JPH0121634B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an amorphous silicon solar cell containing fluorine. WESpear and others discovered that the conductivity of amorphous silicon obtained by plasma decomposition of silane (SiH ₄ ) could be greatly changed by doping it with PH ₃ or B ₂ H ₆ (1976). Since solar cells using amorphous silicon were prototyped by Carlson et al. (1976), they have attracted attention, and research has been actively conducted to improve the efficiency of amorphous silicon thin-film solar cells. Amorphous silicon obtained by plasma decomposition of silane has problems with heat resistance, and Straebler-
There is a theory that the Wronski effect can cause a decline in the characteristics of solar cells, and SROvshinsky believes that amorphous silicon containing fluorine (a-Si:F:H), which is obtained by glow discharge decomposition of _SiF4 , has a high heat resistance. In addition to reporting that the Straebler-Wronski effect was small, they also reported that they subsequently fabricated an MIS type a-Si:F:H solar cell and obtained an efficiency of 6.6%. However, the structure of this MIS type solar cell is Mo/n type a-Si:F:H/i type a-Si:
F: H/Nb ₂ O ₃ /Pd-Au, and the thickness of Nb ₂ O ₃ was as small as 30 Å, so reproducibility was poor and the manufacturing process was complicated, making it unsuitable for industrial production. . On the other hand, generally the pin type structure is
Although the manufacturing process is simple and suitable for industrial production,
a-Si:F:H obtained by glow discharge decomposition of _SiF4
The efficiency of pin type solar cells using SiH ₄
The problem was that the efficiency was lower than that of pin solar cells using a-Si:H etc. obtained by glow discharge decomposition. The present inventors have conducted extensive research to improve the efficiency of pin-type solar cells obtained by glow discharge decomposition of _SiF4 , and have found that pin-type solar cells using a-Si:F:H The present invention was completed based on the discovery that efficiency can be greatly improved by providing an intrinsic layer of hydrogenated amorphous silicon at the -i interface. The details will be explained below. The amorphous silicon containing fluorine (hereinafter referred to as a-Si:F:H) used in the present invention is a combination of fluorinated silane (SiF ₄ ) or its derivative, and/or this and silane (SiH ₄ ) or its derivative. If necessary, the mixture is mixed with hydrogen or an inert gas such as argon or helium diluted with hydrogen, and subjected to high frequency glow decomposition or DC glow discharge decomposition using a capacitive coupling method or an inductive coupling method. The present invention relates to a pin type solar cell using this a-Si:F:H in the i-layer (intrinsic layer). Figure 1 shows the structure of this type of conventional product, where 1 is a substrate made of stainless steel or molybdenum,
2 is n-type a-Si:H or a-Si:F:H, 3 is intrinsic a-Si:F:H, 4 is p-type a-Si:H or a-Si:F:H, 5 is a transparent electrode such as ITO or _SnO2 . In a solar cell with this structure, the open circuit voltage is
Voc is as low as 0.3volts, and short circuit current Jsc is also low.
Since it was as small as 3 mA/cm ² , the efficiency η was only about 0.45%. The reason for this is thought to be as follows. That is, glow discharge decomposition of SiF ₄ requires H ₂ or SiH ₄ as a hydrogen source, and therefore, HF is inevitably generated by glow discharge decomposition.
Since this HF is a strong etching agent for Si,
The a-Si:F:H deposited on the substrate will be etched. Therefore, the a-Si deposited on the substrate:
It is presumed that the surface of the F:H layer has many defects and the recombination of carriers at the bonding interface increases, resulting in poor efficiency. FIG. 2 shows the structure of one embodiment of the present invention. Here, 7 is an n-type amorphous semiconductor,
6 is intrinsic a-Si:H, 3 is intrinsic a-Si:H:
F, 8 is a p-type amorphous semiconductor, 1 is a substrate,
5 is a transparent electrode. The intrinsic a-Si:H layer 6 contains silane (SiH ₄ ) or polysilane (SinH _2o+2 ),
It is obtained by diluting it with hydrogen or an inert gas if necessary and decomposing it by glow discharge, and its thickness needs to be about 30 Å or more. However, this true a-
If the thickness of Si:H becomes too large, it may cause problems in the heat resistance of the cell, so it is preferably 1000 Å or less. Further, as a method for obtaining this a-Si:H layer 6, after an intrinsic a-Si:F:H layer is deposited, the layer may be annealed with hydrogen plasma. Moreover, between the intrinsic a-Si:H:F layer 3 and the n-type amorphous semiconductor layer 7, this intrinsic a-
Si:H may be added. As the amorphous semiconductor used for the n-type layer and the p-type layer, a-
Si:H, a-Si:F:H obtained from fluorinated silane or its derivatives, hydrogenated or fluorinated amorphous silicon carbide obtained from silane or fluorinated silane and hydrocarbon (hereinafter a-SiC :H, a-SiC:F:H)
