TWI596785B - Solar cell structure and method for manufacturing the same - Google Patents

Description

Solar cell structure and forming method thereof

This invention relates to solar cells, and more particularly to their construction and method of formation.

In recent years, the global industry has flourished. Although the traditional energy supply method is cheaper, it has potential problems such as radiation and environmental pollution. Therefore, green alternative energy has become the focus of research and development of various research units, among which solar cells are the most eye-catching. Traditional solar cells are mainly dominated by twins. However, in recent years, various thin film solar cells have flourished. However, copper, indium and selenium series solar cells are preferred if nontoxic, high efficiency and high stability are considered.

Copper indium gallium selenide (CIGS) is a chalcopyrite structure compound with a crystal structure of a square structure. Because of its high optical absorption coefficient, wide range of absorption bands, high chemical stability, and direct energy gap, it is equivalent. Suitable as a material for solar cells. A general CIGS battery is sequentially an electrode layer, a CIGS layer, a CdS layer, an i-ZnO layer, an AZO layer, and a finger electrode formed as appropriate on the substrate. The i-ZnO layer on the CdS layer can alleviate the problem of incomplete buffer layer coverage and effectively suppress the leakage current of the battery. In addition, the i-ZnO layer can reduce the damage of the CdS layer by ion bombardment when the AZO layer is sputtered. However, the thickness of the i-ZnO layer is generally as high as 50 nm to 100 nm, so that part of the incident light is absorbed to reduce the efficiency of the solar cell. rate. On the other hand, the i-ZnO layer has a large resistance value and is not suitable for current collection.

In summary, new CIGS cell structures are currently needed to overcome the problems caused by conventional i-ZnO layers.

A solar cell structure according to an embodiment of the invention includes: a substrate; a metal electrode on the substrate; an absorption layer on the metal electrode; a buffer layer on the absorption layer; a titanium oxide layer on the buffer layer, and titanium oxide The layer has a thickness greater than 0 and less than 10 nm; and a transparent conductive oxide layer on the titanium oxide layer.

A method for forming a solar cell structure according to an embodiment of the present invention includes: forming a metal electrode on a substrate; forming an absorption layer on the metal electrode; forming a buffer layer on the absorption layer; forming a titanium oxide layer on the buffer layer, and oxidizing The thickness of the titanium layer is greater than 0 and less than 10 nm; and the transparent conductive oxide layer is formed on the titanium oxide layer, wherein the step of forming the titanium oxide layer on the buffer layer is atomic layer deposition, and the temperature of the atomic layer deposition is between 100 ° C and Between 180 ° C, and the precursor before atomic layer deposition is titanium tetraisopropoxide.

10‧‧‧Substrate

11‧‧‧Metal electrodes

13‧‧‧absorbing layer

15‧‧‧buffer layer

17‧‧‧Titanium oxide layer

19‧‧‧Transparent conductive oxide layer

21‧‧‧ finger electrodes

100‧‧‧ solar cells

Fig. 1 is a schematic view showing a solar cell in an embodiment of the present invention.

1 is a schematic view of a solar cell 100 in an embodiment of the present invention. First, a substrate 10 such as plastic, stainless steel, glass, quartz, or other common substrate materials is provided. Next, a metal electrode 11 is formed on the substrate 10, which may be formed by sputtering, physical vapor deposition, or spray coating. In an embodiment of the invention, The metal electrode 11 may be chromium, molybdenum, copper, silver, gold, platinum, other metals, or alloys thereof. Next, an absorbing layer 13 is formed on the metal electrode 11. In an embodiment of the invention, the absorbing layer 13 may be copper indium gallium selenide (CIGS), copper indium gallium selenide (CIGSS), copper gallium selenide (CGS), copper gallium selenide (CGSS), or copper indium selenide ( CIS). The method for forming the absorption layer 13 may be a vapor deposition method, a sputtering method, a plating method, or a method of coating a nano particle, and is referred to Solar Energy, 77 (2004) page 749-756 and Thin Solid Films, 480-481 ( 2005) page 99-109.

