, Na-Se-O) corresponding to impurities on the surface of the light absorbing layer 30, It is necessary to prevent the deterioration of the performance of the solar cell.

According to the present invention, the surface heat treatment and cleaning may be performed on the surface of the light absorbing layer 30 after the light absorbing layer 30 is formed. The alkaline compound (Na-O, Na-Se-O) may be removed to increase the open-circuit voltage (Voc) to increase the relative efficiency.

The surface heat-treated in air _{(air), N 2, Ar} , O2, H 2 is carried out in one or preferably at least one gas atmosphere selected from the group consisting of 0, and H ₂ O _2, not limited to this.

The surface heat treatment is preferably performed at a temperature of 100 ° C to 250 ° C, but is not limited thereto. At this time, when the surface heat treatment is performed at a temperature of less than 100 ° C, the reaction activation energy is low at the surface of the light absorption layer 30, so that alkali compounds such as Na-O and Na-Se-O are not sufficiently formed. Excessive oxidation of the surface of the light absorbing layer 30 proceeds due to excessive reaction activation at the surface of the light absorbing layer 30 and the oxide layer is formed at the interface between the light absorbing layer 30 and the buffer layer 40 Thus, there is a problem that the efficiency of the solar cell 1 is lowered.

In other words, Na exists in excess in the surface of the light absorbing layer 30 relative to the inside of the light absorbing layer 30, and this Na binds with O or the like to form an alkali compound (Na-O, Na-Se-O) Is present at the interface between the light absorbing layer 30 and the buffer layer 40 (or inside or on the buffer layer 40), thereby lowering the efficiency of the solar cell 1. That is, the surface heat treatment is a pretreatment process for intentionally promoting the reactivity of alkaline compounds such as Na-O and Na-Se-O to effectively remove a larger amount of alkaline compound impurities. That is, the surface heat treatment is performed in the temperature range described above, so that the oxidation of the surface of the light absorbing layer 30 is prevented from proceeding excessively while sufficiently activating the alkali compounds such as Na-O and Na-Se-O.

The surface heat treatment is preferably performed for 1 minute to 30 minutes, but is not limited thereto. At this time, when the surface heat treatment is performed for less than 1 minute, there is a problem that the reaction activation energy is low at the surface of the light absorbing layer 30 and alkali compounds such as Na-O and Na-Se-O are not sufficiently formed. Minute, excessive oxidation of the surface of the light absorbing layer 30 proceeds due to excessive reaction activation on the surface of the light absorbing layer 30 to form an oxide layer at the interface between the light absorbing layer 30 and the buffer layer 40, The efficiency of the solar cell 1 is lowered.

At this time, the surface heat treatment may be performed in Ex-situ or In-situ, and may be performed under vacuum or atmospheric pressure.

After the surface heat treatment, the cleaning may be performed by supplying at least one of a cleaning solution, a cleaning gas, and a plasma.

Specifically, the cleaning may be carried out in one or more cleaning solutions selected from the group consisting of NH ₄ OH, HNO ₃ , HCl, H ₂ SO ₄ , NH ₄ F, HF, H ₂ O ₂ , CdSO ₄ , KCN and DI- can do.

That is, the cleaning solution may be at least one selected from the group consisting of NH ₄ OH, HNO ₃ , HCl, H ₂ SO ₄ , NH ₄ F, HF, H ₂ O ₂ , CdSO ₄ , KCN and DI-water. The cleaning solution serves to remove alkaline compounds (Na-O, Na-Se-O) corresponding to impurities on the surface of the light absorbing layer 30.

The cleaning may be performed at a temperature ranging from 25 ° C to 120 ° C, but is not limited thereto. At this time, when the treatment of the surface of the light absorbing layer 30 is performed at a temperature of less than 25 ° C, there is a problem that the surface of the light absorbing layer is not cleaned or only part of the surface is washed due to a poor reactivity between the cleaning solution and the surface of the light absorbing layer 30, When the cleaning is performed at a temperature exceeding 120 캜, the thickness of the light absorbing layer 30 is reduced due to excessive cleaning of the surface of the light absorbing layer 30 due to excessive reaction of the cleaning solution and the surface of the light absorbing layer 30, There is a problem that the performance of the solar cell is deteriorated by causing the composition of the absorption layer 30 to change.

