JP2013008866A - Thin film photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film photoelectric conversion device in which photoelectric conversion efficiency is improved by increasing the open voltage and the short circuit current density of the thin film photoelectric conversion device including a crystalline silicon photoelectric conversion layer.SOLUTION: Between the one conductivity type layer 41 and the photoelectric conversion layer 42 of a crystalline silicon photoelectric conversion unit 4, an interface layer 44 consisting of a substantially intrinsic silicon composite layer is placed. The interface layer 44 consisting of a substantially intrinsic silicon composite layer is formed of a layer where the crystalline silicon phase is dispersed into a parent phase amorphous silicon oxygenation.

Description

  The present invention relates to an improvement of a thin film photoelectric conversion device, and more particularly to a thin film photoelectric conversion device having an improved photoelectric conversion efficiency due to an increase in open circuit voltage and short circuit current density of a thin film photoelectric conversion device using a crystalline silicon semiconductor. Note that the terms “crystalline” and “microcrystal” in the present specification are also used in the case of partially containing amorphous, as used in this technical field.

  In recent years, photoelectric conversion devices that convert light into electricity using the photoelectric effect inside semiconductors have attracted attention and development has been vigorously conducted. Among these photoelectric conversion devices, silicon-based thin film photoelectric conversion devices are large at low temperatures. Since it can be formed on a glass substrate or a stainless steel substrate having an area, cost reduction can be expected.

  Such a silicon-based thin film photoelectric conversion device generally includes a transparent electrode layer, one or more photoelectric conversion units, and a back electrode layer that are sequentially stacked on a transparent insulating substrate. Here, the photoelectric conversion unit generally has a p-type layer, an i-type layer, and an n-type layer laminated in this order or vice versa, and the i-type photoelectric conversion layer occupying the main part is amorphous. Is called an amorphous photoelectric conversion unit, and those having an i-type layer crystalline are called crystalline photoelectric conversion units.

  The photoelectric conversion layer is a layer that absorbs light and generates electron-hole pairs. In general, in a silicon-based thin film photoelectric conversion device, an i-type layer of a pin junction is a photoelectric conversion layer. The i-type layer which is a photoelectric conversion layer occupies the main film thickness of the photoelectric conversion unit.

  The i-type layer is an intrinsic semiconductor layer that does not ideally contain a conductivity determining impurity. However, even if a small amount of impurities is included, if the Fermi level is in the middle of the forbidden band, it functions as a pin junction i-type layer, so that it is a substantially intrinsic (substantially i-type) layer. Call it. In general, the substantially intrinsic layer is formed without adding a conductivity determining impurity to the source gas. In this case, a conductivity determining impurity may be included in an allowable range that functions as an i-type layer. Further, the substantially i-type layer may be formed by intentionally adding a small amount of conductivity-type determining impurities in order to remove the influence of impurities caused by the atmosphere or the underlayer on the Fermi level.

  As a method for improving the conversion efficiency of a photoelectric conversion device, a photoelectric conversion device employing a structure called a stacked type 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 optical forbidden band width is disposed on the light incident side of the photoelectric conversion device, and subsequently has a small optical forbidden band width (for example, Si− By arranging a rear photoelectric conversion unit including a photoelectric conversion layer (such as a Ge alloy), it is possible to perform photoelectric conversion over a wide wavelength range of incident light, and improve the conversion efficiency of the entire device by effectively using incident light Is planned.

  For example, a two-junction thin film photoelectric conversion device in which an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked is known as a hybrid thin film photoelectric conversion device. In this case, the wavelength of light that can be photoelectrically converted by i-type amorphous silicon (a-Si) is up to about 700 nm on the long wavelength side, whereas i-type crystalline silicon has a longer wavelength of about 1100 nm. Can be photoelectrically converted. In the case of this two-junction thin film photoelectric conversion device, the photoelectric conversion unit on the light incident side is referred to as a front photoelectric conversion unit, and the photoelectric conversion unit on the rear side is referred to as a rear photoelectric conversion unit.

  Furthermore, as a technique for improving the efficiency of the multilayer thin film photoelectric conversion device, intermediate transmission reflection made of a material having conductivity and a lower refractive index than the material forming the thin film photoelectric conversion unit is provided between the thin film photoelectric conversion units. There are methods for forming layers. By having such an intermediate transmission reflection layer, it is possible to design to reflect light on the short wavelength side and transmit light on the long wavelength side, and more effectively perform photoelectric conversion in each thin film photoelectric conversion unit. . For example, when an intermediate transmission / reflection layer is inserted into a hybrid photoelectric conversion device including a front amorphous silicon photoelectric conversion unit and a rear crystalline silicon photoelectric conversion unit, the film thickness of the amorphous silicon photoelectric conversion layer is increased. In addition, the current generated by the front photoelectric conversion unit can be increased. In addition, when the intermediate transmission / reflection layer is included, the amorphous silicon photoelectric conversion layer necessary for obtaining the same current value can be made thinner than when the intermediate transmission / reflection layer is not included. It becomes possible to suppress the deterioration of the characteristics of the amorphous silicon photoelectric conversion unit due to the photodegradation (Staebler-Wronski effect) that becomes conspicuous as the thickness of the porous silicon layer increases.

  The open circuit voltage of the crystalline photoelectric conversion unit is as low as about 55% of that of the amorphous photoelectric conversion unit, and improvement of the open circuit voltage can be cited as a problem for improving the photoelectric conversion efficiency. When the crystallization rate of the photoelectric conversion layer of the crystalline silicon semiconductor layer is lowered, the open circuit voltage can be increased, but there is a problem that the short circuit current density is lowered.

