JPH0474442A - Manufacture of cds-zns solid-solution thin film - Google Patents

Abstract

PURPOSE:To make a defect small, to make a mobility high and to make a resistance low by a method wherein CdS and ZnS are vapor-deposited simultaneously on a light-transmitting substrate to form a semiconductor thin film, the film is exposed to a vapor of CdCl2 at a high temperature, the film is activated and a solid solution is formed. CONSTITUTION:ZnS and CdS:In are vapor-deposited on a glass substrate by using two evaporation sources; a hybrid vapor deposition film of ZnS, CdS and In in a total thickness of 1.1mum is formed in a molar ratio of CdS to ZnS of 8:2. The amount of In is set at and 0.1 to 2mol% against the total of CdS of and ZnS. The hybrid film of ZnS, CdS and In is heat-treated in a saturated vapor of CdCl2; it is changed to a solid solution and is crystallized (activation process); In is added effectively. When it ts changed to the solid solution, an absorption edge wavelength is shifted to the side of a short wavelength. When the film formed by simultaneously vapor-depositing ZnS, CdS and In is activated and heat-treated in the vapor of CdCl2, it is possible to obtain a solid-solution film whose characteristic is excellent. Even when a solid solution of CDS-ZInS having other compositional ratios of CdS to ZnS is used, and even when Al or Ga is used instead of In, the same effect can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides Cd which is effective for use in light-transmitting window layers of solar cells, etc.
The present invention relates to a method for manufacturing an S-ZnS solid solution thin film.

Conventional technologyIt is expected that energy supply will become increasingly difficult in the near future, and increasing the efficiency and lowering the cost of solar cells has become a major issue.Thin-film solar cells, which can easily be made into larger areas, have significantly lower costs. There is a strong desire to improve the energy conversion efficiency. This thin-film solar cell has compound semiconductors (II-VI group, III-VI2
Types using thin films are being widely developed. Structure of a solar cell using a compound semiconductor thin film (table) An n-type CdS-based semiconductor layer as a window layer that has a wide band gap and transmits light, and a p-type CdTe-based semiconductor layer that has a narrow band gap and serves as an absorption layer that absorbs light. Alternatively, a beta junction in which CuIn5e=based semiconductor layers are stacked is used.For example, ITO (Indium Tin 0
An n-type CdS layer and then a p-type CdTe layer are formed on a glass substrate provided with an oxide (xide) by a vapor deposition method, and finally a metal electrode is provided to form a solar cell. Alternatively, an n-type CdS layer is formed on a glass substrate by screen printing and baking, then a p-type CdTe layer is formed by screen printing and baking, and finally a metal electrode layer is formed to form a solar cell.

C(]5− with wider bandgap instead of CdS
Using a ZnS solid solution thin film is very effective in increasing the amount of transmitted light and increasing the conversion efficiency.

The method for forming this CdS-ZnS solid solution thin film is to evaporate CdS and ZnS independently from two precisely temperature-controlled evaporation sources and deposit them on a substrate to form a solid solution thin film. Furthermore, in order to make the solid solution thin film I'L even lower in resistance, a donor impurity such as In is simultaneously evaporated from another evaporation source and added into the solid solution thin film. The composition distribution in the depth direction of the film formed in this way is C mountain Zλ S,
In order to form a window layer made of a low-resistance semiconductor thin film with a wide bandgap, the ratio of In etc. must be constant or the gradient distribution must be precisely controlled. In order to maintain the ratio at a predetermined value in the depth direction, two to three evaporation sources whose temperatures are precisely controlled are required.

Means for Solving the Problems CdS and ZnS are simultaneously deposited on a transparent substrate to form a semiconductor thin film, and this thin film is activated by exposing it to CdCl2 vapor at a high temperature to form a solid solution.

Effect: According to the method of the present invention, CdS- with a wide bandgap
ZnS and CdS are deposited using inexpensive evaporation equipment to form a ZnS solid solution thin film.
A film deposited simultaneously by two sources (the ratio of the deposition rate of both is not constant, but the molar ratio of the total amount should be constant), that is, a film deposited with non-uniform composition in the depth direction is formed using CdCl2.
A solid solution can be easily formed by activation heat treatment in steam, and since it is an activated film, it has far fewer defects, higher mobility, and lower resistance than a vapor-deposited film. By adding In or the like, it is possible to further lower the resistance, which is effective for increasing the efficiency of solar cells.

Example The present invention will be explained in detail below.

ZnS and CdS:In were simultaneously evaporated onto a glass substrate (Corning, #7059) using two evaporation sources, with a molar ratio of CdS and ZnS of 8:2 and a total thickness of 1.
．． A 1 μm thick ZnS, CdS, and In mixed vapor deposited film was formed.The amount of In was 0 and 0.1 to 2 mol% based on the total amount of CdS and ZnS.This Z-nS, CdS,
The In hybrid film is heat-treated in CdC15 saturated vapor at 450-650°C to form a solid solution and simultaneously cause crystallization (
(activation process), effective addition of In is performed. The absorption edge wavelength shifts to the short wavelength side due to solid solution formation, and the solid solution formation is insufficient below 450°C, and the transmittance is poor above 650°C. Spectral transmittance of a film activated at 4450 to 650°C As shown in Table 1, NiCr/Au vapor deposited electrodes were provided on the solid solution film activated at 550°C.
The electrical conductivity properties measured by the method of
Shown in the table. Spectral transmittance is Tr%), electrical conductivity is σ(
Ω-' cm-1, the number of carriers is n (cm-3),
Mobility is shown in μ (cmI-'5ee-') For comparison, CdS, Z
Simultaneous vapor deposition of nS and In (substrate temperature 150°C) L, 400
As shown in Table 1 and Table 2, the properties of films annealed at
This is considered to reflect that the solid solution film formed by the activation method has fewer defects.

Therefore, the mobility is much higher than that of the solid solution film of the conventional method, and a solid solution film with excellent properties can be obtained by subjecting a film formed by co-evaporation of ZnS, CdS, and In to activation heat treatment in CdCl2 vapor. ZnS, CdS, In
are simultaneously deposited without precise control, that is, there may be compositional unevenness in the depth direction, but the composition becomes uniform in the subsequent activation heat treatment process. In addition, In may be added to the lnS evaporation source, or may be added by evaporation from a separate source for simultaneous evaporation of CdS and ZnS. % Using solid solution CdS-ZnS with other composition ratios of CdS and ZnS, L and In
Similar effects can be obtained by using Al or Ga instead.

Effects of the Invention The present invention has the following advantages: Wider bandgap effective for improving conversion efficiency using inexpensive equipment ＼ Low resistance Cds-Z
It becomes possible to easily form an nS solid solution thin film. This is effective in improving the conversion efficiency and reducing costs of solar cells.

Claims (2)

[Claims] (1) On a transparent substrate, CdS and ZnS are simultaneously deposited to form a semiconductor thin film, and the thin film is coated with CdCl at high temperature.
A method for producing a CdS-ZnS solid solution thin film, which comprises activating it and forming a solid solution by exposing it to the vapor of _2. (2) The CdS-Zn according to claim 1, wherein the semiconductor thin film contains In, Ga, or Al in advance.
Method for producing S solid solution thin film.