The cleaning solution was H ₂ SO ₄ Or H ₂ O ₂ is preferably carried out at a temperature of 90 ° C to 120 ° C, but is not limited thereto.

The cleaning may be performed for 30 seconds to 5 minutes.

The cleaning may be performed by supplying at least one of a cleaning gas and a plasma.

The cleaning gas consisting of _{NH 3, ClF 3, F 2} , H 2 O, O 2, N 2 O, NF 3 , and preferably one or more selected from the group consisting of N _2, and NH _3, ClF ₃ and F ₂ More preferably, it is at least one selected from the group consisting of, but not limited to.

The flow rate of the cleaning gas is preferably 30 sccm to 5000 sccm, but is not limited thereto. In this case, the flow rate of the cleaning gas is determined according to the size of the chamber. When the flow rate of the cleaning gas is less than 30 sccm, the cleaning uniformity due to a small amount of the cleaning gas becomes defective. When the flow rate of the cleaning gas exceeds 5000 sccm The turbulence gas flow due to excessive gas injection is formed to result in poor cleaning uniformity and the performance of the solar cell is deteriorated due to excessive cleaning of the light absorbing layer 30. [

The flow time of the cleaning gas is preferably from 1 minute to 60 minutes, but is not limited thereto. At this time, the flow time of the cleaning gas is determined according to the size of the chamber. When the flow time of the cleaning gas is less than 1 minute, there is a problem that the cleaning uniformity due to a small amount of cleaning gas becomes defective. If it exceeds 60 minutes, there is a problem that the performance of the solar cell is deteriorated due to excessive cleaning of the light absorbing layer 30.

Plasma refers to molecules in a gaseous state that absorb a certain amount of high energy and are present as electrically neutral grains (electrons, anions, cations, electrons, and radicals). It has high energy reactivity and high reactivity with other substances.

The plasma is formed by at least one reaction gas selected from the group consisting of Ar, N ₂ , O ₂ , H ₂ O, H ₂ , He, CH ₄ , NH ₃ , CF ₄ , C ₂ H ₂ and C ₃ H ₈ And is preferably formed by a mixed reaction gas composed of Ar and N ₂ , but is not limited thereto.

Specifically, the plasma is generated by introducing one or more elements selected from the group consisting of Ar, N ₂ , O ₂ , H ₂ O, H ₂ , He, CH ₄ , NH ₃ , CF ₄ , C ₂ H ₂ and C ₃ H ₈ It is more preferable that the reaction gas or the mixed reaction gas composed of Ar and N ₂ is supplied and then generated at a vacuum or an atmospheric pressure by applying power, but the present invention is not limited thereto.

The flow time of the plasma is preferably from 1 minute to 30 minutes, but is not limited thereto. At this time, when the flow time of the plasma is less than 1 minute, there is a problem that the washing uniformity due to insufficient cleaning of the light absorbing layer 30 becomes poor. When the flow time of plasma exceeds 30 minutes, excessive ion impact the performance of the solar cell is deteriorated due to excessive cleaning of the light absorption layer 30 due to bombardment.

The cleaning is most efficient when the cleaning gas and the plasma are supplied at the same time.

The cleaning is preferably performed at a temperature of 25 ° C to 120 ° C, but is not limited thereto. At this time, when the cleaning is performed at a temperature of less than 25 ° C, there is a problem that the surface of the light absorbing layer 30 is not cleaned or only a part of the surface is cleaned due to at least one of the cleaning gas and the plasma and the reactivity failure of the light absorbing layer 30 , Excessive cleaning of the surface of the light absorbing layer 30 due to excessive reactivity of the surface of the light absorbing layer 30 and at least one of the cleaning gas and the plasma may be performed when the treatment of the surface of the light absorbing layer 30 is performed at a temperature exceeding 120 캜 Thereby deteriorating the performance of the solar cell.