(Prior Example 1)
In Patent Document 1, for the purpose of increasing the open-circuit voltage, carbon, oxygen, and nitrogen are formed on the p / i interface of a thin film photoelectric conversion device having a structure of p-type microcrystalline silicon / i-type microcrystalline silicon / n-type microcrystalline silicon. An example is disclosed in which an interface layer containing any one of 1 × 10 ²⁰ atoms / cm ³ or more is inserted, and the crystal fraction of the interface layer is lower than that of the p layer. In the example, B ₂ H ₆ having the same flow rate as that of the p layer is used for this interface layer, and it is clearly shown that the interface layer of the first example is p-type. In the example, the open circuit voltage is improved, but the short circuit current density is decreased.

(Prior Example 2)
Patent Document 2 discloses a stacked thin film photoelectric conversion device using an n-type silicon composite layer as an intermediate transmission / reflection layer as a material for a low refractive index layer. The silicon composite layer includes a silicon crystal phase dispersed in an amorphous alloy matrix of silicon and oxygen, contains an oxygen concentration in the film of 40 atomic% or more and 60 atomic% or less, and with respect to light having a wavelength of 600 nm. It has a refractive index of 1.7 or more and 2.1 or less, and has a thickness greater than 20 nm and smaller than 130 nm. As the structure of the solar cell, p-type amorphous silicon carbide layer / i-type amorphous silicon photoelectric conversion layer / n-type microcrystalline silicon layer / n-type silicon composite layer / p-type microcrystalline silicon layer / i-type crystalline material A structure in which a silicon photoelectric conversion layer / n-type microcrystalline silicon layer is sequentially laminated is disclosed.

JP 2003-258286 A JP 2005-45129 A

  There is a problem that it is difficult to improve the open circuit voltage without reducing the short-circuit current density of the thin film photoelectric conversion device including the crystalline silicon photoelectric conversion unit.

  In view of the above, the present invention provides a thin film photoelectric conversion device with improved photoelectric conversion efficiency by suppressing a decrease in short-circuit current density of a thin film photoelectric conversion device including a crystalline photoelectric conversion unit and improving an open circuit voltage. Objective.

  A thin film photoelectric conversion device according to the present invention is a thin film photoelectric conversion device including a photoelectric conversion unit in which a one conductivity type layer, a substantially intrinsic semiconductor photoelectric conversion layer, and a reverse conductivity type layer are arranged in the order closer to the light incident side, The photoelectric conversion layer is a crystalline silicon photoelectric conversion unit including a substantially intrinsic crystalline silicon semiconductor layer, and is substantially intrinsic between one conductive type layer and the photoelectric conversion layer of the crystalline silicon photoelectric conversion unit. The problem is solved by disposing an interface layer made of a silicon composite layer, wherein the silicon composite layer is a layer in which a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix.

  By arranging a substantially intrinsic silicon composite layer as an interface layer at the p / i interface of the crystalline photoelectric conversion unit, a wide gap interface layer is inserted, and the open-circuit voltage of the thin film photoelectric conversion device is reduced. To increase. In addition, since the interface layer is a substantially intrinsic silicon composite layer, the absorption coefficient is smaller than that of the p-type silicon composite layer having the same refractive index, and the light absorption loss is suppressed. The short circuit current density is improved. Further, since the interface layer is a substantially intrinsic silicon composite layer, the crystallization rate is higher than that of the p-type silicon composite layer having the same refractive index, and the crystalline photoelectric conversion layer is formed on the interface layer. In this case, the interface layer becomes an underlayer having a high crystallization rate, the crystallization rate of the crystalline photoelectric conversion layer thereon is increased, and the short-circuit current density of the thin film photoelectric conversion device is improved.

  The thin film photoelectric conversion device according to the present invention is also effective when applied to a laminated thin film photoelectric conversion device. In particular, a part of the reverse conductivity type layer of the amorphous silicon photoelectric conversion unit as the front photoelectric conversion unit includes an n-type silicon composite layer as the transparent intermediate reflection layer, and a crystalline silicon photoelectric conversion unit is disposed as the rear photoelectric conversion unit. The structure of the laminated thin film photoelectric conversion device is desirable.

The interface layer of the present invention desirably has a refractive index of 2.2 to 3.0 for 600 nm light. Alternatively, in the interface layer of the present invention, it is desirable that the peak intensity ratio of the TO mode peak of the crystalline silicon component to the peak derived from the amorphous component measured by Raman scattering is 3 or more and 6 or less. Alternatively, it is desirable that the dark conductivity is 10 ⁻⁸ S / cm or more and 10 ⁻¹ S / cm or less.

According to a first aspect of the present invention, “in order from the light incident side, one or more photoelectric conversion units in which a transparent electrode layer, one conductive type layer, a substantially intrinsic semiconductor photoelectric conversion layer, and a reverse conductive type layer are disposed; A thin film photoelectric conversion device including a back electrode layer,
At least one photoelectric conversion unit is a crystalline silicon photoelectric conversion unit in which the photoelectric conversion layer includes a substantially intrinsic crystalline silicon semiconductor layer,
Between the one conductive type layer of the crystalline silicon photoelectric conversion unit and the photoelectric conversion layer, an interface layer composed of a substantially intrinsic silicon composite layer is disposed,
The silicon composite layer is a thin film photoelectric conversion device characterized in that a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix.

  The second aspect of the present invention is “the thin film photoelectric conversion device as described above, comprising two or more photoelectric conversion units, and the closest photoelectric conversion unit on the light incident side is an amorphous silicon whose photoelectric conversion layer is substantially intrinsic. It is a “stacked thin film photoelectric conversion device” which is an amorphous photoelectric conversion unit including a semiconductor layer.

  A third aspect of the present invention is “the laminated thin film photoelectric conversion device, wherein at least a part of the reverse conductivity type layer of the amorphous photoelectric conversion unit is crystalline silicon in an amorphous oxygenated silicon matrix”. A laminated thin film photoelectric conversion device, which is an n-type silicon composite layer in which phases are dispersed.

  A fourth aspect of the present invention is the above-described thin film photoelectric conversion device, wherein the interface layer has a refractive index of 2.2 to 3.0 with respect to light having a wavelength of 600 nm. Device ".

