JP2006310694A - Integrated multi-junction thin film photoelectric conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an integrated muli-junction thin film photoelectric conversion device and its manufacturing method capable of satisfactorily outputting generated electric power without causing leakage in each photoelectric conversion unit, in an integrated multi-junction thin film photoelectric conversion device permitting a silicon composite layer to be applied to an intermediate reflecting layer. <P>SOLUTION: The integrated multi-junction thin film photoelectric conversion device 101 is constituted by integrating multi-junction thin film photoelectric conversion cells each including at least one set of two thin film photoelectric conversion units connected in series via an intermediate layer on a substrate 102 as illustrated in FIG. 1. In the device, the material of the interlayer is n-type Si<SB>1-X</SB>O<SB>X</SB>(0.3<X<0.6), and the amount of doping of an impurity in an intermediate layer adjacent p-type semiconductor layer 106a adjacent to the intermediate layer partly constituting at least one thin film photoelectric conversion unit 106 of thin film photoelectric conversion units 104, 106 of the one set is ≤5,000 ppm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tandem thin film photoelectric conversion including a conductive intermediate reflection layer (or an intermediate layer) that partially reflects and transmits light between an amorphous photoelectric conversion unit layer and a crystalline photoelectric conversion unit layer. It relates to the improvement of the characteristics of the device.

  Note that the terms “crystalline” and “microcrystal” in the present specification include those that partially include an amorphous material.

  In recent years, in order to achieve both cost reduction and high efficiency of a photoelectric conversion device, a thin film photoelectric conversion device that has almost no problem in terms of resources has attracted attention and has been vigorously developed. Thin film photoelectric conversion devices are expected to be applied to various applications such as solar cells, optical sensors, and displays. An amorphous silicon photoelectric conversion device, which is one of thin film photoelectric conversion devices, can be formed on a large-area glass substrate or stainless steel substrate at a low temperature, so that cost reduction can be expected.

  A thin film photoelectric conversion device generally includes a first electrode, one or more semiconductor thin film photoelectric conversion units, and a second electrode, the surfaces of which are sequentially stacked on an insulating substrate. One thin film photoelectric conversion unit includes an i-type layer sandwiched between a p-type layer and an n-type layer.

  Most of the thickness of the thin film photoelectric conversion unit is occupied by the i-type layer which is a substantially intrinsic semiconductor layer, and the photoelectric conversion action mainly occurs in the i-type layer. Therefore, the i-type layer, which is a photoelectric conversion layer, is preferably thicker for light absorption, but if it is thicker than necessary, the deposition takes cost and time.

  On the other hand, the p-type or n-type conductive layer plays a role of generating a diffusion potential in the photoelectric conversion unit, and the magnitude of the diffusion potential causes an open end voltage, which is one of the important characteristics of the thin film photoelectric conversion device. The value depends. However, these conductive layers are inactive layers that do not contribute to photoelectric conversion, and light absorbed by impurities doped in the conductive layers does not contribute to power generation and is lost. Therefore, it is preferable that the thicknesses of the p-type and n-type conductive layers be as thin as possible within a range that generates a sufficient diffusion potential.

  Here, the photoelectric conversion unit or the thin-film solar cell has an amorphous i-type photoelectric conversion layer that occupies the main part regardless of whether the p-type and n-type conductivity type layers included therein are amorphous or crystalline. Those having a high quality are referred to as amorphous photoelectric conversion units or amorphous thin film solar cells, and those having a crystalline i-type layer are referred to as crystalline photoelectric conversion units or crystalline thin film solar cells.

  Generally, a semiconductor used for a photoelectric conversion layer has a light absorption coefficient that decreases as the wavelength increases. In particular, when the photoelectric conversion material is a thin film, sufficient light absorption does not occur in a wavelength region having a small absorption coefficient, so that the photoelectric conversion amount is limited by the film thickness of the photoelectric conversion layer. Therefore, by forming a light scattering structure that makes it difficult for light incident in the photoelectric conversion device to escape to the outside, it has been devised to increase the substantial optical path length, obtain sufficient absorption, and generate a large photocurrent. Yes. For example, when light is incident from the substrate side, a textured transparent conductive film having an uneven surface shape is used as the light incident side electrode.

  As a method for improving the conversion efficiency of a thin film photoelectric conversion device, a method of forming a stacked photoelectric conversion device in which two or more photoelectric conversion units are stacked is known. In this method, a front photoelectric conversion unit including a photoelectric conversion layer having a large band gap on the light incident side of the photoelectric conversion device (in this application, a photoelectric conversion unit relatively disposed on the light incident side is referred to as a front photoelectric conversion unit, A photoelectric conversion unit disposed on the side relatively far from the light incident side is referred to as a rear photoelectric conversion unit.) A photoelectric conversion layer having a small band gap (for example, Si-Ge alloy) is sequentially disposed behind the photoelectric conversion unit. By including the rear photoelectric conversion unit including the photoelectric conversion, it is possible to perform photoelectric conversion over a wide wavelength range of incident light, thereby improving the conversion efficiency of the entire apparatus. Among stacked thin film photoelectric conversion devices, a stack of an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit is referred to as a hybrid photoelectric conversion device. In the hybrid photoelectric conversion device, the wavelength of light that amorphous silicon can photoelectrically convert is about 800 nm on the long wavelength side, but crystalline silicon can photoelectrically convert longer light up to about 1100 nm. Therefore, it is possible to effectively photoelectrically convert a wider range of incident light.