The cleaning may be performed for 30 seconds to 5 minutes.

As described above, the cleaning by supplying at least one of the cleaning gas and the plasma and the formation of the buffer layer 40 may be performed separately in other devices, but it is more preferable to perform the cleaning in-situ in terms of process efficiency and cost reduction Do.

The buffer layer 40 Atomic layer  Formation by evaporation

Hereinafter, the step of forming the buffer layer 40 on the light absorption layer 30 by atomic layer deposition will be described.

The buffer layer 40 is formed on the light absorbing layer 30 and may be formed of at least one layer. At this time, the buffer layer 40 is an n-type semiconductor layer and the light absorbing layer 30 is a p-type semiconductor layer. Therefore, the light absorbing layer 30 and the buffer layer 40 form a pn junction. Since the light absorption layer 30 and the front electrode layer 50 have a large difference in lattice constant and energy band gap, a good junction can be formed by inserting the buffer layer 40 having a band gap in the middle of the two materials .

Conventionally, the buffer layer is mainly formed by CdS or the like by chemical solution deposition (CBD), but this causes contamination, which is problematic in terms of environmental aspects. Accordingly, the present invention solves the conventional problem by using a Cd-free buffer layer formed by atomic layer deposition (ALD) on the light absorption layer 30 as the buffer layer 40.

The buffer layer 40 may be a Cd-free buffer layer, but is not limited thereto. That is, the Cd-free buffer layer refers to a buffer layer that does not contain cadmium so that an eco-friendly process can be performed without being subjected to environmental regulations.

When the buffer layer 40 is a Cd-free buffer layer and contains a composition of Zn (O, S), atomic layers of Zn, S, Zn, and O may be repeatedly formed by atomic layer deposition. In this case, the molar ratio of O: S in the buffer layer 40 may be 3: 1 to 10: 1.

The band gap energy of the buffer layer 40 is preferably 3.2 eV to 3.6 eV, more preferably 3.25 eV to 3.55 eV, but is not limited thereto. When the buffer layer 40 contains only the ZnO composition, the band gap energy is 3.2 eV. When the buffer layer 40 contains only the ZnS composition, the band gap energy is 3.6 eV and the O : ≪ / RTI > S, the bandgap energy of the above range can be obtained.

The thickness of the buffer layer 40 is preferably 3 nm to 100 nm, more preferably 3 nm to 50 nm, but is not limited thereto. At this time, if the thickness of the buffer layer 40 is less than the above range, the buffer layer 40 is not uniformly formed, and a portion where the front electrode layer 50 contacts the light absorbing layer 30 is generated, If the thickness of the buffer layer 40 is more than the above range, the transmittance of the buffer layer 40 is reduced, and the amount of light entering the light absorbing layer 30 is reduced to reduce the light conversion efficiency. In particular, by forming the buffer layer 40 to have a thickness of 50 nm or less, there is an improvement in throughput and a capacity-up effect in the manufacturing process.

According to the present invention, the surface heat treatment may be performed on the surface of the buffer layer 40 after the buffer layer 40 is formed. The shunt resistance R shunt due to the diffusion of the alkali compound (Na-O, Na-Se- To increase the charging factor (FF) and the relative efficiency.

At this time, specific conditions of the surface heat treatment and the surface heat treatment are as described above.

As a result of the cleaning after the surface heat treatment and the surface heat treatment, the Na content in the buffer layer 40 is minimized. It is preferable that the Na content of the buffer layer 40 is 0.5 at% to 2 at% It is not limited.

3 is a graph showing a Na content profile in a light absorption layer and a buffer layer of a solar cell including a buffer layer formed by atomic layer deposition according to an embodiment of the present invention.

