WO2012013155A1

WO2012013155A1 - Cdte solar battery and method of preparing the same

Info

Publication number: WO2012013155A1
Application number: PCT/CN2011/077766
Authority: WO
Inventors: Rui DENG; Yong Zhou; Wenyu Cao
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2010-07-29
Filing date: 2011-07-28
Publication date: 2012-02-02
Anticipated expiration: 2013-01-29
Also published as: CN201780976U

Abstract

A CdTe solar battery is provided, comprising: a back electrode layer (6); a transition layer (5) formed on the back electrode layer (6); a CdTe layer (4) formed on the transition layer (5); a CdS layer (3) formed on the CdTe layer (4); a transparent electrical conductive layer (2) formed on the 5 CdS layer (3) and a substrate (1) formed on the transparent electrical conductive layer (2). The transition layer (5) may comprise a first transition layer (51) made from ZnTe and a second transition layer (52) made from Cu 2 Te which is formed on the back electrode layer (6). A method of preparing a CdTe solar battery is also provided.

Description

CdTe SOLAR BATTERY AND METHOD OF PREPARING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority to and benefits of Chinese Patent Application No. 201020280813.8, filed with the State Intellectual Property Office, P. R. C. on July 29, 2010, the content of which is incorporated herein by reference in its entirety

FIELD

The present disclosure relates to the field of compound solar battery, more particularly to a CdTe solar battery and a method of preparing the same.

BACKGROUND

CdTe is a compound semiconductor with a most suitable bandgap for photoelectric energy conversion. Solar batteries made from this semiconductor may directly convert solar energy into electric energy, and the conversion efficiency thereof is high theoretically. CdTe may be deposited easily to form a large area film while maintaining a high depositing rate. Further, the manufacturing cost of the CdTe solar battery may be reduced, and therefore compared with the silicon solar battery, the CdTe solar battery may be a new solar battery with a wide application perspective.

Normally, the structure of the CdTe solar battery may have a structure as follows. From the top down, the CdTe solar battery may comprise a glass substrate, a transparent electrical conductive layer, an n-CdS layer, a p-CdTe layer, and a back electrode layer. Metals are usually used for forming the back electrode layer, but the CdTe has high work function (5.5eV). Therefore, it may be difficult to form good ohmic contact between the metal and CdTe, thus greatly affecting the performance of the CdTe solar batteries.

Presently for the CdTe solar battery, a transition layer may be added between the p-CdTe layer and the back electrode layer to form good ohmic contact. The structure of the solar battery is shown in Fig. 1. From the top down, the solar battery may comprise a glass substrate Γ , a transparent electrical conductive layer 2 an n-CdS layer 3 a p-CdTe layer 4 a transition layer 5^' and a back electrode layer 6\ The transition layer 5^λ may be usually a p-ZnTe layer. Although the ZnTe layer may increase the ohmic contact performance to a certain degree, the effect thereof may not meet the desired requirement. Following research shows that the transition layer may be a ZnTe: Cu layer, that is, the ZnTe layer is doped with Cu atom. The ZnTe : Cu layer may improve the ohmic contact performance of the battery, but the diffusion of Cu doping atom may lead to the reduction of the battery performance. There is still a method to prepare the ZnTe : Cu layer, that is, the ZnTe layer is usually deposited for a period of time and then doped with Cu atom. The transition layer may improve the crystal lattice matching and the battery performance, but the doping material still exists in the transition layer in the form of an atomic state, so that the diffusion may appear after long time usage, and therefore the battery performance may be reduced. SUMMARY

In view thereof, a CdTe solar battery may be provided, which may not lead to the reduction of the battery performance while maintaining good ohmic contact. Further, a method of preparing the CdTe solar battery is also need to be provided.

One embodiment of the present disclosure may provide a CdTe solar battery. The CdTe solar battery may comprise: a back electrode layer; a transition layer formed on the back electrode layer; a CdTe layer formed on the transition layer; a CdS layer formed on the CdTe layer; a transparent electrical conductive layer formed on the CdS layer; and a substrate formed on the transparent electrical conductive layer. The transition layer comprises: a first transition layer made from ZnTe; and a second transition layer made from 0¾Τβ formed on the back electrode layer.