A buffer layer 15 is then formed on the absorber layer 13. In an embodiment of the invention, the buffer layer 15 may be cadmium sulfide, zinc sulfide, zinc tin oxide, zinc oxide, zinc magnesium oxide or indium sulfide. In an embodiment of the invention, the buffer layer 15 has a thickness greater than zero and less than or equal to 30 nm. If the solar cell 100 does not have the buffer layer 15 (i.e., the subsequently formed TiO ₂ layer 17 is in direct contact with the absorbing layer 13), it takes a period of time (e.g., 10 minutes to 1 hour) to achieve the highest efficiency. If the thickness of the buffer layer 15 is too large, in addition to a decrease in the amount of transmitted light, the battery efficiency will be lowered due to a large increase in series resistance. The method for forming the buffer layer 15 can be referred to Solar Energy, 77 (2004) page 749-756, and the chemicals used are cadmium sulfate (or indium sulfate), thiourea, and ammonia water, and the operating temperature is about 50 ° C to 75 ° C. between.

The titanium oxide layer 17 is then deposited on the buffer layer 15 by atomic layer deposition, the atomic layer deposition temperature is between 100 ° C and 180 ° C, and the precursor before the atomic layer deposition may be titanium tetraisopropoxide. If the temperature at which the atomic layer is deposited is too high, the absorption layer 13 is damaged. If the temperature at which the atomic layer is deposited is too low, in addition to a drastic decrease in the coating speed, the carbon in the precursor cannot be removed, so that the film quality is greatly degraded. In an embodiment of the invention, the titanium oxide layer 17 is an amorphous phase. It is worth noting that the precursor may not contain a halogen such as TiCl ₄ , TiBr ₄ , or the like prior to atomic layer deposition to avoid corrosion of the buffer layer 15 (or even the absorbing layer 13) underneath the halogen generated during deposition. In an embodiment of the invention, the thickness of the titanium oxide layer 17 is greater than 0 and less than 10 nm. If the thickness of the titanium oxide layer 17 is too thick, the amount of transmitted light is lowered, and the battery efficiency is further lowered. If the titanium oxide layer 17 is absent (ie, the subsequently formed transparent conductive oxide layer 19 directly contacts the buffer layer 15), the leakage current of the battery cannot be effectively suppressed, and the ion bombardment buffering when the transparent conductive oxide layer 19 is sputtered cannot be avoided. Destruction of layer 15. On the other hand, the thickness of the titanium oxide layer 17 is related to the composition of the absorption layer 13. For example, if the absorbing layer 13 is copper indium gallium selenide (CIGS), the thickness of the titanium oxide layer 17 is greater than 0 and less than 10 nm.

A transparent conductive oxide layer 19 is then formed on the titanium oxide layer 17. In an embodiment of the invention, the transparent conductive oxide layer 19 may be indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), aluminum gallium. Zinc oxide (AGZO), cadmium tin oxide, zinc oxide, zirconium dioxide, or other transparent conductive material. The transparent conductive oxide layer 19 can be formed by a sputtering method, an evaporation method, an atomic layer deposition method, a thermal cracking method, a nanoparticle coating method, and the like.

In an embodiment of the invention, the finger electrodes 21 are formed on the transparent conductive oxide layer 19 as appropriate. The finger electrode 21 may be made of a nickel-aluminum alloy, and may be formed by sputtering, lithography, etching, and/or other suitable processes. In an embodiment of the invention, when the surface area of the transparent conductive oxide layer 19 is small, the finger electrodes 21 may be omitted.

Compared with the i-ZnO layer which is conventionally sandwiched between the buffer layer and the transparent conductive oxide layer, the above titanium oxide layer 17 has a small electrical resistance and a high light incident amount, so that the solar cell can have better photoelectric conversion. effectiveness.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

Example

Example 1 (the titanium oxide layer is interposed between the buffer layer and the transparent conductive oxide layer)

First, 1000 nm of Cr and Mo were respectively plated on the stainless steel substrate through a sputtering process as metal electrodes. Then, a CuInGa nanoparticle oxidation precursor is coated on the Mo film by a coating method, and then passed through a reduction and selenization process to prepare a CIGSeS absorption layer (about 3000 nm). The CIGSeS absorber layer was then cleaned using a 5 wt% KCN aqueous solution to remove the copper selenium compound, i.e., to form an absorber layer. Next, a 50 nm thick CdS film was plated on the absorption layer by a chemical bath method to serve as a buffer layer, wherein the temperature of the chemical bath method was controlled at 65 °C. Then, a 3 nm thick titanium oxide layer was prepared on the buffer layer by atomic layer deposition, the process temperature was controlled at 120 ° C, and the precursor was titanium tetraisopropoxide. Then, a 300 nm AZO layer was plated on the titanium oxide layer as a transparent conductive oxide layer, and finally a Ni-Al finger electrode was plated on the transparent conductive oxide layer to complete the solar cell structure.

