JPH03166771A - Thin film solar cell - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a thin film solar cell that uses amorphous silicon (hereinafter referred to as a-St) as its main material and performs photoelectric conversion using a pin junction structure. [Prior Art] Thin-film solar cells using amorphous semiconductors, especially a-Sl thin films, have the advantages of being easy to increase in area and requiring low raw material costs, and are expected to be used as low-cost solar cells. Normally, a-St solar cells are made by forming a transparent electrode with a transparent conductive film such as SnOx on a transparent substrate such as glass, and using a plasma CVD method using glow discharge decomposition on top of the substrate. p-type.i-type, a of n-type
-51 layers are sequentially formed, and metal electrodes such as M or Al are formed by vacuum evaporation or sputtering. [Problems to be Solved by the Invention] However, the film quality of the a-Sl film formed by the plasma CVD method deteriorates under light irradiation, and the deterioration of the film quality of the l layer causes problems in solar cells. The so-called Stebler-Wronsky effect, which reduces efficiency, has been a problem. On the other hand, the a-51 film formed by thermal CVD has less deterioration in film quality due to light.
Therefore, there is no decrease in efficiency as a solar cell. In the thermal CVD method, the reaction chamber is heated to a film temperature of 450 to 500°C in a He or H atmosphere at atmospheric pressure or reduced pressure, then a reaction gas is introduced to cause thermal decomposition, and the reaction chamber is set on a support. deposited on a substrate. The substrate used is a polished metal plate such as stainless steel or an insulating plate such as glass with M or Ag electrodes formed on it.Reactive gas for the a-Sf film is as follows: SL
When forming an n-layer using thHh as the main gas and H8 or L as the diluent gas, Pll. Add
Add 81H& when p-layer formalization is required. Further, the p-type or n-type doped layer formed at the top is sometimes formed by plasma CVD or the like at a low temperature of about 150 to 200° C. in order to suppress diffusion of impurities. FIG. 2 shows an example of such a thin film solar cell, showing an n-type a-Sl layer 12 formed by thermal CVD on a conductive substrate 11 made of stainless steel, and an l-type a-Sl layer 12 formed by WiCVD. 51 layer 13 and a p-type a-Sl layer 14 formed by the plasma CVD method, and further covered with a transparent electrode 15 made of a transparent conductive film. This solar cell generates an electromotive force by light 10 incident through a transparent electrode 15, and a terminal 1 provided on a substrate 11 generates an electromotive force.
6. Taken out from the terminal 17 provided on the transparent electrode 15. However, although the solar cells manufactured by this method do not deteriorate in characteristics due to light, the film temperature is 450~450℃.
Because the temperature was as high as 500°C, there was a problem in that the metal that contained the substrate was diffused into the a-Sl layer, degrading the characteristics of the solar cell. An object of the present invention is to provide a thin-film solar cell in which the thermal CVD method is applied to an a-Sl film to suppress deterioration due to light, and the diffusion of metal from the substrate into the a-Sl film can be suppressed. There is a particular thing. [Means for Solving the Problems] In order to achieve the above object, the thin film solar cell of the present invention includes a low resistance polycrystalline silicon layer of the first conductivity type formed on an insulating substrate by a thermal CVD method. The A-51 layer of the L-type formed by A-51 and the A-31 layer of the second conductivity type formed by the plasma CVD method are sequentially laminated. [Function] Since the L layer is formed by thermal CVD, there is little deterioration of the film quality due to light. In addition, the low-resistance polycrystalline silicon layer in contact with the substrate forms part of the p-1-n structure as an n-type or p-type semiconductor layer, and also serves as an electrode. There is no need to use a metal substrate, which is a source of temperature contamination. Furthermore, since the p-layer or n-layer above the l-layer is formed by plasma CVD, which is carried out at low temperatures, impurities contained in polycrystalline silicon do not diffuse into the l-layer, resulting in a clean semiconductor junction. and high efficiency can be obtained. [Example] Figure 1 shows a thin film solar cell according to an example of the present invention. This solar cell consists of a glass substrate with a n
A p-type polycrystalline silicon layer 2 is formed by a thermal CVD method, an l-type a-Si layer 3 is deposited on top of it by a thermal CVD method, and a p-type a-Si layer 4 is deposited thereon by a plasma CVD method. -i-n structure. A transparent conductor tM5 is formed on the p layer 4.
is formed and acts as a transparent electrode. This solar cell also
The light 10 incident from the top surface generates an electromotive force, which is extracted from the terminal 16 provided on the polycrystalline silicon layer 2 and the terminal 17 provided on the transparent electrode 5. FIG. 3 is a sectional view of the solar cell manufacturing apparatus shown in FIG. 1. This device consists of a thermal CVD chamber 61 and a plasma CVD chamber 61.