Another embodiment of the present disclosure may provide a method of preparing the CdTe solar battery. The method may comprise steps of: (a) forming a transparent electrical conductive layer on a substrate; (b) forming a CdS layer on the transparent electrical conductive layer; (c) forming a CdTe layer on the CdS layer; (d) forming a transition layer on the CdTe layer; and (e) forming a back electrode layer on the transition layer. The transition layer may comprise: a first transition layer made from ZnTe, and a second transition layer made from C¾Te which is formed on the back electrode layer.

With the CdTe solar battery and the method of preparing the same according to an embodiment of the present disclosure, not only may the short circuit current density be obviously increased by about 25%, but also the conversion efficiency of the solar battery may be increased to about 12.5%, for example. Furthermore, the performance of the CdTe solar battery according to an embodiment of the present disclosure may not be reduced but may be stable.

Additional aspects and advantages of the embodiments of the present disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the disclosure will become apparent and more readily appreciated from the following descriptions taken in conjunction with the drawings, in which:

Fig. 1 is a cross-sectional view of a CdTe solar battery in prior art; Fig. 2 is a cross-sectional view of a CdTe solar battery according to an embodiment of the present disclosure; and

Fig. 3 is a flow chart of preparing a CdTe solar battery according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the present disclosure. The embodiments described herein with reference to the accompanying drawings are explanatory and illustrative, which are used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure.

The CdTe solar battery according to an embodiment of the present disclosure will be described in detail with reference to Fig. 2. As shown in Fig. 2, the CdTe solar battery may comprise a substrate 1, a transparent electrical conductive layer 2, a CdS layer 3, a CdTe layer 4, a transition layer 5 and a back electrode layer 6. The transparent electrical conductive layer 2 is formed on the substrate 1, the CdS layer 3 is formed on the transparent electrical conductive layer 2. The CdTe layer 4 is formed on the CdS layer 3. The transition layer 5 is formed on the CdTe layer 4. The back electrode layer 6 is formed on the transition layer 5. As shown in Fig. 2, the transition layer 5 may comprise a first transition layer 51 made from ZnTe and a second transition layer 52 made from Cu₂Te and formed on the back electrode layer 6.

Accordingly, the transition layer in the CdTe solar battery is divided into two layers, and the second transition layer 52 may be made from Cu₂Te instead of the Cu atom, so that the diffusion of Cu₂Te may not be as serious as that of the Cu atom in the prior art. Moreover, the first transition layer made from ZnTe is disposed between the CdTe layer and the second transition layer made from Cu₂Te, so that the first transition layer made from ZnTe may efficiently prevent Cu in the second transition layer from diffusing into the CdTe layer so as to prevent the battery performance from being reduced, and good Cu doping ratio may be maintained so as to form good ohmic contact between the CdTe layer and the back electrode layer.

In addition, compared with the conventional Cu doping technology the complex co-deposition technology may be avoided, thus simplifying the manufacturing process and increasing the finished product ratio. That is, with the CdTe solar battery according to an embodiment of the present disclosure, the cost of the transition layer may be reduced, thus reducing the producing cost of the CdTe solar battery.

With the CdTe solar battery according to an embodiment of the present disclosure, not only may the short-circuit current density be obviously increased by about 25%, but also the conversion efficiency of the solar battery may be increased to about 12.5%. Furthermore, the performance of the CdTe solar battery according to an embodiment of the present disclosure may not be reduced but may be stable.

According to an embodiment of the present disclosure, the substrate 1 may be a glass substrate with good transparency, good heat resistance and high strength. In one embodiment, an ultra-white glass substrate may be used as the substrate 1. In another embodiment, a FTO substrate may be used as the glass substrate, and the thickness of the glass substrate may be about 1mm to 5mm.

According to an embodiment of the present disclosure, the transparent electrical conductive layer may offer good electrically conductive performance so that the electron may be easily educed. According to an embodiment of the present disclosure, the indium oxide film doped with Sn In₂0₃ : Sn (ITO), ZnO:Al (ZAO), In₂0₃:Mo (IMO), or Sn0₂:F (FTO) may be used as the transparent electrical conductive layer.

