JP4443274B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a technology for improving the efficiency of a photoelectric conversion device.

  With the expansion of the solar cell market, thin-film silicon solar cells have attracted attention as next-generation solar cell technologies for reducing costs. The thin film silicon solar cell is formed by depositing a silicon thin film having a film thickness of about several μm on a glass substrate, a stainless steel substrate or the like by a plasma CVD method or the like. Therefore, not only the amount of silicon used can be reduced, but also a large area solar cell can be formed by a single film formation, so that the cost can be reduced. In addition, since the thin-film silicon semiconductor layer can be formed by a low-temperature process of 500 ° C. or less, the input energy at the time of manufacture can be greatly reduced as compared with a bulk crystal solar cell that requires a temperature of 1500 ° C. or more. .

The photoelectric conversion layer of the thin film silicon solar cell is generally formed of a semiconductor thin film such as hydrogenated amorphous silicon or hydrogenated microcrystalline silicon.
As described above, the thin-film silicon solar cell has the advantage of being able to reduce the cost due to the simultaneous formation of large areas and the effect of reducing input energy, but it is practically compared with bulk crystal solar cells. As a result, the market has not expanded significantly. The main factor is considered to be a low photoelectric conversion efficiency compared with the bulk crystal solar cell. In other words, the lower the photoelectric conversion efficiency of the solar cell, the more the number of solar cell modules for covering the same power generation capacity, and the installation cost increases at the same time, so low-cost thin-film silicon solar cells are used. Nevertheless, there is a problem that the system price is not necessarily lower than that of a bulk crystal solar cell. Therefore, high efficiency is an important issue for full-scale spread of thin film silicon solar cells.

  One of the conventional techniques used for increasing the efficiency of a thin-film silicon solar cell is a wide band gap of a semiconductor layer (hereinafter referred to as a window layer) on the light incident surface side of the solar cell. The thin-film silicon solar cell can increase the short-circuit current density by reducing the light absorption loss in the layer and increase the open-circuit voltage by increasing the diffusion potential by widening the band gap of the window layer. Can be increased. As a conventional technique related to the wide band gap of the window layer as described above, there is a thin film solar cell described in Patent Document 1. The thin film solar cell described in the document includes a p-type conductive p-type layer, a substantially intrinsic i-type layer, and a photoelectric conversion layer including at least one pin junction formed by laminating an n-type conductive n-type layer. A thin-film photoelectric conversion element having a conductive and light-transmissive first electrode provided on the light incident side of the photoelectric conversion layer, and a second electrode provided on a surface facing the first electrode , The i-type layer constituting the pin junction is made of microcrystalline silicon or microcrystalline silicon germanium, and at least one of the p-type layer and the n-type layer in contact therewith is a mixed crystal of microcrystalline silicon carbide and microcrystalline silicon. It is characterized by being.

Since the band gap of microcrystalline silicon carbide is larger than the band gap of microcrystalline silicon, light absorption in the p-type layer or the n-type layer is reduced, and photoelectric conversion efficiency is improved.
JP 2002-16271 A

  In the conventional thin film solar cell, in order to generate the wide band gap effect due to the inclusion of microcrystalline silicon carbide, the carbon content of the mixed crystal of microcrystalline silicon carbide and microcrystalline silicon is at least 10 atomic% or higher. It is necessary to make the concentration (see paragraph 9 of Patent Document 1).

  However, if the carbon content is 10 atomic% or more, the band gap discontinuity and mismatch increase between the layer containing microcrystalline silicon carbide and the i-type layer, so that the high-concentration defect region with a short carrier lifetime is obtained. On the contrary, the photoelectric conversion efficiency may decrease. In addition, in order to suppress the occurrence of the high-concentration defect region, a microcrystalline silicon layer not containing carbon or an interface layer with a gradually reduced carbon concentration is inserted between the layer containing microcrystalline silicon carbide and the i-type layer. (See paragraphs 7 and 8 of Patent Document 1). However, since the formation of the interface layer requires a technique for forming a very thin thin film uniformly over a large area, it causes an increase in manufacturing process costs and a decrease in yield. It is desirable to improve the photoelectric conversion efficiency without using.

  This invention is made | formed in view of the situation which concerns, and provides the photoelectric conversion apparatus with which high photoelectric conversion efficiency is obtained, without adding high concentration carbon to a p-type layer or an n-type layer.

  The photoelectric conversion device of the present invention includes a photoelectric conversion layer having a first conductive type layer made of a semiconductor, an i-type layer made of a microcrystalline semiconductor, and a second conductive type layer made of a semiconductor stacked in this order, and the first conductive type At least one of the layer and the second conductivity type layer is a carbon-containing layer made of microcrystalline silicon containing carbon atoms.

  The inventor makes at least one of the first conductivity type layer and the second conductivity type layer a carbon-containing layer made of microcrystalline silicon containing carbon atoms, so that the amount of carbon contained in the carbon-containing layer is small. For example, even when the concentration of carbon atoms is 0.1 to 9.8 atomic%, it has been found that high photoelectric conversion efficiency can be obtained, and the present invention has been completed.

  According to the present invention, high photoelectric conversion efficiency can be obtained even when the amount of carbon contained in the carbon-containing layer is small. Furthermore, since the amount of carbon contained in the carbon-containing layer is small, the band gap discontinuity or mismatch between the carbon-containing layer and the i-type layer is small. Therefore, it is not necessary to provide an interface layer between the two layers, and a photoelectric conversion device that is simple, inexpensive, and has high photoelectric conversion efficiency can be obtained.