  The fifth aspect of the present invention is “the thin-film photoelectric conversion device as described above, wherein the interface layer has a peak intensity ratio of a TO mode peak of a crystalline silicon component to a peak derived from an amorphous component measured by Raman scattering of 3 or more. It is a thin film photoelectric conversion device ”characterized in that it is 6 or less.

A sixth aspect of the present invention is “the thin film photoelectric conversion device, wherein the interface layer has a dark conductivity of 10 ⁻⁸ S / cm or more and 10 ⁻¹ S / cm or less. It is a “photoelectric conversion device”.

  A seventh aspect of the present invention is the “thin film photoelectric conversion device, wherein the film thickness of the interface layer is not less than 5 nm and not more than 15 nm”.

  An interfacial layer composed of a substantially intrinsic silicon composite layer is disposed between one conductive type layer of the crystalline silicon photoelectric conversion unit and the photoelectric conversion layer, and the silicon composite layer is in an amorphous oxygenated silicon matrix. In addition, the layer in which the crystalline silicon phase is dispersed increases the open-circuit voltage and suppresses the decrease in the short-circuit current density, thereby improving the photoelectric conversion efficiency.

1 is a schematic cross-sectional view of a stacked thin film photoelectric conversion device according to one embodiment of the present invention. 1 is a schematic cross-sectional view of an integrated thin film photoelectric conversion module according to one embodiment of the present invention. The typical sectional view of the lamination type thin film photoelectric conversion device concerning another embodiment of the present invention. The typical sectional view of the lamination type thin film photoelectric conversion device concerning the comparative example by the conventional method. Crystal silicon Raman peak intensity ratio with respect to the refractive index of light with a wavelength of 600 nm of substantially intrinsic (SiO (i) in the figure) and p-type (SiO (p) in the figure) silicon composite layers. Dark conductivity with respect to the refractive index of light having a wavelength of 600 nm of substantially intrinsic (SiO (i) in the figure) and p-type (SiO (p) in the figure) silicon composite layers. Absorption coefficient (alpha) with respect to light energy (E) of silicon composite layers of substantially intrinsic type (SiO (i) in the figure) and p type (SiO (p) in the figure). Raman scattering spectra of substantially intrinsic (SiO (i)) and p-type (SiO (p)) silicon composite layers and p-type microcrystalline silicon layers (uc-Si (p)).

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each drawing of the present application, dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Moreover, in each figure, the same referential mark represents the same part or an equivalent part.

  In the thin film photoelectric conversion device including the conventional crystalline silicon photoelectric conversion unit, the present inventors have developed a thin film photoelectric conversion device in order to improve the open-circuit voltage and suppress the decrease in short-circuit current density and improve the photoelectric conversion efficiency. The structure of the converter was studied.

  When a p-type silicon composite layer having a crystallization rate lower than that of p-type microcrystalline silicon is used as the wide gap material in the crystalline silicon photoelectric conversion unit as in the first example, Voc increases, but Jsc is On the contrary, a problem has been found in which Eff decreases. In the configuration of the first example, the thickness of the p layer is a p-type microcrystalline silicon + p-type silicon composite layer and is substantially thick, and it can be said that the increase in Voc is simply an effect of increasing the film thickness. . As the p-type layer becomes thicker, it can be said that the absorption loss increases and Jsc decreases.

  Further examination of the silicon composite layer reveals that if the p-type silicon composite layer contains conductivity-determining impurities, the absorption coefficient increases and the crystallinity that can be detected by the Raman peak intensity ratio decreases. It was.

As a result of intensive studies on a structure that increases the Voc of the crystalline photoelectric conversion unit and does not decrease the Jsc, it is invented that the problem can be solved by introducing a substantially intrinsic silicon composite layer into the p / i interface. Found. In the case of microcrystalline silicon, the dark conductivity of p-type microcrystalline silicon is about 10 ⁻² S / cm to 1 S / cm, whereas the dark conductivity of substantially intrinsic microcrystalline silicon is 10 ⁻ It is known that the intrinsic type has a low dark conductivity of 2 to 4 digits compared to the p-type, and has a high resistance of about ⁶ S / cm to 10 ⁻⁴ S / cm. The silicon composite layer is a layer in which a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix, and, as in the case of microcrystalline silicon, silicon that is substantially intrinsic to the p-type silicon composite layer. It is expected by those skilled in the art that the composite layer has a dark conductivity that is several orders of magnitude lower, and it is not common practice to use an intrinsic type silicon composite layer at the p / i interface.

  However, when the inventor diligently studied the interface layer, when compared at the same refractive index, the crystallization rate of the substantially intrinsic silicon composite layer is higher than the crystallization rate of the p-type silicon composite layer, It has been found that the dark conductivity shows almost the same value, and when used as an interface layer, the open circuit voltage can be improved. This is contrary to the case in which the first example was intended to improve the open-circuit voltage by lowering the crystallization rate of the interface layer. The improvement is realized. Surprisingly, the present inventors have found that the short-circuit current density can be improved even though the interface layer is added to increase the layer.

FIG. 5 shows the Raman peak intensity ratio with respect to the refractive index at a wavelength of 600 nm of the silicon composite layer. The intensity ratio between the TO mode peak of the crystalline silicon component near the wave number of 520 cm ⁻¹ and the TO mode peak of the amorphous silicon near 480 cm ⁻¹ is shown on the vertical axis. In the figure, SiO (i) indicates a substantially intrinsic silicon composite layer, and SiO (p) indicates a p-type silicon composite layer. Comparing with the same refractive index near the refractive index of 2.5, it can be seen that the peak intensity ratio of SiO (i) is about twice as high as that of SiO (p).

FIG. 6 shows the dark conductivity with respect to the refractive index at a wavelength of 600 nm of the silicon composite layer. Comparing with the same refractive index near the refractive index of 2.5, it can be seen that SiO (i) and SiO (p) show substantially the same dark conductivity of 10 ⁻⁵ S / cm.

