JP2011181768A - Method for manufacturing photoelectric conversion device - Google Patents

Abstract

A photoelectric conversion device that suppresses a decrease in the amount of generated current and exhibits high power generation characteristics in a long wavelength region even when the germanium concentration in an i layer mainly containing crystalline silicon germanium is increased. For the purpose.
A photoelectric conversion layer 3 having a pin junction or a nip junction formed by laminating a p layer 31, a crystalline silicon germanium i layer 32, and an n layer 33 on a substrate 1 with a transparent conductive film 2 is provided. A method for manufacturing a photoelectric conversion device, comprising: a film forming process for forming the crystalline silicon germanium i layer 32 having a germanium concentration of 10 atomic% or more and 50 atomic% or less by a plasma CVD method. The oxygen-containing impurity gas is added at a rate such that the area of the quantum efficiency spectrum is larger than the case where the oxygen-containing impurity gas is not added to the sum of the silicon-based gas flow rate and the germanium-based gas flow rate. The concentration of oxygen contained in the quality silicon germanium i layer 32 is controlled.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a photoelectric conversion device, and more particularly to a method for manufacturing a photoelectric conversion device in which a power generation layer is formed by film formation.

  As a photoelectric conversion device used for a solar cell that converts sunlight energy into electric energy, a thin film of a p-type semiconductor (p layer), an i-type semiconductor (i layer), and an n-type semiconductor (n layer) is formed by plasma CVD. 2. Description of the Related Art A thin-film silicon photoelectric conversion device including a photoelectric conversion layer having a pin junction formed by film formation or the like is known.

  A crystalline silicon germanium film has been developed as one of the films of a photoelectric conversion layer used in a thin film silicon solar cell. It is known that the crystalline silicon germanium film has a narrow gap as compared with crystalline silicon and has excellent absorption characteristics in the infrared region. Crystalline silicon germanium is expected to be a photoelectric conversion material that can absorb high wavelength sunlight and achieve high efficiency by using it as a laminated structure with other photoelectric conversion materials such as amorphous silicon and crystalline silicon. Has been.

Patent Document 1 includes a method for manufacturing a photoelectric conversion device including a microcrystalline silicon germanium i layer containing germanium in an amount of 50 atomic% or more, and forming the microcrystalline silicon germanium i layer at a film forming temperature of 100 ° C. to 250 ° C. Is disclosed.
Patent Document 2 discloses a photoelectric conversion in which a short-circuit current is improved by forming a microcrystalline silicon germanium i layer by a plasma CVD method using a source gas having a microcrystalline silicon germanium i layer and a reduced oxygen concentration. An apparatus manufacturing method is disclosed.

JP 2009-38064 A (Claim 1 and paragraph [0006]) JP 2007-180364 A (Claim 3 and paragraph [0010])

  In a photoelectric conversion device including a crystalline silicon germanium i layer having a pin junction, increasing the germanium concentration in the crystalline silicon germanium i layer can increase the amount of light absorption in a long wavelength region having a wavelength of 800 nm or more. Can do. On the other hand, when the germanium concentration in the crystalline silicon germanium i layer is increased, the p-type defect level in the crystalline silicon germanium i layer increases. In such a crystalline silicon germanium i layer, since the built-in electric field becomes weak, the spectral sensitivity spectrum is remarkably lowered.

For example, in the region where the germanium concentration in the crystalline silicon germanium i layer is 20 atomic% or less, the amount of generated current is improved as the germanium concentration is increased. However, when the germanium concentration in the i layer exceeds 20 atomic%, the sensitivity in the short wavelength region with a wavelength of 800 nm or less decreases as the germanium concentration increases, and the amount of generated current tends to decrease.
Moreover, even if the germanium concentration in the crystalline silicon germanium i layer is 20 atomic% or less, the sensitivity in the short wavelength region is lowered when the crystalline silicon germanium i layer is thicker than 1 μm. Therefore, the generated current gradually decreases as the film thickness increases.

  In order to increase the efficiency of solar cells, further increase in short-circuit current is required. However, as described above, under the high germanium concentration condition where the amount of light absorption is large, photogenerated carriers cannot be extracted effectively, and the amount of generated current is reduced.

  In the photoelectric conversion device disclosed in Patent Document 1, generation of p-type defect levels is suppressed by lowering the film forming temperature of the i layer, and a significant decrease in spectral sensitivity spectrum accompanying an increase in germanium concentration is suppressed. ing. However, it is necessary to lower the film forming temperature as the germanium concentration increases, and as a result, the higher the germanium concentration, the smaller the crystal grain size and the lower the power generation characteristics.

