This application relates to a photovoltaic device.
Recently, as existing energy sources such as oil and charcoal and so on are expected to be exhausted, attention is now paid to alternative energy sources which can be used in place of the existing energy sources. Among the alternative energy sources, sunlight energy is abundant and has no environmental pollution. For this reason, more and more attention is paid to the sunlight energy.
A photovoltaic device, that is to say, a solar cell converts directly sunlight energy into electrical energy. The photovoltaic device uses mainly photovoltaic effect of semiconductor junction. In other words, when light is incident and absorbed to a semiconductor pin junction formed through a doping process by means of p-type and n-type impurities respectively, light energy generates electrons and holes at the inside of the semiconductor. Then, the electrons and the holes are separated by an internal field so that a photo-electro motive force is generated at both ends of the pin junction. Here, if electrodes are formed at the both ends of junction and connected with wires, an electric current flows externally through the electrodes and the wires.
In order that the existing energy sources such as oil is substituted with the sunlight energy source, it is required that a degradation rate of the photovoltaic device should be low and a stability efficiency of the photovoltaic device should be high, which are produced by the elapse of time.
One aspect of this invention includes a photovoltaic device. The photovoltaic device includes: a substrate; a first electrode disposed on the substrate; a photoelectric transformation layer disposed on the first electrode, the photoelectric transformation layer comprising a light absorbing layer which comprises at least one pair of an intrinsic first sub-layer and an intrinsic second sub-layer, each of which comprises a hydrogenated amorphous silicon based material and a hydrogenated proto-crystalline silicon based material having a crystalline silicon grain, and comprises a non-silicon based element; and a second electrode disposed on the photoelectric transformation layer.
Another aspect of this invention includes a photovoltaic device. The photovoltaic device includes: a substrate; a first electrode disposed on the substrate; a photoelectric transformation layer disposed on the first electrode, the photoelectric transformation layer comprising a light absorbing layer which comprises at least one pair of an intrinsic first sub-layer and an intrinsic second sub-layer, each of which comprises hydrogenated micro-crystalline silicon germanium and hydrogenated micro-crystalline silicon; and a second electrode disposed on the photoelectric transformation layer.
The light absorbing layer may be divided into a first area and a second area, the first area is constituted by the at least one pair of the first sub-layer and the second sub-layer, and the second area is constituted by a single layer.
The embodiment will be described in detail with reference to the following drawings.
Embodiments will be described in a more detailed manner with reference to the drawings.
In detail, the first electrodes 210 are disposed on the substrate 100. The first electrodes 210 are spaced from each other at a regular interval in such a manner that adjacent first electrodes are not electrically short-circuited. The photoelectric transformation layer 230 is disposed on the first electrode 210 in such a manner as to cover the area spaced between the first electrodes at a regular interval. The second electrodes 250 are disposed on the photoelectric transformation layer 230 and spaced from each other at a regular interval in such a manner that adjacent second electrodes are not electrically short-circuited. In this case, the second electrode 250 penetrates the photoelectric transformation layer and is electrically connected to the first electrode 210 such that the second electrode 250 is connected in series to the first electrode 210. The adjacent photoelectric transformation layers 230 are spaced at the same interval as the interval between the second electrodes. The protecting layer 300 is disposed on the second electrode in such a manner as to cover the area spaced between the second electrodes and the area spaced between the photoelectric transformation layers.
The photoelectric transformation layer 230 includes a p-type semiconductor layer 231, a light absorbing layer 233 and an n-type semiconductor layer 235. The light absorbing layer 233 includes at least one pair of an intrinsic first sub-layer 233A and an intrinsic second sub-layer 233B. The first sub-layer 233A includes a hydrogenated amorphous silicon based material. The second sub-layer 233B includes a hydrogenated proto-crystalline silicon based material. The first sub-layer 233A and the second sub-layer 233B also include a non-silicon based element. The second sub-layer 233B includes a crystalline silicon grain surrounded by the hydrogenated amorphous silicon based material. Even though it is shown in
The light absorbing layer 233-1 and 233-2 include first sub-layer 233-1A and 233-2A and second sub-layer 233-1B and 233-2B stacked on the first sub-layer. Here, the light absorbing layer 233-1 included in the first photoelectric transformation layer 230-1 includes the intrinsic first sub-layer 233-1A and the intrinsic second sub-layer 233-1B. The first sub-layer 233-1A includes a hydrogenated amorphous silicon based material and the second sub-layer 233-1B includes the hydrogenated proto-crystalline silicon based material. The light absorbing layer 233-2 included in the second photoelectric transformation layer 230-2 includes the first sub-layer 233-2A and the second sub-layer 233-2B. The first sub-layer 233-2A includes hydrogenated micro-crystalline silicon germanium and the second sub-layer 233-2B includes hydrogenated micro-crystalline silicon.