  By the way, in the stacked photoelectric conversion device, since each photoelectric conversion unit is connected in series, the short circuit current density (Jsc) as the photoelectric conversion device is limited to the smallest value among the current values generated in each photoelectric conversion unit. Is done. Therefore, it is preferable that the current values of the respective photoelectric conversion units are equal, and further, the conversion efficiency can be expected to increase as the absolute value of the current increases.

  Further, in a stacked thin film photoelectric conversion device, a light-transmitting and light-reflective and conductive intermediate reflective layer may be interposed between a plurality of stacked thin film photoelectric conversion units. In this case, a part of the light reaching the intermediate reflection layer is reflected, the amount of light absorption in the photoelectric conversion unit located on the light incident side of the intermediate reflection layer is increased, and the current value generated in the photoelectric conversion unit Can be increased. That is, the effective film thickness of the photoelectric conversion unit located on the light incident side with respect to the intermediate reflection layer apparently increased.

  For example, when an intermediate reflective layer is inserted into a hybrid photoelectric conversion device composed of an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit, the amorphous silicon photoelectric conversion is performed without increasing the film thickness of the amorphous silicon layer. The current generated by the unit can be increased. Alternatively, the amorphous silicon photoelectric conversion unit due to photodegradation that becomes conspicuous as the thickness of the amorphous silicon layer increases because the thickness of the amorphous silicon layer necessary to obtain the same current value can be reduced. It is possible to suppress the deterioration of characteristics.

  The intermediate reflective layer is often composed of a transparent conductive metal oxide layer such as polycrystalline ITO or ZnO, particularly ZnO. However, since ZnO is formed by a method such as sputtering or spraying, it is necessary to use equipment different from a semiconductor thin film generally formed by plasma CVD, etc., which requires equipment costs and increases production tact time. A problem occurs. Furthermore, in particular, when a sputtering method is used for forming ZnO, there is a problem that the performance may be deteriorated due to sputtering damage to the underlying semiconductor thin film.

Further, in order to suppress the influence on the series resistance of the solar cell, it is necessary to make a good ohmic contact at the interface between the transparent conductive metal oxide layer and the semiconductor thin film. For this reason, the dark conductivity of the transparent conductive metal oxide layer is 1.0 × 10 ² S / cm to 1.0 × 10 ³ S / cm by doping impurities or changing the degree of oxidation. It needs to be adjusted to a higher value.

  In particular, ZnO is generally known to be difficult to make ohmic contact at the interface with amorphous silicon or crystalline silicon. If the dark conductivity is lower than this range, the ohmic contact between the intermediate reflection layer and the front photoelectric conversion unit and between the intermediate reflection layer and the rear photoelectric conversion unit cannot be made, the contact resistance increases, and the cell fill factor ( FF) is lowered, and the characteristics of the photoelectric conversion device are deteriorated. On the other hand, if the dark conductivity is higher than this range, the transmittance of the transparent conductive metal oxide layer is lowered, the short-circuit current density (Jsc) is lowered, and the characteristics of the photoelectric conversion device are deteriorated.

However, in the case where a silicon oxide layer of one conductivity type containing a silicon crystal phase in an amorphous alloy of silicon and oxygen (referred to as a silicon composite layer (Si _1-X O _x ) in this application) is used as the intermediate reflection layer, If the oxygen concentration in the film is increased, a low refractive index can be realized, and a high reflection effect at the interface between the amorphous silicon and the silicon composite layer can be obtained. In addition, even if the one-conductivity-type silicon composite layer has a high oxygen concentration in the film, it can realize a high dark conductivity by including a silicon crystal phase. As a result, by using the silicon composite layer, it is possible to achieve both a high reflection effect and a high dark conductivity, and the power generation current of the first photoelectric conversion unit is increased to improve the characteristics of the stacked photoelectric conversion device. .

  For this reason, in Patent Document 1, in order to provide a multi-junction thin film solar cell that does not contain impurities and does not generate pinholes, has high conversion efficiency, and is easy to manufacture, a plurality of pin-type cells are stacked. And at least one of the two layers (the n layer or the p layer) forming a boundary between the upper cell on the light incident side and the lower cell on the non-incident side, or a part of the layer, In the multi-junction thin film solar cell that is a low refractive index layer having a refractive index lower than that of the semiconductor layer above the layer or a part of the layer, the low refractive index layer is a silicon oxide semiconductor layer. That is, in Patent Document 1, instead of an n-type microcrystalline silicon layer in which a low refractive index layer (corresponding to an intermediate layer in the present application) is conventionally formed at a low temperature, or a metal oxide layer formed by sputtering or vapor deposition, silicon By using an oxide semiconductor layer, the device characteristics can be improved and the yield can be improved by reducing the refractive index, introducing impurities, and reducing pinholes.

  By the way, a large area thin film photoelectric conversion device is usually formed as an integrated thin film photoelectric conversion module. The integrated thin film photoelectric conversion module has a structure in which a plurality of photoelectric conversion cells, which are photoelectric conversion devices divided into small areas, are connected in series on a glass substrate. Each photoelectric conversion cell is generally formed by sequentially forming and patterning a transparent electrode layer, one or more thin film semiconductor photoelectric conversion units, and a back electrode layer on a glass substrate. .