  The carbon-containing layer is made of microcrystalline silicon. In general, microcrystalline silicon can be formed at a lower temperature than microcrystalline silicon carbide or the like. Therefore, the photoelectric conversion device of the present invention can be manufactured with less energy. Furthermore, the photoelectric conversion layer can be formed on an inexpensive substrate such as a low melting point plastic substrate, which leads to a reduction in manufacturing cost.

  Moreover, according to this invention, the photoelectric conversion apparatus with high photoelectric conversion efficiency can be obtained by making the density | concentration of the carbon atom of a carbon containing layer into 0.1-9.8 atomic%.

  The photoelectric conversion device of the present invention includes a photoelectric conversion layer having a first conductive type layer made of a semiconductor, an i-type layer made of a microcrystalline semiconductor, and a second conductive type layer made of a semiconductor stacked in this order, and the first conductive type At least one of the layer and the second conductivity type layer is a carbon-containing layer made of microcrystalline silicon containing carbon atoms.

  Specifically, the photoelectric conversion device of the present invention is implemented, for example, in the following manner.

1. Super straight type structure 1-1. General Matters The photoelectric conversion device according to the first embodiment of the present invention includes a transparent conductive layer, the photoelectric conversion layer, and the back electrode stacked in this order on a translucent substrate. In this case, the light transmissive substrate side is the light incident surface. Moreover, it is preferable to provide a back surface transparent conductive layer between the photoelectric conversion layer and the back surface electrode.

1-2. Translucent Substrate As the translucent substrate, a glass plate, a translucent resin having heat resistance such as polyimide or polyvinyl, or a laminate of them is preferably used. There is no particular limitation as long as the entire apparatus can be structurally supported. Further, a metal film, a transparent conductive film, or an insulating film may be coated on the surface.

1-3. Transparent conductive layer The transparent conductive layer is made of a transparent conductive material. For example, a single layer or a stacked layer of transparent conductive films such as ITO, tin oxide, or zinc oxide can be used. Since the transparent conductive layer plays a role as an electrode, it is preferable that the electrical conductivity is high, and a layer whose electrical conductivity is improved by adding a small amount of impurities can also be used. Examples of the method for producing the transparent conductive layer include known methods such as a sputtering method, a CVD method, an electron beam evaporation method, a sol-gel method, a spray method, and an electrodeposition method. Further, it is desirable that an uneven shape is formed on the surface of the transparent conductive layer. This unevenness can scatter and refract incident light incident from the translucent substrate side to extend the optical path length, so that the light confinement effect in the photoelectric conversion layer is enhanced and the short circuit current can be expected to be improved. As the method for forming the unevenness, in addition to the method of forming the transparent conductive layer once and then forming it by mechanical processing such as etching or sandblasting, it is formed by crystal growth of the film material when forming the transparent conductive layer. A method using surface irregularities, a method utilizing the formation of regular surface irregularities because the crystal growth surface is oriented, or the like may be used.
A substrate (trade name Asahi-U) in which a tin oxide layer is deposited on a white plate glass by a CVD method is used as a substrate utilizing unevenness formed during crystal growth of a film material, and sputtering is further performed on the substrate. A zinc oxide layer may be deposited by the method. In this case, when the photoelectric conversion layer is formed later, it is more preferable because the tin oxide layer can be prevented from being damaged by plasma.

1-4. Photoelectric conversion layer 1-4-1. General Matters The photoelectric conversion layer is formed on the transparent conductive layer. The photoelectric conversion layer includes a first conductive type layer made of a semiconductor, an i-type layer made of a microcrystalline semiconductor, and a second conductive type layer made of a semiconductor in this order. At least one of the first conductivity type layer and the second conductivity type layer is made of microcrystalline silicon containing carbon atoms. Here, “microcrystal” means a state in which a crystal phase and an amorphous phase are mixed. Therefore, “microcrystalline silicon” means a state in which crystalline silicon and amorphous silicon are mixed. The term “microcrystalline silicon containing carbon atoms” means a state in which carbon atoms are contained in the microcrystalline silicon. In other words, this means a state that does not substantially contain the crystalline phase of silicon carbide. This state can be confirmed by, for example, that when a Raman scattering spectrum of the microcrystalline silicon containing the carbon atom is observed, a peak attributed to a silicon-carbon bond in the silicon carbide crystal is not substantially detected. it can. This state may also be confirmed by substantially not detecting a diffraction peak attributed to the silicon carbide crystal structure in the X-ray diffraction method.
The carbon atom content in the first conductivity type layer or the second conductivity type layer can be determined by secondary ion mass spectrometry (SIMS). Further, “containing carbon atoms” does not include a case where a trace amount of carbon atoms is contained, for example, a case where carbon atoms are contained at a concentration of less than 0.01 atomic%. Also, the terms “microcrystalline silicon” and “amorphous silicon” are intended to include hydrogenated microcrystalline silicon and hydrogenated amorphous silicon, respectively, commonly used in the art.

1-4-2. First conductivity type layer and second conductivity type layer 1-4-2-1. General Matters The first conductivity type layer and the second conductivity type layer are layers made of semiconductors of n type and p type, or vice versa. As the conductivity determining element of the p-type layer, impurity atoms such as boron, aluminum, or gallium can be used. As the conductivity determining element of the n-type layer, impurity atoms such as phosphorus, nitrogen or oxygen can be used.

