JP3100692B2 - Method for manufacturing CuInSe2-based photoelectric conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a photoelectric conversion device using chalcopyrite type CuInSe ₂ which is a direct transition semiconductor capable of forming a thin film and having a large light absorption coefficient over a wide wavelength range. Is p
The present invention relates to a method for manufacturing the photoelectric conversion element, wherein a surface treatment of a CuInSe ₂ layer is performed before an n-junction is formed to improve photovoltaic power of the element.

[0002]

_2. Description of the Related Art In a conventionally known method for manufacturing a CuInSe ₂ -based photoelectric conversion element, when an n-type semiconductor layer is laminated on a p-type CuInSe ₂ layer and pn junction is performed, 2%
Etching with bromine-methanol solution containing bromine [Solar
Cells, 16 , 529 (1986)], and etching with an aqueous bromine solution [US Pat. No. 4,909,863] for the purpose of in-plane uniformity of characteristics.

However, the etching with a bromine-methanol solution is difficult to control the etching amount due to the high etching rate, and is not suitable for etching a CuInSe ₂ thin film.

[0004] Further, Cu for the purpose of uniforming the characteristics in the plane is used.
When performing etching with a bromine aqueous solution for smoothing the surface of the InSe ₂ film, the etching must be performed with a thickness of about 0.1 to 1.5 μm.
For example, it has never been considered to perform the method for a thin film having a thickness of 0.1 μm or less.

Further, in order to perform etching of a thickness of 0.1 to 1.5 μm in a relatively short time, the bromine concentration of the aqueous bromine solution needs to be 0.02 mol / l or more. In the etching process, a relatively large amount of bromine must be used, and there is a problem in terms of safety and economy.

[0006]

As described above, the conventional etching method using an aqueous bromine solution requires a Cu film having a sufficient film thickness.
The purpose of this is to smooth the surface of the InSe ₂ film.
m or less could not be used for ultra-thin films.

On the other hand, in the present invention, CuIn
When producing a Se ₂ -based photoelectric conversion element, C
The uInSe ₂ thin film is subjected to an etching process, and this process must be an etching method that can be performed more safely and economically than before.

[0008]

The present inventors have SUMMARY OF THE INVENTION The intensive research to solve the斯Ru problem, was the photoluminescence measurement for a sample before and after etching of the CuInSe ₂ film, the surface of the CuInSe ₂ film It has been found that the impurity level concentration on the surface is substantially reduced only by etching very thinly, thereby providing the present invention.

That is, the present invention provides a p-type CuIn
In manufacturing a photoelectric conversion element in which an n-type semiconductor layer is laminated on a Se ₂ thin film layer to form a pn junction, a bromine aqueous solution having a bromine concentration of 0.01 mol / l or less is used before laminating the n-type semiconductor layer. The present invention relates to a method for producing a CuInSe ₂ -based photoelectric conversion element, characterized in that the photoelectromotive force of the element is improved by etching away the surface of the CuInSe ₂ thin film layer with a very small thickness of 100 to 500 ° (angstrom). It is.

[0010]

Generally, p-type CuInSe ₂ and CdS or ZnO
When a photoelectric conversion element is manufactured by forming a pn junction with an n-type semiconductor such as described above, it is considered that if the surface impurity level concentration of p-type CuInSe ₂ is large, the interface state concentration also increases at the pn junction interface. I have. In this case, if the interface state concentration is high, electrons and holes generated by absorption of light energy, for example, often recombine via the interface state, and as a result, generation of photovoltaic power occurs. And the sensitivity of the photoelectric conversion element was poor. Therefore, CuInS
to improve the sensitivity of e ₂ based photoelectric conversion element, CuInSe
One of the problems was to reduce the surface impurity level concentration of No. ₂ .

The present inventors have studied various methods for reducing the surface impurity level concentration of CuInSe ₂ .
It has been found that etching with an aqueous bromine solution having a relatively low etching rate is effective.

Therefore, a thickness of 0.5 formed on a glass substrate is required.
A μm CuInSe ₂ film was etched at about 200 A with an aqueous bromine solution having a bromine concentration of 0.005 mol / l, and changes in photoluminescence before and after etching were examined. FIG. 1 shows the measurement results when a Kr laser beam having a wavelength of 647 mm was used as the excitation light in this test. As can be seen from FIG. 1, 0.9 eV (approximately
It was recognized that the peak position near 1.35 μm) shifted to the longer wavelength side.

The peak near 0.9 eV is considered to be the luminescence due to the transition between the donor and the acceptor [see, for example, Solid State Communications, 18 , 395 (197
6)], the following equation holds between the luminescence energy hν and each impurity level. Formula: hν = Eg− (Ed + Ea) + e ² / εr Eg: Forbidden band width of semiconductor Ed: Energy difference between bottom of conduction band and donor level Ea: Energy difference between top of valence band and acceptor level e: Electron Charge ε: Dielectric constant r: Distance between donor and acceptor

In this case, when the number of donors and acceptors is large, r is short and hν is large on average, but when the number of donors and acceptors is relatively small, r is averaged.
Becomes longer and hν becomes smaller.

