JPS61292377A - Amorphous silicon photo-cell - Google Patents

Abstract

PURPOSE:To improve the conversion efficiency of an amorphous silicon photo- cell by forming an N-layer with smaller photo-absorption coefficient. CONSTITUTION:The photo-cell is manufactured by evaporating a transparent conductive film ITO2 consisting of In2O3-SnO2 on a transparent glass substrate 1, and depositing a P-type a-Si layer 3, an I-type a-Si layer 4, an N-type a-Si layer 5, and an N-type fine crystalline Si layer 6 on the ITO2 in order. An Al electrode layer 7 is formed on the N-type fine crystalline Si layer 6 by evaporation. Thus, a pin layer 30 is formed between the ITO2 and the electrode 7. The fine crystalline Si layer 6 with smaller absorption coefficient is used for the N-type layer 6 so as to reduce the absorption deficiency during the turnaround between the N-type layers 5 and 6, with larger amount of the light reintroduced into the I-layer in comparison with the case where only an N-type a-Si is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to improving the conversion efficiency of pin type amorphous silicon solar cells (hereinafter referred to as pin type A-5I solar cells).

(Prior art) In order to improve the conversion efficiency of conventional pin type A-3T solar cells, it is necessary to increase the amount of sunlight that is reflected at the interface between the N layer and the AI electrode layer and reabsorbed within the I layer. is considered to be one of the effective means.

Therefore, in the past, studies have been made to construct the n-layer using microcrystalline Si, which has a small light absorption coefficient.

(Problems to be Solved by the Invention) However, according to research conducted by the present inventors, when the n-layer is composed of microcrystalline Si, an interfacially altered layer is formed between the i-layer and the n-layer, and in this altered layer, It was found that carrier recombination was promoted, and as a result, the photocurrent decreased in the long wavelength region, and the conversion efficiency did not improve.

According to studies by the present inventors, the reason for this is that the interface between the i-layer and n-layer is damaged by high-energy plasma particles during the formation of microcrystalline Si, resulting in the formation of the above-mentioned altered layer. Conceivable.

In the present invention, without forming the above-mentioned altered layer,
A technical problem to be solved is to improve conversion efficiency by forming an n-layer with a small light absorption coefficient.

(Means for Solving the Problems) Therefore, in order to achieve the above technical problem, the present invention provides a p-type amorphous silicon layer and an r'J layer on a substrate.
In an amorphous silicon solar cell formed by sequentially stacking amorphous silicon layers, an n-type amorphous silicon layer is deposited on the i-type amorphous silicon layer, and an n-type microcrystalline silicon layer is deposited on the n-type amorphous silicon layer. Adopt technical means of equipping.

(Function) As described above, in the present invention, the n-layer is composed of an amorphous silicon layer and a 2N microcrystalline layer with a small light absorption coefficient, so compared to a case where the n-layer is formed only of an amorphous silicon layer. , the absorption loss of light passing through the n-layer is reduced by #.

In addition, since the n-type amorphous silicon layer is interposed between the i-type amorphous silicon layer and the n-type microcrystalline silicon layer, one layer is formed by high-energy plasma particles generated when forming the n-type microcrystalline silicon layer. damage is prevented, and no recombination layer is formed at the boundary between the i-layer and n-layer.

(Example) The present invention will be described in detail below based on an example shown in the drawings.

FIG. 1 shows the structure of a solar cell to which the present invention is applied. In this implementation, as shown in FIG. 1, a transparent conductive film (ITO) 2 made of In, O, -3nO2 was deposited by electron beam on a transparent glass substrate 1. The a-3i layer 3, the i-type a-3i layer 3, the n-type a-5iN5, and the n-type machine crystalline Si layer 6 are sequentially deposited by plasma CVD. Further, on the n-type mechanical crystal Si layer 6, a /l electrode layer with a thickness of 600 to 700
Formed with a film thickness of nm. Therefore, a pin layer 30 is formed between the ITO 2 and the Al electrode layer 7.

Here, the present inventors formed the pin layer 30 under the following conditions.

