JPS5936836B2 - Amorphous thin film solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an amorphous thin film solar cell with improved characteristics by using two types of amorphous semiconductor materials in combination.

In recent years, attempts have been made to effectively utilize solar energy from various fields, and active efforts have been made to develop solar cells as well as devices that use conventional single crystal semiconductors and thin film solar cells that use amorphous semiconductors.

Amorphous thin-film solar cells are actively being developed as a resource-saving, low-cost solar cell device by making the film thinner because the semiconductor substrate can be obtained through a relatively simple manufacturing process and the absorption coefficient is large. There is. This type of amorphous thin film solar cell is an amorphous semiconductor (hereinafter abbreviated as a-SiHx) thin film solar cell whose main constituents are silicon and hydrogen, which are created by glow discharge of monosilane (SiH4) gas. , and an amorphous semiconductor whose main constituents are silicon tetrafluoride (SiF4) and fluorine (hereinafter abbreviated as a-SiFx) created by glow discharge of silicon tetrafluoride (SiF4) gas.
Thin film solar cells have been put into practical use. The former a-SiHx
The amorphous thin film solar cell using a-SiF3c achieved a photoelectric conversion efficiency of 5.5% with the Schottky structure and 4.5% with the pin structure. has a Schottky structure, and a higher photoelectric conversion efficiency has been obtained.

Table 1 shows the physical properties of a-SiHx and a-SiFx, and FIG. 1 shows an example of the doping characteristics. a-SiFx has a minimum energy level density N(E) in the gear of 1016
cm-3 eV-1, 1017 cm-3 of a-SiHx
One order of magnitude smaller than eV-1.

It can be said that it is a higher quality intrinsic amorphous semiconductor than Bla-SiHx. However, looking at the doping characteristics, a-SiFx
Because it contains fluorine, the doping efficiency of the p-type dopant B (boron) is lower than that of a-SiHx, as shown in Figure 1, and the p-type electrical conductivity is 10-S to 10-2υ-1. a
-1 to 2 orders of magnitude smaller than 10-10 cm-1 of SiHx.

However, the electrical characteristics of the Ba-SiFxl tip type amorphous semiconductor are inferior to those of a-SiHx. Due to the above characteristics, a-SiFx has conventionally been used as a material for shot-type amorphous thin-film solar cells that do not use a p-type layer.
Although better solar cell characteristics have been obtained than those using a
-Since SiFxOp type cannot be obtained, it has been rejected.
On the other hand, a-SiHc provides a more effective p-type amorphous semiconductor than a-SiFx, but the photoelectric conversion efficiency of a Pn structure or Pin structure solar cell using only a-SiHx is normal. In the manufacturing method of 2.0 to 2.5%, the maximum value was 4.5% in a micro-area cell. The present invention was made in view of the problem of improving the photoelectric conversion efficiency of Pn structure or Pin structure amorphous thin film solar cells in the above-mentioned conventional devices,
An n-type layer made of a-SiFx whose minimum energy level density in the gap is smaller than that of a-SiHx or an intrinsic layer that is not doped with impurities (hereinafter referred to as i-type), and a p-type layer (a-SiFx<7) Better quality than A-SiHx
By combining p-type layers created from Pn structure or P
This is an in-structure amorphous thin-film solar cell with improved light and electricity conversion efficiency.

Furthermore, amorphous a-Sillx. ! Since the interface with -a-SiFx is amorphous with Si as its main component, there is no adverse electrical effect due to the difference in lattice constants as in single-crystal silicon. FIG. 2 shows a specific example of the Pin structure amorphous thin film solar cell according to the present invention.

In the figure, 1 is a glass substrate, and 1. T. O(In
, O, -SnO,) transparent conductive film 2 at a substrate temperature of 250 to 4
Formed by electron beam evaporation at 50°C.

