JPS62276884A - Thin film solar cell element - Google Patents

Abstract

PURPOSE:To enhance electrical characteristics of solar cell element by using silicon carbide hydride (fluorination) thin film, in which amorphous and crystallite phases are mixed as a p-type semiconductor thin film of an optical incidence side. CONSTITUTION:Hydride (fluorination) p-type SiC (p-type muc-SiC: H (:F)), in which crystallite and amorphous phases are mixed at least as window layers of pin-types solar cells is used. Accordingly, conductivity can be improved by maintaining a wideband gap to inhibit a power loss due to a series of resistance components in a solar cell element, thereby utilizing effectively incident lights at i layer 3 where a further active layer is obtained. The use of p-type SiC enables a thin film solar cell element to have the high collecting efficiency of lights.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention <Industrial Application Field> The present invention relates to a thin film solar cell element with further improved performance in a solar cell based on amorphous silicon.

<Conventional technology> In recent years, thin-film solar cells using amorphous Noricon as a matrix have been rapidly put into practical use as low-cost solar cells, and photoelectric conversion efficiencies exceeding 10% have been reported at the laboratory level. There is. Many of these high-performance amorphous solar cells use p-type amorphous SiC as the light incident side and are of the pin type or (pin) type.
X=2. 3-) type, and it is said that it is advantageous to have the p-type layer on the light incident side from the viewpoint of device reliability.

However, as mentioned above, the photoelectric conversion efficiency of thin-film solar cells based on amorphous silicon is around 12% at the laboratory level, and the conversion efficiency of crystalline solar cells is around 20%. This is far beyond the level of current performance, and further improvements in performance are considered necessary.

<Problems to be Solved by the Invention> As already mentioned, L near-morphous solar cells based on the pin type conventionally use hydrogenated amorphous silicon carbide (hereinafter abbreviated as a-SiC0H) as the p-type window layer.
has been used. This p-type a-SiC:H is considered to have the following advantages and disadvantages. It is true that p-type a-SiC:) (has a smaller optical bandgap (
E0p') is thick (E for p-type a SiC:H
0pt<18eV, p-type a-SiC:H with E0p'>
1.8 eV), it can increase the efficiency of light utilization in the intrinsic (type 1) layer, which is the photoelectric conversion active layer, and is also expected to have the effect of suppressing back diffusion of photogenerated carriers (electrons) due to the wide band gap. can. Figure 4 shows the thin film solar cell (cell) based on this difference in Eopt from the perspective of effective use of light.
These are the calculation results of simulating the light collection efficiency for each wavelength of light. From the figure, Eopt ranges from 1.8eV to 2.
It can be seen that the collection efficiency in the short wavelength region of 500 nm or less is improved by expanding the range to 0 eV. Furthermore, p layer E
The calculation results when opt becomes larger are shown in FIG. 4, and the collection efficiency tends to be further improved.

However, on the other hand, there were problems as shown below. Figure 5 shows an amorphous solar cell (100 mW/am2) when a p layer with various p op E as described above is used as a window layer of an actual amorphous solar cell.
These are the cell characteristics results. Open circuit voltage V. C is p-type a-Si
The E Opt is improved as the E Opt becomes larger due to an increase in the (apparent) diffusion potential due to the wide bandgap of C.H. The short-circuit 11 flow Jsc also shows a monotonous increasing trend due to the reduction in the ρ type a-3iC:H absorption loss, etc., which is expected from the calculation results shown in FIG. However, H
Since the fill factor FF of the V curve starts to decrease from around Eo p t~1.9eV, the photoelectric conversion efficiency y7(-J xV
FF) is co p tsc oc
g~2. OeV becomes maximum.

The present inventors believe that the main cause of the decrease in the fill factor FF as described above is that the electrical conductivity of p-type a-SiC:I (E0pt>2
．． It decreases rapidly at OeV, lXl0-'(Ωcm)-'
It was found that the main cause was the appearance of loss due to series resistance as shown below. The table shows the p layer (thickness ~100
The power loss due to the electrical conductivity of the human body and the series resistance of the p-layer in the solar cell element is estimated. 10'
(Ωcm)"-' conductivity, a loss of ~1% occurs, and 10
It is calculated that even a cell with a photoelectric conversion efficiency of 10% has a loss of about 10%.

Table In view of the above-mentioned problems, an object of the present invention is to
The object of the present invention is to improve the electrical properties of C:H in order to make the most of its good optical properties, thereby providing a thin film solar cell with even higher performance.

Means for Solving the Problems> The thin film solar cell element according to the present invention is made of n-type, i (intrinsic) type, and p-type hydrogenated (fluorinated) amorphous silicone (a
A pin type or pinpin-((pin)) is a stack of semiconductor thin films based on -SiC.H(:F)).

In X=2.3...) type thin film solar cells, the p-type semiconductor thin film on the light incident side is made of hydrogenated (fluorinated) noricon carbide (p-type μc-S) containing a mixture of amorphous and microcrystalline phases. It is characterized by using an iC:H(:F)) thin film.

Effect> In the p-type μc-SiC:H(:F) thin film on the light incident side, the conductivity improves without decreasing the optical bandgap, so the series resistance within the solar cell element decreases. , power loss is reduced. Furthermore, the diffusion potential also increases. As a result, the photoelectric conversion rate increases.

<Example> As an example of the present invention, hydrogenated (fluorinated) SiC containing a mixture of microcrystalline phase and amorphous phase was used as a p-type semiconductor thin film.
We aim to apply (p-type μc-SiC:H(:F)) to the window layer of amorphous solar cells, especially TCO/pin.
/The effect will be explained in the case of a substrate type solar cell element.