  FIG. 1 is a schematic cross-sectional view of a stacked thin film photoelectric conversion device 100 according to an example of an embodiment of the present invention. On the transparent substrate 1, a transparent electrode layer 2, an amorphous silicon photoelectric conversion unit 3 as a front photoelectric conversion unit, a crystalline silicon photoelectric conversion unit 4 as a rear photoelectric conversion unit, and a back electrode layer 5 are arranged in this order. An interface layer 44 is provided between the p-type layer and the photoelectric change layer of the rear photoelectric conversion unit.

  A plate-like member or a sheet-like member made of glass, transparent resin or the like is used for the transparent substrate 1 used in a photoelectric conversion device of a type in which light enters from the substrate side. In particular, it is preferable to use a glass plate as the transparent substrate 1 because it has a high transmittance and is inexpensive.

  That is, since the transparent substrate 1 is located on the light incident side of the thin film photoelectric conversion device, it is preferable that the transparent substrate 1 be as transparent as possible so that more sunlight is transmitted and absorbed by the photoelectric conversion unit. From the same intention, it is preferable to provide a non-reflective coating on the light incident surface of the transparent substrate 1 in order to reduce the light reflection loss on the sunlight incident surface.

The transparent electrode layer 2 is preferably made of a conductive metal oxide such as SnO ₂ or ZnO, and is preferably formed using a method such as CVD, sputtering, or vapor deposition. The transparent electrode layer 2 desirably has the effect of increasing the scattering of incident light by having fine irregularities on its surface.

  It is desirable that the front photoelectric conversion unit, which is a top cell, is composed of, for example, an amorphous silicon photoelectric conversion unit 3. The amorphous silicon photoelectric conversion unit 3 is formed by stacking, for example, a p-type layer, an i-type layer, and an n-type layer in this order by plasma CVD. Specifically, a p-type amorphous silicon carbide layer 31 having a thickness of 5 to 40 nm doped with 0.01 atomic% or more of boron, and a substantially i-type amorphous silicon photoelectric film having a thickness of 50 to 400 nm. A conversion layer 32 and an n-type microcrystalline silicon layer 33 having a thickness of 5 to 40 nm doped with 0.01 atomic% or more of phosphorus are deposited in this order.

  The rear photoelectric conversion unit is composed of a crystalline silicon photoelectric conversion unit 4. The crystalline silicon photoelectric conversion unit 4 is formed by stacking a p-type layer, an interface layer, an i-type layer, and an n-type layer in this order by plasma CVD. Specifically, a p-type microcrystalline silicon layer 41 having a thickness of 5 to 40 nm doped with 0.01 atomic% or more of boron, an interface layer 44 made of a substantially intrinsic silicon composite layer, and a substantially intrinsic thickness. A crystalline silicon photoelectric conversion layer 42 with a thickness of 0.5 to 5 μm and an n-type microcrystalline silicon layer 43 with a thickness of 1 to 40 nm doped with 0.01 atomic% or more of phosphorus are deposited in this order.

  Here, in an example of the embodiment of the present invention, a substantially intrinsic silicon composite layer is disposed as an interface layer between the p-type layer of the crystalline silicon photoelectric conversion unit and the crystalline silicon photoelectric conversion layer. It is a feature of the present invention. The interface layer 44 is a layer in which a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix. Since the silicon crystal phase is surrounded by an amorphous silicon alloy, a substantial band gap is widened, and a wide gap layer at the p / i interface of the crystalline photoelectric conversion unit is inserted. As a result, the open circuit voltage of the thin film photoelectric conversion device increases. In addition, since the interface layer is a substantially intrinsic silicon composite layer, the absorption coefficient is smaller than that of the p-type silicon composite layer having the same refractive index, and light absorption loss is suppressed. The short circuit current density of the device is improved. Further, since the interface layer is a substantially intrinsic silicon composite layer, the crystallization rate is higher than that of the p-type silicon composite layer having the same refractive index, and the crystalline photoelectric conversion layer is formed on the interface layer. In this case, the interface layer becomes an underlayer having a high crystallization rate, the crystallization rate of the crystalline photoelectric conversion layer thereon is increased, and the short-circuit current density of the thin film photoelectric conversion device is improved.

The substantially intrinsic interface layer (i-SiOx) uses SiH ₄ , CO ₂ , and H ₂ as the reaction gas under so-called microcrystal production conditions with a large H ₂ / SiH ₄ ratio, and CO ₂ / SiH. It has been experimentally found that it can be produced by plasma CVD using a ratio of ₄ to about 0.3-3. At this time, the plasma conditions are as follows: a capacitively coupled parallel plate electrode, a power frequency of 10 to 100 MHz, a power density of 50 to 500 mW / cm ² , a pressure of 50 to 1000 Pa, and a H ₂ / SiH ₄ ratio of 50 to 500 times. The substrate temperature is 150 to 250 ° C. When the CO ₂ / SiH ₄ ratio is increased, the oxygen concentration in the film increases monotonously. However, the carbon concentration in the film was 1 atomic% or less even when the CO ₂ / SiH ₄ ratio was changed in the range of 0 to 4, and it was found by experiment that it hardly enters the film compared with oxygen. The oxygen concentration in the film is preferably 5 atom% or more and 40 atom% or less, and more preferably 10 atom% or more and 30 atom% or less. By setting the oxygen concentration to 5 atomic% or more, the band gap of the interface layer is widened, and the Voc of the thin film photoelectric conversion device is improved. Further, by setting the oxygen concentration to 30 atomic% or less, the dark conductivity can be increased, the contact resistance between the interface layer and the adjacent layer can be reduced, and the FF can be increased. Moreover, since the silicon crystal phase can be easily included in the interface layer by setting the oxygen concentration to 30 atomic% or less, when the crystalline silicon photoelectric conversion layer is formed thereon, the interface layer has high crystallinity. It becomes an underlayer, which is desirable because the crystallization rate of the crystalline silicon photoelectric conversion layer is increased and the short-circuit current density is improved.