  FIG. 1 is a cross-sectional view schematically showing an example of a conventional integrated thin film photoelectric conversion module having no intermediate reflection layer in which a plurality of stacked photoelectric conversion devices are connected in series. An integrated thin film photoelectric conversion module 101 shown in FIG. 1 includes a transparent electrode layer 103, a front photoelectric conversion unit 104 that is an amorphous silicon photoelectric unit, and a rear photoelectric conversion unit that is a crystalline silicon photoelectric conversion unit on a glass substrate 102. 106 and a back electrode layer 107 are sequentially stacked.

  As shown in FIG. 1, the integrated thin film photoelectric conversion module 101 is provided with first and second separation grooves 121 and 123 and a connection groove 122 for dividing the thin film. The first and second separation grooves 121 and 123 and the connection groove 122 are parallel to each other and extend in a direction perpendicular to the paper surface. Note that the boundary between the adjacent photoelectric conversion cells 110 is defined by the first and second separation grooves 121 and 123.

  The first separation groove 121 divides the transparent electrode layer 103 corresponding to each photoelectric conversion cell 110, has an opening at the interface between the transparent electrode layer 103 and the amorphous silicon photoelectric conversion unit 104, and The surface of the transparent substrate 102 is the bottom surface. The first separation groove 121 is filled with an amorphous material constituting the amorphous silicon photoelectric conversion unit 104 and electrically insulates the adjacent transparent electrode films 103 from each other.

  The second separation groove 123 is provided at a position away from the first separation groove 121. The second separation groove 123 divides the front photoelectric conversion unit 104, the rear photoelectric conversion unit 106, and the back electrode layer 107 corresponding to each photoelectric conversion cell 110, and has an opening on the top surface of the back electrode layer 108. And has an interface between the transparent electrode layer 103 and the front photoelectric conversion unit 104 as a bottom surface. The second separation groove 123 electrically insulates the back electrode layers 107 between the adjacent photoelectric conversion cells 110.

The connection groove 122 is provided between the first separation groove 121 and the second separation groove 123. The connection groove 122 divides the front photoelectric conversion unit 104 and the rear photoelectric conversion unit 106, has an opening at the interface between the rear photoelectric conversion unit 106 and the back electrode layer 107, and the transparent electrode layer 103 and the front photoelectric conversion unit. The interface of the unit 104 is the bottom surface. The connection groove 122 is embedded with a metal material constituting the back electrode layer 107 and electrically connects one back electrode layer 107 and the other transparent electrode layer 103 of the adjacent photoelectric conversion cells 110. . That is, the connection groove 122 and the metal material filling the connection groove 122 serve to connect the photoelectric conversion cells 110 juxtaposed on the glass substrate 102 in series.
JP 2003-258279 A

  In view of the above-described problems, the present invention provides an integrated multi-junction thin film photoelectric conversion device in which a silicon composite layer is applied to an intermediate reflection layer, and there is no leakage in each photoelectric conversion unit, and generated power is sufficiently output. An object of the present invention is to provide an integrated multi-junction thin film photoelectric conversion device and a method for manufacturing the same.

An integrated multi-junction thin film photoelectric conversion device of the present invention is an integrated multi-junction thin film in which a multi-junction thin film photoelectric conversion cell including at least one set of two thin film photoelectric conversion units connected in series via an intermediate layer on a substrate is integrated. A photoelectric conversion device, wherein the material of the intermediate layer is n-type Si _1-X O _X (where 0.3 <X <0.6), and at least one of the set of thin film photoelectric conversion units The impurity doping amount of the p-type semiconductor layer adjacent to the intermediate layer adjacent to the intermediate layer constituting a part of the thin film photoelectric conversion unit is 2500 ppm or more and 5000 ppm or less.

  In this way, by limiting the impurity doping amount of the p-type semiconductor layer adjacent to the intermediate layer, it is possible to reduce leakage in the one set of thin film photoelectric conversion units and to sufficiently extract the generated power. Become.

  In addition, since the material of the p-type semiconductor layer adjacent to the intermediate reflective layer is a p-type silicon-based semiconductor, defects at the interface can be reduced without band discontinuity.

  Furthermore, boron as an impurity is doped in the p-type semiconductor layer adjacent to the intermediate layer, so that a good p-type silicon-based semiconductor can be easily formed.

  By the way, the present invention is characterized in that the intermediate layer adjacent p-type semiconductor layer constitutes a part of a thin film photoelectric conversion unit formed by sandwiching the intermediate layer from the substrate. That is, it refers to the p-type semiconductor layer on the rear photoelectric conversion unit side formed on the intermediate reflection layer, and the leakage of the rear photoelectric conversion unit is reduced, and the generated power can be sufficiently taken out.

  Moreover, the material of the n-type semiconductor layer adjacent to the intermediate reflective layer adjacent to the intermediate layer constituting at least the thin film photoelectric conversion unit on the substrate side of the pair of thin film photoelectric conversion units is n-type microcrystalline silicon. Thus, a good junction is formed between the n-type semiconductor layer and the intermediate reflective layer, and the n-type semiconductor layer is made of microcrystalline silicon, so that it becomes a seed layer of microcrystalline silicon when forming the intermediate reflective layer. It also plays a role, and it becomes possible to form a good intermediate reflective layer.