One of the first conductivity type layer and the second conductivity type layer is a carbon-containing layer made of microcrystalline silicon containing carbon atoms. In this case, even when the amount of carbon contained in the carbon-containing layer is small, high photoelectric conversion efficiency can be obtained. The reason why the high photoelectric conversion efficiency can be obtained is not necessarily clear, but the band gap of the carbon-containing layer is widened to increase the diffusion potential, the interface passivation of the crystal grain boundary due to the amorphous phase containing carbon atoms, and the carbon-containing layer / i. It is conceivable that interface recombination is reduced by the effect of mold layer interface passivation. In addition, since the open circuit voltage improvement effect appears at a low carbon concentration as compared with the prior art, the increase in defect density due to the addition of impurities is small, the decrease in the activation efficiency of the conductivity determining element due to the addition of impurities can be suppressed, the addition of impurities Advantages such as the ability to suppress the increase in the ratio of the amorphous phase in the carbon-containing layer due to the flammability and the need for an interface layer to suppress the discontinuity of the band gap with the i-type layer (such as the addition of low-concentration carbon effective.
The other of the first conductivity type layer and the second conductivity type layer is made of a semiconductor. Specifically, Si _x C _1-x in which carbon is added to silicon, or Si _x Ge in which germanium is added. _It consists of _1-x . This layer is polycrystalline, microcrystalline or amorphous. Further, this layer is preferably made of microcrystalline silicon or amorphous silicon, and more preferably made of microcrystalline silicon containing carbon atoms.

1-4-2-2. Carbon concentration The carbon-containing layer preferably has a carbon atom concentration (hereinafter referred to as “carbon concentration”) of 0.1 to 9.8 atomic%. This is because a particularly high photoelectric conversion efficiency can be obtained in this case.

  Moreover, it is preferable that the carbon concentration contained in a carbon containing layer is 3.3-9.8 atomic%. In this case, an even larger open-circuit voltage improving effect can be obtained, and as a result, higher photoelectric conversion efficiency can be obtained. When the carbon concentration is 3.3 atomic% or more, the effects such as the increase of the diffusion potential and the reduction of interface recombination appear synergistically, so that a higher open-circuit voltage can be obtained. It is thought that conversion efficiency can be obtained.

1-4-2-3. Hydrogen concentration Moreover, it is preferable that the concentration of hydrogen atoms contained in the carbon-containing layer (hereinafter referred to as “hydrogen concentration”) is 5 to 15 atomic%. When it is lower than 5 atomic%, the photoelectric conversion efficiency decreases. This is because the open-circuit voltage, short-circuit current density, and form factor decrease due to the fact that the band gap of microcrystalline silicon is reduced, the transmittance is lowered, and the passivation effect by hydrogen atoms is not sufficiently obtained. This is probably because of this. Moreover, when it is higher than 15 atomic%, the photoelectric conversion efficiency is lowered. This is presumably because the atomic arrangement of silicon is disturbed by hydrogen atoms that have excessively entered microcrystalline silicon. Here, the hydrogen concentration is a value obtained by secondary ion mass spectrometry (SIMS).

1-4-2-4. Formation temperature It is preferable that a carbon containing layer is formed at 90-250 degreeC. When the temperature is lower than 90 ° C., an etching effect due to atomic hydrogen in the plasma tends to occur, and it is difficult to form a carbon-containing layer uniformly. Further, when the temperature is higher than 250 ° C., hydrogen is likely to be desorbed from the microcrystalline silicon, and the volume fraction of the crystal phase is decreased due to the decrease in the hydrogen coverage on the surface of the microcrystalline silicon growth. In addition, since the carbon-containing layer does not need to contain a silicon carbide crystal phase, there is no reason for the high temperature.

  Moreover, by changing the formation temperature of the carbon-containing layer, the hydrogen concentration of the carbon-containing layer can be easily controlled. By setting the temperature to 90 to 250 ° C., the hydrogen concentration of the carbon-containing layer is 5 to 15 atomic%. can do.

1-4-3. i-type layer The i-type layer is made of a microcrystalline semiconductor to which no impurity is added, and is preferably made of microcrystalline silicon. However, a small amount of impurity elements may be included as long as it is a substantially intrinsic semiconductor. The i-type layer may be made of Si _x C _1-x to which carbon is added, Si _x Ge _1-x to which germanium is added, or the like.

1-4-4. Formation Method Each layer of the photoelectric conversion layer can be formed by a CVD method (atmospheric pressure CVD, low pressure CVD, plasma CVD, thermal CVD, hot wire CVD, MOCVD method, or the like). The silicon-containing gas used when forming each layer by the CVD method is not particularly limited as long as it contains silicon atoms such as SiH ₄ or Si ₂ H _6, but generally SiH ₄ is often used. As a diluent gas used together with the silicon-containing gas, H ₂ , Ar, or He can be used, but H ₂ is often used when forming amorphous silicon or microcrystalline silicon. Further, when forming the p-type layer or the n-type layer, a doping gas is used together with the silicon-containing gas and the dilution gas, and the doping gas is not particularly limited as long as it includes a target type conductivity determining element. In general, B ₂ H ₆ is often used when the p-type conductivity determining element is boron, and PH ₃ is often used when the n-type conductivity determining element is phosphorus. When the photoelectric conversion layer is formed by the above plasma CVD method, the existence ratio of the amorphous phase and the crystalline phase is controlled by appropriately controlling the film forming parameters such as the substrate temperature, pressure, gas flow rate, and input power to the plasma. Is possible. As the carbon-containing gas to be used for the carbon-containing layer formed, it is possible to use those containing carbon atoms such as a hydrocarbon (such as CH ₄ or C ₂ H _6).

1-5. Backside transparent conductive layer Preferably, a backside transparent conductive layer is formed on the photoelectric conversion layer. In this case, the effect of improving the light confinement and the light reflectance with respect to the incident light can be obtained. In addition, diffusion of elements contained in the back electrode to the photoelectric conversion layer can be suppressed. A back surface transparent conductive layer can be formed by the same material and manufacturing method as the transparent conductive layer described in 1-3.