  The present invention has been made in view of such circumstances, and even when the germanium concentration in the i layer mainly composed of crystalline silicon germanium is increased, the decrease in the amount of generated current is suppressed, An object is to manufacture a photoelectric conversion device exhibiting high power generation characteristics in a long wavelength region.

  In order to solve the above problems, the present invention provides a pin junction or a nip junction in which a p-type semiconductor layer, a crystalline silicon germanium i-type semiconductor layer, and an n-type semiconductor layer are stacked on a substrate with a transparent conductive film. A process for producing a photoelectric conversion device having a photoelectric conversion layer comprising: forming a crystalline silicon germanium i-type semiconductor layer having a germanium concentration of 10 atomic% to 50 atomic% by a plasma CVD method And the film-forming step has a larger area of the quantum efficiency spectrum than when the oxygen-containing impurity gas is not added to the sum of the silicon-based gas flow rate and the germanium-based gas flow rate. Provided is a method for manufacturing a photoelectric conversion device which is added in such a ratio and controls the concentration of oxygen contained in the crystalline silicon germanium i layer.

  The germanium concentration of the crystalline silicon germanium i-type semiconductor layer (crystalline silicon germanium i layer) is preferably at least 10 atomic% in order to obtain high quantum efficiency in the long wavelength region. However, if germanium is added too much, the band gap becomes too small and the open voltage of the solar cell is extremely reduced. Therefore, the germanium concentration is preferably 50 atomic percent or less, more preferably 30 atomic percent or less. preferable.

  As a result of diligent research, the present inventors have found that a dangling bond of crystalline germanium such as microcrystalline germanium or polycrystalline germanium is p-type in a crystalline silicon germanium i-type semiconductor layer (crystalline silicon germanium i layer). Although a defect level is formed, it has been found that by adding a predetermined amount of oxygen to the crystalline silicon germanium i layer, there is an effect of reducing the p-type defect level density in the crystalline silicon germanium i layer. .

According to the present invention, even when the germanium concentration in the crystalline silicon germanium i layer is increased, the generation of p-type defect levels is suppressed by controlling the oxygen concentration in the crystalline silicon germanium i layer. It becomes possible to do. In a state where silicon and germanium are mixed, oxygen bonds not only to germanium but also to silicon. Therefore, the oxygen-containing impurity gas is added at a predetermined ratio with respect to the sum of the flow rates of the silicon-based gas and the germanium-based gas in consideration of the amount of oxygen combined with silicon. By doing so, a desired p-type defect level density reduction effect can be obtained. The “silicon-based gas” is a gas made of Si hydride such as SiH ₄ or Si ₂ H ₆ or SiF ₄ . The “germanium-based gas” is a gas composed of GeH ₄ , Ge ₂ H ₆ , GeF ₄ or the like.

  The addition amount of the oxygen-containing impurity gas is set to an amount such that the area of the quantum efficiency spectrum is larger than when no oxygen-containing impurity gas is added. Thereby, the power generation performance of the photoelectric conversion device can be improved.

  In the above invention, adding the oxygen-containing impurity gas in an amount such that the maximum value of the quantum efficiency spectrum in a wavelength region of 300 nm or more and 1200 nm or less is shorter than the case where the oxygen-containing impurity gas is not added. preferable.

  In Patent Document 2, the short-circuit current of the photoelectric conversion device is improved by reducing the oxygen concentration in the crystalline silicon germanium i layer to a predetermined value. However, according to studies by the present inventors, there is an optimum value for the concentration of oxygen contained in the crystalline silicon germanium i layer. If the oxygen concentration of the crystalline silicon germanium i layer is low, the effect of reducing the p-type defect level cannot be sufficiently obtained. On the other hand, if the oxygen concentration of the crystalline silicon germanium i layer is too high, the sensitivity in the long wavelength region is lowered, thereby reducing the short-circuit current. Therefore, the oxygen concentration in the crystalline silicon germanium i layer is not simply reduced, but by adding the oxygen-containing impurity gas so that the oxygen concentration in the crystalline silicon germanium i layer is within the optimum value range, It becomes possible to manufacture the photoelectric conversion device with improved short-circuit current more reliably.

The optimum value of the oxygen concentration contained in the crystalline silicon germanium i layer depends on conditions such as the germanium concentration contained in the crystalline silicon germanium i layer, the film thickness of the crystalline silicon germanium i layer, and the material of the transparent conductive film. Different.
According to the study by the present inventors, when the amount of the oxygen-containing impurity gas is increased, the area of the quantum efficiency spectrum is increased as the first stage, and when a certain threshold is exceeded, the long wavelength of the quantum efficiency spectrum is set as the second stage. The spectral height on the side does not change much, the spectral height on the short wavelength side (<700 nm) increases, and the maximum value on the short wavelength side or the maximum value of the quantum efficiency spectrum tends to shift to the short wavelength side. When another threshold is exceeded, the quantum efficiency spectrum on the long wavelength side starts to decrease as the third stage. When the quantum efficiency spectrum is in the first stage or the second stage, the power generation characteristics of the photoelectric conversion device can be improved.