Hydrogenated or fluorinated amorphous silicon nitride obtained by glow discharge decomposition of silane or fluorinated silane and ammonia, or hydrazine or nitrogen (hereinafter a-SiN: H, a
-SiN:F:H) or hydrogenated or fluorinated amorphous silicon carbon nitride obtained from silane, hydrocarbon, ammonia, etc. (hereinafter a-SiCN:H, a-SiCN:F:
(denoted as H) is used. In particular, in the p-type layer on the side where light enters, a-SiC:H, a-SiC:F:H, a
-SiN:H, a-SiN:F:H, a-SiCN:H,
a-SiCN:F:H is preferred. The n-type layer is also preferable because these amorphous semiconductors have excellent chemical resistance and are resistant to HF. n-type amorphous semiconductor layer 7
The thickness of 100 to 500 Å is usually used, and the thickness of the intrinsic a-
The thickness of the Si:F:H layer 3 is 2000 Å to 10000 Å.
The thickness of the p-type amorphous semiconductor layer 8 is 50 to 300 Å,
The thickness is preferably 70 to 150 Å. Further, even if the n-type layer 7 and the p-type layer 8 in FIG. 2 are replaced, the solar cell can function satisfactorily. However, in this case, an intrinsic a-Si:H layer of about 30% is formed between the intrinsic a-Si:F:H layer 3 and the p-type layer adjacent thereto.
It is necessary to add Å to 1000 Å. FIG. 3 shows an embodiment of another aspect of the present invention, in which a transparent substrate 10 made of glass or the like is ITO, 11 is _SnO2 , and 10 and 11 function as transparent electrodes. 8 is a p-type amorphous semiconductor, 6 is an intrinsic a
-Si:H, 3 is an intrinsic a-Si:F:H, 7 is an n-type amorphous semiconductor, and 13 is an electrode made of aluminum, molybdenum, or the like. When depositing on a transparent substrate such as glass in this way, if the transparent electrode is only ITO10, a-Si:
F: Since it is etched when H is deposited,
It is preferable to apply SnO ₂ 11 to about 50 Å to 500 Å. As the p-type amorphous semiconductor layer 8, a-SiC:H, a-SiN:H, a-SiC:
F:H, a-SiN:F:H, a-SiCN:H, a
-SiCN:F:H is particularly preferred. Because p
type amorphous semiconductor layer such as a-Si:H or a
When using -Si:F:H, a-
This is because it is easily etched by HF generated when depositing the Si:F:H layer 3. 6 is true a
-Si:H, thickness 30 Å to 1000 Å, 3 is intrinsic a-
Si:F:H, 7 is an n-type amorphous semiconductor layer, a-Si:H, a-Si:F:H, a-SiC:
H, a-SiC:F:H, a-SiN:H, a-
SiN:F:H, a-SiCN:H, a-SiCN:F:
H etc. are used. Plasma decomposition for depositing these amorphous semiconductors is typically performed at substrate temperatures of 200°C to 400°C. In addition, control of n-type or p-type is performed by p
Elements from group V of the periodic table, such as aluminum and boron, are added to the mold, and elements from group V of the periodic table, such as phosphorus and arsenic, are added to the reaction gas as their hydrides or fluorides. This is done by mixing and decomposing with glow discharge, or by ion implantation of these elements. As described above, in the present invention, in a pin type amorphous silicon solar cell, the i-layer has a multilayer structure, and the first i-layer is made of intrinsic a-Si:F:
The feature is that an intrinsic a-Si:H layer with a thickness of about 30 Å to 1000 Å is applied to the p-i interface as the second i-layer, and the conventional a-Si:F:H single layer is replaced with an i
This results in a significant improvement in efficiency compared to solar cells that use multi-layered solar cells. Next, this revolutionary efficiency improvement effect will be explained using examples. Example A quartz reaction tube with an inner diameter of 11 cm was used for glow discharge decomposition using a high frequency of 13.56 MHz. Each of the required amorphous semiconductors was decomposed by glow discharge using the following gas composition and deposited on the substrate. Also, the substrate temperature was fixed at 270°C. a-Si:H (10% _SiH4 / _H2 ) a-Si:F:H ( _SiH4 / _H2 = 6) a-SiC:H ( _CH4 / _SiH4 = 2) a-SiN:H ( _NH3 / _SiH4 =0.3) a-SiCN:H
(NH ₃ :CH ₄ :SiH ₄ =0.2:5:1) The structure shown in FIG. 2 was used as an example, and the structure shown in FIG. 1 was used as a control example. Both substrates 1 are made of SS (stainless steel). For each transparent electrode 5, ITO was deposited by electron beam evaporation. The thickness of p-type layers 8 and 4 is both 100 Å, and intrinsic a-Si:
The thickness of the F:H layer 3 is 4000 Å, and the thickness of the n-type layers 7 and 2 is 500 Å. The thickness of the intrinsic a-Si:H layer (second i-layer) unique to the present invention is
It was set to 500Å. Furthermore, the p-type amorphous semiconductor is
It was obtained by doping with B ₂ H ₆ , and the boron temperature in the deposited film was approximately 0.1 atom% in each case. Also, the n-type amorphous semiconductor
It was obtained by doping with PH ₃ , and the phosphorus concentration in the deposited film was about 0.5 atom% in each case. Regarding the various solar cells obtained, AM-1
J- with solar simulator (100mW/cm ² )
Determine the V characteristics and calculate the short circuit current as shown in Table 1.
Jsc (mA/cm ² ), open circuit voltage Voc (volts), fill factor
Described in terms of FF (%) and conversion efficiency η (%).