1-6. Back Electrode The back electrode only needs to have at least one conductive layer, and the higher the light reflectivity, the higher the conductivity. The back electrode is formed on the photoelectric conversion layer or on the back transparent conductive layer. The back electrode can be formed of a metal material such as silver, aluminum, titanium, or palladium having a high visible light reflectance, or an alloy thereof. The back electrode can be formed by a CVD method, a sputtering method, a vacuum evaporation method, an electron beam evaporation method, a spray method, a screen printing method, or the like. The back electrode reflects light that has not been absorbed by the photoelectric conversion layer and returns it to the photoelectric conversion layer again, which contributes to an improvement in photoelectric conversion efficiency.

1-7. Others A super-straight type photoelectric conversion device usually includes a first conductive type layer, an i-type layer, and a second conductive type layer stacked in this order on a transparent substrate on which a transparent conductive layer is formed. Either the first conductivity type layer or the second conductivity type layer may be a carbon-containing layer, but the first conductivity type layer is preferably a carbon-containing layer. Since the incident light passes through the first conductivity type layer, the i-type layer, and the second conductivity type layer in this order, the effect of providing the carbon-containing layer is large because the first conductivity-type layer is a carbon-containing layer. Because it becomes.

  Further, according to the present invention, since the carbon content of the first conductivity type layer can be reduced, the crystallization rate of the first conductivity type layer can be increased. The first conductivity type layer serves as an underlayer for forming the i-type layer. By increasing the crystallization rate of the first conductivity type layer, the crystallization rate of the i-type layer formed thereon is also increased. As a result, the photoelectric conversion efficiency can be improved.

  That is, the first conductivity type layer is excellent as a window layer and excellent as an underlayer. Conventionally, since such a layer could not be formed, the present invention brings about an excellent effect particularly in a super straight type photoelectric conversion device.

  In addition, it is preferable that both a 1st conductivity type layer and a 2nd conductivity type layer are carbon containing layers. In this case, in addition to the above effects, further improvement in photoelectric conversion efficiency can be expected by making the second conductivity type layer a carbon-containing layer.

The crystallization rate Ic / Ia was determined by (1) exposing the layer to be measured, (2) irradiating the surface of the layer with an argon ion laser (514.5 nm) at about 10 mW, and (3) the Raman. The peak height of the crystalline semiconductor near 520 cm ⁻¹ obtained by measuring the scattering spectrum is Ic, the peak height of the amorphous semiconductor near 480 cm ⁻¹ is Ia, and (4) Ic and Ia It can obtain | require by the method provided with the process of calculating | requiring each peak intensity ratio Ic / Ia. Note that the crystallization rate has a positive correlation with the volume fraction of the crystalline semiconductor portion included in the microcrystalline semiconductor layer.

  The layer to be measured can be exposed by removing the upper layer by an oblique polishing method or the like.

2. Super straight type structure (stacked type)
2-1. Configuration, Action A photoelectric conversion device according to the second embodiment of the present invention has a transparent conductive layer, a plurality of photoelectric conversion layers (each photoelectric conversion layer is as described above), and a translucent substrate. A back electrode is provided in this order. Moreover, it is preferable to provide a back surface transparent conductive layer between the photoelectric conversion layer and the back surface electrode. Moreover, it is preferable that the intermediate | middle layer is formed between the two photoelectric conversion layers adjacent up and down. The plurality of photoelectric conversion layers include, for example, a first photoelectric conversion layer and a second photoelectric conversion layer stacked in this order from the substrate side.

  Since the first photoelectric conversion layer is located on the light incident side, only the light transmitted through the first photoelectric conversion layer is incident on the second photoelectric conversion layer located on the back electrode side. For this reason, advantages of the stacked structure include that the incident light spectrum region can be divided and received so that light can be used effectively and a high open-circuit voltage can be obtained. In order to enhance the above effect, if the first photoelectric conversion layer on the light incident side is laminated so that the forbidden band width of the second photoelectric conversion layer is larger than the forbidden band width of the second photoelectric conversion layer, the short wavelength light of the incident light is reduced. Since the long wavelength light is absorbed by the second photoelectric conversion layer in the first photoelectric conversion layer, each wavelength region can be used effectively. Each of the photoelectric conversion layers is stacked so that the pin bonding directions are the same. This is the same when there are three or more photoelectric conversion layers.

2-2. Each component The structure and manufacturing method of each component excluding the intermediate layer are the same as those described above.

  The intermediate layer is preferably made of a transparent conductive film. By providing the intermediate layer, a part of the light incident on the first photoelectric conversion layer from the substrate side is reflected by the intermediate layer, and the remaining light is transmitted through the intermediate layer to the second photoelectric conversion layer. Since the light enters, the amount of light incident on each photoelectric conversion layer can be controlled. As a result, the photocurrent value of each photoelectric conversion layer is equalized, and the photogenerated carriers generated in each photoelectric conversion layer can contribute to the short-circuit current of the stacked photoelectric conversion device without waste, resulting in the stacked photoelectric conversion as a result. The short circuit current of the device can be increased and the photoelectric conversion efficiency can be improved.

3. Substrate type structure 3-1. General Matters A photoelectric conversion device according to the third embodiment of the present invention includes the photoelectric conversion layer, the transparent conductive layer, and the grid electrode on a substrate made of metal or a substrate whose surface is covered with metal. Prepare one after another. In this case, the grid electrode side is the light incident surface.