As shown in FIG. 3, the Na content of the buffer layer 40 may have a peak value at a surface (region (3)) in contact with the light absorbing layer 30. This is because Na exists in excess in the surface (③ region) of the light absorbing layer 30 relative to the inside (④ region) of the light absorbing layer 30, and this Na binds with O and the like to form an alkali compound (Na- O) is formed at the interface between the light absorbing layer 30 and the buffer layer 40 (or inside or on the buffer layer 40). Specifically, the Na content of the buffer layer 40 decreases sharply along the thickness direction from the surface in contact with the light absorbing layer 30 (region ③), remains constant (region ②), and then the front electrode layer 50 ) (Fig. 1 (a)). As the Na content increases, the buffer layer is formed by the thermal ALD, so that the alkali compound diffuses and the Na bonds with the O to form the alkali compound (Na-O, Na-Se-O) And is present at the interface between the buffer layer 40 and the transparent electrode layer 50 (or the transparent resistive layer 60).

As a result of the cleaning after the surface heat treatment and the surface heat treatment, the content of at least one impurity selected from the group consisting of C, H and OH in the buffer layer 40 is preferably within 3 wt%, but is not limited thereto. At this time, if the content of the impurity exceeds the range and exists in the buffer layer 40, a conductive path between the light absorption layer 30 and the front electrode layer 50 is formed, and the shunt resistance R-shunt decreases there is a problem. At this time, the content of impurities can be confirmed through analysis such as XRD, AES, SIMS and the like.

The front electrode layer 50  formation

Hereinafter, the step of forming the front electrode layer 50 on the buffer layer 40 will be described.

The front electrode layer 50 is formed on the buffer layer 40. The front electrode layer 50 is a window layer forming a pn junction with the light absorbing layer 30 by sputtering or the like, (Indium Tin Oxide) doped with Al or Al ₂ O ₃ , or the like.

The front electrode layer 50 may have a double structure in which an n-type ZnO thin film containing ZnO doped with a material containing a Group III element having excellent electro-optical properties is deposited on an i-type ZnO thin film containing ZnO .

The thickness of the i-type ZnO thin film is preferably 10 nm to 70 nm, more preferably 40 nm to 50 nm, but is not limited thereto. Further, the thickness of the n-type ZnO thin film is preferably 250 nm to 1000 nm, more preferably 500 nm to 1000 nm, but is not limited thereto.

At this time, since the i-type ZnO thin film functions as a transparent electrode on the entire surface of the solar cell, it is preferable that it is formed of an undoped ZnO thin film having high light transmittance and good electrical conductivity. In addition, the n-type ZnO thin film deposited on the i-type ZnO thin film has a low resistance value by doping ZnO with aluminum (Al) or alumina (Al ₂ O ₃ ), and the production cost relative to ITO (Indium Tin Oxide) There is an economical advantage because it is low.

ZnO Containing The transparent resistive layer 60  formation

Hereinafter, a step of forming a transparent resistance layer 60 including ZnO on the buffer layer 40 after forming the buffer layer 40 will be described.

The transparent resistance layer 60 corresponds to an additional non-conductive layer for preventing damage between the buffer layer 40 and the front electrode layer 50. The transparent resistance layer 60 may be omitted or may be formed with a minimum thickness.

The transparent resistance layer 60 is preferably formed of i-ZnO having a high light transmittance, but is not limited thereto. The thickness of the transparent resistance layer 60 is preferably 10 nm to 50 nm in terms of cell efficiency.

The transparent resistance layer 60 is preferably an amorphous phase, but is not limited thereto. Since the transparent resistive layer 60 is formed of amorphous material, the sheet resistance is very high. The amorphous transparent resistive layer 60 can be formed at a low process temperature of about 100 ° C. by atomic layer deposition. The sheet resistivity Rs can be measured using a device such as a 4-point probe. At this time, The sheet resistance measured is from hundreds of kohm / sq to several Mohm / sq. In addition, crystal peaks should not be observed through XRD analysis.

According to the present invention, the surface heat treatment may be performed on the surface of the transparent resistive layer 60 after the transparent resistive layer 60 including ZnO is formed. The alkaline compound (Na-O, Na-Se-O) The shunt resistance (R shunt) due to diffusion can be increased to increase the charging factor (FF) and the relative efficiency.

At this time, specific conditions of the surface heat treatment and the surface heat treatment are as described above.