  In particular, if 1% to 2.8% of phosphorus is doped as an impurity in the n-type semiconductor layer adjacent to the intermediate layer, the absorption by the impurity is small and the n-type semiconductor layer has good conductivity. .

An integrated multijunction thin film photoelectric conversion device in which a multijunction thin film photoelectric conversion cell including at least one pair of two thin film photoelectric conversion units connected in series via an intermediate layer on a substrate is integrated, and the material of the intermediate layer Is an n-type Si _1-X O _X , and an impurity in the p-type semiconductor layer adjacent to the intermediate layer adjacent to the intermediate layer constituting a part of at least one thin film photoelectric conversion unit of the one set of thin film photoelectric conversion units If the doping amount is 5000 ppm or less, the resistance of the current path from the p-type semiconductor layer through the connection groove is increased, and the leakage current can be reduced. In other words, since the photoelectric conversion characteristics can be sufficiently extracted from each photoelectric conversion unit, the efficiency is improved.

The present inventors actually made and studied an integrated multi-junction thin film photoelectric conversion device having an intermediate layer as shown in FIG. 2 using n-type Si _1-X O _X as a material for the intermediate layer. As a result, when the p-type microcrystalline silicon layer 106a of the rear photoelectric conversion unit 106 is formed under the conventional film forming conditions and an integrated multi-junction thin film photoelectric conversion device is manufactured, a leakage current is generated on the rear photoelectric conversion unit side 106 side. As a result, the inventors have found that the characteristics of the integrated photoelectric conversion module are deteriorated, and have arrived at the present invention.

  That is, in the conventional integrated multi-junction thin film photoelectric conversion device without the intermediate reflection layer shown in FIG. 1, there was no leakage in spectral sensitivity in the front photoelectric conversion unit and the rear photoelectric conversion unit, but as shown in FIG. In the integrated multi-junction thin film photoelectric conversion device in which the intermediate reflection layer is inserted between the front photoelectric conversion unit and the rear photoelectric conversion unit, the spectral sensitivity in the rear photoelectric conversion unit does not usually appear in the vicinity of 500 nm as shown in FIG. Sensitivity was observed. That is, a leak occurs in the rear photoelectric conversion unit, and the electric power generated in the rear photoelectric conversion unit is not sufficiently output.

  As shown in FIG. 3, this leakage current can be understood from the fact that an apparent sensitivity that does not usually appear in the vicinity of 500 nm is observed as the spectral sensitivity on the rear photoelectric conversion unit side in the spectral sensitivity measurement of the integrated photoelectric conversion module. This is due to the provision of the intermediate reflection layer 105, which changes the conductivity of the p-type microcrystalline silicon layer 106a of the rear photoelectric conversion unit 106 formed thereon, in a direction parallel to the substrate. This is probably because the current flowed easily and also played the role of the electrode layer. That is, the rear photoelectric conversion unit 106 is short-circuited in the current path of the p-type microcrystalline silicon layer 106a, the connection groove 123, and the back electrode layer 107, and a leak current flows. Therefore, the p-type microcrystalline silicon layer 106a formed under the conventional conditions cannot sufficiently extract the electric power generated in the rear photoelectric conversion unit 106.

  From these, the present inventors are an integrated multi-junction thin film photoelectric conversion device in which a multi-junction thin film photoelectric conversion device in which two or more stages of photoelectric conversion units are stacked is integrated, and the electric power generated in each photoelectric conversion unit is obtained. It has been found that in order to take out sufficiently, it is important to set the doping amount of the impurity layer adjacent to the intermediate reflection layer within a certain limited range.

  Hereinafter, the present invention will be described in detail with reference to a schematic cross-sectional view of a two-junction thin film silicon-based photoelectric conversion device having the intermediate layer of FIG. 2 which is a photoelectric conversion device according to one embodiment of the present invention. The present invention is not limited to this.

  Each component of the two-junction thin film silicon photoelectric conversion device of the present invention will be described.

As the substrate 102, for example, a light-transmitting insulating substrate such as a metal substrate, a glass plate, or a flexible transparent resin film can be used. Although the metal substrate has a structure different from that shown in FIG. 2, it is omitted here. In general, a glass substrate is used as a translucent insulating substrate, a large-area plate can be obtained at a low cost, transparency and insulation are high, and both main surfaces mainly composed of SiO ₂ , Na ₂ O and CaO are smooth. Soda lime plate glass can be used.

The transparent electrode layer 103 can be composed of a transparent conductive oxide layer such as an ITO film, a SnO ₂ film, or a ZnO film. The transparent electrode film 103 may have a single layer structure or a multilayer structure. The transparent electrode film 103 can be formed using a vapor deposition method known per se such as a vapor deposition method, a CVD method, or a sputtering method. A surface texture structure including fine irregularities is preferably formed on the surface of the transparent electrode film 103. The depth of the unevenness is preferably 0.05 μm or more and 1.0 μm or less, and the distance between one peak is preferably 0.05 μm or more and 1.0 μm or less. By forming such a texture structure on the surface of the transparent electrode film 103, it becomes possible to increase the light confinement effect.

  In the two-junction thin film silicon photoelectric conversion device according to the present invention shown in FIG. 2, the front photoelectric conversion unit 104 that is an amorphous silicon photoelectric unit, the intermediate reflection layer 105, and the rear photoelectric conversion unit that is a crystalline silicon photoelectric conversion unit. 106 and a back electrode layer 107 are sequentially stacked.