According to the above invention, it is preferable to add the oxygen-containing impurity gas in such an amount that the area of the quantum efficiency spectrum in the wavelength region of 800 nm or more and 1200 nm or less is larger than when the oxygen-containing impurity gas is not added.
By doing so, a photoelectric conversion device with high long wavelength sensitivity can be manufactured.

According to the above invention, the oxygen-containing impurity gas is CO ₂ gas, and the CO ₂ gas is flowed at a flow rate of 0.3% or more and 3% or less with respect to the sum of the silicon-based gas flow rate and the germanium-based gas flow rate. It is preferable that the crystalline silicon germanium i-type semiconductor layer having the germanium concentration of 10 atomic% or more and 30 atomic% or less is added.
By adding the CO ₂ gas within the above range, the crystalline silicon germanium i-type semiconductor layer containing oxygen within the optimum value range can be formed.

  According to the present invention, the p-type defect level of germanium is reduced by adding a predetermined amount of impurity gas (mainly oxygen) during the formation of the crystalline silicon germanium i layer. As a result, even when the germanium concentration contained in the crystalline silicon germanium i layer increases, a photoelectric conversion device that can obtain a high power generation current can be manufactured.

It is the schematic which shows the structure of the photoelectric conversion apparatus which concerns on this embodiment. It is a graph showing the relationship between the CO ₂ amount and the carrier concentration of crystalline germanium thin film. It is a graph showing the relationship between the CO ₂ amount and the oxygen concentration. 3 is a graph showing a quantum efficiency spectrum of Example 1. 6 is a graph showing a quantum efficiency spectrum of Example 2. 6 is a graph showing a quantum efficiency spectrum of Example 3. 10 is a graph showing a quantum efficiency spectrum of Modification 1. It is a graph which shows the quantum efficiency spectrum of the modification 2 and the modification 3.

Hereinafter, an embodiment of a method for producing a photoelectric conversion device according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration of a photoelectric conversion device manufactured by the method for manufacturing a photoelectric conversion device according to the present embodiment. The photoelectric conversion device 100 is a single-type silicon solar cell, and includes a substrate 1, a transparent electrode layer 2, a solar cell photoelectric conversion layer 3, and a back electrode layer 4. Here, the silicon-based is a generic name including silicon (Si), silicon carbide (SiC), and silicon germanium (SiGe). Further, the crystalline silicon system means a silicon system other than the amorphous silicon system, and includes microcrystalline silicon and polycrystalline silicon.

  A glass substrate having a flat surface (for example, 50 mm × 50 mm × plate thickness: 1.1 mm, Corning # 1737) is used as the substrate 1.

Next, a transparent conductive film having a film thickness of about 2 μm mainly composed of GZO (Ga-doped ZnO) is formed as a transparent electrode layer 2 on the glass substrate 1 using a sputtering apparatus in a reduced pressure atmosphere. The film forming temperature can be selected from room temperature to 200 ° C. After film formation, an etching process is performed by a wet method or a dry method. At this time, a texture with appropriate irregularities is formed on the surface of the transparent conductive film. In the case of a wet process, dilute hydrochloric acid is used as an etching solution. The concentration, liquid temperature, and treatment time may be adjusted as appropriate. In this embodiment, it is preferable that the haze rate with respect to the wavelength of 800 nm to 1100 nm of the transparent electrode layer 2 is 80% or more.
In the present embodiment, the manufacturing method of the transparent electrode layer 2 employs a sputtering method, but may be an MOCVD method or a thermal CVD method. Further, although GZO is used as the transparent electrode layer 2, AZO (Al-doped ZnO) or SnO ₂ : F may be used.

  Next, heat treatment of the transparent electrode layer 2 is performed by lamp annealing (from room temperature to 600 ° C. for about 15 minutes in a vacuum). The sheet resistance of the transparent electrode layer 2 subjected to the heat treatment is preferably in the range of 10Ω / □ or more and 40Ω / □ or less.

Next, a titanium oxide film 21 and a zinc oxide film 22 may be sequentially formed as a conductive antireflection layer. In that case, the titanium oxide film 21 is formed on the transparent electrode layer 2. The titanium oxide film 21 contains titanium oxide as a main component and may contain a dopant or the like in order to improve conductivity. The thickness of the titanium oxide film 21 is preferably in the range of 10 nm to 100 nm. The titanium oxide film 21 is formed by sputtering at a substrate temperature of about 300.degree.
The zinc oxide film 22 is formed on the titanium oxide film 21. The zinc oxide film 22 contains zinc oxide as a main component and may contain a dopant or the like in order to improve conductivity. The thickness of the zinc oxide film 22 is preferably in the range of 1 nm to 50 nm. The zinc oxide film 22 is formed by sputtering in the same manner as the titanium oxide film so that it can be continuously formed with the titanium oxide film 21.

