JPH0474480A - Solar cell and its manufacture - Google Patents

Abstract

PURPOSE:To increase outstandingly the conversion efficiency by using activated CdS or CdS-ZnS solid solution, as main composition, which was heat-treated and formed in the CdCl2, and by removing the surface layer of the n-type semiconductor connected with a light-absorbing layer with etching method. CONSTITUTION:On a translucent substrate 1 equipped with a transparent conductive layer, CdS or CdS-ZnS are laminated and vapor deposited, and a thin film of a semiconductor is formed. The thin film is exposed to vapor of CdCl2 at high temperatures and is activated. As a result, n-type semiconductor layer with the main composition of Cd or CdS-ZnS solid solution is formed. The surface layer of the n-type semiconductor is removed with etching method, and a window layer is formed, a light-absorbing layer 4 of a P-type semiconductor is formed on the window layer 3. In addition, anelectrode layer 5 is formed. After forming a film deposited with CdS, ZnS, and In by vapor at the same time, a CdS-ZnS solid solution film is obtained by activating treatment in the CdCl2 vapor. Then, the surface layer of the film is removed by sputter etching. As a result, a solar cell with excellent characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solar cell having a CdS or CdS-Z nS solid solution thin film as a light-transmitting window layer, and a method for manufacturing the same.

Conventional technologyIt is expected that energy supply will become increasingly difficult in the near future, and high efficiency and low cost of solar cells has become a major issue.Thin film solar cells, which can easily be made into large areas, have significantly lower costs. Therefore, it is strongly desired to improve the energy conversion efficiency. This thin film solar cell has a compound semiconductor (II-Vl group YI-111-VI
(Group 2) W4 film (D) is being widely developed. Solar cell structure using compound semiconductor thin film (N-type Cd as a window layer that has a wide band gap and transmits light)
S-based semiconductor layer and p-type CdTe-based or CuInSe2 as an absorption layer that has a narrow band gap and absorbs light.
A betero junction in which semiconductor layers are stacked is used. For example, IT○(■ndium T in
An n-type CdS layer and then a p-type CdTe layer are formed by vapor deposition on a glass substrate provided with 0xide), and finally metal electrodes are provided to form a solar cell. and sintering to form an n-type CdS layer, and then similarly screen printing and sintering to form a p-type CdS layer.
Finally, a metal electrode layer is provided on the Te layer to form a solar cell.

Wider bandgap CdS-Z instead of CdS
Using an nS solid solution thin film is very effective in increasing the amount of transmitted light and increasing the conversion efficiency. As a method for forming this CdS or CdS-Z nS solid solution thin film,
In our prior invention, we used CdS or CdS and ZnS.
Simultaneous force ＼ To show that high efficiency can be achieved by using a laminated vapor deposited film subjected to activation heat treatment in CdCb vapor at high temperature.Problems to be solved by the invention In this way, CdS or CdS-Z Although using an nS activated film as a window layer is effective in increasing efficiency, the conversion efficiency is still unsatisfactory. Especially the open circuit voltage V o
An improvement in o is desired.

Means for Solving the Problems In a solar cell having a laminated structure of a window layer of an n-type semiconductor and a light absorption layer of a p-type semiconductor, the n-type semiconductor is made of CdCl.
Activated CdS or Cd formed by heat treatment in 2 steam
The structure is mainly made of S-ZnS solid solution, and the surface layer in contact with the light absorption layer is removed by an etching method.

In addition, in a method for manufacturing a solar cell, a semiconductor thin film is formed by depositing CdS or CdS and ZnS simultaneously or in a layered manner on a transparent substrate provided with a transparent conductive layer, and the thin film is exposed to CdCla vapor at high temperature. Activated to form a semiconductor layer mainly composed of C(]S or CdS-ZnS solid solution.
The surface layer of the semiconductor layer is removed by an etching method to form a window layer, a P-type semiconductor light absorption layer is formed thereon, and an electrode layer is formed thereon.Constitution and manufacture of the solar cell of the present invention Depending on the method, the surface layer of the thin film mainly composed of activated CdS or CdS-ZnS solid solution is removed by etching, which reduces defects and areas with high impurity concentration, making it possible to form a good pn junction. Recombination at the joint surface is suppressed. As a result, the open circuit voltage V0° becomes higher and the conversion efficiency also becomes higher.

EXAMPLE The structure of a solar cell according to the present invention is shown in FIG. Reference numeral 1 denotes a transparent substrate, on which a transparent conductive layer 2 is provided.