3-2. Substrate As the substrate, a substrate such as a metal such as stainless steel (SUS) or aluminum can be used. Further, as the substrate, a glass, a heat-resistant polymer film (such as polyimide, PET, PEN, PES, or Teflon (registered trademark)) or ceramics coated with metal or the like may be used. Moreover, you may use what laminated | stacked these for a board | substrate.

  The substrate preferably has a heat resistance of about 200 ° C. The substrate preferably has a thickness of 0.1 to 10 mm. Further, the substrate may be provided with irregularities on its surface. In addition, an insulating film, a conductive film, a buffer layer, or the like may be formed over the substrate, or a composite layer combining these may be formed.

3-3. Photoelectric conversion layer A photoelectric conversion layer is formed on the substrate. The configuration and manufacturing method of the photoelectric conversion layer are the same as those described in 1-4.

3-4. Transparent conductive layer A transparent conductive layer is formed on the photoelectric conversion layer. The configuration and manufacturing method of the transparent conductive layer are the same as those described in 1-3.

3-5. Grid electrode A grid electrode is preferably formed on the transparent conductive layer. Known configurations and manufacturing methods of the grid electrode can be used.

4). Others In this specification, the phrase “on the substrate” includes the case of “on the substrate via a protective film or an insulating film”. The same applies to other words such as “on the membrane” or “on the layer”.

  Further, “0.1 to 9.8 atomic%” includes 0.1 atomic% and 9.8 atomic% in the range. The same applies to other ranges.

(Example 1 to Example 8)
1. Structure FIG. 1 is a cross-sectional view showing the structure of a photoelectric conversion apparatus 1 according to Embodiments 1 to 8 of the present invention. A photoelectric conversion device 1 (super straight type) according to this example includes a transparent conductive layer 5 made of zinc oxide, a photoelectric conversion layer 7 on a translucent substrate 3 made of white plate glass (trade name: Asahi-U), A back transparent conductive layer 9 made of zinc oxide and a back electrode 11 made of silver are provided in this order.

  The photoelectric conversion layer 7 has a p-type layer 7a, an i-type layer 7b, and an n-type layer 7c each made of microcrystalline silicon in this order, and the p-type layer 7a contains carbon atoms. The carbon concentration of the p-type layer 7a varies depending on the film forming conditions and is 0.002 to 14.8 atomic%.

2. Production of Photoelectric Conversion Device According to Examples 1 to 8 Photoelectric conversion device 1 was produced by the following steps.

  First, the transparent conductive layer 5 made of zinc oxide was formed to a thickness of 50 nm on the translucent substrate 3 made of white plate glass (trade name: Asahi-U) by magnetron sputtering.

  Next, on the obtained substrate, a p-type layer 7a, an i-type layer 7b, and an n-type layer 7c each made of microcrystalline silicon were laminated in this order by the plasma CVD method to form the photoelectric conversion layer 7.

In the p-type layer 7a, SiH ₄ , H ₂ , B ₂ H ₆ and CH ₄ were used as source gases. The H ₂ / SiH ₄ gas flow rate ratio was 150 times, and the B ₂ H ₆ / SiH ₄ gas flow rate ratio was changed as shown in Table 1. The CH ₄ / SiH ₄ gas flow rate ratio was also changed as shown in Table 1, and the carbon concentration in the film at that time was also shown in Table 1. The forming temperature was 140 ° C. For the carbon concentration and hydrogen concentration in the film, values (atomic%) obtained as a result of performing secondary ion mass spectrometry on the p-type layer are described. The results of measuring the crystallization rate of the p-type layer 7a are also shown in Table 1. The p-type layer 7a is desirably thin as long as it does not impair the function as the p-type layer 7a in order to increase the amount of light incident on the i-type layer 7b, which is a photoactive layer. In this embodiment, the p-type layer 7a has a thickness of 30 nm. .

The i-type layer 7b uses SiH ₄ and H ₂ as source gases. The H ₂ / SiH ₄ gas flow rate ratio was 80 times and the film thickness was 2500 nm. The formation temperature was 200 ° C.

For the n-type layer 7c, SiH ₄ , H ₂ and PH ₃ were used as source gases. The H ₂ / SiH ₄ gas flow rate ratio was 20 times, and the PH ₃ / SiH ₄ gas flow rate ratio was adjusted so that the phosphorus concentration in the film was 0.01 atomic%. The film thickness of the n-type layer 7c was 20 nm. The formation temperature was 200 ° C.

  Next, the back reflective layer 9 made of zinc oxide was formed with a thickness of 50 nm by magnetron sputtering. Next, the back electrode 11 made of silver with a thickness of 500 nm was formed by electron beam evaporation, and the manufacture of the single-junction photoelectric conversion device 1 with a super straight structure was completed.

3. Production of Photoelectric Conversion Device According to Comparative Example 1 The p-type layer 7a was formed without including CH ₄ gas in the reaction gas used to form the p-type layer 7a. Other conditions are the same as in the first embodiment. The p-type layer 7a was subjected to secondary ion mass spectrometry similar to that in the above example. As a result, the carbon concentration and the hydrogen concentration were 0.002 atomic% and 10.0 atomic%, respectively. Further, from the measurement of Raman spectrum, the crystallization ratio was 4.3.

4). Test Results The photoelectric conversion device thus obtained was measured for current-voltage characteristics with a cell area of 1 cm ² under AM1.5 (100 mW / cm ² ) irradiation conditions. The results are summarized in Table 1. In addition, the dependence of photoelectric conversion efficiency on carbon concentration is shown in FIG. In addition, FIG. 3 is a graph which shows the relationship between the carbon concentration contained in a carbon containing layer, and photoelectric conversion efficiency.