The solar cell photoelectric conversion layer 3 includes a p layer 31, a crystalline silicon germanium i layer 32, and an n layer 33.
The p layer 31 is mainly made of B-doped microcrystalline silicon and has a thickness of 10 nm to 60 nm.
The crystalline silicon germanium i layer 32 is mainly microcrystalline silicon germanium, and has a film thickness of 1.0 μm or more and 3.4 μm or less. The germanium concentration of the crystalline silicon germanium i layer 32 is 10 atomic% or more and 50 atomic% or less.
The n layer 33 has a laminated structure in which amorphous silicon, crystalline silicon, or a combination of the two is used, and the film thickness of the entire n layer is 20 nm to 100 nm.

The p layer 31 and the n layer 33 use SiH ₄ , H ₂ , B ₂ H ₆ or PH ₃ as a source gas, a reduced pressure atmosphere: 3000 Pa or less, a substrate temperature: about 140 to 230 ° C., a plasma generation frequency: 13 MHz or more and 100 MHz. The film is formed under the following conditions.

The crystalline silicon germanium i layer 32 uses a plasma CVD apparatus and uses SiH ₄ gas, GeH ₄ gas, and H ₂ gas as source gases, a reduced pressure atmosphere: 3000 Pa or less, a substrate temperature: about 200 ° C., and a plasma generation frequency: 40 MHz or more. Film is formed at 100 MHz or less. At this time, the impurity gas containing oxygen is added at a predetermined ratio with respect to the sum of the flow rates of the SiH ₄ gas and the GeH ₄ gas. In this embodiment, CO ₂ gas is selected as the impurity gas containing oxygen.

In this embodiment, SiH ₄ gas and GeH ₄ gas are used as source gases. However, SiH ₄ gas may be Si ₂ H ₆ gas or SiF ₄ gas, and GeH ₄ gas may be Ge ₂ H ₆ or GeF _4. good.
In this embodiment, the impurity gas containing oxygen is CO ₂ gas. However, other impurity gas containing oxygen such as CO, O ₂ , H ₂ O, and N ₂ O may be selected. In this case, since the gas decomposition efficiency by plasma depends on the gas type, it is necessary to set a flow rate suitable for each gas type.
Further, it is preferable that the hydrogen flow rate is appropriately changed according to the amount of CO ₂ added so that the crystallinity of the crystalline silicon germanium i layer 32 does not decrease.

As described above, in the film forming process of the crystalline silicon germanium i layer 32, the generation of p-type defect levels in the crystalline silicon germanium i layer 32 is suppressed by adding an impurity gas containing oxygen. Can do.
In order to confirm the above effect, the carrier concentration was measured when oxygen was added to crystalline germanium. A flow rate ratio of CO ₂ gas to GeH ₄ gas was changed from 0 to 4, and a crystalline germanium thin film (germanium concentration 100%) having a thickness of about 500 nm was formed on a glass substrate (Corning # 1737). Was used as a measurement sample. At this time, the hydrogen flow rate was appropriately increased according to the amount of CO ₂ added so that the crystallinity of crystalline germanium did not decrease. The crystallinity was evaluated by a Raman scattering spectrum, and the ratio of crystalline germanium having a wave number of 300 cm ^{−1 to} the peak of amorphous germanium having a wave number of 270 cm ⁻¹ was used as an index of the crystallization rate. An Al electrode was deposited on the sample, and Hall measurement was performed using the van der Pauw method under application of an alternating magnetic field.

FIG. 2 shows the relationship between the CO ₂ addition amount and the carrier concentration in the crystalline germanium thin film. In the figure, the horizontal axis represents the ratio of the flow rate of CO _{2 to} the GeH ₄ gas flow rate, and the vertical axis represents the carrier concentration. According to FIG. 2, the hole concentration due to the p-type defect level decreased with an increase of CO ₂ by about two orders of magnitude, and majority carriers became electrons when CO ₂ / GeH ₄ > 1.5. From the above results, it was confirmed that the p-type level caused by dangling bonds of crystalline germanium was inactivated by the addition of CO _{2 in} the film forming process.