  The amorphous silicon photoelectric conversion unit 104 includes an amorphous silicon photoelectric conversion layer. A p-type semiconductor layer 104a, an amorphous silicon photoelectric conversion layer 104b, and an n-type semiconductor layer 104c are sequentially formed from the transparent electrode film 103 side. It has a laminated structure. These p-type semiconductor layer, amorphous silicon photoelectric conversion layer, and n-type semiconductor layer can all be formed by a plasma CVD method.

  On the other hand, the crystalline silicon photoelectric conversion unit 106 includes a crystalline silicon photoelectric conversion layer. For example, a p-type semiconductor layer 106a, a crystalline silicon photoelectric conversion layer 106b, and an n-type semiconductor layer 106c are provided from the intermediate reflection layer 105 side. It has a stacked structure. These p-type semiconductor layer, crystalline silicon photoelectric conversion layer, and n-type semiconductor layer can all be formed by a plasma CVD method.

  The thickness of the amorphous silicon photoelectric conversion unit 104 is preferably in the range of 0.01 μm to 0.5 μm, and more preferably in the range of 0.1 μm to 0.3 μm.

  The n-type semiconductor layer 104c may be amorphous silicon, but microcrystalline silicon is more preferable. By using microcrystalline silicon, it is possible to improve the crystallinity of crystalline silicon in the silicon composite layer which is an intermediate reflective layer formed thereon. Further, it is more preferable that phosphorus is doped in the range of 1% to 2.8% as an impurity. If the phosphorus concentration is higher than ˜2.8%, the absorption of impurities increases, resulting in a decrease in Jsc. If it is less than 1%, sufficient conductivity and diffusion potential cannot be obtained, and the conversion efficiency decreases.

  On the other hand, the thickness of the crystalline silicon photoelectric conversion unit 106 is preferably in the range of 0.1 μm to 10 μm, and more preferably in the range of 0.1 μm to 5 μm. The p-type semiconductor layer 106a has an impurity doping amount of 2500 ppm or more and 5000 ppm or less. By setting it to 5000 ppm or less, the resistance of the current path from the p-type semiconductor layer through the connection groove is increased, and the leakage current can be reduced. Moreover, when it is 2500 ppm or more, since the series resistance can be reduced, high conversion efficiency is achieved. Furthermore, it is more preferable to use boron as an impurity. By using boron as an impurity, a good p-type semiconductor can be formed. Further, it is preferable to use a silicon composite layer as a back surface reflection layer for a part of the n-type semiconductor layer 106c.

Part of the intermediate reflective layer 105 and the back reflective layer 106c has a refractive index of 2.5 or less, preferably 2.0 or less, for light having a wavelength of 600 nm. If the refractive index is greater than 2.5, sufficient reflection cannot be obtained, and a sufficient light confinement effect cannot be obtained. The refractive index is measured as follows. A silicon alloy layer containing conductivity-determining impurities, oxygen, nitrogen and crystalline silicon under the same conditions as when a part of the intermediate reflective layer 105 or the back reflective layer 106c is formed on a transparent and insulating substrate such as a glass substrate The refractive index is measured by measuring about 0.1 to 0.4 μm and measuring the formed layer by spectroscopic ellipsometry. It is also possible to determine the film thickness at the same time. The conductivity of the silicon alloy layer formed at this time is 1.0 × 10 ⁻⁹ S / cm or more, and the measurement of the conductivity is performed as follows. When a 1 mm × 15 mm aluminum electrode is formed on the silicon alloy layer formed to have a thickness of about 0.1 to 0.4 μm by a vacuum deposition method with an interval of 1 mm, a voltage of 100 V is applied between the two electrodes. Calculated from the current value. The value obtained by spectroscopic ellipsometry is used for the film thickness of the silicon alloy layer used for the calculation at this time. If the conductivity is less than 1.0 × 10 ⁻⁹ S / cm, the series resistance increases and the conversion efficiency decreases.

  The back electrode film 107 not only functions as an electrode, but also reflects the light that has entered the front photoelectric conversion unit 104 and the back photoelectric conversion unit 106 from the substrate 102 and arrived at the back electrode film 107 to reflect the back photoelectric conversion unit 106 and It also has a function as a reflective layer that re-enters the front photoelectric conversion unit 104. The back electrode film 107 can be formed to a thickness of, for example, about 200 nm to 400 nm using silver, aluminum, or the like by a vapor deposition method, a sputtering method, or the like.

  A transparent conductive thin film made of a non-metallic material such as ZnO is provided between the back electrode film 107 and the front photoelectric conversion unit 104 and the rear photoelectric conversion unit 106, for example, in order to improve the adhesion between them. (Not shown) can be provided.

  As shown in FIG. 2, the integrated thin film photoelectric conversion module 101 is provided with first and second separation grooves 121 and 123 and a connection groove 122 for dividing the thin film. The first and second separation grooves 121 and 123 and the connection groove 122 are parallel to each other and extend in a direction perpendicular to the paper surface. Note that the boundary between the adjacent photoelectric conversion cells 110 is defined by the first and second separation grooves 121 and 123.