Examples 2-1 and 2-2

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 5 nm.

Example 3

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 7 nm.

Example 4

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 9 nm.

Example 5

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 10 nm.

Example 6

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 15 nm.

Example 7

Similar to Example 1, the difference was that the thickness of the titanium oxide layer was increased to 30 nm.

Comparative Examples 1 to 7 (i-ZnO layer is interposed between the buffer layer and the transparent conductive oxide layer)

First, 1000 nm of Cr and Mo were respectively plated on the stainless steel substrate through a sputtering process as metal electrodes. Then, a CuInGa nanoparticle oxidation precursor is coated on the Mo film by a coating method, and then passed through a reduction and selenization process to prepare a CIGSeS absorption layer (about 3000 nm). The CIGSeS absorber layer was then cleaned using a 5 wt% KCN aqueous solution to remove the copper selenium compound, i.e., to form an absorber layer. Next, a 50 nm thick CdS film was plated on the absorption layer by a chemical bath method to serve as a buffer layer, wherein the temperature of the chemical bath method was controlled at 65 °C. Then, a 50 nm thick i-ZnO layer is prepared on the buffer layer by a sputtering process, and then a 300 nm AZO layer is plated on the i-ZnO layer as a transparent conductive oxide layer, and finally a Ni is plated on the transparent conductive oxide layer. - Al finger electrode to complete the solar cell structure of the comparative example.

The above comparative examples and the examples belong to the same structure before the formation of the i-ZnO layer/titanium oxide layer. Experimentally, the semi-finished product of the solar cell can be divided into two sets of semi-finished products having the same area after forming the buffer layer, and then the i-ZnO/AZO/Ni-Al finger electrodes (Comparative Examples 1 to 7) and the titanium oxide layer are respectively formed. AZO/Ni-Al finger electrodes (Examples 1 to 7).

As shown in Tables 1 to 8, the effect of different thicknesses of the titanium oxide layer on the electrical properties of the battery can be compared. As the thickness increases (5 nm to 30 nm), the V _{oc of the} solar cell decreases (0.564 V to 0.541 V), that is, excessively long atomic layer deposition (ALD) time causes excessive diffusion of Cd ions to lower the V _{oc of the} battery. Further, as the thickness of the titanium oxide was increased, the J _sc of the battery of the example was slightly lowered. As the thickness of the titanium oxide layer increases, the FF of the solar cell decreases significantly, mainly due to a decrease in R _sh and an increase in R _s . In summary, when the thickness of the titanium oxide layer is increased, the efficiency of the solar cell is significantly reduced (from 12.96% (5 nm) to 11.36% (30 nm)). When the thickness of the titanium oxide layer was reduced from 5 nm (as in Examples 2-1, 2-2) to 3 nm (as in Example 1), the efficiency of Example 1 was slightly lower than that of Examples 2-1 and 2-2.

As shown in the fourth table, solar cells of two different structures in Comparative Example 3 and Example 3 were respectively contained. The electrical measurement results showed that the open circuit voltage (V _oc ) of the two structures did not change significantly. When the short-circuit current (J _sc ) of the battery was compared, the solar cell of the example was about 0.62 mA/cm ² (2.0%) higher than that of the solar cell of the comparative example, and it was inferred that the titanium oxide film had a high light transmittance. If the fill factor (FF) of the two structures is compared, there is no significant difference, that is, the series resistance (R _s ) of the two is not significantly different from the parallel resistance (R _sh ). Comparing the battery efficiencies of the two, it can be seen from Table 4 that the battery efficiency of the embodiment is about 0.25% higher than that of the comparative example, and the increase in efficiency is mainly due to the increase in short-circuit current.

It is worth noting that the efficiency of solar cells is better considering the comparative examples and examples on the same battery to avoid experimental errors. For example, the efficiency of Example 1 in Table 1 is higher than that of Comparative Example 1 (12.85-12.66) / 12.66 = +1.5%, and the efficiency of Example 2-1 in Table 2 is higher than that of Comparative Example 2-1. Should be (12.96-12.68) / 12.68 = +2.2%, the efficiency of Example 2-2 in Table 3 is higher than that of Comparative Example 2-2 (12.62-12.26) / 12.26 = +2.9%, in Table 4 The efficiency of Example 3 over Comparative Example 3 should be (12.78-12.53) / 12.53 = +2.0%, and the efficiency of Example 4 in Table 5 should be (12.86-12.65) / 12.65 = +1.6%. The efficiency of Example 5 in Table 6 is higher than (1.72-12.56) / 12.56 = +1.2%, and the efficiency of Example 6 in Table 7 is higher than (12.12-12.65) / 12.65. =-4.2%, and the efficiency of Example 7 in Table 8 over the comparative example should be (11.36-12.51) / 12.51 = -9.2%. In summary, when the thickness of the titanium oxide layer is less than 10 nm, the efficiency of the solar cell can be increased more than when the thickness of the titanium oxide layer is greater than or equal to 10 nm ( +1.5%).