Next, when the germanium concentration in the crystalline silicon germanium i layer 32 is 10 atomic%, 20 atomic%, and 30 atomic%, the amount of CO ₂ gas added to the sum of the flow rates of SiH ₄ gas and GeH ₄ gas is The oxygen concentration in the crystalline silicon germanium i layer 32 when changed was confirmed.
A crystalline silicon germanium i layer having a germanium concentration of 10 atomic%, 20 atomic%, and 30 atomic% was formed on a crystalline silicon substrate with a natural oxide film. The CO ₂ gas concentration in the film formation was 0%, 0.3%, 1%, 2% and 3%, and the film thickness was about 500 nm. Amorphous silicon (film thickness: 500 nm) was formed on the i layer for the purpose of preventing the diffusion of atmospheric impurities from the outside. After the sample was taken out into the atmosphere, the germanium concentration and oxygen concentration in the crystalline silicon germanium i layer were measured by SIMS.

FIG. 3 shows the oxygen concentration in the crystalline silicon germanium i layer 32. In the figure, the horizontal axis represents the flow rate (%) of CO ₂ with respect to the sum of the flow rates of SiH ₄ gas and GeH ₄ gas, and the vertical axis represents the oxygen concentration. It was confirmed that the oxygen concentration in the crystalline silicon germanium i layer changed linearly with respect to the CO ₂ gas concentration, and was almost independent of the germanium concentration. Oxygen concentration in the crystalline silicon germanium i layer is, CO ₂ when gas concentration of 0.3% 8.4 × ^{10 18} atoms ^/ cm 3 ^~1.1 × ^{10 19} atoms ^/ cm 3, CO ₂ gas concentration In the case of 1%, 3.2 × 10 ¹⁹ pieces / cm ^{3 to} 3.9 × 10 ¹⁹ pieces / cm ³ , and in the case where the CO ₂ gas concentration is 2%, 6.9 × 10 ¹⁹ pieces / cm ³ to 8 × 10 ¹⁹ pieces ^/ cm 3, CO ₂ gas concentration was 3% for about 1.4 × ^{10 20} atoms / cm ^3.

  The predetermined ratio is determined by determining the conditions such as the concentration of germanium contained in the crystalline silicon germanium i layer 32, the film thickness of the crystalline silicon germanium i layer 32, the material of the transparent conductive film, and the like. Check and set the optimum gas addition range. The optimum addition amount range is derived from the area and shape of the obtained quantum efficiency spectrum by producing a photoelectric conversion device in which only the addition amount of the impurity gas containing oxygen is changed, measuring its quantum efficiency, and so on. good.

In the film forming process of the crystalline silicon germanium i layer 32 of the present embodiment, when the amount of impurity gas containing oxygen is increased, the shape of the quantum efficiency spectrum largely changes in three stages. In the first stage, the area of the quantum efficiency spectrum increases. In the second stage, the maximum value of the quantum efficiency spectrum is shifted to the short wavelength side. In the third stage, the quantum efficiency spectrum on the long wavelength side starts to decrease. When the quantum efficiency spectrum is in the shape of the second stage, preferably the shape of the boundary between the second stage and the third stage, the area of the quantum efficiency spectrum is maximized. That is, the oxygen concentration in the crystalline silicon germanium i layer can be brought close to the optimum value by adding the oxygen-containing impurity gas so that the maximum value of the quantum efficiency spectrum is shifted to the short wavelength side.
In the present embodiment, an impurity gas containing an amount of oxygen is added such that the area value of the quantum efficiency spectrum is larger than that in which no impurity gas containing oxygen is added. It is further desirable that the maximum value of the quantum efficiency spectrum is on the short wavelength side as compared with that in which no impurity gas containing oxygen is added.

In the step of forming the crystalline silicon germanium i layer 32, the source gas is preferably introduced into the plasma CVD apparatus through an oxygen reducing means such as a purifier. Commercially available source gas inevitably contains oxygen. For example, the specifications of a general high-purity gas cylinder are: SiH ₄ gas: O ₂ , CO, CO ₂ , H ₂ O <1 ppm, GeH ₄ gas: O ₂ , CO ₂ <1 ppm H ₂ O <5 ppm, H ₂ gas : O ₂ , CO, CO ₂ <0.05 ppm H ₂ O <0.5 ppm. As described above, oxygen inevitably contained in the raw material gas cylinder varies depending on the lot of the gas cylinder. In this embodiment, since the amount of CO ₂ added in the step of forming the crystalline silicon germanium i layer 32 is very small, the degree of purification of the source gas affects the control of the oxygen concentration in the crystalline silicon germanium i layer 32. There is also a possibility of affecting. Therefore, the oxygen concentration in the crystalline silicon germanium i layer 32 can be controlled more stably by reducing the inevitable oxygen contained in the source gas by the oxygen reducing means.