[Table] As is clear from Table 1, in all of the control examples, Jsc is extremely small and Voc is also small at 0.2 volts or less, so the diffusion potential of the pin junction is not sufficiently formed. I understand that. Also, the control example is
Since FF is also small, η is extremely small at 0.2% or less.
In contrast, in the embodiment of the present invention, Voc is
It is over 0.67volts and shows large values for both Jsc and FF.
p-type amorphous semiconductor layer and intrinsic a-Si:F:H
It can be seen that by adding a layer of intrinsic a-Si:H (second i-layer) of only 500 Å between the layer (first i-layer), η can be greatly increased. In particular, a-SiC:H, a-SiN:H, which has a large optical bandgap in the p layer,
This effect becomes even more remarkable by using a-SiCN:H or the like. ITO/p type a-
SiC: H/i type a-Si: H/i type a-Si:F:
In the H/n-type a-Si:F:H/SS type solar cell, the i-type a-Si:H layer (second i-layer)
Table 2 shows the solar cell characteristics when the thickness of the solar cell is changed.

【table】

[Table] As can be seen from Table 2, adding only a 50 Å intrinsic a-Si:H layer (second i layer) has a large effect of improving η. Even if the thickness of this a-Si:H layer exceeds 1000 Å, it will still show a large η, but the a-Si:H layer (second i
If the thickness of the a-Si:F:H layer (first i-layer) becomes too thick, the inherent heat resistance of the a-Si:F:H layer (first i-layer) tends to not be utilized, so it is desirable that the a-Si:H layer has a thickness of 1000 Å or less. .

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the structure of a conventional pin type solar cell, and FIGS. 2 and 3 are schematic sectional views showing the structure of an embodiment of the present invention.

Claims (1)

[Claims] 1 The i-layer of a p-i-n type amorphous silicon solar cell contains fluorinated silane (SiF ₄ ) or its derivative and hydrogen, or fluorinated silane or its derivative and silane or its derivative. In a solar cell using intrinsic a-Si:F:H obtained by glow discharge decomposition, a layer of intrinsic a-Si:H obtained by glow discharge decomposition from silane or its derivative is placed between the p layer and the i layer. An amorphous silicon solar cell characterized in that it is provided with a second i-layer consisting of an a-Si:H layer obtained by hydrogen plasma annealing of the a-Si:F:H layer or a-Si:F:H layer. 2 The thickness of the intrinsic a-Si:H layer is from about 30 Å to
The amorphous silicon solar cell according to claim 1, wherein the amorphous silicon solar cell has a thickness of 1000 Å. 3 Among the amorphous semiconductors of the p-layer or n-layer, at least the layer on the side where light enters is a-SiC:
H, a-SiC:F:H, a-SiN:H, a-
SiN:F:H, a-SiCN:H, a-SiCN:F:
The amorphous silicon solar cell according to claim 1 or 2, characterized in that it is made of an amorphous semiconductor selected from H. 4 The amorphous semiconductor constituting the pin type solar cell is coated with ITO on a transparent substrate such as glass.
4. An amorphous silicon solar cell according to claim 1, wherein the amorphous silicon solar cell is deposited on a multilayered substrate comprising 50 Å to about 500 Å of SnO ₂ .