JPH0125235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin-film silicon solar cell in which an amorphous silicon layer having a bond is provided on a transparent insulating substrate and a photovoltaic force is generated by light incident from the substrate side.

Amorphous solar cells are considered suitable for low-cost solar cells due to the following points.

(1) Because it is grown at a low temperature (200-400℃), the energy required for production is much lower than that of single-crystal silicon.

(2) Since the absorption coefficient near the peak of the sunlight spectrum is about an order of magnitude larger, solar cells can be constructed with a thin film of about 1 μm.

(3) Low-temperature growth and amorphous structure allow for greater freedom in selecting substrate materials, making it easy to increase the area.

(4) By switching the gas during the growth process, pn
Continuous automatic formation such as bonding is possible.

(5) By growing on an insulating substrate, series-connected solar cells can be formed without going through a wiring process.

FIG. 1 is a conceptual diagram of the structure of an amorphous silicon solar cell. A transparent insulating substrate 1 made of glass or the like has a transparent electrode 2 thereon, which is usually an ITO film, a SnO ₂ film, or a composite film thereof. P-type, i-type (no additives), and n-type amorphous silicon layers 3 and 4 are formed on the transparent electrode 2 by glow discharge decomposition of diborane, monosilane mixed gas, monosilane gas alone, and phosphine and monosilane mixed gas, respectively. , 5 are formed. The thicknesses of layers 3, 4, and 5 are about 100 Å, about 5000 Å, and several hundred Å, respectively. A metal electrode 6 is provided on the n-layer 5 by vapor deposition or the like, and photovoltaic force is extracted from the transparent electrode 2 and the metal electrode 6.
However, if the contact resistance between the metal electrode 6 and the amorphous silicon layer 5 is large, a problem arises in that the output power of the solar cell is reduced.

The present invention solves this problem and provides a thin-film silicon solar cell in which a metal electrode contacts the opposite substrate side of an amorphous silicon layer having a bond formed on a transparent insulating substrate via a transparent electrode. The aim is to ensure a small contact resistance between the electrode and the amorphous silicon layer.

This object is achieved in that at least the zone on the metal electrode side of the impurity-doped amorphous silicon layer in contact with the metal electrode of the solar cell is made of microcrystalline amorphous silicon.

Embodiments of the present invention will be described below with reference to the drawings. 2, the difference from the solar cell shown in FIG. 1 is that an n-type microcrystalline amorphous silicon layer 7 is inserted between an n-type amorphous silicon layer 5 and a metal electrode 6. In FIG. This microcrystalline layer 7 can be generated by increasing the high frequency discharge power during glow discharge formation by high frequency input. It has been found that the contact resistance between such a microcrystalline layer and a metal electrode is always low. This effect is particularly great for metal electrodes by screen printing and firing conductive pastes. Metal electrode 6 in a solar cell with the structure shown in Figure 1
When created by screen printing, the form factor is small and the output power is low, as shown by the broken line 31 of the output characteristics in FIG. The cause of this is the contact resistance between the electrode 6 and the n-type layer 5. By inserting the microcrystalline layer 7 as shown in FIG. 2 according to the present invention, it is confirmed that the current increases as shown by the solid line 32 and the output increases due to the increase in the form factor. It was done. Such a low contact resistance was obtained even when the contacting silicon layer was a p-type microcrystalline layer.

Instead of inserting the microcrystalline layer between the usual amorphous layer 5 and the metal electrode 6 as shown in FIG.
The entire n-type layer 5 in FIG. 1 may be a microcrystalline layer. The microcrystalline layer, which contains microcrystalline grains of about 60 Å, is 40,000 times more conductive than a normal amorphous silicon layer, which significantly reduces the internal series resistance of the solar cell. Figure 4 shows a case where a normal amorphous silicon layer is used as the n-type layer on the metal electrode side of a solar cell using a vapor-deposited metal electrode (line 41) and a case where a microcrystalline silicon layer is used (line 42). ), and as the current increased, the form factor increased and the maximum extractable output significantly increased. The increase in current in this case is greater than would be expected from the reduction in internal series resistance and contact resistance. In FIG. 2, the light enters the transparent substrate 1 and the amorphous silicon layer 3,
It was found that this is because the light absorbed by 4 and 5, that is, near-infrared light, is reflected by the metal electrode 6 and enters the amorphous silicon layer again, generating photovoltaic force. Since the light transmittance of microcrystalline silicon is twice that of amorphous silicon, the amount of re-incoming light is large, and the resulting photovoltaic force is significantly larger than that of conventional solar cells. Moreover, since there is less recombination of carriers than when carriers are generated by near-infrared light by increasing the thickness of the amorphous silicon layer, the generated carriers can be used efficiently.

Furthermore, by using microcrystalline silicon with low activation energy for the layer in contact with the metal electrode,
Due to the so-called backsurf field effect, which increases the internal electric field in this vicinity, the current that can be taken out increases.

As described above, the present invention reduces contact resistance and increases output power by microcrystallizing the amorphous silicon layer that contacts the metal electrode of a solar cell. It has become possible to apply this technology, reducing the cost of solar cells.
This can have a very large effect on increasing the area.

[Brief explanation of drawings]

Fig. 1 is a conceptual cross-sectional view of a conventional example of a thin-film silicon solar cell, Fig. 2 is a conceptual cross-sectional view of an embodiment of the present invention, and Fig. 3 is a comparison of its output characteristics with that of a solar cell with a conventional structure. Figure 4 is an output current/voltage diagram showing a comparison of the output characteristics of another embodiment of the present invention using vapor-deposited metal electrodes with that of a conventional structure.
It is a voltage diagram. 1... Translucent insulating substrate, 2... Transparent electrode, 3...
...P-type amorphous silicon layer, 4...Additive-free amorphous silicon layer, 5...N-type amorphous silicon layer, 6...
Metal electrode, 7... n-type microcrystalline amorphous silicon layer.

Claims (1)

[Claims] 1. An amorphous silicon layer having a bond via a transparent electrode is formed on a transparent insulating substrate, and a conductive paste is formed on the side opposite to the substrate by screen printing and baking a conductive paste. 1. A thin film solar cell in which at least a band on the metal electrode side of an impurity-doped amorphous silicon layer in contact with the metal electrode is made of microcrystalline amorphous silicon.