The following can be understood from Table 1 and FIG. Since the p-type layer 7a of Comparative Example 1 that did not use CH ₄ gas at the time of forming the p-type layer 7a contains 0.002 atomic% of carbon, the plasma CVD apparatus used in the above-described process is removed from the vacuum chamber. It shows that carbon impurities existing as gas or residual gas are mixed in the p-type layer 7a at the time of formation.

  In Comparative Example 1, the open-circuit voltage is 0.500 V, whereas in Examples 1 to 8 in which the p-type layer 7a is formed so that the carbon concentration is 0.1 atomic% or more, the open-circuit exceeds this value. Voltage and short circuit current density were obtained. In particular, in Example 5, the effect of improving the open circuit voltage was maximized, and an open circuit voltage of 0.553 V was obtained.

  The reasons why the open circuit voltage and thus the photoelectric conversion efficiency were improved in Examples 1 to 7 were that the band gap of the p-type layer 7a was widened and the diffusion potential was increased, and that the grain boundary due to the amorphous phase containing carbon atoms was increased. This is considered to be due to the fact that interface recombination has been reduced by the effects of interface passivation and p / i-type layers 7a and 7b interface passivation (an effect of improving the photoelectric conversion efficiency by adding carbon).

  Example 1 in which the carbon concentration is 0.01 atomic% is a carbon concentration at which the band gap increase due to the carbon atoms and the passivation effect of the crystal grain boundaries and the p / i-type layers 7a and 7b are not obtained so much. It is considered that the photoelectric conversion efficiency did not change much compared to Comparative Example 1. That is, in order to greatly improve the photoelectric conversion efficiency, it is preferable that the carbon concentration in the p-type layer 7a is 0.1 atomic% or more.

Further, in Examples 3 to 7 where the carbon concentration is 3.3 atomic% or more, a larger open circuit voltage improvement effect is obtained than in Examples 1 and 2 where the carbon concentration is lower than 3.3 atomic%. Thus, the photoelectric conversion efficiency is greatly improved. The reason is that in Examples 3 to 7, the carbon concentration is a sufficient amount in which the increase in the band gap due to carbon atoms, the crystal grain boundaries, the interface between the p / i-type layers 7a and 7b, and the passivation effect appear synergistically. It is thought that it was because it was. Therefore, in order to further improve the photoelectric conversion efficiency, it is preferable to set the carbon concentration in the p-type layer 7a to 3.3 atomic% or more.
Moreover, Example 8 whose carbon concentration is 14.8 atomic% is lower than the thing of the comparative example 1 about the photoelectric conversion efficiency. This is because the shape factor is greatly reduced, and when the carbon concentration is 14.8 atomic% or more, the discontinuity and mismatch of the band gap increase at the interface with the i-type layer 7b. it is conceivable that. Therefore, in order to improve the photoelectric conversion efficiency, it is preferable that the carbon concentration in the p-type layer 7a is 9.8 atomic% or less.

(Example 9 to Example 12)

  The film formation temperature when forming the p-type layer 7a was changed as shown in Table 2 to form the p-type layer 7a. Other conditions are the same as in Example 5. FIG. 1 is also a cross-sectional view illustrating the structure of the photoelectric conversion device 1 according to the ninth to twelfth embodiments of the present invention.

The photoelectric conversion device thus obtained was measured for current-voltage characteristics with a cell area of 1 cm ² under irradiation conditions of AM 1.5 (100 mW / cm ² ). The results are summarized in Table 2. Further, the dependence of photoelectric conversion efficiency on carbon concentration is shown in FIG. FIG. 4 is a graph showing the relationship between the hydrogen concentration contained in the carbon-containing layer and the photoelectric conversion efficiency.

The following can be seen from Table 2 and FIG. In Example 9 where the hydrogen concentration of the p-type layer 7a is 3 atomic%, the open circuit voltage is 0.508 V, the short-circuit current density is 23.1 mA / cm ² , the form factor is 0.701, and the conversion efficiency is 8.23%. On the other hand, in Examples 5, 10 and 11 in which the p-type layer 7a is formed so that the hydrogen concentration is 5 to 15 atomic%, the open circuit voltage, the short-circuit current density and the shape factor which exceed these values in all cases. Obtained and the photoelectric conversion efficiency became larger than Example 9. FIG. The cause of this is that Example 9 has a low hydrogen concentration, so that the band gap of microcrystalline silicon is reduced, the transmittance is lowered, and the passivation effect by hydrogen atoms cannot be sufficiently obtained. It is done. That is, in order to sufficiently obtain the effect of improving the photoelectric conversion efficiency due to the carbon addition, it is preferable that the hydrogen concentration of the p-type layer 7a is 5 atomic% or more.

  Example 12 in which the hydrogen concentration was 18 atomic% had a lower photoelectric conversion efficiency than the other examples. In addition, the form factor was greatly reduced. As one of the causes, since the hydrogen concentration of the p-type layer 7a of Example 12 is high, there is a possibility that the atomic arrangement of silicon is disturbed by hydrogen atoms that have excessively entered microcrystalline silicon, thereby generating defects. Can be considered. That is, in order to sufficiently obtain the effect of improving the photoelectric conversion efficiency due to the carbon addition, it is desirable that the hydrogen concentration of the p-type layer 7a is 15 atomic% or less.