  In forming an i-layer film mainly composed of microcrystalline silicon germanium by the plasma CVD method, the distance d between the plasma discharge electrode and the surface of the substrate 1 is preferably 3 mm or more and 10 mm or less. If it is smaller than 3 mm, it is difficult to keep the distance d constant from the accuracy of each component device in the film forming chamber corresponding to the large substrate, and there is a possibility that the discharge becomes unstable because it is too close. When it is larger than 10 mm, it is difficult to obtain a sufficient film forming speed (1 nm / s or more), and the uniformity of the plasma is lowered and the film quality is lowered by ion bombardment.

  An Ag film having a thickness of 150 nm or more and 500 nm or less is formed as the back electrode layer 4 by using a sputtering apparatus in a reduced pressure atmosphere at room temperature. As the protective film 42 for protecting the Ag film, a ZnO film: 10 nm or more and 20 nm or less may be stacked. For the purpose of reducing the contact resistance between the n layer 33 and the back electrode layer 4 and improving the light reflection, a film thickness of 40 nm is formed between the photoelectric conversion layer 3 and the back electrode layer 4 as a back transparent electrode layer 41 by a sputtering apparatus. A GZO (Ga-doped ZnO) film or an AZO (Al-doped ZnO) film having a thickness of 100 nm or less may be formed.

After the back electrode layer 4 is laminated, cell separation is performed as appropriate, and post-annealing at 180 ° C. to 200 ° C. is performed for 2 hours and 10 minutes. After that, power generation characteristics are evaluated. As the cell separation method, a laser etching method or a plasma etching method can be applied. The cell size is, for example, an area of 1 cm ² .

  The p-i-n type photoelectric conversion device is completed through the above steps. The photoelectric conversion device may be of a single type, but a photoelectric conversion unit using an amorphous silicon-based material or a crystalline silicon-based material for the i layer is provided in a pi / n / p- stage before the photoelectric conversion unit of the present invention. A higher conversion efficiency can be obtained by laminating like i-n and p-i-n / p-i-n / p-i-n.

  In addition, although the manufacturing method of the pin type photoelectric conversion apparatus was demonstrated in the said embodiment, this invention is applicable also to the manufacturing method of an nip type photoelectric conversion apparatus. Further, the i layer may contain impurities such as B and P. That is, the present invention can also be applied to a method for manufacturing a pn photoelectric conversion device.

Using a glass substrate 1 having a flat surface (5 cm × 5 cm × plate thickness: 1.1 mm), single-type solar cells (Examples 1 to 3) having the configuration shown in FIG. 1 were produced according to the embodiment.
Transparent electrode layer 2: GZO film: Average film thickness 1000 nm
Antireflection layer: TiO ₂ film 22 / AZO film 23, average film thickness 70 nm / 10 nm
p layer 31: Average film thickness 15 nm
Crystalline silicon germanium i layer 32: Average film thickness of 1000 to 3400 nm
n layer 33: Average film thickness 60 nm
Back surface transparent electrode layer 41: GZO film 41 / average film thickness 40 nm
Back electrode layer 4: Ag film / average film thickness 200 nm
Protective film 42: ZnO film / average film thickness 20 nm

Example 1
In Example 1, the concentration of CO ₂ gas added during film formation is 0%, 1.6%, 2.4%, or 3.0%, respectively, the germanium concentration is 30 atomic%, and the film thickness is 1 μm. A single type solar battery cell having the silicon germanium i layer 32 formed thereon was produced. The spectral sensitivity characteristics of Example 1 were measured under the white bias irradiation conditions of AM1.5 (100 mW / cm ² ) under the conditions of normal temperature, bias voltage 0 V, and light receiving area 1 cm ² .

FIG. 4 shows the quantum efficiency spectrum of Example 1. In the figure, the horizontal axis represents wavelength and the vertical axis represents quantum efficiency. By increasing the CO ₂ gas concentration in the step of forming the crystalline silicon germanium i layer 32, the area of the quantum efficiency spectrum increased over the entire wavelength region (300 nm to 1200 nm). Moreover, the spectrum on the long wavelength side of the quantum efficiency spectrum when the CO ₂ gas concentration was 3.0% was lower than the quantum efficiency spectrum when the CO ₂ gas was not added.

Next, Table 1 shows the maximum values at each CO ₂ concentration.

The maximum value of the quantum efficiency spectrum when the CO ₂ gas concentration was 3.0% was shifted to the short wavelength side as compared to the quantum efficiency spectrum when no CO ₂ gas was added.

＊１ ＣＯ_２／（ＳｉＨ_４＋ＧｅＨ_４）％ For Example 1, it was measured AM1.5 (100mW / cm ²⁾ current-voltage characteristics per area 1 cm ² under the irradiation condition.
Table 2 shows the solar cell current-voltage characteristics of Example 1.