  The presence or absence of the crystalline silicon phase in the interface layer can be detected by manufacturing the interface layer on a glass substrate under the same film-forming conditions as the stacked thin film photoelectric conversion device, and using Raman scattering spectrum, X-ray diffraction method, spectroscopic ellipsometry, etc. it can.

  Alternatively, the crystalline silicon phase can be detected by performing wet etching or plasma etching on the thin film photoelectric conversion device to expose the interface layer. In this case, in order to increase the detection sensitivity of the crystal phase of the interface layer exposed on the outermost surface, in the case of measuring the Raman scattering spectrum, a laser microscope Raman apparatus using a short wavelength laser, for example, a laser having a wavelength of 532 nm or less, is used. Use. Alternatively, X-ray diffraction measurement is performed by an in-plane method. Alternatively, spectroscopic ellipsometry is used.

  Alternatively, the presence or absence of the crystalline silicon phase can also be detected from a cross-sectional image of a transmission electron microscope (TEM) of the thin film photoelectric conversion device. A cross-sectional image of the TEM can be taken from 200,000 times to 500,000 times to confirm the presence or absence of a silicon crystal phase. In particular, when a dark field image is taken, the silicon crystal phase can be easily confirmed because the portion that appears bright is the crystal phase.

The interface layer is measured by Raman scattering, and has the intensity of the TO mode peak intensity (Ic) of the crystalline silicon component around 520 cm ⁻¹ and the intensity of the TO mode peak intensity (Ia) of the amorphous silicon component around 480 cm ^−1. The ratio (Ic / Ia) is preferably 3 or more and 6 or less. When Ic / Ia is 3 or more, a crystalline silicon phase is surely generated, which is preferable. Even if there is no conductivity type determining impurity, dark conductivity can be increased. When Ic / Ia is 3 or more, crystallinity is improved and Jsc is increased when a crystalline silicon photoelectric conversion layer is formed on the interface layer. When Ic / Ia is 6 or less, it is considered that the lattice spacing of the crystalline silicon phase surrounded by the amorphous silicon alloy is likely to be widened, and the band gap is widened to increase the Voc of the crystalline photoelectric conversion unit.

The dark conductivity of the interface layer is preferably 10 ⁻⁸ S / cm or more and 10 ⁻¹ S / cm or less. By setting the dark conductivity of the interface layer to 10 ⁻⁸ S / cm or more, the contact resistance between the interface layer and the adjacent layer can be reduced, and the FF of the thin film photoelectric conversion device can be increased. In addition, it is preferable that the dark conductivity of the interface layer is 10 ⁻¹ S / cm or less because leakage current can be reduced and current loss can be reduced. In particular, by setting the dark conductivity to 10 ⁻¹ S / cm or less, when the thin film photoelectric conversion device is integrated with a laser scribe or the like, the leakage current is suppressed and the FF is increased, and the characteristics of the photoelectric conversion device are increased. Is desirable because it increases.

  The refractive index of light having a wavelength of 600 nm of the interface layer is preferably 2.2 or more and 3.0 or less, and more preferably 2.3 or more and 2.8 or less. When the refractive index at a wavelength of 600 nm of the interface bonding layer is 2.2 or more, it is desirable because the crystallization rate of the interface layer is increased, the dark conductivity is increased, and Voc and FF are improved. Further, when the refractive index is 3.0 or less, the band gap of the interface layer is widened to increase Voc, lower the absorption coefficient, and increase Jsc. The refractive index of light having a wavelength of 600 nm in the interface layer can be measured by spectroscopic ellipsometry.

  The thickness of the interface layer is desirably 5 nm or more and 150 nm or less. If the interface layer is thin, the increase in Voc is small. Therefore, in order to sufficiently improve Voc, it is desirable that the thickness of the interface layer be 5 nm or more. If the interface layer is too thick, absorption loss increases. Therefore, in order to increase Jsc, the film thickness of the interface layer is desirably 150 nm or less.

As the back electrode layer 5, it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition. Between the photoelectric conversion unit and the metal layer, ITO, may be formed a layer made of SnO 2, conductive oxides such as _ZnO (not shown).

  1 shows a two-junction stacked thin-film photoelectric conversion device. However, if a crystalline silicon photoelectric conversion unit is included, a single-junction thin-film photoelectric conversion device or a multi-junction in which three or more junction photoelectric conversion units are stacked. Needless to say, the thin film photoelectric conversion device may be used.

  Although FIG. 1 shows a thin film photoelectric conversion device in which light is incident from the substrate side, it goes without saying that the present invention is also effective in a thin film photoelectric conversion device in which light is incident from the opposite side of the substrate. When light is incident from the side opposite to the substrate, for example, the substrate, the back electrode layer, the crystalline silicon photoelectric conversion unit, the front photoelectric conversion unit, and the transparent electrode layer may be stacked in this order. In this case, the crystalline silicon photoelectric conversion unit is preferably stacked in the order of an n-type layer, a crystalline silicon photoelectric conversion layer, an interface layer, and a p-type layer, and the front photoelectric conversion unit includes an n-type layer, a photoelectric conversion layer, It is desirable to stack in the order of the p-type layer.

  Needless to say, the present invention is also effective in an integrated thin film photoelectric conversion device in which a series connection structure is formed on the same substrate using laser patterning. In the case of an integrated thin film photoelectric conversion device, laser patterning can be easily performed. Therefore, a structure in which light is incident from the substrate side as shown in FIG. 1 is desirable.

  Hereinafter, examples according to the present invention and comparative examples according to the prior art will be described in detail. In the drawings, the same members are denoted by the same reference numerals, and redundant description is omitted. Moreover, this invention is not limited to a following example, unless the meaning is exceeded.