Next, phosphine gas (PH, /H,, lOO ~ 500 vppm) was added to a hydrogen gas-based mixed gas (SiF, /H,) with 60 to 95% silicon tetrafluoride gas SiF4 added.
) is used as a raw material, and n+ type a-SiF is produced by low-pressure glow discharge (operating pressure 0.2 to 10 t0rr).
x (hereinafter referred to as a-SiFO(n+)) layer 3 from 100 to
Form 300A. Next, silicon tetrafluoride mixed gas (SiF4/H,) without phosphine gas added was used as a raw material, and almost intrinsic a-SiFx was produced by low-pressure glow discharge.
(hereinafter referred to as a-SiFx (1)) layer 4 is 5000 to 1
0000λ is formed. Next, a mixed gas (SiH4) containing 10% monosilane gas (SiH4) added to a hydrogen gas base.
/H2) with a small amount of diborane gas (B, H6/H,) added as a raw material, p+ type a is produced by low-pressure glow discharge.
-SiHx (hereinafter referred to as a-SiHx (p+)) layer 5 having a thickness of about 300 to 500λ is formed. These amorphous films are formed at a substrate temperature of 250 to 350°C and a pressure of 0.5 to 10 t0r.
The growth rate was 1 to 4 λ/Sec. Next, an aluminum electrode 6 is formed by mask evaporation with a thickness of 1 to 5 μm using an electron beam evaporation device. 1. configured as above. T. O/a-Si
Fx(n+)/a-SiFx(1)/a-SiHx(p
+)/Al structure amorphous thin film solar cell is a conventional a-S
Compared to a Pin structure amorphous thin film solar cell using only iHx, better characteristics were obtained in terms of open circuit voltage, short circuit current, and conversion efficiency. That is, the device obtained by the present invention
Under O, open circuit voltage 0.75V, short circuit current 16mA
/D, FF=0.65, and photoelectric conversion efficiency=5.6%. In addition, in the Pin structure amorphous thin film solar cell made only of a-SiHx, the i-layer, that is, the a-SiHx (1) obtained by glow discharge of only monosilane gas (SiH4/H2) without doping, is of weak n-type. , Pi
A junction exists at the boundary between the p layer and the i layer within the n structure.

Also, the depletion layer is 0.2 to 0.5 in a-SiHx (1).
Since the width is on the order of μm, considering that the diffusion length of the carrier in a-SiHx (1) is short, the Pin structure is formed from the light-receiving surface side by a-SiHx (p+)/a-SiHx (
1)/a-SiHx(n+). On the other hand, the Pn or Pin structure amorphous thin film solar cell using a-SiFx (1) of the present invention has a-SiFx (1)
is a weak n-type like a-SiHx(1), but the minimum energy level density in the gap is a-SiHx(1).
The depletion layer is one order of magnitude smaller than that of a-SiHx (1), and the depletion layer is larger than that of a-SiFC. i) The diffusion length of the carrier in
-SiHx (1) Since it is several times longer than that in (1), a-RiFx is
(n+)/a-SiFx(IVa-SilIx(P+)
or vice versa, a-SiHx(p+)/a
-SiFx(1)/a-SiFx(n+). FIG. 3 shows an amorphous thin film solar cell having a-SiHx (p+)/a-SiFx (1)/a-SiFx (n+) from the light-receiving surface side. In this case, ITO2' and a-SiH
About 10 a-SiFx(n+)7 is added between x(p+)5'
0A is inserted. This is ITO2′ and a-SiHx
The purpose is to avoid direct contact with (p+)5″ and improve the contact characteristics between ITO and Pin cells.1a-SiHx
The contact between (p+) and a-SiFx (n+) is ohmic. As described above, according to the present invention, an amorphous semiconductor thin film made from monosilane and an amorphous semiconductor thin film made from silicon tetrafluoride, which have conventionally been treated as different amorphous semiconductor materials, can be made from different materials. By effectively utilizing the characteristics possessed by Pn or Pin structure to form an amorphous thin film solar cell, the photoelectric conversion efficiency can be significantly improved, and the effective use of solar energy can be greatly improved as a low-cost solar cell device. It is something to move forward with.

[Brief explanation of drawings]

Figure 1 shows the doping characteristics of amorphous semiconductors, Figure 2 shows the doping characteristics of amorphous semiconductors.
The figure is a sectional view showing one embodiment of the present invention, and FIG. 3 is a sectional view showing another embodiment of the invention. 2: Transparent conductive film, 3: P-type layer made from a-SiHx, 4: I-type layer made from a-SiFx, 5: a-
n-type layer made from SiFx, 6: electrode.

Claims (1)

[Claims] 1. In an amorphous thin film solar cell having a pn structure or pin structure as a base unit, an amorphous film whose main constituents are silicon and hydrogen, which is created by glow discharge of monosilane (SiH_4) as a p-type amorphous semiconductor. An n-type or intrinsic amorphous semiconductor is made of an amorphous semiconductor material whose main constituents are silicon and fluorine created by glow discharge of silicon tetrafluoride (SiF_4). An amorphous thin film solar cell featuring: