JPH0563103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crystalline silicon solar cell having a heterojunction, and particularly to a device structure with high photoelectric conversion efficiency.

[Conventional technology]

In order to increase the photoelectric conversion efficiency of silicon solar cells with pn or pin junctions, it is important to prevent not only the loss of photogenerated carriers within the semiconductor bulk but also the loss at the semiconductor surface.
Particularly regarding the latter, it is an important issue to prevent recombination of the photogenerated carriers under the light-incident silicon surface or electrode section. As an example of countermeasures, the loss at the light incident silicon surface is reduced by oxidizing the silicon surface. Regarding prevention of injection carrier recombination below the electrode, a method has been proposed in which an n ⁺ polycrystalline Si layer is interposed between the electrode and the n ⁺ layer to form an n ⁺ n ⁺ junction.
(Annual Progress Report: Fotovoltaics, (April 1986) p. 15 (Annual
Progress Report: Photovoltaics, April (1986)
(See p.15).

[Problem that the invention seeks to solve]

The above-mentioned prior art does not take into consideration the use of a semiconductor layer having a wide forbidden band width, and therefore does not provide a sufficiently effective prevention of minority carrier recombination.

An object of the present invention is to provide a structure of a photoelectric conversion device that does not have the drawbacks of the prior art and has high photoelectric conversion efficiency.

[Means for solving problems]

The above purpose is to form an N ⁺ or P ⁺ layer consisting of a semiconductor layer with a heterojunction multilayer structure consisting of crystalline silicon and a semiconductor with a wider bandgap in contact with one of the pn junctions made of crystalline silicon. This is achieved by a heterojunction semiconductor device. Note that semiconductors with a large forbidden band width include oxygen, nitrogen,
It may also contain hydrogen.

The method for forming the semiconductor layer with a wide forbidden band width is as follows:
Plasma CVD method using silane gas as the main raw material,
Examples include sputtering method, thermal CVD method, optical CVD method, and molecular beam evaporation method. For example, by using the plasma CVD method using silane-based gas, the forbidden band width can be varied from 1.1 to 2.0 eV, and the amount of crystals can be varied depending on the type of gas, gas concentration, and plasma CVD conditions. It is possible to control the physical properties of

Also, other reactive gases such as CH ₄ , (CH ₃ ) ₂ ,
By adding SiH ₂ , O ₂ , NH ₃ or the like, a semiconductor layer with a larger forbidden band width can be formed. In this case, the plasma CVD method in particular has excellent control over film thickness and doping, and has high practical value.

Furthermore, by using this method, a heterojunction having an arbitrary band structure can be formed by stacking semiconductor layers having different forbidden band widths. In particular, if a thin semiconductor layer with a wide forbidden band width is present at the interface, injection of minority carriers into the thin semiconductor layer can be effectively prevented.

[Effect]

The heterojunction effect between the silicon heterosemiconductor and crystalline silicon will be explained with reference to FIGS. 1 and 2.

Figure 1 shows an N ⁺ type hetero semiconductor layer and a P type single crystal.
It is a band structure diagram of a junction with Si. For example, it is known that the average forbidden band width of microcrystalline Si formed by plasma CVD is approximately 1.4 eV, and it is composed of a crystalline part (Eg = 1.1 eV) and an amorphous part (Eg = 1.8 eV). It is being This heterostructure prevents holes from being injected into the N ⁺ emitter layer, as shown by the arrow.

Figure 2 shows a p ⁺ type hetero semiconductor layer and a p type single crystal Si
It is a band structure diagram of the junction with. P type single crystal Si
By joining the P ⁺ type hetero semiconductor layers, the electrons in P generated by photoexcitation move to PP ⁺
It is repelled from the interface and, as a result, effectively taken out to the outside, resulting in an improvement in conversion efficiency.

〔Example〕

Examples of the present invention will be described below.

Example 1 A specific application example will be explained using FIG.

1, 2 and 3 are a base layer, an emitter layer and a collector layer, respectively, and 4 is a hetero semiconductor layer. 5 and 6 are an oxidized passivation layer and an antireflection film, and 7 and 8 are an emitter electrode and a collector electrode, respectively.