As a result of the cleaning after the surface heat treatment and the surface heat treatment, the content of at least one impurity selected from the group consisting of C, H and OH in the transparent resistive layer 60 is preferably within 3 wt%, but is not limited thereto. At this time, when the content of the impurity exceeds the above range and exists in the transparent resistive layer 60, a conductive path between the light absorbing layer 30 and the front electrode layer 50 is formed, and the shunt resistance R shunt is reduced There is a problem. At this time, the content of impurities can be confirmed through analysis such as XRD, AES, SIMS and the like.

The solar cell 1 according to the present invention can remove the impurities on the surface of the light absorbing layer 30 by increasing the open voltage V _oc by increasing the relative efficiency by forming the light absorbing layer 30, After the formation of the buffer layer 40 or the formation of the transparent resistive layer 60 containing ZnO, the shunt resistance R shunt due to diffusion of the alkaline compound is increased by surface heat treatment and cleaning, And the relative efficiency can be increased.

Further, the solar cell 1 according to the present invention has an advantage that a large area of 4 inches or more can be obtained.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the following examples.

[ Example ]

Example  One

A Mo based alloy formed on a sodalime glass substrate was coated by a DC sputtering method to form a 0.5 μm rear electrode layer. Cu, In, Ga, and Se precursors were deposited on the back electrode layer by DC sputtering method and then heat-treated at 550 ° C for 30 to 60 minutes in an atmosphere of Se to form a light absorbing layer containing a CIGS compound of 2 μm. Thereafter, the light absorption layer was subjected to a surface heat treatment at 200 캜 for 5 minutes in an atmosphere of 1 atm and air, and dipped in a cleaning solution composed of DI-water at room temperature (25 캜) for 3 minutes to remove impurities . A 40 nm thick Zn (O, S) buffer layer was formed on the light absorption layer by atomic layer deposition and then coated by RF sputtering to form a 50 nm thick i-type ZnO thin film and a 1000 nm thick n-type ZnO thin film, The battery was finally prepared.

Example  2

The same procedure as in Example 1 was conducted except that the surface was heat-treated for 10 minutes.

Example  3

The same procedure as in Example 1 was carried out except that the surface was heat-treated for 15 minutes.

Example  4

After forming the light absorption layer, a Zn (O, S) buffer layer of 40 nm and a ZnO transparent resistive layer of 20 nm were formed on the light absorption layer by atomic layer deposition without performing another surface heat treatment and cleaning. Thereafter, the transparent resistive layer was subjected to the surface heat treatment at 200 캜 for 5 minutes in an atmosphere of 1 atm and air, and the same procedure as in Example 1 was carried out.

Example  5

After the surface heat treatment, the surface of the transparent resistive layer was removed by dipping in a cleaning solution composed of DI-water at room temperature (25 ° C) for 3 minutes, and the same procedure as in Comparative Example 1 was carried out.

Comparative Example  One

The same procedure as in Example 1 was carried out except that the surface heat treatment was not performed at all.

Experimental Example  : Open-circuit voltage of solar cell ( V _oc ) evaluation

The open-circuit voltage (V _oc ) of the solar cells prepared according to Examples 1 to 3 and Comparative Example 1 was evaluated, and the results are shown in Table 1.

division V _oc
(mV) Relative
efficiency(%) Example 1 560 110.3 Example 2 575 118.8 Example 3 590 125.0 Comparative Example 1 530 100.0

As shown in Table 1, the open-circuit voltage (V _oc ) of the solar cell is higher than that of the comparative example 1 in the case of the examples 1 to 3, and the relative efficiency is increased. This is a result of removing the impurities on the surface of the light absorbing layer by forming the light absorbing layer, then performing surface heat treatment and cleaning.