  The first separation groove 121 divides the transparent electrode layer 103 corresponding to each photoelectric conversion cell 110, has an opening at the interface between the transparent electrode layer 103 and the amorphous silicon photoelectric conversion unit 104, and The surface of the transparent substrate 102 is the bottom surface. The first separation groove 121 is filled with an amorphous material constituting the amorphous silicon photoelectric conversion unit 104 and electrically insulates the adjacent transparent electrode films 103 from each other.

  The second separation groove 123 is provided at a position away from the first separation groove 121. The second separation groove 123 divides the front photoelectric conversion unit 104, the rear photoelectric conversion unit 106, and the back electrode layer 107 corresponding to each photoelectric conversion cell 110, and has an opening on the top surface of the back electrode layer 107. And has an interface between the transparent electrode layer 103 and the front photoelectric conversion unit 104 as a bottom surface. The second separation groove 123 electrically insulates the back electrode layers 107 between the adjacent photoelectric conversion cells 110.

  The connection groove 122 is provided between the first separation groove 121 and the second separation groove 123. The connection groove 122 divides the front photoelectric conversion unit 104 and the rear photoelectric conversion unit 106, has an opening at the interface between the rear photoelectric conversion unit 104 and the back electrode layer 107, and the transparent electrode layer 103 and the front photoelectric conversion unit. The interface 104 is the bottom surface. The connection groove 122 is embedded with a metal material constituting the back electrode layer 107 and electrically connects one back electrode layer 107 and the other transparent electrode layer 103 of the adjacent photoelectric conversion cells 110. . That is, the connection groove 122 and the metal material filling the connection groove 122 serve to connect the photoelectric conversion cells 110 juxtaposed on the glass substrate 102 in series.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on some Examples with a comparative example, this invention is not limited to the following description examples, unless the meaning is exceeded.

Example 1
As Example 1, an integrated multi-junction thin film photoelectric conversion device shown in FIG. SnO ₂ having irregularities was used as the transparent electrode film 103 on the glass substrate 102 having a thickness of 0.7 mm. A separation groove 121 was formed by laser scribing so as to electrically insulate the transparent electrode films 103 adjacent to the transparent electrode 103 from each other.

  Thereafter, silane, hydrogen, methane and diborane are introduced as reactive gases on the transparent electrode film 103 to form a p-type semiconductor layer 104a, and silane is introduced as a reactive gas to form an amorphous silicon photoelectric conversion layer 104b having a thickness of 250 nm. Then, silane, hydrogen and phosphine were introduced as reaction gases to form an n-type semiconductor layer 104c having a thickness of 5 nm, thereby forming an amorphous silicon photoelectric conversion unit 104. When forming the n-type semiconductor layer, the phosphine / silane gas flow ratio was set to 0.25%.

  After the amorphous silicon photoelectric conversion unit 104 was formed, silane, hydrogen, phosphine and carbon dioxide were introduced as reaction gases to form an intermediate reflective layer 105 having a thickness of 70 nm.

  Thereafter, silane, hydrogen and diborane were introduced as reaction gases to form a p-type semiconductor layer 106a having a thickness of 20 nm. At this time, the diborane / silane gas flow rate ratio was set to 0.25%, and the integrated multi-junction thin film photoelectric conversion device 101 was formed. As a result, the boron doping amount in the p-type semiconductor layer 106a is 5000 ppm as shown in Table 1.

  After forming the p-type semiconductor layer 106a, hydrogen and silane are introduced as reaction gases to form a crystalline silicon photoelectric conversion layer 106b of 2.5 μm, and then silane, hydrogen and phosphine are introduced as reaction gases to form an n-type semiconductor layer 106c. The crystalline silicon photoelectric conversion unit 106 was formed by forming 5 nm. Further, silane, hydrogen, phosphine, and carbon dioxide were introduced as reactive gases into part of the n-type semiconductor layer 106c to form a silicon composite layer having a thickness of 60 nm. The amorphous silicon photoelectric conversion unit 104, the intermediate reflection layer 105, and the crystalline silicon photoelectric conversion unit 106 were all formed by plasma CVD.

  Thereafter, a connection groove 122 that plays a role of connecting the photoelectric conversion cells 110 juxtaposed on the glass substrate 102 in series by laser scribing is formed, and a ZnO film is formed by sputtering to improve the adhesion to the back reflective layer. After forming 30 nm, an Ag film was similarly formed by sputtering to form the back electrode 107. Finally, in order to electrically insulate the back electrode layers 107 between adjacent photoelectric conversion cells 110, separation grooves 123 were formed by laser scribing.

The photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Example 1 are obtained by irradiating AM1.5 light with a light amount of 100 mW / cm ² at 25 ° C. using a solar simulator. Efficiency was measured. As a result, as shown in Table 1, a high conversion efficiency of 12.2% was obtained.

（比較例１）
図１のような中間反射層を有さない構造で、その他の条件を実施例１と同条件で形成した。この比較例１の集積化多接合薄膜光電変換装置１０１の光電変換特性を実施例１と同様にして測定したところ１１．８％であった。実施例１の中間反射層を有する構造よりも集積化モジュールの変換効率が低かった。しかし、表１に示すように分離セルにくらべて集積化モジュールは実施例１と比較例１との差が少ない。

(Comparative Example 1)
The other conditions were the same as in Example 1 with the structure having no intermediate reflection layer as shown in FIG. The photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 1 were measured in the same manner as in Example 1 and found to be 11.8%. The conversion efficiency of the integrated module was lower than that of the structure having the intermediate reflective layer of Example 1. However, as shown in Table 1, the integrated module has a smaller difference between Example 1 and Comparative Example 1 than the separation cell.