  In order to increase the hydrogen concentration of the p-type layer 7a to 18 atomic%, it is necessary to supply a large amount of atomic hydrogen at a low temperature during the formation of the p-type layer 7a. It is difficult to form a p-type layer having sufficient uniformity. In Example 12 in which the p-type layer 7a having a hydrogen concentration of 18 atomic% was obtained by setting the p-type layer 7a formation temperature to 50 ° C., the shape factor was greatly reduced. One possible cause is that a leak current may have occurred where the p-type layer 7a is unevenly formed on the substrate. In Example 11 in which the p-type layer 7a formation temperature was 90 ° C., the p-type layer 7a was uniformly formed on the substrate, and no significant reduction in the shape factor was observed. It is desirable that the temperature be higher than or equal to ° C.

  In Example 9 where the formation temperature of the p-type layer 7a is 300 ° C., the photoelectric conversion efficiency is lower than in Examples 5, 10 and 11. This is due to the fact that the formation temperature of the p-type layer 7a in Example 9 is high, so that desorption of hydrogen atoms from the microcrystalline silicon is likely to occur, and the hydrogen coverage on the microcrystalline silicon growth surface. It is conceivable that the volume fraction of the crystal phase has decreased due to the decrease in. Further, since the p-type layer 7a does not need to contain a crystal phase of microcrystalline silicon carbide, the p-type layer need not be formed at a particularly high temperature. Therefore, the p-type layer 7a should be formed at a temperature of 250 ° C. or lower. Is desirable.

  Therefore, in order to form the above-described p-type layer 7a having a hydrogen concentration of 5 to 15 atomic%, it is desirable that the p-type layer 7a formation temperature be 90 to 250 ° C.

According to the above consideration, when the carbon concentration of the p-type layer 7a is 0.1 to 9.8 atomic%, the wide band gap of the p-type layer 7a and the crystal grain boundaries and the p / i-type layer 7a, A photoelectric conversion device with high photoelectric conversion efficiency can be obtained without forming an interface layer due to the passivation effect of the 7b interface or the like. Therefore, in this case, in addition to high efficiency, it can be considered that it can greatly contribute to cost reduction and yield improvement.
Further, it is desirable that the carbon concentration of the p-type layer 7a is 3.3 to 9.8 atomic%, since a higher open-circuit voltage is obtained, and thus a photoelectric conversion device with higher photoelectric conversion efficiency can be obtained. Further, it is more preferable that the hydrogen concentration of the p-type layer 7a is in the range of 5 to 15 atomic% because the effect of adding carbon atoms can be sufficiently obtained. Moreover, in order to form the p-type layer 7a having a hydrogen concentration in the above range, it is desirable that the formation temperature is 90 to 250 ° C.
(Example 13 and Example 14)

1. Structure FIG. 2 is a cross-sectional view showing the structure of the photoelectric conversion device 13 according to Embodiment 13 and Embodiment 14 of the present invention. The photoelectric conversion device 13 according to this example includes a transparent conductive layer 5 made of zinc oxide, a first photoelectric conversion layer 17, and a second on a light-transmitting substrate 3 made of white plate glass (trade name: Asahi-U). The back surface conductive layer 9 made of zinc oxide and the back electrode 11 made of silver are laminated in this order.

  The photoelectric conversion layer 17 is configured by stacking a p-type layer 17a, an i-type layer 17b, and an n-type layer 17c made of microcrystalline silicon in this order, and the photoelectric conversion layer 27 is made of p-type made of microcrystalline silicon. The mold layer 27a, the i-type layer 27b, and the n-type layer 27c are stacked in this order. In Example 13, the p-type layer 17a does not contain a carbon atom, and the p-type layer 27a contains a carbon atom. In Example 14, both p-type layers 17a and 27a contain carbon atoms.

2. Production of photoelectric conversion device according to Example 13 Photoelectric conversion device 13 according to Example 13 was produced by the following steps.

  First, the transparent conductive layer 5 made of zinc oxide was formed to a thickness of 50 nm on the translucent substrate 3 made of white plate glass (trade name: Asahi-U) by magnetron sputtering.

  Next, a p-type layer 17a, an i-type layer 17b, and an n-type layer 17c, each made of microcrystalline silicon, are stacked in this order on the obtained substrate by a plasma CVD method, thereby forming a photoelectric conversion layer 17. Further, the photoelectric conversion layer 27 was formed by laminating the p-type layer 27a, the i-type layer 27b, and the n-type layer 27c in this order.

For the first photoelectric conversion layer 17, CH ₄ gas was not used when the p-type layer 17a was formed, and for the second photoelectric conversion layer 27, CH ₄ gas was used when the p-type layer 27a was formed.

The p-type layer 17a uses SiH ₄ , H ₂ and B ₂ H ₆ as source gases, the H ₂ / SiH ₄ gas flow rate ratio is 5 times, and the B ₂ H ₆ / SiH ₄ gas flow rate ratio is boron in the film. The concentration was adjusted to 0.01 atomic%. The film thickness of the p-type layer 17a was 20 nm.

The i-type layer 17b uses SiH ₄ and H ₂ as source gases. The H ₂ / SiH ₄ gas flow rate ratio was 20 times and the film thickness was 300 nm.

For the n-type layer 17c, SiH ₄ , H ₂ and PH ₃ were used as source gases. The H ₂ / SiH ₄ gas flow rate ratio was 20 times, and the PH ₃ / SiH ₄ gas flow rate ratio was adjusted so that the phosphorus concentration in the film was 0.01 atomic%. The film thickness of the n-type layer 17c was 20 nm.

  The formation conditions and film thicknesses of the p-type layer 27a, i-type layer 27b, and n-type layer 27c of the second photoelectric conversion layer 27 were the same as those in Example 5. Accordingly, the carbon concentration and the hydrogen concentration in the p-type layer 27a are 5.1 atomic percent and 10 atomic percent, respectively.