(1) P-type a-3t layer 3 Raw material gas: 10%S i H4/A r 22.5s
ccm: 10% CHa /Hz 7.
8sccm:300ppm 13zHh/Ar 5
．． Osccm substrate temperature: 230°C Internal pressure: Q, 5 torr Discharge power: 10w 13.56MH2 film thickness: 20nm (2) I-type a-3t layer 4 Source gas: 10%S i Ha /A r 45s
ccm substrate temperature: 230°C Internal pressure: 0.5 torr Discharge power: 10w 13.56MHz film thickness near 00nm (3) N-type a-3i layer 5 Raw material gas: 1O%S i H4/Hz 20scc
m: 11000pp PH3/H220SCCIl+
Substrate temperature: 230°C Internal pressure: Q, 5 torr Discharge power: 10w 13.56MH2 film thickness: 3 layers m (4) N-type microcrystalline Si layer 6 Source gas: 10%S i Ha /Hz 20se
cm: 1000 ppm PH3/Hz 20
sccm substrate temperature: 230℃ Internal pressure: 0.5 torr Discharge power: 20W 13.56MHz film
Thickness: 30 nm Note that in the formation of the pin layer 30, p-type a-3i
The degree of vacuum before forming layer 3 was 3 x 10-'' torr, and after forming p-type a-3i layer 3, it was evacuated until it reached a degree of vacuum of about 3 x 10-' torr, and the i-type a-3i layer was 6 i-type a-S i ji After 4 deposition, 3×1
Vacuum to around O-btorr and remove the n-type a-3i.
Form layer 5. After the n-type a-3i layer 5 is completed, only the discharge power is increased while the n-type microcrystalline S
The process moves on to forming the i-layer 6. That is, n-type 5-3i layer 5 to n
The transition to the type machine crystal S i ii 6 is formed in a continuous discharge.

Next, the operation of this embodiment having the above configuration will be explained.

When sunlight is incident on the a-3i solar cell formed as described above from the glass substrate l side indicated by arrow A in FIG. 1, photoelectric conversion occurs and the cell functions as a solar cell.

Here, the light incident into the first layer 4 is absorbed by the first layer 4 and excites electron-hole pairs, but since the absorption coefficient of the first layer 4 is wavelength dependent, the short wavelength light is absorbed by the first layer 4. At the interface between and 1 layer 4,
Long wavelength light is mainly absorbed near the interface between the 1st layer 4 and the 0th layer 5. However, long wavelength light is not efficiently absorbed in layer 1 4, and a considerable amount of light reaches the interface between layer 1 4 and layer 0 5. Those lights pass through the 0 layer 5.6 and are reflected at the interface between the n layer and the /l electrode film 7, and are again reflected in the 1 layer 4.
However, according to this embodiment, since the microcrystalline St layer 6 with a small absorption coefficient is used as the n layer 6, the absorption loss during the round trip to the 0 layer 5.6 is reduced, and the 1 The amount of light reintroduced into layer 4 is greater than when only n-type a-3t is used.

However, if the n-layer is simply changed to microcrystalline Si, an altered film (recombination film) will be formed at the interface between layer 1 4 and layer 0 5 due to plasma damage during n-type microcrystalline Si film formation. The purpose of the period is not achieved.

Therefore, as in this embodiment, 1 layer 4 and n-type microcrystal 81 layer 60
By inserting the n-type 5-3i layer 5 between them as a damage mitigation layer, formation of the above-mentioned altered layer was prevented, and the intended purpose was achieved.

FIG. 2 shows a comparison of the spectral characteristics between the case where an n-type mechanical crystal St is simply used and the structure shown in FIG. 1 according to the present invention.

In Fig. 2, the horizontal axis shows the incident light wavelength, and the vertical axis shows the photocurrent I pH when no bias voltage is applied to the solar cell.

(λ) and the photocurrent 1 pHV when bias voltage is applied (
λ).

In addition, the curves a1, az, bl, b, ,C in Fig. 2
Table 1 shows the relationship between I and Cz.

Table 1 As can be seen from Table 1, curves a12a2, bl, and b2 in FIG. A case is shown in which the structure is composed of only a type microcrystalline Si layer.