Furthermore, a laminated structure of a window layer 3 made of an n-type semiconductor and a light absorption layer 4 made of a p-type semiconductor is formed thereon, and an electrode layer 5 is formed thereon to constitute a solar cell. The window layer 3 is mainly composed of activated CdS or CdS-ZnS solid solution formed by heat treatment in Cdc 12 vapor, and even if the surface layer in contact with the light absorption layer 4 is removed by an etching method, the manufacturing method (more transparent) On a transparent substrate 1 provided with a conductive layer 2, a semiconductor thin film is formed by depositing CdS or CdS and ZnS simultaneously or in a stacked manner, and the thin film is heated to CdCl2 at high temperature.
Activated by exposure to vapor of CdS or CdS-Z
An n-type semiconductor layer mainly composed of nS solid solution is formed, and its surface layer is removed by an etching method to form a window layer 3. A light absorption layer 4 of a p-type semiconductor is formed thereon, and an electrode layer 5 is formed thereon.
It forms the

Hereinafter, specific examples of the present invention will be described.

A C layer with a molar ratio of CdS and ZnS of 8:2 and a total thickness of 1.1 μm was placed on a glass substrate provided with a transparent conductive layer I'TO.
A simultaneous composite vapor deposition film of dS, ZnS, and In is formed. I
The amount of n is 0.1% based on the total amount of CdS and ZnS. This CdS, ZnS, and In hybrid film is heat-treated in CdCl2 vapor at 550° C. to cause solid solution formation and crystallization simultaneously (activation process), thereby effectively adding In. By forming a solid solution, the absorption edge wavelength shifts to the shorter wavelength side. Approximately 0.05 μm of the surface layer of this activated Cd@, 5Zns2S solid solution based n-type semiconductor layer is removed by sputter etching to form a window layer with a thickness of 5 μm on top.
A thick P-type semiconductor light absorption layer mainly made of CdTe is formed by vapor deposition, and a Cu electrode is formed thereon. For comparison, we also investigated the characteristics of solar cells formed in the same manner as above, except that sputter etching was not performed. Table 1 shows the characteristics of these solar cells with respect to irradiation light of AMl, 5 (84 mW 7 cm2). Note that Voc (V) is the release voltage, Jsc (mA7 cm2) is the closed-circuit electric fishing curve factor, and η (%) is the conversion. As shown in Table 1, the characteristics of the solar cell obtained by the method of the present invention are far superior to those obtained by the conventional method. This is CdS or CdS-ZnS whose surface layer has been removed by etching according to the present invention.
A solar cell equipped with an activated solid solution film is a prior invention (PAT1).
5. PAT17) solar cell CdS or CdS
This is thought to reflect the fact that there are fewer defects and impurities than in the −Z nS activated film, so there are also fewer recombination centers.

A solar cell was formed by forming a co-deposited film of C+jS, ZnS, and In in this way, and then removing the surface layer of the CdS-ZnS solid solution film obtained by performing activation heat treatment in CdCl2 vapor by sputter etching. has excellent properties. The etching method for the surface layer is not limited to the sputter etching method.In addition, as a method for forming a solid solution, ZnS and CdS:In may be deposited in layers, and a uniform composition can be obtained in the subsequent activation heat treatment process. Cd of
It becomes S-Z nS solid solution. At this time, In may be added to the ZnS evaporation source. Addition of In increases optical transmittance and electrical conductivity. CclS alone with LCdS and ZnS
Similar effects can be obtained by using a solid solution CdS-ZnS with a different composition ratio of L or by using A1 or Ga instead of In.

Effects of the Invention According to the present invention, it is possible to easily obtain an excellent solar cell with extremely high conversion efficiency. Since this solar cell is formed using a thin film, the cost can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a solar cell in one embodiment of the present invention. 1... Transparent substrate, 2... Transparent conductive screen 3...
Window 4...Light absorption #5...Name of electrode attorney Patent attorney Shigetaka Awano 1 person Figure 1

Claims (2)

[Claims] (1) In a solar cell having a stacked structure of an n-type semiconductor window layer and a P-type semiconductor light absorption layer, the n-type semiconductor is C
1. A solar cell mainly composed of activated CdS or CdS-ZnS solid solution formed by heat treatment in dCl_2 vapor, and characterized in that a surface layer in contact with the light absorption layer is removed by an etching method. (2) On a transparent substrate provided with a transparent conductive layer, CdS or CdS and ZnS are deposited simultaneously or laminated to form a semiconductor thin film, and the thin film is activated by exposing it to CdCl_2 vapor at high temperature. A semiconductor layer mainly composed of CdS-ZnS solid solution is formed, the surface layer of the semiconductor layer is removed by an etching method to form a window layer, a light absorption layer of a P-type semiconductor is formed on top of the window layer, and an electrode is formed on top of the window layer. A method for manufacturing a solar cell, comprising forming a layer.