Therefore, when the spectrum of the etched CuInSe ₂ is observed as described above, 0.9e
Peak position long wavelength side in the vicinity of V, i.e. that has moved to a lower energy side, CuInSe ₂ When film deposition of, Ya donor believed to have been present in a large amount on the film surface near than the interior of the CuInSe ₂ film It is presumed that the acceptor was removed by etching.

That is, the CInSe ₂ film surface is gently etched using a low-concentration aqueous solution of bromine to form C
It is considered that the surface impurity level concentration of the uInSe ₂ film could be reduced. Actually, when a photoelectric conversion element manufactured by laminating a CdS film on a CuInSe ₂ film subjected to such etching treatment was used, a significant improvement in photovoltaic power was confirmed as compared with a conventional product without treatment.

Hereinafter, the present invention will be described in detail with reference to embodiments.

[0018]

Example 1 A glass plate with a Mo sputtered film having a thickness of about 0.1 μm was used as a substrate, and Cu was applied on the substrate at 600 A and In.
Were sequentially laminated by 1,400 A vapor deposition. Then, the Cu, I
A 0.5 μm-thick p-type Cu film is formed on a substrate by vapor-phase selenization in which the n-layered film is heated at 400 ° C.
An InSe ₂ film was produced.

On the other hand, an aqueous solution having a Br ₂ concentration of 0.005 mol / l and a KBr concentration of 150 g / l is prepared in advance, and the p
The CuInSe ₂ film is immersed for 10 seconds to obtain CuInSe ₂
The film surface was etched away by 200A. Next, after washing with pure water and drying, the non-doped C is added to the CuInSe ₂ film.
dS of 2,000A, and further In-doped CdS of 8,
Each of 000 A was vapor-deposited to produce a photoelectric conversion element.

[0020] The resulting photoelectric conversion element is irradiated with a halogen lamp light was measured photovoltaic, CuInSe ₂
It was confirmed that the open-circuit voltage and the short-circuit current were increased about 3 times and about 2 times, respectively, as compared with the photoelectric conversion element manufactured without etching the film, and as a result, the photovoltaic power was increased about 6 times.

[0021]

Comparative Example 1 A p-type CuInSe ₂ film having a thickness of 0.5 μm was formed on a glass substrate having a Mo film by the same means as in Example 1.

On the other hand, an aqueous solution containing a Br ₂ concentration of 0.02 mol / l and a KBr concentration of 150 g / l is prepared in advance, and the p-type CuInSe ₂ film is immersed in this solution for 10 seconds to obtain CuIn.
The surface of the Se ₂ film was removed by 0.1 μm. Next, after washing with pure water and drying, CuInSe was
CdS was laminated on the _two films to produce a photoelectric conversion element.

When the obtained photoelectric conversion element was irradiated with a halogen lamp light and the photoelectromotive force was measured, CuInSe ₂
The open-circuit voltage and the short-circuit current were almost the same as those of the photoelectric conversion element manufactured without performing the above etching, and no improvement in the photovoltaic power was observed after all.

The following can be considered as the reasons why the effect of improving the photovoltaic power did not appear as compared with the etching of the first embodiment. (1) CuInSe due to too high etching rate
₂ Deterioration due to etching of the film surface. (2) If the CuInSe ₂ film has a partly thin portion due to an excessive amount of etching, the etching there reaches Mo as a base, and Mo and C are stacked during CdS lamination.
dS is in direct contact and short-circuited.

From the above results, in the method of the present invention, from the viewpoint of controllability of the etching amount and prevention of excessive etching, the bromine concentration of the bromine aqueous solution is set to 0.01 mol / l or less, and the etching amount is 100 to 500 A in thickness. It was confirmed that it was necessary to use a very small amount.

[0026]

Effect of the Invention Conventionally, when forming a pn junction with the CuInSe ₂ film, there was be etched using relatively high concentrations of bromine-containing solution as a pretreatment for CuInSe ₂ film, Ya safety There were problems with economics,
Due to the high etching rate, it was not suitable for processing thin films. However, the method of the present invention can solve the above problem by only etching the surface of the CuInSe ₂ film very thinly using a low-concentration aqueous bromine solution.
A uInSe ₂ -based photoelectric conversion element can be manufactured.

[Brief description of the drawings]

FIG. 1 is a spectrum diagram of photoluminescence of CuInSe ₂ showing the effect of an etching process.

Continued on the front page. (72) Inventor Kazuto Ito 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Eiji Kikuchi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-2-177572 (JP, A) JP-A-64-7526 (JP, A) US Pat. No. 4,099,863 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01L 31/04-31/078 H01L 21/306-21/308

Claims (1)

(57) [Claims] 1. A p-type CuInSe ₂ thin film layer on a substrate has n
In by stacking type semiconductor layer for manufacturing a photoelectric conversion element to form a pn junction, concentrated bromine before stacking the n-type semiconductor layer
Using a bromine aqueous solution having a degree of 0.01 mol / l or less
By etching away the surface of the Se ₂ thin film layer with a very small thickness of 100 to 500 ° (angstrom) ,
CuInSe ₂ characterized by improving photovoltaic power
Method for manufacturing a photoelectric conversion element.