Example 1
As Example 1, a thin film photoelectric conversion device 100 having the structure shown in FIG. Further, an integrated thin film photoelectric conversion module 901 having the structure shown in FIG. 2 was formed by laser scribing. As the transparent substrate 1, a glass substrate having a thickness of 4 mm and 910 mm × 455 mm was used. On the transparent substrate 1, a transparent electrode layer 2 was produced by a thermal CVD method using a SnO ₂ film having minute pyramidal surface irregularities and an average thickness of 700 nm. The sheet resistance of the obtained transparent electrode layer 2 was about 9Ω / □. The haze ratio measured with a C light source was 12%, and the average height difference d of the surface irregularities was about 100 nm. The haze ratio was measured based on JISK7136.

  Next, a first separation groove 903 was formed in the transparent electrode layer 2 using a YAG laser having a wavelength of 1064 nm, and then washed and dried.

  On this transparent electrode layer 2, using a capacitively coupled high-frequency plasma CVD apparatus having parallel plate electrodes with a frequency of 13.56 MHz, an amorphous silicon photoelectric conversion unit 3 and a backward photoelectric conversion unit are used as the front photoelectric conversion unit. A crystalline silicon photoelectric conversion unit 4 was sequentially produced as a unit.

The amorphous silicon photoelectric conversion unit 3 introduces SiH ₄ , H ₂ , CH _4, and B ₂ H ₆ as a reaction gas and forms a p-type amorphous silicon carbide layer 31 as a single conductivity type layer with a thickness of 15 nm. SiH ₄ is introduced to form an amorphous silicon photoelectric conversion layer 32 having a thickness of 350 nm, and then SiH ₄ , H ₂ and PH ₃ are introduced as reaction gases to form an n-type microcrystalline silicon layer 33 having a thickness of 20 nm as a reverse conductivity type layer. It was produced by.

Next, a crystalline silicon photoelectric conversion unit 4 was produced. SiH ₄ , H ₂ and B ₂ H ₆ are introduced as reaction gases to form a p-type microcrystalline silicon layer 41 having a thickness of 10 nm as one conductivity type layer, and then an interface layer 44 made of a substantially intrinsic silicon composite layer is formed to a thickness of 10 nm. Then, SiH ₄ and H ₂ were introduced as reaction gases to form a crystalline silicon photoelectric conversion layer 42 having a thickness of 1.5 μm. Thereafter, SiH ₄ , H _2, and PH ₃ were introduced as reaction gases to form an n-type microcrystalline silicon layer 43 with a thickness of 10 nm, thereby producing an n-type layer 43 that is a reverse conductivity type layer.

The gas flow rate ratio when forming the p-type microcrystalline silicon layer 41 is SiH ₄ / B ₂ H ₆ / H ₂ = 1 / 0.005 / 300. The film was formed at a power frequency of 13.56 MHz, a power density of 200 mW / cm ² , a pressure of 350 Pa, and a substrate temperature of 200 ° C. The peak intensity ratio of the TO mode peak of the crystalline silicon component to the TO mode peak of the amorphous silicon component measured by Raman scattering of the p-type microcrystalline silicon layer was 2.8.

The flow rate ratio of the gas when forming the interface layer 44 made of a substantially intrinsic silicon composite layer is SiH ₄ / CO ₂ / H ₂ = 1 / 0.75 / 300. The film was formed at a power frequency of 13.56 MHz, a power density of 200 mW / cm ² , a pressure of 350 Pa, and a substrate temperature of 200 ° C. At this time, the interface layer 44 has an oxygen concentration in the film of 23 atomic%, a refractive index for light of 600 nm is 2.5, and the TO mode peak of the crystalline silicon component with respect to the TO mode peak of the amorphous silicon component measured by Raman scattering. The peak intensity ratio was 4.3, and the dark conductivity was 1.4 × 10 ⁻⁵ S / cm.

The Raman scattering peak intensity ratio and dark conductivity are the same on the glass substrate under the same conditions except that the film formation time is longer than that of the interface layer 44 or the p-type microcrystalline recon layer 41 of the thin film photoelectric conversion device. 200 nm was prepared and measured. The dark conductivity was obtained from voltage-current characteristics by preparing an Al coplanar electrode on the interface layer on the glass substrate. The oxygen concentration in the film was measured by photoelectron spectroscopy (XPS). The Raman scattering peak intensity ratio was measured using a micro Raman apparatus using a laser having a wavelength of 532 nm.

  Subsequently, a connection groove 905 was formed through the semiconductor layer 30 including the front photoelectric conversion unit 2 and the rear photoelectric conversion unit 3 using a 532 nm second harmonic YAG laser.

  Thereafter, as the back electrode layer 5, an Al-doped ZnO film having a thickness of 30 nm and an Ag film having a thickness of 300 nm were sequentially formed by sputtering.

  Finally, a second separation groove 904 is formed through the front photoelectric conversion unit 2, the semiconductor layer 30 including the rear photoelectric conversion unit 3, and the back electrode layer 5 using a 532 nm second harmonic YAG laser. Formed.

When the thin film photoelectric conversion module 901 obtained as described above was irradiated with AM 1.5 light at a light quantity of 100 mW / cm ² and the output characteristics were measured, as shown in Example 1 of Table 1, the open circuit voltage was measured. (Voc) was 1.371 V, short circuit current density (Jsc) was 11.58 mA / cm ² , fill factor (FF) was 0.729, and conversion efficiency (Eff) was 11.42%.

(Comparative Example 1)
As Comparative Example 1, a thin film photoelectric conversion module according to the conventional method shown in FIG. Comparative Example 1 was fabricated in the same manner as in Example 1 except that the interface layer 44 of FIG. 1 was not present.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Comparative Example 1 were measured in the same manner as in Example 1, Voc = 1.342 V, Jsc = 11.47 mA / cm ² , FF = 0.726, Eff = 11.18%.

(Comparative Example 2)
As Comparative Example 2, a conventional thin film photoelectric conversion module was produced. Comparative Example 2 was fabricated in the same manner as in Example 1 except that a p-type silicon composite layer having a thickness of 10 nm was used for the interface layer instead of the interface layer 44 in FIG.