* 1 CO ₂ / (SiH ₄ + GeH ₄ )%

According to Table 2, when the CO ₂ / (SiH ₄ + GeH ₄ ) ratio was 2.4%, the current value increased by about 8 mA / cm ² compared to the case where CO ₂ was not added. The open circuit voltage and fill factor also increased slightly, and the conversion efficiency increased by about 1% in absolute value. However, if the CO ₂ addition amount is excessive, the short wavelength sensitivity is increased, but the current value for a long wavelength of 800 nm or more is lowered, resulting in deterioration of the solar cell characteristics.

(Example 2)
In Example 2, the concentration of CO ₂ gas added during film formation is 0%, 0.3%, 0.55%, 0.77%, or 1.0%, respectively, the germanium concentration is 20 atomic%, and the film thickness Produced a single solar cell having a crystalline silicon germanium i layer 32 of 1.75 μm. The spectral sensitivity characteristics of Example 2 were measured in the same manner as in Example 1.

FIG. 5 shows the quantum efficiency spectrum of Example 2. In the figure, the horizontal axis represents wavelength and the vertical axis represents quantum efficiency. Table 3 shows the maximum value at each CO ₂ concentration in Example 2.

As in Example 1, the area of the quantum efficiency spectrum increased in the entire wavelength region by increasing the CO ₂ gas concentration. In addition, the quantum efficiency spectrum when the CO ₂ gas concentration is 1.0% is compared with the quantum efficiency spectrum when the CO ₂ gas is not added, and the maximum value is shifted to the short wavelength side. The spectral height on the side was only slightly reduced. Thus, in Example 2, when the CO ₂ gas added at the time of film formation is added at a concentration exceeding 1.0%, it is considered that the spectrum on the long wavelength side is lowered.

＊１ ＣＯ_２／（ＳｉＨ_４＋ＧｅＨ_４）％ Using Example 2, the current-voltage characteristics were measured in the same manner as in Example 1.
Table 4 shows the solar cell current-voltage characteristics of Example 2.

* 1 CO ₂ / (SiH ₄ + GeH ₄ )%

When the CO ₂ / (SiH ₄ + GeH ₄ ) ratio was 0.77%, the current value increased by 6 mA / cm ² as compared to the case where CO ₂ was not added. The open circuit voltage also increased slightly, and the conversion efficiency increased by about 1%. However, if the amount of CO ₂ added is excessive, the short wavelength sensitivity is increased, but the long wavelength sensitivity is decreased, and thus the solar cell characteristics are deteriorated.

(Example 3)
In Example 3, a crystalline silicon germanium i layer 32 having a germanium concentration of 10 atomic% and a film thickness of 3.4 μm is formed by setting the CO ₂ gas concentrations added during film formation to 0% and 0.3%, respectively. A single type solar cell was prepared. The spectral sensitivity characteristics of Example 3 were measured in the same manner as in Example 1.

FIG. 6 shows the quantum efficiency spectrum of Example 3. In the figure, the horizontal axis represents wavelength and the vertical axis represents quantum efficiency. Table 5 shows the maximum values in each CO ₂ concentration of Example 3.

The addition of CO ₂ greatly increased the area of the short wavelength region (<700 nm) of the quantum efficiency spectrum, and the maximum value of the spectrum shifted to the short wavelength side.

＊１ ＣＯ_２／（ＳｉＨ_４＋ＧｅＨ_４）％ Using Example 3, the current-voltage characteristics were measured in the same manner as in Example 1.
Table 6 shows the solar cell current-voltage characteristics of Example 3.

* 1 CO ₂ / (SiH ₄ + GeH ₄ )%

When the CO ₂ / (SiH ₄ + GeH ₄ ) ratio was 0.3%, the current value increased by about 4 mA / cm ² as compared to the case where CO ₂ was not added. The conversion efficiency increased by about 0.5%.

(Modification 1)
In Modification 1, SnO ₂ : F manufactured by Asahi Glass Co., Ltd. is used for the transparent electrode layer 2, the CO ₂ gas concentration added at the time of film formation is 0% and 3.0%, respectively, and the germanium concentration is 30 atomic%, A single-type solar battery cell in which a crystalline silicon germanium i layer 32 having a thickness of 1 μm was formed was produced. Other configurations were the same as those in Example 1. The spectral sensitivity characteristics of Modification 1 were measured in the same manner as in Example 1.
In FIG. 7, the quantum efficiency spectrum of the modification 1 is shown. In the figure, the horizontal axis represents wavelength and the vertical axis represents quantum efficiency. The addition of CO ₂ significantly increased the area of the short wavelength region (<700 nm) of the quantum efficiency spectrum.