Next, the back reflective layer 9 made of zinc oxide was formed with a thickness of 50 nm by magnetron sputtering. Next, the back electrode 11 made of silver with a thickness of 500 nm was formed by electron beam evaporation, and the manufacture of the stacked photoelectric conversion device 13 with a super straight type structure was completed.
3. Production of Photoelectric Conversion Device According to Example 14 In this example, CH ₄ gas was used when forming both the p-type layers 17a and 27a of the first and second photoelectric conversion layers 17 and 27. Other conditions are the same as in Example 13. The H ₂ / SiH ₄ gas flow rate ratio at the time of forming the p-type layer 17a is 5 times, and the B ₂ H ₆ / SiH ₄ gas flow rate ratio is adjusted so that the boron concentration in the film becomes 0.01 atomic%, and CH ₄ / The SiH ₄ gas flow ratio was adjusted so that the carbon concentration in the film was 5.1 atomic%. The hydrogen concentration is 10.0 atomic%.

4). Production of photoelectric conversion device according to Comparative Example 2 The reaction gas used for forming the p-type layers 17a and 27a of the first and second photoelectric conversion layers 17 and 27 does not include CH ₄ gas, and the p-type layer 17a 27a was formed. Other conditions are the same as in Example 13. The H ₂ / SiH ₄ gas flow rate ratio at the time of forming the p-type layer 27a was adjusted to 150 times, and the B ₂ H ₆ / SiH ₄ gas flow rate ratio was adjusted so that the boron concentration in the film was 0.01 atomic%.

5). Test Results The photoelectric conversion device thus obtained was measured for current-voltage characteristics with a cell area of 1 cm ² under AM1.5 (100 mW / cm ² ) irradiation conditions. The results are summarized in Table 3.

  Compared to Comparative Example 2 in which both the p-type layers 17a and 27a of the first and second photoelectric conversion layers 17 and 27 contain almost no carbon atoms, the p-type layer 27a of the second photoelectric conversion layer 27 is 5.1. In Example 13 containing atomic% of carbon atoms, the open circuit voltage and short circuit current density were large, and high conversion efficiency was obtained. This is because the second photoelectric conversion layer 27 contains 0.1 to 9.8 atomic% carbon atoms and 5 to 15 atomic% hydrogen atoms in the p-type layer film. This is probably because the effect of improving the open circuit voltage and the short circuit current density was obtained in the layer 27.

  Furthermore, in Example 14 in which the p-type layers 17 a and 27 a of the first and second photoelectric conversion layers 17 and 27 both contain 5.1 atomic% of carbon atoms, Since the photoelectric conversion layer 17 of 1 also has the effect of improving the open circuit voltage and the short circuit current density, higher conversion efficiency than that of Example 13 was obtained.

  According to the above consideration, the p-type layers 17a and 27a of the first and second photoelectric conversion layers 17 and 27 contain 0.1 to 9.8 atomic% of carbon atoms, and 5 to 15 hydrogen atoms. It has been clarified that the photoelectric conversion efficiency is improved in the stacked photoelectric conversion device by increasing the open-circuit voltage and the short-circuit current density as in the single-layer photoelectric conversion device.

It is sectional drawing which shows the structure of the photoelectric conversion apparatus which concerns on Example 1-Example 12 of this invention. It is sectional drawing which shows the structure of the photoelectric conversion apparatus which concerns on Example 13 and Example 14 of this invention. It is a graph which shows the relationship between the carbon concentration contained in a carbon content layer, and photoelectric conversion efficiency. It is a graph which shows the relationship between the hydrogen concentration contained in a carbon content layer, and photoelectric conversion efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single layer type photoelectric conversion apparatus 3 Translucent substrate 5 Transparent conductive layer 7 Photoelectric conversion layer 9 Back surface transparent conductive layer 11 Back surface electrode 13 Stacked type photoelectric conversion layer 17 1st photoelectric conversion layer 27 2nd photoelectric conversion layer 7a, 17a, 27a p-type layer 7b, 17b, 27b i-type layer 7c, 17c, 27c n-type layer

Claims (6)

A photoelectric conversion layer having a first conductive type layer made of a semiconductor, an i-type layer made of a microcrystalline semiconductor, and a second conductive type layer made of a semiconductor stacked in this order, and the first conductive type layer and the second conductive type layer At least one is a carbon-containing layer made of microcrystalline silicon containing carbon atoms ,
When a Raman scattering spectrum of the microcrystalline silicon is observed, a peak attributed to a silicon-carbon bond in the silicon carbide crystal is not substantially detected, or a silicon carbide crystal structure is measured when the microcrystalline silicon is measured by an X-ray diffraction method. A photoelectric conversion device in which a diffraction peak attributed to is substantially not detected .   The photoelectric conversion device according to claim 1, wherein the carbon-containing layer has a concentration of carbon atoms contained in the carbon-containing layer of 0.1 to 9.8 atomic%.   The photoelectric conversion device according to claim 1, wherein the carbon-containing layer has a concentration of carbon atoms contained in the carbon-containing layer of 3.3 to 9.8 atomic%.   The photoelectric conversion device according to claim 1, wherein the carbon-containing layer has a concentration of hydrogen atoms contained therein of 5 to 15 atomic%.   The photoelectric conversion device according to any one of claims 1 to 4, wherein the carbon-containing layer is formed at 90 to 250 ° C.   A photoelectric conversion device comprising a transparent conductive layer, the photoelectric conversion layer according to any one of claims 1 to 5 and a back electrode stacked in this order on a translucent substrate.

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