  Therefore, the spectral sensitivity of the integrated multi-junction thin film photoelectric conversion device 101 formed in Example 1 and Comparative Example 1 was measured. The measurement method of spectral sensitivity measurement is as follows. The wavelength range of the probe light was set to 300 nm to 1200 nm, which is the sensitivity wavelength band of the integrated thin film polycrystalline photoelectric conversion device 101. The wavelength resolution was 20 nm. Calibration was performed using ND filters on the light emitted from the Xe lamp so that the probe light was 5 μW in the entire wavelength region. A single-crystal silicon photodiode was used as the calibration detector, and the current value was measured with a picoampere meter.

  When measuring the spectral sensitivity of the front photoelectric conversion layer 104, the color bias light having a wavelength longer than the sensitivity of the front photoelectric conversion layer is applied to the rear photoelectric conversion layer, and the probe light is chopped by the chopper and the current value at each wavelength is measured. Detected with a lock-in amplifier. Note that the probe light and the color bias light are applied to the front surface of the integrated multi-junction photoelectric conversion device 101. When the spectral sensitivity of the rear photoelectric conversion layer 106 is measured, the color bias light described above can be used at a wavelength shorter than the sensitivity of the rear photoelectric conversion layer.

  The column of the rear photoelectric conversion layer relative spectral sensitivity (500 nm) in Table 1 shows the value of the relative spectral sensitivity of the rear photoelectric conversion layer 106 at a wavelength of 500 nm. As a result of the spectral sensitivity measurement, as is clear from Table 1, in Example 1, the relative spectral sensitivity at the wavelength of 500 nm of the rear photoelectric conversion layer 106 is not seen in the separation cell, but apparent sensitivity appears in the integrated module. Therefore, it was found that there was a leak in the rear photoelectric conversion layer 106. Moreover, the value of the rear photoelectric conversion layer relative spectral sensitivity (500 nm) of the integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 1 is almost equal to that of the separation cell and is close to 0, and there is no leakage in the rear photoelectric conversion layer 106. I understood. As described above, the integrated module having the intermediate reflection layer of Example 1 has a conversion efficiency higher than that of the structure of Comparative Example 1 that does not have the intermediate reflection layer due to the occurrence of leakage that can be recognized by spectral sensitivity. It was found that there was no significant improvement.

(Example 2)
From the above knowledge, in order to eliminate leakage in the rear photoelectric conversion layer 106, the diborane / silane gas flow rate ratio in the formation conditions of the p-type semiconductor layer 106a is set to 0. As the integrated multi-junction thin film photoelectric conversion device 101 of Example 2. An integrated multi-junction thin film photoelectric conversion device 101 of Example 2 was formed in the same manner as Example 1 except that the content was 20%. As a result, the boron doping amount in the p-type semiconductor layer 106a is 4000 ppm as shown in Table 1.

  When the spectral sensitivity of the rear photoelectric conversion layer relative spectral sensitivity was measured in the same manner as in Example 1, the value of the rear photoelectric conversion layer relative spectral sensitivity (500 nm) of the integrated multi-junction thin film photoelectric conversion device 101 of Example 2 is the separation cell. It was found that there is no leakage in the rear photoelectric conversion layer 106, which is almost equal to 0 and close to 0.

  When the photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Example 2 were measured in the same manner as in Example 1, the conversion efficiency was 12.4%, which was higher than that of Example 1.

(Example 3)
Further, the integrated multi-junction thin film photoelectric conversion device 101 of Example 3 was carried out in the same manner as in Example 1 except that the diborane / silane gas flow rate ratio in the formation conditions of the p-type semiconductor layer 106a was 0.13%. The integrated multi-junction thin film photoelectric conversion device 101 of Example 3 was formed. As a result, the boron doping amount in the p-type semiconductor layer 106a is 2500 ppm as shown in Table 1.

  When the spectral sensitivity of the rear photoelectric conversion layer relative spectral sensitivity was measured in the same manner as in Example 1, the value of the rear photoelectric conversion layer relative spectral sensitivity (500 nm) of the integrated multi-junction thin film photoelectric conversion device 101 of Example 2 is the separation cell. It was found that there is no leakage in the rear photoelectric conversion layer 106, which is almost equal to 0 and close to 0.

  When the photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Example 2 were measured in the same manner as in Example 1, the conversion efficiency decreased to 11.9% compared to Example 2.

(Comparative Example 2)
The integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 2 is the same as Example 1 except that the diborane / silane gas flow rate ratio in the formation conditions of the p-type semiconductor layer 106a is further reduced to 0.10%. The integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 2 was formed. As a result, the boron doping amount in the p-type semiconductor layer 106a is 2000 ppm as shown in Table 1. When the spectral sensitivity of the rear photoelectric conversion layer relative spectral sensitivity was measured in the same manner as in Example 1, the value of the rear photoelectric conversion layer relative spectral sensitivity (500 nm) of the integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 2 was determined as a separation cell. It was found that there is no leakage in the rear photoelectric conversion layer 106, which is almost equal to 0 and close to 0.

