JP2015032774A - Manufacturing method for solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for solar battery, capable of enhancing power generation performance by lowering, to a suitable range, a copper/group-III element ratio of a surface layer of a light absorption layer of a chalcopyrite light absorption layer by selenide method.SOLUTION: A light absorption layer is immersed into ammonia aqueous solution containing a trace quantity of zinc sulfate. Copper and group-III element of a surface layer are removed by ammonia, however, removal of the group-III element is suppressed by zinc sulfate and thus copper/group-III element ratio can be lowered to achieve a suitable value.

Description

  The present invention relates to a method for manufacturing a solar cell having a chalcopyrite light absorption layer as a main element.

  One power generation technology that supplements thermal power generation and nuclear power generation is solar power generation. In solar power generation, sunlight is converted into electrical energy by a solar cell. Solar cells based on silicon crystals or silicon amorphous and those based on compound semiconductors are known.

Then, as the compound semiconductor, Cu (In, Ga) method of manufacturing a solar cell according to the light absorbing layer a chalcopyrite-type compound, such as Se ₂ has been proposed (e.g., see Patent Document 1).

  As described in Patent Document 1, as a method for forming a chalcopyrite type light absorption layer, after forming a metal precursor on a surface electrode, heat treatment is performed in a hydrogen selenide atmosphere to selenize the metal precursor. A so-called selenization method for forming a chalcopyrite type light absorption layer is known. This method has a feature that is superior in mass productivity compared to other methods such as vapor deposition.

  After the chalcopyrite type light absorption layer is formed as described above, a buffer layer such as cadmium sulfide or indium sulfide is further laminated by a method such as chemical bath deposition. The buffer layer is an n-type semiconductor, the chalcopyrite light absorption layer is a p-type semiconductor, and a pn junction is formed at the interface between the light absorption layer and the buffer layer. After the buffer layer, a transparent electrode layer such as aluminum-added zinc oxide is formed.

  The solar cell having the above chalcopyrite type light absorption layer takes out electrons and holes excited by light energy as electric power, but the excited electrons and holes are recombined due to defects in the light absorption layer and can be taken out. The power may decrease. As one of the factors of the recombination, the content ratio (molar ratio) of copper and the group III element, which are components of the light absorption layer, is related, so that the copper / group III element ratio is about 0.9 to 1.1. It is desirable to do. However, when the chalcopyrite type light absorption layer is formed by the above selenization method, the copper (Cu) / III group element ratio of the surface layer tends to be larger than 1.1.

JP 2003-282908 A

  This invention makes it a subject to provide the manufacturing method of the solar cell which makes the copper / III group element ratio of the surface layer of a chalcopyrite type light absorption layer into a suitable range, and improves electric power generation performance in view of the above-mentioned problem.

The invention according to claim 1 includes a light absorption layer forming step of forming a chalcopyrite type light absorption layer containing copper and a group III element as components, and a buffer layer formation step of forming a buffer layer on the light absorption layer. In the manufacturing method of the solar cell including,
After the light absorbing layer forming step and before the buffer layer forming step, the light absorbing layer is immersed in an aqueous solution containing zinc sulfate and ammonia to reduce the copper / III group element ratio of the surface layer of the light absorbing layer. It is characterized by interposing a copper reduction step.

  The invention according to claim 2 is characterized in that the group III element is indium and / or gallium.

  The invention according to claim 3 is characterized in that the concentration of zinc sulfate in the aqueous solution is 4 to 10 mmol per liter.

  In the invention according to claim 1, the light absorption layer is immersed in an aqueous solution in which zinc sulfate is added to ammonia.

  Although it is not clear, it was confirmed from experiments that copper and group III elements are removed by ammonia, but removal of group III elements is suppressed by the action of zinc sulfate. Since copper is mainly removed by etching and the group III element remains, the copper / group III element ratio decreases. Thus, the copper / III group element ratio of the surface layer of the light absorption layer can be set to a suitable ratio, and the power generation performance can be improved.

  In the invention according to claim 2, since the group III element is indium and / or gallium, a CIGS solar cell having copper, indium, gallium, and selenium as main components and good power generation performance can be obtained.

  In the invention which concerns on Claim 3, the density | concentration of the zinc sulfate in aqueous solution shall be 4-10 mmol per liter. Within this range, removal of the group III element can be suppressed, and zinc does not enter the light absorption layer, so that the influence of zinc on the light absorption layer can be eliminated.