The cell structure of such a solar cell element is shown in FIG. For example, stainless steel or the like is used as the substrate 1, and a layer 2 of n-type hydrogenated amorphous silicon or hydrogenated (fluorinated) silicon containing a mixture of n-type microcrystalline and amorphous phases is formed thereon by a glow discharge method or a photo-CVD method. 20~l
It is deposited in the range of oom. Next, an intrinsic (1) type hydrogenated amorphous silicone (a-S
i:H) Layer 3 is laminated to a thickness of 400 to 700 nm.

Furthermore, hydrogenated (fluorinated) p-type 5ic (p-type μc-SiC:H(:F)) with a mixture of microcrystalline phase and amorphous phase
The above TCO/pin is obtained by laminating layers 4 in a range of 3 to 20 nm, and finally forming a transparent conductive film (TC○) 5 and an AQ layer 6.6 as a collector electrode in sequence by EB method or sputtering method. /A substrate type thin film solar cell can be created.

Microcrystallization of amorphous silicon can be easily obtained especially in impurity-doped films (p-type, n-type), and can dramatically improve conductivity (1xlO
-'(Ωcm)-') is possible.

The present inventors have applied this method to p-type amorphous silicon carbide, which makes it possible to utilize the wide optical bandgap of hydrogenated (fluorinated) p-type SiC even more effectively. . Therefore, as at least the window layer of a pin solar cell, hydrogenated (fluorinated) p-type 5iC (p-type μc
By using -8iC:H(:Fno, (1)
It is possible to improve conductivity while maintaining a wide bandgap, suppress power loss due to the Norise resistance component within the solar cell element, and make more effective use of incident light in the single active layer.

(2) Furthermore, microcrystalization brings the Fermi level of the p-type layer closer to the valence band side (p-type a-
It is possible to bring it closer to 0.2 to 0.5 eV compared to 3iC). Therefore, it is possible to obtain a diffusion potential that is about 02 to 0.5 eV higher than that of the conventional one, and it is possible to incorporate a larger electric field into the type 1 photoactive layer, and this effect roughly increases Jso, vo. .

An improvement in r'F can be expected.

This situation is shown as a band profile in Figure 2 (a) (b).
)It was shown to. Here, FIG. 2(a) shows the conventional p-type a-
3iC:H, and FIG. 2(b) shows the case of p-type μc-SiC:H(·F) of this example.

○ and ・respectively indicate photogenerated carriers, and one point R1
m indicates the Fermi level. Diffusion potential 1 bit of this example
212' is larger than the diffusion potential of 11°12 in the conventional example.

(3) Furthermore, generally the short wavelength side is 400 nm due to microcrystalization.
The absorption coefficient in the vicinity becomes smaller than before ( l
Because I O-5 (0-5 (to a degree), the absorption loss due to the p layer near the short wavelength side 400 nm is even lower.
expected to be intimidating. FIG. 3 shows calculation results simulating differences in collection efficiency (spectral sensitivity characteristics) of solar cells due to differences in absorption coefficients around 00 nm. In this example, p-type μc-3iC:H(:F)(E0pt~2.
0ev) collection efficiency (b) is the conventional p-type a-SiC
:H (E0p' ~ 2.1 eV) Collection efficiency (a) is larger on the lower wavelength side.

In the example explained above, a pin type thin film solar cell was explained, or a (pin) type thin film solar cell (x=2).

Regarding 3.), similar effects can be obtained by using μc-SiC:H(·F) as the p-type semiconductor on the light incident side.

<Effects of the invention> As detailed above, the pin type can be basically closed and the amorphous sun? Hydrogenated (fluorinated) p-type 5iC (p-type μc
It has been revealed that a thin film solar TL cell element with high collection efficiency can be obtained by using -3iC:H(:F)).

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a thin film solar cell element. FIGS. 2(a) and 2(b) show the conventional p-type layer-SiC:H film and the p-type μc-SiC:H film of this example, respectively.
F) Schematic diagram of the band profile of the membrane. FIG. 3 is a graph of solar N and pond collection efficiency. FIG. 4 is a graph showing the collection efficiency of a solar cell in terms of optical bandgap E Opt. Figure 5 shows the solar cell characteristics of the conventional p-type layer-3iC:H (
Jsc, ■. . , FF) as the optical bandgap Eol
: It is a graph shown for H. I...Substrate, 2...N-type layer, 3...I-type layer, 4...
・P-type layer, 5 ・Transparent conductive film, 6, 6...Collector electrode. Patent Applicant: Nyap Co., Ltd. Agent: Patent Attorney: Maeda Ao et al.

Claims (2)

[Claims] (1) Hydrogenation (fluorination) of n-type, i (intrinsic) type, and p-type
PIN type or PINP, which is a stack of semiconductor thin films based on amorphous silicon (a-Si:H(:F))
In... ((pin)_x, x = 2, 3...) type thin film solar cells, at least the p-type semiconductor thin film on the light incident side is hydrogenated (fluorinated) in which an amorphous phase and a microcrystalline phase coexist. ) silicon carbide (p-type μc-Si
A thin film solar cell element characterized by using a C:H(:F)) thin film. (2) The conductivity of the p-type semiconductor thin film at room temperature is 10
p-type μc-SiC with a mixture of amorphous phase and microcrystalline phase having characteristics of ^-^3 (Ωcm)^-^1 or more, activation energy of 0.1 eV or less, and optical band gap of 2.0 eV or more: The thin film solar cell element according to claim 1, characterized in that a H(:F) thin film is used.