(2) Solar cells Shunt Resistance (R shunt ) And Charging factor ( FF ) evaluation

The shunt resistance (R shunt) and the charge factor (FF) of the solar cell manufactured according to Examples 4 to 5 and Comparative Example 1 were evaluated, and the results are shown in Table 2.

division R shunt
(Ohm) FF
(%) Relative
efficiency(%) Example 4 1749 65.4 102.3 Example 5 2349 65.7 103.9 Comparative Example 1 1504 65.0 100.0

As shown in Table 2, in Examples 4 to 5, the shunt resistance (R shunt) of the solar cell was higher than that of Comparative Example 1, and it was confirmed that the charging factor (FF) and the relative efficiency were increased. This is a result of preventing diffusion of an alkali compound (Na-O, Na-Se-O) by forming a transparent resistive layer and then performing surface heat treatment or cleaning.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (18)

(a) forming a rear electrode layer on a substrate;
(b) forming a light absorption layer on the rear electrode layer;
(c) forming a buffer layer on the light absorption layer by atomic layer deposition; And
(d) forming a front electrode layer on the buffer layer,
Further comprising a surface heat treatment step after the step (b) or the step (c)
A method of manufacturing a solar cell.
The method according to claim 1,
After the formation of the buffer layer in the step (c), a transparent resistance layer containing ZnO is further formed on the buffer layer
A method of manufacturing a solar cell.
The method according to claim 1,
The surface heat treatment is performed under at least one gas atmosphere selected from the group consisting of air, N ₂ , Ar, O ₂ , H ₂ O and H ₂ O ₂
A method of manufacturing a solar cell.
The method according to claim 1,
The surface heat treatment is performed at a temperature of 100 ° C to 250 ° C
A method of manufacturing a solar cell.
The method according to claim 1,
The surface heat treatment is performed for 1 minute to 30 minutes
A method of manufacturing a solar cell.
The method according to claim 1,
After the surface heat treatment, the substrate is cleaned by at least one cleaning solution selected from the group consisting of NH ₄ OH, HNO ₃ , HCl, H ₂ SO ₄ , NH ₄ F, HF, H ₂ O ₂ , CdSO ₄ , KCN and DI- doing
A method of manufacturing a solar cell.
The method according to claim 1,
After the surface heat treatment, at least one of a cleaning gas and a plasma is supplied and cleaned
A method of manufacturing a solar cell.
8. The method of claim 7,
The cleaning gas may be at least one selected from the group consisting of NH ₃ , ClF ₃ , F ₂ , H ₂ O, O ₂ , N ₂ O, NF ₃ and N ₂
A method of manufacturing a solar cell.
8. The method of claim 7,
The plasma is formed by at least one reaction gas selected from the group consisting of Ar, N ₂ , O ₂ , H ₂ O, H ₂ , He, CH ₄ , NH ₃ , CF ₄ , C ₂ H ₂ and C ₃ H ₈ .
A method of manufacturing a solar cell.
8. The method according to claim 6 or 7,
The cleaning is carried out at a temperature of from < RTI ID = 0.0 > 10 C <
A method of manufacturing a solar cell.
8. The method according to claim 6 or 7,
The cleaning is carried out for 30 seconds to 5 minutes
A method of manufacturing a solar cell.
Board;
A rear electrode layer formed on the substrate;
A light absorbing layer formed on the rear electrode layer;
A buffer layer formed on the light absorption layer by atomic layer deposition; And
And a front electrode layer formed on the buffer layer,
The Na content of the buffer layer is 0.5 at% to 2 at%
Solar cells.
13. The method of claim 12,
Wherein the Na content of the buffer layer has a peak value at a surface in contact with the light absorbing layer
Solar cells.
13. The method of claim 12,
The Na content of the buffer layer is rapidly decreased along the thickness direction from the surface in contact with the light absorbing layer, is maintained constant, and then increased at the surface in contact with the front electrode layer
Solar cells.
13. The method of claim 12,
The substrate may be a sodalime glass substrate
Solar cells.
16. The method of claim 15,
The sodium content of the sodalime glass substrate is 13 at% to 15 at%
Solar cells.
13. The method of claim 12,
The content of at least one impurity selected from the group consisting of C, H and OH in the buffer layer is within 3 wt%
Solar cells.
13. The method of claim 12,
Further comprising a transparent resistive layer including ZnO between the buffer layer and the front electrode layer
Solar cells.

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