The flow rate ratio of the gas when forming the interface layer made of the p-type silicon composite layer is SiH ₄ / CO ₂ // B ₂ H ₆ / H ₂ = 1 / 1.1 / 0.005 / 300. The film was formed at a power frequency of 13.56 MHz, a power density of 200 mW / cm ² , a pressure of 350 Pa, and a substrate temperature of 200 ° C. At this time, the p-type interface layer has an oxygen concentration in the film of 27 atomic%, a refractive index for light of 600 nm is 2.5, and the TO mode peak of the crystalline silicon component with respect to the TO mode peak of the amorphous silicon component measured by Raman scattering. The peak intensity ratio of the peak was 1.7, and the dark conductivity was 1.6 × 10 ⁻⁵ S / cm.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Comparative Example 1 were measured in the same manner as in Example 1, Voc = 1.356 V, Jsc = 11.17 mA / cm ² , FF = 0.725, Eff = 10.98%.

(Comparison between Example 1 and Comparative Examples 1 and 2)
In Example 1, by using an interface layer made of a substantially intrinsic silicon composite layer, Voc, Jsc, and FF are all increased and Eff is improved as compared with Comparative Example 1. On the other hand, Comparative Example 2 has almost the same refractive index as Example 1, but uses a p-type silicon composite layer as an interface layer, and Voc increases as compared with Comparative Example 1, but Jsc. Decreased and Eff decreased. In both Example 1 and Comparative Example 2, it can be said that Voc was improved by arranging a wide gap layer at the p / i interface of the crystalline silicon unit. However, the p-type silicon composite layer of Comparative Example 2 has an absorption loss due to a higher absorption coefficient or a lower Raman peak intensity ratio than the substantially intrinsic silicon composite layer of Example 1. As a result, it can be said that Jsc is reduced by reducing the crystallization rate of the crystalline silicon photoelectric conversion layer formed on the interface layer. The reason why Jsc in Example 1 increased from Comparative Example 1 is not clear, but because the silicon composite layer is substantially intrinsic, it also functions as an active layer and increased generation of carriers due to light absorption. Presumed.

  FIG. 7 shows the light energy of the substantially intrinsic interface layer (SiO (i) in the figure) used in Example 1 and the p-type interface layer (SiO (p) in the figure) used in Comparative Example 2. The absorption coefficient (alpha) for E) is shown. Each interface layer was formed on a glass substrate under the same film forming conditions as those used in the photoelectric conversion device except that the film thickness was increased to 200 nm. As can be seen from FIG. 7, when compared with the same refractive index, the substantially intrinsic silicon composite layer has a smaller absorption coefficient than the p-type silicon composite layer.

  Further, the band gap (so-called Taus gap) obtained from the X-axis intercept when plotting E on the X-axis and √ (αE) on the Y-axis is 2.64 eV for the interface layer of Example 1, and the interface layer of Comparative Example 2 Was 2.66 eV.

FIG. 8 shows an interface layer (SiO (i) in the figure) made of a substantially intrinsic silicon composite layer used in Example 1, and an interface layer (SiO in the figure) made of a p-type silicon composite layer used in Comparative Example 2. (P)), and the Raman scattering spectrum of the p-type microcrystalline silicon layer (uc-Si (p)) used in Example 1 and Comparative Example 2. As is clear from FIG. 8, the peak of the crystalline silicon TO mode component in the vicinity of 520 cm ⁻¹ is higher in SiO (i) than in SiO (p) and high in crystallinity. It can also be seen that SiO (i) has a sharper crystalline silicon component peak and higher crystallinity than uc-Si (p). The intensity ratio of the crystalline silicon component peak to the amorphous silicon component peak is 4.3, 2.8, and 1.7 in the order of uc-Si (i), uc-Si (p), and SiO (p). ing.

(Example 2)
As Example 2, a thin film photoelectric conversion module having the structure shown in FIG. Example 2 was produced in the same manner as in Example 1 except that the thickness of the interface layer 44 was 15 nm.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Example 2 were measured in the same manner as in Example 1, Voc = 1.367 V, Jsc = 11.38 mA / cm ² , FF = 0.636, Eff = 11.45%.

(Example 3)
As Example 3, a thin film photoelectric conversion module having the structure shown in FIG. Example 3 was produced in the same manner as in Example 1 except that the thickness of the interface layer 44 was 5 nm.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Example 3 were measured in the same manner as in Example 1, Voc = 1.351 V, Jsc = 1.47 mA / cm ² , FF = 0.636, Eff = 11.28%.

(Comparison between Examples 1 to 3 and Comparative Example 1)
When the film thickness of the interface layer of the substantially intrinsic silicon composite layer was changed, Voc and Jsc were maximized at a film thickness of 10 nm. The reason why Voc is lower in Example 3 than in Example 1 is that the thickness of the interface layer, which is a wide gap layer, is not sufficient. On the other hand, Voc slightly decreased in Example 2 compared to Example 1 because the electric field applied to the interface layer was increased and the electric field applied to the crystalline silicon photoelectric conversion layer was weakened when the interface layer was too thick. Thus, it is estimated that Voc has decreased. The reason why Example 3 has a lower Jsc than that of Example 1 is considered to be that the optical layer generated in the interface layer is small because the interface layer is thin. The reason why Jsc slightly decreased in Example 2 compared to Example 1 can be attributed to an increase in absorption loss due to the interface layer. The FF of Example 2 increased from that of Example 1 because the crystallization rate of the interface layer increased as the thickness of the interface layer increased, and the contact resistance between the interface layer and the crystalline silicon photoelectric conversion layer increased. This is thought to be due to a decline.

Example 4
As Example 4, a thin film photoelectric conversion module having the structure shown in FIG. In Example 4, the refractive index of the interface layer 44 with respect to light having a wavelength of 600 nm was set to 2.3, and the gas flow rate ratio during the formation of the interface layer was SiH ₄ / CO ₂ / H ₂ = 1 / 1.1 / 300. Except for this, the same structure as in Example 1 was produced.