The CdS layer and the CdTe layer form the P-N junction of the CdTe solar battery. In one embodiment, the purity of the CdS layer and the CdTe layer may be about 99.9% and about 99.999% respectively which may be termed as 3N and 5N in the art. In one embodiment, the thickness of the CdS layer may be about 50nm to about 300nm, and the thickness of the CdTe layer may be about Ιμπι to about ΙΟμπι.

The transition layer may function to increase the ohmic contact between the CdTe layer 4 and the back electrode layer 6. According to an embodiment of the present disclosure, the thickness of the transition layer 5 may be about 15nm to about lOOnm. As shown in Fig. 2, the transition layer 5 is divided into two layers: the first transition layer 51 and the second transition layer 52. The first transition layer 51 is a ZnTe layer, and the second transition layer 52 is a Cu₂Te layer.

In one embodiment, the first transition layer 51 may be thicker than the second transition layer 52, so that the diffusion of Cu may be decreased, and good Cu doping ratio may also be maintained to ensure good ohmic contact between the CdTe layer 4 and the back electrode layer 6. In one embodiment, the thickness of the first transition layer 51 may be about lOnm to about 50nm, and the thickness of the second transition layer 52 may be about 5nm to about 20nm. In another embodiment, the thickness of the first transition layer 51 may be about 20nm to 30nm, and the thickness of the second transition layer 52 may be about 8nm to 15nm The transition layer 5 may be prepared through radio frequency sputtering deposition or vacuum evaporation deposition, which will be described below.

The back electrode layer 6 may mainly function to conduct electricity. Metals with excellent electrical conductivity and small resistance, such as Au, Ag, Ni, Cu, and Mo, may be used for forming the back electrode layer 6. In one embodiment, the thickness of the back electrode layer 6 may be about 80nm to about 500nm.

In the following, a method of preparing a CdTe solar battery according to the present disclosure as described above may be described in detail with reference to Fig. 3. As shown in Fig. 3, the method may comprises the steps of: (a) forming a transparent electrical conductive layer on a substrate (S 101); (b) forming a CdS layer on the transparent electrical conductive layer (S 102); (c) forming a CdTe layer on the CdS layer (S103); (d) forming a transition layer on the CdTe layer (SI 04); and (e) forming a back electrode layer on the transition layer (S I 05).

The steps will be described in detail step by step hereinafter.

S 101 : a transparent electrical conductive layer is formed on a substrate.

The substrate 1 may be a glass substrate with excellent transparency, good heat resistance and high strength. According to an embodiment of the present disclosure, the conductive glass with a thickness of about 1mm to about 5mm may be used as the substrate I, and the glass substrate 1 may be pretreated at first through the following steps. The glass substrate 1 may be firstly washed with acetone for about lOmin to about 60min by ultrasonic wave to remove lipids on the surface of the glass substrate 1, then washed with a cleaning agent for about lOmin to about 60min by ultrasonic wave to remove inorganic contaminants on the surface of the glass substrate 1, and finally washed with deionized water for about lOmin to about 60min by ultrasonic wave to remove impurities on the surface of the glass substrate 1. After the washing processes, the glass substrate 1 may be dried and then washed with plasma in a pretreatment room.

After the pretreatment step, the transparent electrical conductive layer 2 may be formed on the substrate 1. The indium oxide film doped with Sn In₂0₃: Sn (ITO), ZnO:Al (ZAO), In₂0₃:Mo (IMO), or Sn0₂:F (FTO) may be used for forming the transparent electrical conductive layer 2 through target material sputtering and so on.

S I 02: a CdS layer is formed on the transparent electrical conductive layer.

The semi finished product obtained in the step S I 01 may be put into a CdS coating device, and the CdS powder with high purity is used as a sublimation source, and then the inert gas (Ar/0₂) may be introduced into the CdS coating device after the CdS coating device is vacuumized until the pressure is about lOPa to about 200Pa. The flow rate of the inert gas may be about lml/min to about 20ml/min, the temperature of the sublimation source may be about 450^°C to about 700^°C , and the temperature of the substrate may be about normal temperature to about 500 ^°C . Then, coating is performed for about lmin to about 30min under the above conditions to form the CdS layer 3 with a thickness of about 50nm to about 300nm on a lower surface of the transparent electrical conductive layer 2.

S I 03 : a CdTe layer is formed on the CdS layer.