As shown in FIG. 4, in the single solar cell using ZnO of Example 1, the addition of 3% CO ₂ is clearly excessive, and the short wavelength sensitivity is increased while the long wavelength sensitivity is greatly decreased. is doing. On the other hand, in the single type solar cell using the SnO ₂ : F substrate shown in FIG. 7, the addition of 3% of CO ₂ is an appropriate amount, the short wavelength sensitivity is increased, and no significant change is observed in the long wavelength sensitivity. Since SnO ₂ : F has smaller surface irregularities and sharper irregular projections than ZnO, forming a crystalline silicon solar cell on such a substrate induces crystal grain boundaries and increases the dangling bond density. It has been reported. When SnO ₂ : F is used, it is considered that more germanium dangling bonds are formed as compared with ZnO. Therefore, it has been found that more oxygen concentration is required to inactivate this.

(Modification 2 and Modification 3)
In the second modification, the single-layered silicon silicon germanium i layer 32 having a germanium concentration of 20 atomic% and a film thickness of 1 μm is formed with the CO ₂ gas concentration added during film formation being 0% and 0.3%, respectively. Type solar cells were produced. Other configurations are the same as those of the first modification.
In the third modification, a single solar cell having the same configuration as that in the second modification except that the film thickness of the crystalline silicon germanium i layer 32 is set to 2 μm. The spectral sensitivity characteristics of Modification 2 and Modification 3 were measured in the same manner as in Example 1.

In FIG. 8, the quantum efficiency spectrum of the modification 2 and the modification 3 is shown. In the figure, the horizontal axis represents wavelength and the vertical axis represents quantum efficiency. According to FIG. 8, in the second modification and the third modification, the area of the short wavelength region (<700 nm) of the quantum efficiency spectrum was increased by the addition of CO ₂ gas. When the CO ₂ gas was not added, the short wavelength sensitivity was greatly lowered when the thickness of the crystalline silicon germanium i layer 32 was increased from 1 μm to 2 μm. According to the above results, increasing the film thickness has the same effect as increasing the germanium concentration. When the film thickness is 1 μm, high short wavelength sensitivity is obtained by adding 0.3% of CO ₂ gas, but the addition amount of CO ₂ gas is insufficient in a cell having a film thickness of 2 μm. Short wavelength sensitivity was still low.

Using modification 2 and modification 3, the current-voltage characteristics were measured in the same manner as in Example 1.
Table 7 shows the solar cell current-voltage characteristics of Modification 2 and Modification 3.

According to Table 7, in both Modification 2 and Modification 3, the addition of CO ₂ gas not only increased the short-circuit current, but also improved the conversion efficiency.

According to this embodiment, when CO ₂ gas is added at a predetermined ratio with respect to the sum of the flow rates of SiH ₄ gas and GeH ₄ gas in the process of forming the crystalline silicon germanium i layer 32, the short-circuit current increases. In addition, open circuit voltage, fill factor and conversion efficiency can be improved.

1 Substrate 2 Transparent electrode layer 3 Photoelectric conversion layer 4 Back electrode layer

Claims (4)

A photoelectric conversion device having a photoelectric conversion layer having a pin junction or a nip junction formed by stacking a p-type semiconductor layer, a crystalline silicon germanium i-type semiconductor layer, and an n-type semiconductor layer on a substrate with a transparent conductive film A manufacturing method comprising:
A film forming step of forming the crystalline silicon germanium i-type semiconductor layer having a germanium concentration of 10 atomic% or more and 50 atomic% or less by a plasma CVD method;
The film forming step is such that the area of the quantum efficiency spectrum is larger than the case where the oxygen-containing impurity gas is not added to the sum of the silicon-based gas flow rate and the germanium-based gas flow rate. A method for manufacturing a photoelectric conversion device, which is added to control a concentration of oxygen contained in the crystalline silicon germanium i-type semiconductor layer.   2. The oxygen-containing impurity gas is added in an amount such that a maximum value of the quantum efficiency spectrum in a wavelength region of 300 nm to 1200 nm is shorter than a case where the oxygen-containing impurity gas is not added. A method for manufacturing a photoelectric conversion device.   3. The oxygen-containing impurity gas is added in an amount such that an area of a quantum efficiency spectrum in a wavelength region of 800 nm or more and 1200 nm or less is larger than a case where the oxygen-containing impurity gas is not added. A method for manufacturing a photoelectric conversion device. The oxygen-containing impurity gas is CO ₂ gas,
The CO ₂ gas is added at a flow rate of 0.3% or more and 3% or less with respect to the sum of the silicon-based gas flow rate and the germanium-based gas flow rate, and the germanium concentration is 10 atomic percent or more and 30 atomic percent or less. The method for manufacturing a photoelectric conversion device according to any one of claims 1 to 3, wherein the crystalline silicon germanium i-type semiconductor layer is formed.

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