It is a flowchart explaining the manufacturing process of the solar cell which concerns on this invention. It is the graph which investigated the ratio of the copper / III group element. It is the graph which investigated the correlation of an open circuit voltage and current density.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.

As shown in FIG. 1A, a back electrode 12 is formed on a glass substrate 11.
Next, as shown in FIG. 1B, an indium layer 14 is formed on the back electrode 12 by sputtering using an indium target 13.
Next, as shown in FIG. 1C, a copper-gallium alloy layer 16 is formed on the indium layer 14 by sputtering using a copper-gallium alloy target 15.

  Next, as shown in FIG.1 (d), it inserts into the selenization furnace 18, and selenizes in a high temperature hydrogen selenide atmosphere. As a result, a chalcopyrite light absorption layer 19 made of copper, indium, gallium, and selenium is formed (light absorption layer forming step).

Next, as shown in FIG. 1E, the light absorption layer 19 and the like are immersed in an etching tank 22 filled with an aqueous solution 21 containing zinc sulfate and ammonia.
The aqueous solution 21 is an alkaline solution in which ammonia and zinc sulfate are dissolved in pure water at a concentration of 400 to 4000 mmol / liter (0.4 to 4.0 M / l) and 4 to 10 mmol / liter, respectively. The light absorption layer 19 and the like are immersed in the aqueous solution 21 maintained at room temperature (25 ° C.) to 60 ° C. for 1 to 60 minutes. Under this condition, the surface layer of the light absorption layer 19 is processed in FIG. This treatment mainly removes the copper component (copper reduction process).

  Next, as shown in FIG. 1 (f), an n-type buffer layer 23 is formed on the light absorbing layer 19, and as shown in FIG. 1 (g), a transparent electrode is formed on the buffer layer 23 by sputtering. 24 is formed. Thus, the solar cell 10 was completed.

  An example in which the copper reduction process described in FIG. 1E was performed and a comparative example in which the copper reduction process was not performed will be compared. That is, what implements all of FIG.1 (a)-(g) is an "Example", FIG.1 (e) is not implemented, FIG.1 (a)-(d) and (f), (g). What implements is called a “comparative example”.

First, the copper / group III element ratio in the light absorption layer 19 was investigated.
As shown in FIG. 2, the copper / group III element ratio tends to increase in the surface layer of the light absorption layer in both the example and the comparative example. However, in the comparative example, the copper / III element ratio was 1.25, but in the example, the ratio was 1.08, which was lower than that of the comparative example, and could be 1.1 or less.

  Next, the IV characteristics were evaluated by measuring the open circuit voltage and current density (output current per unit area of the battery) for the solar cells of the example and the comparative example.

FIG. 3 shows the IV characteristics of the example and the comparative example. The wavy line is a comparative example, and the solid line is an example.
According to this IV characteristic, the maximum power of the example is obtained at the point P1, and the maximum power of the comparative example is obtained at P2. Comparing the maximum power of the example and the comparative example, the output of the example was improved by 3% compared to the comparative example.

This output improvement is considered to be based on the fact that the copper / III group element ratio of 1.25 in FIG. 2 is improved to 1.08.
According to the method of the present invention, it is possible to improve the power generation performance by reducing the group III element while reducing the copper component in the surface layer of the light absorption layer and thereby reducing the copper / group III element ratio.

  The process diagram of FIG. 1 shows a preferred example, and other than the process of the present invention can be changed as appropriate.

  The present invention is suitable for a method for manufacturing a solar cell having a chalcopyrite light absorption layer as a main element.

  DESCRIPTION OF SYMBOLS 10 ... Solar cell, 19 ... Chalcopyrite type light absorption layer (light absorption layer), 21 ... Aqueous solution, 23 ... Buffer layer.

Claims (3)

In a solar cell manufacturing method including a light absorption layer forming step of forming a chalcopyrite type light absorption layer containing copper and a group III element as a component, and a buffer layer formation step of forming a buffer layer on the light absorption layer,
After the light absorbing layer forming step and before the buffer layer forming step, the light absorbing layer is immersed in an aqueous solution containing zinc sulfate and ammonia to reduce the copper / III group element ratio of the surface layer of the light absorbing layer. The manufacturing method of the solar cell characterized by interposing the copper reduction process to be made.   The method for manufacturing a solar cell according to claim 1, wherein the group III element is indium and / or gallium.   The method for manufacturing a solar cell according to claim 1 or 2, wherein the concentration of the zinc sulfate in the aqueous solution is 4 to 10 mmol per liter.

Images