The semi finished product obtained in the step S I 02 may be put into a work rest of a CdTe coating device, and the CdTe powder with high purity is used as the sublimation source. Then, the inert gas Ar may be introduced into the CdTe coating device after the CdTe coating device is vacuumized until the pressure is about lOPa to about 200Pa. The flow rate of the inert gas may be about lml/min to about 20ml/min, the temperature of the sublimation source may be about 550^°C to about 800^°C, and the temperature of the substrate may be about 300 ^°C to about 550^°C . Then, coating is performed for about 5min to about 30min under the above conditions to form the CdTe layer 4 with a thickness of about 2μηι to about 5μηι on a lower surface of the CdS layer 3, which may be also called as an N-type layer 3.

S I 04: a transition layer is formed on the CdTe layer.

As described above, the transition layer 5 may comprise a first transition layer 51 and a second transition layer 52. The first transition layer 51 may be a ZnTe layer; and the second transition layer 52 may be a Cu₂Te layer and formed on a lower surface of the first transition layer 51.

The semi finished product obtained in the step S I 03 may be put into a vacuum sputtering device,for example, JPGF-600A Magnetron Sputtering Coating Machine available from Beijing Beiyi Innovation Vacuum Technology Co., Ltd., and a frequency radio power source with a power of about 600W may be used. ZnTe is used as the target material and then sputtered continuously for about lmin to about 30min to form the ZnTe layer 51 on a lower surface of the CdTe layer 4. The ZnTe layer is the first transition layer 51. Alternatively, the thickness of the first transition layer 51 may be about lOnm to about lOOnm.

The semi finished product obtained in the above step may be put into an vacuum sputtering equipment, for example, JPGF-600A Magnetron Sputtering Coating Machine available from Beijing Beiyi Innovation Vacuum Technology Co., Ltd., and a frequency radio power source with a power of about 200W may be used. Cu₂Te is used as the target material and then sputtered continuously for about lmin to about 30min to form the Cu₂Te layer 52 on a lower surface of the ZnTe layer 51. The Cu₂Te layer is the second transition layer 52. Alternatively, the thickness of the second transition layer 52 may be about lOnm to about lOOnm.

S I 05: a back electrode layer is formed on the transition layer.

The semi finished product obtained in step S I 04 may be put into a vacuum sputtering equipment (for example, JPGF-600A Magnetron Sputtering Coating Machine available from Beijing Beiyi Innovation Vacuum Technology Co., Ltd.). The target material may be at least one material selected from the group consisting of Mo, Ni, Cu, Ag, and combinations thereof, then a metal electrode layer with a thickness of about 50nm to about 300nm is formed by sputtering, and the metal electrode layer is the back electrode layer 6. After the step S105 is finished, the CdTe solar battery according to an embodiment of the present disclosure may be obtained.

The transition layer may be divided into two layers according to the above method, and the second transition layer 52 may be made from Cu₂Te instead of the Cu atom, so that the diffusion of Cu₂Te may not be as serious as that of the Cu atom in the prior art. Moreover, the first ZnTe transition layer 51 is disposed between the CdTe layer 4 and the 0¾Τβ layer 52, so that the first ZnTe transition layer 51 may efficiently prevent Cu in the second transition layer 52 from diffusing into the CdTe layer 4 so as to prevent the battery performance from being reduced, and good Cu doping ratio may be maintained so as to form good ohmic contact between the CdTe layer and the back electrode layer.

The method for preparing the CdTe solar battery according to an embodiment of the present disclosure may be simple in process, and the deposition equipment may also be a conventional one, so that complex treatment processes may be avoided and the producing cost may be reduced accordingly.

In the following, particular embodiments of the present disclosure will be described in detail.

These embodiments should not be construed to limit the scope of the present disclosure in any way.

Embodiment 1

In this embodiment, a CdTe solar battery comprises a glass substrate 1, a transparent electrical conductive layer 2, a CdS layer 3, a CdTe layer 4, a transition layer 5 and a back electrode layer 6 stacked in turn. An ultra-white glass substrate with a thickness of about 2mm is used as the glass substrate 1. The transparent electrical conductive layer 2 is a FTO substrate with a thickness of about Ι μηι. The CdS layer 3 has a thickness of about 200nm, and the CdS powder used as the sublimation source has a purity of at least about 99.999% or 5N. The CdTe layer has a thickness of about 5μηι, and the CdTe powder used as the sublimation source has a purity of at least about 99.999% or 5N.

