Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
2000-09-18
2002-04-09
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
C257S072000
Reexamination Certificate
active
06368944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a photovoltaic element using a non-monocrystalline semiconductor, and a method of and an apparatus for continuously forming the non-monocrystalline semiconductor layer of the photovoltaic element by the plasma CVD method. Particularly, it relates to a method of and an apparatus for mass producing photovoltaic elements such as solar cells using a roll to roll apparatus.
2. Related Background Art
There are various means for improving the photoelectric conversion efficiency of a photovoltaic element using a non-crystalline semiconductor, and it is necessary to improve the characteristics of a p type semiconductor layer, an i type semiconductor layer, an n type semiconductor layer, a transparent electrode, a back electrode, etc. constituting a photovoltaic element using the pin type semiconductor junction.
Particularly, regarding a so-called doping layer such as a p type semiconductor layer or an n type semiconductor layer, it is first required that the density of an activated acceptor or a donor be high and activating energy be small. Thereby, the diffusing potential (built-in potential) when the pin junction is formed becomes great and the open voltage (Voc) of the photovoltaic element becomes great, and photoelectric conversion efficiency is improved.
Next, the doping layer basically does not contribute to the creation of a photocurrent and therefore, it is required that this layer not hinder the incidence of light onto the i type semiconductor layer creating a photocurrent. In order to reduce the absorption by the doping layer, it is important to make the optical band gap wide and make the film thickness of the doping layer small.
As the material of the doping layer having the characteristics as described above, mention may be made of group IV semiconductor material such as Si, SiC, SiN or SiO. Materials in a non-crystalline or microcrystalline form have been studied.
Above all, group IV semiconductor alloy materials having a great band gap have been considered to be suitable because of their small absorption coefficient, and microcrystalline or polycrystalline semiconductor materials have been considered to be suitable because of their small absorption coefficient and small activating energy.
On the other hand, it is required that the interfacial level on the junction interface of homogeneous or heterogeneous junction formed between the doping layer and the i type semiconductor layer be small.
However, the grating consistency between the i type semiconductor layer and the microcrystalline or polycrystalline p type semiconductor layer is not good and therefore, a junction interfacial level is created.
Therefore, a significant reduction in the running property of carries and fill factor (FF) exists and improvement therein has become a task.
As a method of improving mass productivity, a continuous plasma CVD method adopting a roll to roll system is disclosed in U.S. Pat. No. 4,400,409.
According to this method, with a long belt-like member as a substrate, the substrate is continuously conveyed in the lengthwise direction while electrically conductive type semiconductor layers required in a plurality of glow discharging areas are accumulated and formed. An element having semiconductor junction can thus be continuously formed.
FIG. 8
of the accompanying drawings is a schematic view of a typical plasma CVD apparatus of the roll to roll type for successively laminating n, i and p type semiconductor layers to thereby form a photovoltaic element of the single cell type.
The reference numeral
801
designates the whole of an accumulated film forming apparatus. The reference numeral
802
denotes a long electrically conductive magnetic material belt-like member, the reference numeral
803
designates a pay-away chamber for the belt-like member, the reference numeral
804
denotes a take-up chamber for the belt-like member, and the reference numerals
805
to
807
designate accumulated film forming chambers, the reference numeral
805
denoting a chamber for forming an n type layer, the reference numeral
806
designating a chamber for forming an i type layer, and the reference numeral
807
denoting a chamber for forming a p type layer. The reference numeral
809
designates a discharge space. The reference numeral
808
denotes a gas gate, and the reference numerals
810
and
811
designate bobbins.
The procedure of forming semiconductor film will hereinafter be described with reference to FIG.
8
.
The accumulated film forming apparatus
801
has the pay-away chamber
803
for the belt-like member
802
and the take-up chamber
804
for the belt-like member
802
disposed at the opposite ends thereof. The accumulated plasma CVD film forming chambers
805
,
806
and
807
by the plasma for forming a plurality of semiconductor layers are connected in series through the gas gate
808
between the pay-away chamber and the take-up chamber. Scavenging gas such as H
2
gas is introduced into the gas gate
808
and forms a pressure barrier relative to the accumulated film forming chambers at the opposite ends, and the diffusion of the gas between the chambers can be prevented, and this forms a feature of the roll to roll type film forming apparatus. A material gas is supplied to each accumulated film forming chamber, and discharge can be caused in the discharge space
809
by the inputting of high frequency wave or microwave electric power.
Also, each accumulated film forming chamber has exhaust means and a pressure regulating valve and can be maintained in a reduced pressure state of predetermined pressure.
In actual film formation, the long belt-like member
802
is paid away from the pay-away chamber
803
and is passed over the pay-away chamber
804
, and semiconductor layers can be successively accumulated and formed in the discharging space of the accumulated film forming chambers
805
,
806
and
807
while the belt-like member
802
is continuously paid away and moved.
Also, a photovoltaic element of the tandem cell type can be made by adopting a chamber construction in which the n, i and p type layer forming chambers are repetitively arranged.
SUMMARY OF THE INVENTION
So, the present invention has as its object to provide a photovoltaic element in which the junction interface between a non-crystalline i type layer and a microcrystalline electrically conductive type layer has good grating consistency and which has an excellent current-voltage characteristic and excellent photoelectric conversion efficiency by the use of a roll to roll apparatus for improving mass productivity, and a method of and an apparatus for continuously mass-producing such photovoltaic elements.
The photovoltaic element of the present invention is a photovoltaic element comprised of a semiconductor-junctioned element, characterized in that the element includes a first electrically conductive type semiconductor layer, a non-crystalline i type semiconductor layer, a microcrystalline i type semiconductor layer and a second electrically conductive type semiconductor layer comprising microcrystal, and is pin-junctioned.
The photovoltaic element of the present invention is characterized in that the semiconductor layers thereof are formed chiefly of silicon, and the non-crystalline i type semiconductor layer includes germanium. Also, the photovoltaic element of the present invention is characterized in that the element is constructed so as to have a plurality of pin junctions.
Also, the photovoltaic element of the present invention is characterized in that the second electrically conductive type semiconductor layer is constructed so as to be located on the light incidence side.
Also, it is characterized in that the second electrically conductive type semiconductor layer is a p type layer.
Also, it is preferable that the layer thickness of the microcrystalline i type semiconductor layer be 50 to 100 Å.
Also, it is preferable that the layer thickness of the microcrystalline p type semiconductor layer be 80 to 150 Å.
Also, it
Fujioka Yasushi
Hori Tadashi
Kanai Masahiro
Kohda Yuzo
Okabe Shotaro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hoang Quoc
Nelms David
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