The above NPP ⁺ structure was fabricated on a P type single crystal Si substrate 1 by a normal diffusion technique, and an N ⁺ type hetero semiconductor layer 4 was formed on the surface of this N type emitter layer 2 using a plasma CVD method. in this way,
Using a mixed gas of SiH ₄ -H ₂ (molar ratio 1:30) and PH ₃ (PH ₃ /SiH ₄ = 1000 ppm) as a dopant, a high frequency electric field of 13 MHz was applied under a low vacuum of 1 to 3 Torr. As a result of setting the substrate temperature to 200°C, a microcrystalline silicon layer with a specific resistance of 0.01Ω·cm was obtained. The layers and electrodes 5-8 were formed using conventional techniques, resulting in a reverse emitter current density of 10 ^-14 A/cm ² .

Example 2 A case where a stacked hetero semiconductor is used as the hetero semiconductor layer will be described.

A photo-CVD method was used to form the hetero semiconductor layer. In this method, a reactive gas is irradiated with ultraviolet light from a low-pressure mercury lamp, and a semiconductor layer is formed by photolysis. A semiconductor layer with a small forbidden band width is
The Si ₂ H ₆ −SiH ₂ −H ₂ based reactive gas is used to fabricate the Si 2 H 6 −SiH 2 −H 2 semiconductor layer, while the semiconductor layer with a wide forbidden band width is formed using Si ₂ H ₆ −H _{2 .}
Produced using reactive gases. By repeating these methods alternately, laminated wide gap semiconductor layers were formed. The forbidden band width of the obtained N-type hetero semiconductor is approximately 1.5 eV, the specific resistance is 0.05 Ω・cm,
A reverse saturation current comparable to that of Example 1 was obtained.

Example 3 An example of application to a PP ⁺ type isoheterostructure will be explained. In order to form the P ⁺ type hetero semiconductor 4, a plasma CVD method was used. In this method, SiH ₄ −
Using H ₂ -based reaction gas (molar ratio 1:106) and B ₂ H ₆ (B ₂ H ₆ /SiH ₄ = 1000 ppm) as a dopant,
A high frequency electric field of 13 MHz was applied under a low vacuum of 1 to 3 Torr.

The obtained film was P ⁺ type, had an attractive resistance of 1 Ω·cm, and a forbidden band width of 1.8 eV. As a result, the open circuit voltage of the solar cell increased by about 20 mV.

〔Effect of the invention〕

According to the present invention, it is possible to easily provide a crystalline silicon solar cell with a small reverse current and a high photoelectric conversion efficiency.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining the principle of the present invention, and FIG. 3 is a diagram showing the basic structure of the present invention. DESCRIPTION OF SYMBOLS 1... Base layer, 2... Emitter layer, 3... Collector layer, 4... Hetero semiconductor layer, 5... Oxide film, 6... Antireflection film, 7... Emitter electrode, 8
...Collector electrode.

Claims (1)

[Claims] 1. In a crystalline silicon solar cell having a junction consisting of a first crystalline silicon semiconductor layer and a second crystalline silicon semiconductor layer, the junction of the first crystalline silicon semiconductor layer is opposite to the junction of the first crystalline silicon semiconductor layer. a microcrystalline silicon layer and a passivation layer formed in contact with a side surface, and an electrode partially formed on a surface formed of the microcrystalline silicon layer and passivation layer at least in contact with the microcrystalline silicon layer. and the microcrystalline silicon layer has a wider forbidden band width than the first crystalline silicon semiconductor layer and is of the same conductivity type as the first crystalline silicon semiconductor layer. battery. 2. The crystalline silicon solar cell according to claim 1, wherein the microcrystalline silicon layer contains at least one selected from the group consisting of oxygen, nitrogen, and hydrogen. 3. In a crystalline silicon solar cell having a junction consisting of a first crystalline silicon semiconductor layer and a second crystalline silicon semiconductor layer, in contact with a surface of the first crystalline silicon semiconductor layer opposite to the junction. The semiconductor stack has a formed semiconductor stack and a passivation layer, and an electrode is formed on a surface of the semiconductor stack and the passivation layer, at least partially in contact with the semiconductor stack, and the semiconductor stack has a forbidden band. It has a structure in which silicon-based semiconductor layers having a wide width and silicon-based semiconductor layers having a narrow forbidden band width are alternately stacked, and the forbidden band width thereof is larger than that of the first crystalline silicon semiconductor layer,
A crystalline silicon solar cell characterized in that the conductivity type thereof is the same as that of the first crystalline silicon semiconductor layer. 4. The crystalline silicon solar cell according to claim 3, wherein the semiconductor layer with a wide forbidden band width contains at least one member selected from the group consisting of oxygen, nitrogen, and hydrogen.