Example 8

Example 8 is similar to Example 4 except that the thickness of CdS is reduced to 10 nm. The battery preparation method corresponding to Example 8 was similar to that of Example 4 except that the battery of this example did not have the solar cell structure of the comparative example.

Example 9

Example 9 is similar to Example 4 except that the thickness of CdS is reduced to 30 nm. The battery preparation method corresponding to Example 9 was similar to that of Example 4 except that the battery of this example did not have the solar cell structure of the comparative example.

As shown in the table 9, the TiO ₂ layer having a thickness of less than 10 nm can further reduce the thickness of the CdS buffer layer (for example, 30 nm, 10 nm) to improve battery efficiency.

The present invention has been disclosed in several embodiments, and is not intended to limit the scope of the present invention, and may be modified and modified without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

10‧‧‧Substrate

11‧‧‧Metal electrodes

13‧‧‧absorbing layer

15‧‧‧buffer layer

17‧‧‧Titanium oxide layer

19‧‧‧Transparent conductive oxide layer

21‧‧‧ finger electrodes

100‧‧‧ solar cells

Claims (12)

A solar cell structure comprising: a substrate; a metal electrode on the substrate; an absorbing layer on the metal electrode; a buffer layer on the absorbing layer; and a titanium oxide layer on the buffer layer, and The titanium oxide layer has a thickness greater than 0 and less than 10 nm; and a transparent conductive oxide layer is disposed on the titanium oxide layer, wherein the titanium oxide layer is an amorphous phase. The solar cell structure of claim 1, wherein the buffer layer has a thickness greater than 0 and less than or equal to 30 nm. The solar cell structure of claim 1, wherein the metal electrode comprises chromium, molybdenum, copper, silver, gold, platinum, or an alloy thereof. The solar cell structure of claim 1, wherein the absorbing layer comprises copper indium gallium selenide, copper indium gallium selenide, copper gallium selenide, copper gallium selenide, or copper indium selenide. The solar cell structure of claim 4, wherein the absorbing layer is copper indium gallium selenide. The solar cell structure of claim 1, wherein the buffer layer comprises cadmium sulfide, zinc sulfide, zinc tin oxide, zinc oxide, zinc magnesium oxide, or indium sulfide. The solar cell structure of claim 1, wherein the transparent conductive oxide layer comprises indium tin oxide, indium zinc oxide, aluminum zinc oxide , gallium zinc oxide, aluminum gallium zinc oxide, cadmium tin oxide, zinc oxide, or zirconium dioxide. A method for forming a solar cell structure, comprising: forming a metal electrode on a substrate; forming an absorbing layer on the metal electrode; forming a buffer layer on the absorbing layer; forming a titanium oxide layer on the buffer layer, and The thickness of the titanium oxide layer is greater than 0 and less than 10 nm; and a transparent conductive oxide layer is formed on the titanium oxide layer, wherein the step of forming the titanium oxide layer on the buffer layer is atomic layer deposition, and the atomic layer is deposited The temperature is between 100 ° C and 180 ° C, and the precursor before the atomic layer deposition is titanium tetraisopropoxide, wherein the titanium oxide layer is an amorphous phase. The method for forming a solar cell structure according to claim 8, wherein the buffer layer has a thickness greater than 0 and less than or equal to 30 nm. The method for forming a solar cell structure according to claim 8, wherein the absorbing layer comprises copper indium gallium selenide, copper indium gallium selenide, copper gallium selenide, copper gallium selenide, or copper indium selenide. The method for forming a solar cell structure according to claim 10, wherein the absorbing layer is copper indium gallium selenide. The method for forming a solar cell structure according to claim 8, wherein the buffer layer comprises cadmium sulfide, zinc sulfide, zinc tin oxide, zinc oxide, zinc magnesium oxide or indium sulfide.