At this time, the oxygen concentration in the interface layer 44 is 30 atomic%, the refractive index for light of 600 nm is 2.3, and the TO mode peak of the crystalline silicon component with respect to the TO mode peak of the amorphous silicon component measured by Raman scattering. The peak intensity ratio was 3.6, and the dark conductivity was 9.8 × 10 ⁻⁷ S / cm.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Example 4 were measured in the same manner as in Example 1, Voc = 1.366 V, Jsc = 11.36 mA / cm ² , FF = 0.731, Eff = 11.34%. Even in Example 4 where the refractive index of the interface layer 44 was 2.3, Voc and Jsc were improved and Eff was improved as compared with Comparative Example 1.

(Example 5)
As Example 5, a thin film photoelectric conversion module having the structure shown in FIG. In Example 5, as an n-type layer of the amorphous silicon photoelectric conversion unit 3, an intermediate transmission / reflection layer 34 made of an n-type silicon composite layer having a thickness of 50 nm and an n-type microcrystalline silicon layer 34 having a thickness of 10 nm are sequentially arranged. The same structure as in Example 1 was prepared except that the thickness of the crystalline silicon photoelectric conversion layer 44 was 2.5 μm.

The flow rate ratio of the gas when forming the intermediate transmission / reflection layer made of the n-type silicon composite layer is SiH ₄ / CO ₂ / PH ₃ / H ₂ = 1 / 2.3 / 0.02 / 250. The film was formed at a power frequency of 13.56 MHz, a power density of 200 mW / cm ² , a pressure of 350 Pa, and a substrate temperature of 200 ° C. At this time, the n-type intermediate transmission / reflection layer has an oxygen concentration in the film of 44 atomic%, a refractive index for light of 600 nm is 2.0, and the crystalline silicon component relative to the TO mode peak of the amorphous silicon component measured by Raman scattering. The peak intensity ratio of the TO mode peak was 2.0, and the dark conductivity was 1.2 × 10 ⁻⁴ S / cm.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Example 5 were measured in the same manner as in Example 1, Voc = 1.325 V, Jsc = 13.26 mA / cm ² , FF = 0.597, Eff = 12.25%.

(Comparative Example 3)
As Comparative Example 3, a conventional thin film photoelectric conversion module was produced. Comparative Example 3 was fabricated in the same manner as in Example 2 except that the interface layer 44 of FIG. 3 was not present.

As shown in Table 1, when the output characteristics of the photoelectric conversion device of Comparative Example 3 were measured in the same manner as in Example 1, Voc = 1.316V, Jsc = 13.20 mA / cm ² , FF = 0.688, Eff = 11.95%.

(Comparison of Example 5 and Comparative Example 3)
Even in the case where there is an intermediate transmission / reflection layer, the use of a substantially intrinsic silicon composite layer as the interface layer improves Voc, improves Jsc and FF, and increases Eff compared to Comparative Example 3. .

Reference Signs List 1 transparent substrate 2 transparent electrode layer 3 amorphous silicon photoelectric conversion unit 30 semiconductor layer 31 p-type amorphous silicon carbide layer 32 substantially intrinsic amorphous silicon photoelectric conversion layer 33 n-type microcrystalline silicon layer 34 n-type Intermediate transmission reflection layer made of silicon composite layer 4 crystalline silicon photoelectric conversion unit 41 p-type microcrystalline silicon layer 42 photoelectric conversion layer of substantially intrinsic crystalline silicon layer 43 n-type microcrystalline silicon layer 44 substantially intrinsic Interface layer made of a silicon composite layer 100 Laminated thin film photoelectric conversion device 901 Integrated thin film photoelectric conversion module 902 Photoelectric conversion cell 903 First separation groove 904 Second separation groove 905 Connection groove

Claims (7)

In order from the light incident side, a thin-film photoelectric device including a transparent electrode layer, one or more photoelectric conversion units in which one conductive type layer, a substantially intrinsic semiconductor photoelectric conversion layer, and a reverse conductive type layer are disposed, and a back electrode layer. A conversion device,
At least one photoelectric conversion unit is a crystalline silicon photoelectric conversion unit in which the photoelectric conversion layer includes a substantially intrinsic crystalline silicon semiconductor layer,
Between the one conductive type layer of the crystalline silicon photoelectric conversion unit and the photoelectric conversion layer, an interface layer composed of a substantially intrinsic silicon composite layer is disposed,
The thin film photoelectric conversion device is characterized in that the silicon composite layer is a layer in which a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix.   2. The thin film photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit includes two or more photoelectric conversion units, and the photoelectric conversion unit closest to the light incident side includes a substantially intrinsic amorphous silicon semiconductor layer. A laminated thin film photoelectric conversion device which is an amorphous photoelectric conversion unit. The stacked thin film photoelectric conversion device according to claim 2,
At least a part of the reverse conductivity type layer of the amorphous photoelectric conversion unit is an n-type silicon composite layer in which a crystalline silicon phase is dispersed in an amorphous oxygenated silicon matrix. Multilayer thin film photoelectric conversion device.   The thin film photoelectric conversion device according to any one of claims 1 to 3, wherein the interface layer has a refractive index of 2.2 to 3.0 with respect to light having a wavelength of 600 nm. Thin film photoelectric conversion device.   5. The thin film photoelectric conversion device according to claim 1, wherein the interface layer has a peak intensity ratio of a TO mode peak of a crystalline silicon component to a peak derived from an amorphous component measured by Raman scattering. Is 3 or more and 6 or less, The thin film photoelectric conversion apparatus characterized by the above-mentioned. It is a thin film photoelectric conversion device of any one of Claims 1-5, Comprising: The dark conductivity of the said interface layer is 10 < ^-8 > S / cm or more and 10 < ^-1 > S / cm or less, It is characterized by the above-mentioned. A thin film photoelectric conversion device.   7. The thin film photoelectric conversion device according to claim 1, wherein the interface layer has a thickness of 5 nm to 15 nm.

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