In this embodiment, the transition layer 5 comprises a first ZnTe transition layer 51 and a second 0¾Τβ transition layer 52. The first transition layer 51 with a thickness of about 25nm was deposited on the CdTe layer 4, and the second transition layer 52 with a thickness of about lOnm was deposited on the first transition layer 51. The back electrode layer 6 was made from i, and the thickness of the back electrode layer 6 was about 200nm.

In this embodiment, the CdTe solar battery was obtained through the following steps,

(a) The conductive glass with a thickness of about 2mm was used as the substrate 1. Then, the glass substrate was firstly washed with acetone for about 30min by ultrasonic wave to remove lipids on the surface of the glass substrate, then washed with a cleaning agent for about 20min by ultrasonic wave to remove inorganic contaminants on the surface of the glass substrate, and finally washed with deionized water for about 30min by ultrasonic wave to remove impurities on the surface of the glass substrate. After the washing processes, the glass substrate 1 was dried and then washed with plasma in a pretreatment room.

(b) The transparent electrical conductive layer 2 was formed on the glass substrate 1, and Sn0₂:F (FTO) was used as the target material for preparing the transparent electrical conductive layer 2 through target material sputtering method.

(c) The semi finished product obtained in the above steps was put into a CdS coating device, and the CdS powder with a purity of at least about 99.9% was used as the sublimation source, and then the inert gas (Ar/0₂) was introduced into the CdS coating device after the CdS coating device was vacuumized until the pressure was about lOOPa. The flow rate of the inert gas was about lOml/min, the temperature of the sublimation source was about 450^°C , and the temperature of the substrate was about 300 ^°C . Coating was performed for about 25min under the above conditions to form the CdS layer 3 with a thickness of about 50nm to about 300nm on a lower surface of the transparent electrical conductive layer 2.

(d) The semi finished product obtained in the above steps was put into a work rest of a CdTe coating device, and the CdTe powder with a purity of at least about 99.999% or 5N was used as the sublimation source. The inert gas Ar was introduced into the CdTe coating device after the CdTe coating device was vacuumized until the pressure was about lOOPa, the flow rate of the inert gas was about 15ml/min, the temperature of the sublimation source was about 600 ^°C , and the temperature of the substrate was about 350^°C . Coating was performed for about 25min under the above conditions to form the CdTe layer 4 with a thickness of about 5μπι on a lower surface of the CdS layer 3.

(e) The semi finished product obtained in the above steps was put into a vacuum sputtering equipment, for example, JPGF-600A Magnetron Sputtering Coating Machine available from

Beijing Beiyi Innovation Vacuum Technology Co., Ltd., and a frequency radio power source with a power of about 600W was used. ZnTe was used as the target material and then sputtered continuously for about 20min to form the ZnTe layer 51 on a lower surface of the CdTe layer 4. The ZnTe layer was the first transition layer 51. Alternatively, the thickness of the first transition layer 51 was about 25nm.

The semi finished product obtained in the above steps was put into a vacuum sputtering equipment, for example, JPGF-600A Magnetron Sputtering Coating Machine available from Beijing Beiyi Innovation Vacuum Technology Co , Ltd., and a frequency radio power source with a power of about 200W was used. Cu₂Te was used as the target material and then sputtered continuously for about 20min to form the Cu₂Te layer 52 on a lower surface of the ZnTe layer 51. The Cu₂Te layer was the second transition layer 52. Alternatively, the thickness of the second transition layer 52 was about lOnm.

(f) The semi finished product obtained in the above steps was put into the vacuum sputtering equipment, for example, JPGF-600A Magnetron Sputtering Coating Machine available from Beijing Beiyi Innovation Vacuum Technology Co., Ltd.), and i was used as the target material and then sputtered to form the metal electrode layer with a thickness of about 200nm. The metal electrode layer was the back electrode layer 6. After the sputtering was finished, the CdTe solar battery SI was obtained.

Embodiment 2

This embodiment is substantially the same as Embodiment 1, except that: the thickness of the first transition layer is about 50nm, and the thickness of the second transition layer is about 20nm. Then, the CdTe solar battery S2 is obtained.