  When the photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Example 2 were measured in the same manner as in Example 1, the conversion efficiency was 11.7%, which was lower than that of Comparative Example 1 having no intermediate reflective layer. did.

(Comparative Example 3)
As the integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 3, the diborane / silane gas flow rate ratio in the formation conditions of the p-type semiconductor layer 106a is larger than that of Example 1 and is 0.35%. Similarly, the integrated multi-junction thin film photoelectric conversion device 101 of Comparative Example 3 was formed. As a result, the boron doping amount in the p-type semiconductor layer 106a is 7000 ppm as shown in Table 1.

  When the spectral sensitivity of the rear photoelectric conversion layer relative spectral sensitivity was measured in the same manner as in Example 1, in Comparative Example 3, the apparent sensitivity appeared in the integrated module from the relative spectral sensitivity of the rear photoelectric conversion layer 106 at a wavelength of 500 nm. Since the value was larger than that in Example 1, it was found that the leakage in the rear photoelectric conversion layer 106 was larger than that in Example 1.

  When the photoelectric conversion characteristics of the integrated multi-junction thin film photoelectric conversion device 101 of Example 3 were measured in the same manner as in Example 1, the conversion efficiency was 11.7%, which was lower than that of Comparative Example 1 having no intermediate reflective layer. did.

  As described above, from the photoelectric conversion characteristics of any of the integrated multi-junction thin film photoelectric conversion devices 101 of Examples 1 to 3 and Comparative Examples 1 to 3, and the relative spectral sensitivity of the rear photoelectric conversion layer 106 at a wavelength of 500 nm, When the doping amount of impurities in the p-type semiconductor layer 106a of the invention is 5000 ppm or less, the resistance of the current path from the p-type semiconductor layer through the connection groove increases, and the leakage current can be reduced. In other words, since the photoelectric conversion characteristics can be sufficiently extracted from each photoelectric conversion unit, the effect of improving the efficiency was confirmed. Further, if the doping amount of the impurity of the p-type semiconductor layer 106a is 2500 ppm or more and 5000 ppm or less from the photoelectric conversion characteristics, the resistance of the current path from the p-type semiconductor layer through the connection groove is increased, and the leakage current can be reduced. . In other words, since the photoelectric conversion characteristics can be sufficiently extracted from each photoelectric conversion unit, the effect of improving the efficiency was confirmed. However, the photoelectric conversion characteristics are deteriorated when the doping amount of impurities in the p-type semiconductor layer 106a is 2500 ppm or less from the photoelectric conversion characteristics, which is due to an increase in series resistance.

Integrated multi-junction thin film photoelectric conversion device without intermediate reflective layer Integrated multi-junction thin film photoelectric conversion device having an intermediate reflective layer Relative spectral sensitivity of multi-junction cell with intermediate reflective layer and back photoelectric conversion layer of integrated module

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Integrated multi-junction thin film photoelectric conversion apparatus 102 Substrate 103 Transparent conductive layer 104 Front photoelectric conversion unit and amorphous silicon photoelectric conversion unit 104a Front photoelectric conversion unit p-type semiconductor layer 104b Amorphous silicon photoelectric conversion layer 104c Front photoelectric conversion N-type semiconductor layer of conversion unit 105 intermediate reflection layer, silicon composite layer 106 rear photoelectric conversion unit and crystalline silicon photoelectric conversion unit 106a p-type semiconductor layer of rear photoelectric conversion unit 106b crystalline silicon photoelectric conversion layer 106c rear photoelectric conversion unit Part of n-type semiconductor layer and back reflective layer 107 Back electrode layer 121, 123 Separation groove 122 Connection groove

Claims (6)

An integrated multijunction thin film photoelectric conversion device in which a multijunction thin film photoelectric conversion cell including at least one pair of two thin film photoelectric conversion units connected in series via an intermediate layer on a substrate is integrated, and the material of the intermediate layer Is n-type Si _1-X O _X (where 0.3 <X <0.6), and the intermediate portion constituting a part of at least one thin film photoelectric conversion unit of the one set of thin film photoelectric conversion units An integrated multi-junction thin film photoelectric conversion device characterized in that an impurity doping amount of an intermediate layer adjacent p-type semiconductor layer adjacent to the layer is 2500 ppm or more and 5000 ppm or less.   2. The integrated multi-junction thin film photoelectric conversion device according to claim 1, wherein a material of the intermediate layer adjacent p-type semiconductor layer is a p-type silicon-based semiconductor.   3. The integrated multijunction thin film photoelectric conversion device according to claim 1, wherein boron is doped as an impurity in the p-type semiconductor layer adjacent to the intermediate layer.   The integration according to claim 1, wherein the intermediate layer adjacent p-type semiconductor layer constitutes a part of a thin film photoelectric conversion unit formed by sandwiching the intermediate layer from the substrate. Multi-junction thin film photoelectric conversion device.   The material of the intermediate layer adjacent n-type semiconductor layer adjacent to the intermediate layer constituting at least the substrate-side thin film photoelectric conversion unit of the set of thin film photoelectric conversion units is n-type microcrystalline silicon. 5. The integrated multijunction thin film photoelectric conversion device according to any one of 1 to 4.   6. The integrated multi-junction thin film photoelectric conversion device according to claim 1, wherein 1% to 2.8% of phosphorus is doped as an impurity in the intermediate layer adjacent n-type semiconductor layer.

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