In FIG. 2, when curves C3 and bI are compared, or curves Ct and b2 are compared, it can be seen that bl or b2 has higher sensitivity in the long wavelength region (1li) than CI or C2.

As a result, as described above, the n-type microcrystalline Si layer 6 and 1
By interposing the n-type a-5i layer 5 between the layers 4,
It was confirmed that almost no recombination layer was formed at the i-n interface.

Further, when curves a and 5 are compared, or curves a2 and b2 are compared, it can be seen that the sensitivity in the long wavelength region is higher for al or C2 than for curves a and b2.

This means that it is desirable that the discharge power when forming the n-type microcrystalline Si layer 6 be as small as possible. In other words, the thickness of the n-type a-3i layer 5 is 3 nm as described above, which is very thin compared to the thickness of other layers, so the n
If the energy for forming the type microcrystal 6 is too large, there is a possibility that a recombination layer will be formed at the i-n interface.

In addition, in FIG. 2, the larger the bias voltage, the more
It can be seen that the magnitude of the photocurrent decreases because, with increasing bias voltage, the drift velocity in the i-layer decreases and recombination is promoted.

FIG. 3 shows the distribution of conversion efficiency between the solar cell having the structure of this embodiment shown in FIG. The horizontal axis shows the conversion efficiency, and the vertical axis shows the number of solar cells.

In FIG. 3, distribution D1 shows the distribution of conversion efficiency in cells with the structure of the present invention, and distribution D2 shows the distribution of conversion efficiency in cells with the conventional structure.

A total of 158 cells were created for both distributions D+ and Dz, and the conversion efficiency of each was investigated.

From this Figure 3, it can be seen that the average conversion efficiency of the cell with the conventional structure is 6.
9%, according to the present invention, the average efficiency was 8.2%, and it was confirmed that the conversion efficiency was reliably improved compared to the conventional method.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications as described below are possible.

(1) The n-type a-3i layer that alleviates plasma damage is
Similar effects can be obtained not only by plasma CVD but also by optical CVD.

(2) A non-transparent substrate (e.g. stainless steel, ceramic, etc.) is used for the substrate, including a p-layer, an i-layer, an n-type a-3i layer,
N-type microcrystalline SiN transparent electrodes are sequentially formed, and the transparent electrode side (
By injecting light (from the n-layer side), a damage mitigation effect can be obtained, and the short wavelength side anger intensity can be improved.

(3) The technology of the present invention is applicable not only to solar cells but also when forming an active layer of microcrystalline Si in thin film transistors, charge-coupled devices, etc. By forming the a-3i layer thinly, defects at the interface with the insulating film are reduced, resulting in improved performance.

(4) A similar effect can be obtained even if plasma damage is reduced by applying a DC bias voltage to the electrode for generating glow discharge at the initial stage of microcrystalline Si film formation.

(Effects of the Invention) As described above, according to the present invention, the n-type silicon layer can be removed without forming a degraded layer such as a recombination layer at the boundary between the i-type amorphous silicon layer and the n-type silicon layer. This has the effect that the absorption rate of light can be lowered, and as a result, the conversion efficiency of the solar cell can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a solar cell to which the present invention is applied, FIG. 2 is a characteristic diagram showing changes in photocurrent ratio with respect to incident light wavelength, and FIG.
The figure is a characteristic diagram showing the distribution of conversion efficiency of the conventional example and the example of the present invention. ■...Glass substrate, 2...ITo, 3...p type a
-3i layer, 4 -i type a-3i layer, 5-n type a-5i
layer, 6... n-type mechanical crystal St layer, 7... AI electrode layer. Representative Patent Attorney: Takashi Okabe
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Claims (1)

[Claims] In an amorphous silicon solar cell in which a p-type amorphous silicon layer and an i-type amorphous silicon layer are sequentially laminated on a substrate, an n-type amorphous silicon layer deposited on the i-type amorphous silicon layer; , and an n-type microcrystalline silicon layer deposited on the n-type amorphous silicon layer.