Embodiment 3

This embodiment is substantially the same as Embodiment 1, except that the following:

The thickness of the first transition layer is about 13nm, and the thickness of the second transition layer is about 6nm. Then, the CdTe solar battery S3 is obtained.

Embodiment 4

The thickness of the first transition layer is about 30nm, and the thickness of the second transition layer is about 15nm. Then, the CdTe solar battery S4 is obtained.

Embodiment 5

The thickness of the first transition layer is about 20nm, and the thickness of the second transition layer is about 8nm. Then, the CdTe solar battery S5 is obtained.

Comparative Embodiment 1

The transition layer 5 is the ZnTe : Cu layer with a thickness of about 50nm. Then, the CdTe solar battery CI is obtained.

Performance Test

The CdTe solar batteries obtained according to Embodiments 1 to 5 and Comparative Embodiment 1 were tested on a pulse solar simulator (PSS8) and a digital display controller according to the standard IEC 61646:2008 (Thin-Film terrestrial photovoltaic (PV) modules-design qualification and type approval) respectively. From the obtained I-V (current to voltage) curve, the open circuit voltage, the short circuit current, the photoelectrical conversion efficiency and the fill factor are obtained, and the results are shown in Table 1.

Table 1

As shown in the Table 1, compared with Comparative Embodiment 1, the CdTe solar batteries obtained according to Embodiments 1 to 5 may have higher open circuit voltage, lower short circuit current, higher photoelectrical conversion efficiency and higher fill factor, which shows that the battery comprising the transition layer according to an embodiment of the present disclosure may have improved battery performance, and therefore the transition layer may efficiently prevent the performance from being damaged while maintaining excellent ohmic contact.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that changes, alternatives, and modifications all falling into the scope of the claims and their equivalents may be made in the embodiments without departing from spirit and principles of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A CdTe solar battery, comprising:

a back electrode layer;

a transition layer formed on the back electrode layer;

a CdTe layer formed on the transition layer;

a CdS layer formed on the CdTe layer;

a transparent electrical conductive layer formed on the CdS layer; and

a substrate formed on the transparent electrical conductive layer, wherein the transition layer comprises:

a first transition layer made from ZnTe; and

a second transition layer made from Cu₂Te formed on the back electrode layer.

2. The CdTe solar battery according to claim 1, wherein the first transition layer is thicker than the second transition layer.

3. The CdTe solar battery according to claim 1, wherein the thickness of the transition layer is about 15nm to about lOOnm.

4. The CdTe solar battery according to claim 2, wherein the thickness of the first transition layer is about lOnm to about 50nm, and the thickness of the second transition layer is about 5nm to about 20nm.

5. The CdTe solar battery according to claim 4, wherein the thickness of the first transition layer is about 20nm to about 30nm, and the thickness of the second transition layer is about 8nm to about 15nm.

6. The CdTe solar battery according to claim 1, wherein the thickness of the substrate is about lmm to about 5mm;

the thickness of the transparent electrical conductive layer is about Ιμιη to about ΙΟμηι;

the thickness of the CdS layer is about 50nm to about 300nm;

the thickness of the CdTe layer is about Ιμηι to about ΙΟμιη; and

the thickness of the back electrode layer is about 80nm to about 500nm.

7. A method of preparing a CdTe solar battery, comprising steps of:

(a) forming a transparent electrical conductive layer on a substrate;

(b) forming a CdS layer on the transparent electrical conductive layer;

(c) forming a CdTe layer on the CdS layer;

(d) forming a transition layer on the CdTe layer; and

(e) forming a back electrode layer on the transition layer, wherein

the transition layer comprises: a first transition layer made from ZnTe; and

a second transition layer made from Cu₂Te which is formed on the back electrode layer.

8. The method according to claim 7, wherein the step of forming the transition layer further comprises steps of:

depositing the first transition layer made from ZnTe on the CdTe layer; and

depositing the second transition layer made from Cu₂Te on the first transition layer.

9. The method according to claim 8, wherein the first transition layer is deposited by a thickness larger than that of the second transition layer.

10. The method according to claim 8, wherein the thickness of the transition layer by depositing is about 15nm to about lOOnm.