This is a combination of chambers 62. The thermal CVD chamber 6l is housed in an electric furnace 63, and in the plasma CVD chamber 62, a high frequency electrode 64 and an electrode 65 equipped with a heater are arranged facing each other. First, the glass substrate 1 mounted on the support stand 66 was placed in the thermal CVD chamber 61 of this apparatus, and heated for 60 hours in an atmosphere of
It was heated to 0°C. After evacuating from the exhaust pipe 7l, the gas conduit 81 passes through the front chamber 67 to Sl! I# and Pal
An n-type polycrystalline silicon layer 2 having a resistivity sxio-'Ω and a thickness of 1n was formed on the substrate 1 by thermal CVN under a pressure of 1 Torr. This polycrystalline silicon layer 2
Since its sheet resistance is less than 10Ω, it can sufficiently function as an electrode. Next, this l! icVD
118 gas was introduced into a 6L chamber, the temperature was lowered to 480°C, and the temperature was further soaked. After soaking, vacuum the main gas S.
l! H1 diluent gas He was introduced through an 8L gas conduit, the pressure was maintained at 50 Torr, and an L-type A-31 layer 3 was deposited to a thickness of 5000 mm by thermal CVD. After that, the thermal CVD chamber 6l is connected to the exhaust pipe 71, and the plasma CVD chamber 62 is connected to the exhaust pipe 72? After evacuation, the valve 68 was opened, and the substrate 1 was moved to the plasma CVD chamber 62. After the transfer, H was introduced, the substrate temperature was lowered to 200°C, and the temperature was soaked. Next, the exhaust pipe 72 is evacuated, SIH BJhCJHt is introduced from the gas conduit 82, and the pressure is increased to 0.5 T.
A high frequency voltage was applied to the electrode 64, and a p-type a-SIC layer 4 was formed to a thickness of 150 nm by plasma CVD. Furthermore, after evacuation, the air is purged, the valve 69 is opened, the substrate 1 is taken out to the outside, and the n-type a-St
A transparent conductive film 5 was formed on the layer 4. FIG. 4 shows the a-Si solar cell of the embodiment of the present invention shown in FIG.
The cell characteristics of the conventional a-Si solar cells shown in the figure are compared by 191.92. The conversion efficiency of the solar cell based on the present invention was 9.0%, and the conversion efficiency of the solar cell using the conventional method was 7.3%. From this, by adopting the method of the embodiment of the present invention, it is possible to
It was found that there is no diffusion of impurities from the substrate due to the VD method, and efficiency can be improved. In addition, these two solar cells were irradiated with light of 100 sW/1 for 100 hours,
No deterioration was observed in either case. FIG. 5 shows another embodiment of the present invention. A-31 solar cells integrated in series are formed on a glass substrate 1. First, an n-type polysilicon layer is formed on a substrate 1, and laser patterning is performed to divide the layer into n-type regions 21, 22, 23, 24, . . . which also serve as electrodes. On top of that, an l-type a-Sl layer and a plasma C layer are formed by thermal CVD.
A p-type a-SIC layer is formed by VD and divided into i-type regions 31, 32, 33, 34, . . . and p-type regions 41, 42, 43, 44, . . . by laser patterning. An integrated type a-St that generates an electromotive force from the light 10 by forming a transparent conductive film thereon and dividing it into transparent electrodes 51, 52, 53, 54, etc. by laser patterning.
A solar cell is created. When fabricating integrated solar cells using conventional methods, it is necessary to first deposit metal electrodes on an insulating substrate. In this example, this process is not necessary, so an integrated solar cell can be fabricated using a simpler process. In addition, Fig. 1. It is clear that the conductivity type of the solar cell shown in Figure 5 can be easily reversed. [Effects of the Invention] According to the present invention, one layer with a p-1-n structure made of a-St as the main material is formed by thermal CVD to reduce the deterioration of film quality due to the Stepler-Wronski effect. By forming the layer that forms the bond on the substrate side with low-resistance polycrystalline silicon, a metal electrode is no longer required, and a p-1-n junction structure that is not contaminated by metal diffusion during thermal CVD is realized. The efficiency was improved, and as a result, we were able to obtain highly efficient and highly reliable thin-film solar cells. In particular, in series-integrated solar cells, there is no need to form metal electrode flags on an insulating substrate, making it possible to lower costs.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thin film solar cell according to an embodiment of the present invention, FIG. 2 is a sectional view of a conventional thin film solar cell, and FIG. 3 is a sectional view of an apparatus used for manufacturing the solar cell shown in FIG. FIG. 4 is an output characteristic diagram of the solar cell shown in FIGS. 1 and 2, and FIG. 5 is a sectional view of an integrated solar cell according to another embodiment of the present invention. 1: Glass substrate, 2+n-type polycrystalline silicon layer, 3+l-type a-Sl layer, 4: p-type a-SiC layer, 5=transparent electrode, 6
1: Thermal CVD chamber, 62 = Plasma CVD chamber. Figure 1 Figure 2 Figure 1 l Figure 3 Figure 4 Figure 1 Figure 5

Claims (1)

[Claims] 1) A low-resistance polycrystalline silicon layer of the first conductivity type on an insulating substrate, an i-type amorphous silicon layer formed by thermal CVD, and a second conductivity type amorphous silicon layer formed by plasma CVD. A thin film solar cell characterized by being formed by sequentially stacking high quality silicon layers.