While only two photoelectric transformation layers are provided in the present embodiment, three or more photoelectric transformation layers can be also provided. Regarding a second photoelectric transformation layer or a third photoelectric transformation layer among three photoelectric transformation layers, which is far from a side of incident light, the second photoelectric transformation layer or the third photoelectric transformation layer can include a light absorbing layer including a first sub-layer and a second sub-layer. The first sub-layer includes hydrogenated micro-crystalline silicon germanium and the second sub-layer includes hydrogenated micro-crystalline silicon.
With respect to such photovoltaic devices according to the first and the second embodiments, a manufacturing method of the photovoltaic device will be described below in more detail.
As shown in
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As shown in
The light absorbing layer according to the embodiment of the present invention can be included in a single junction photovoltaic device including one photoelectric transformation layer 230 or in a multiple junction photovoltaic device including a plurality of photoelectric transformation layers.
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As shown in
Through such a process, provided is the photoelectric transformation layer 200 having the protecting layer 300 formed thereon. A backsheet or back glass (not shown) can be made on the protecting layer.
In the next place, a manufacturing method of the light absorbing layer will be described in detail with reference to figures.
When the inside of the chamber 310 is actually in a vacuum state, source gas such as hydrogen (H2) and silane (SiH4) and source gas including non-silicon based element are flown to the inside of the chamber 310 through mass flow controllers MFC1, MFC2 and MFC3 and an electrode 340 having a nozzle formed therein.
In other words, the hydrogen can be flown to the chamber through a first mass flow controller MFC1. The silane can he flown to the chamber through a second mass flow controller MFC2. The non-silicon based element such as carbon, oxygen or germanium can be flown to the chamber through a third mass flow controller MFC3.
Here, the angle valve 330 is controlled to maintain the pressure of the chamber 310 constant. When the pressure of the chamber 310 is maintained constant, silicon powder caused by turbulence created in the chamber 310 can be prevented from being generated and deposition condition can be maintained constant. The hydrogen is flown to the chamber in order to dilute the silane and reduces Staebler-Wronski effect.
When the source gases are flown to the chamber and a voltage from an electric power source E is supplied to the electrode, an electric potential difference is generated between the electrode 340 and the plate 300. As a result, the source gas is in a plasma state, and the light absorbing layer is deposited on the p-type semiconductor layer 231 or the n-type semiconductor layer 235.
As shown in
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100501 As shown in
Here, as shown in
As shown in
As shown in
In this case, During one cycle P derived from a sum of a duration time of the first flow rate value α and a duration time of the second flow rate value β, a ratio of the duration time t1 of the first flow rate value α to the duration time t2 of the second flow rate value β is constant in accordance with the elapsed deposition time T.
As described with reference to
In this case, the flow rate of the source gas including non-silicon based element decreases or increases, varying alternately within a range between the first flow rate value α and the second flow rate value β in accordance with the elapsed deposition time T. This will be described later in detail.
As such, the flow rate A of hydrogen and the flow rate B of silane are constant in accordance with the elapsed deposition time T. The flow rate of the source gas including non-silicon based element varies alternately within a range between the first flow rate α and the second flow rate β. Therefore, a hydrogen dilution ratio, that is, a ratio of the flow rate of the silane to the flow rate of the hydrogen, is constant.
In addition, if the flow rate of the source gas including non-silicon based element varies, as shown in
The higher the flow rate of the source gas including non-silicon based element increases, the lower the crystalline and a deposition rate are. The lower the flow rate of the source gas including non-silicon based element decreases, the higher the crystalline and a deposition rate are. Therefore, as shown in
100611 Therefore, when the source gas including the non-silicon based element such as oxygen is supplied to the chamber, the first sub-layer 233A and the second sub-layer 233B include hydrogenated amorphous silicon oxide (i-a-SiO:H). The second sub-layer 233B includes a crystalline silicon grain surrounded by the hydrogenated amorphous silicon oxide (i-a-SiO:H).
When the source gas including the non-silicon based element such as carbon is supplied to the chamber, the first sub-layer 233A and the second sub-layer 233B include hydrogenated amorphous silicon carbide (i-a-SiC:H). The second sub-layer 233B includes a crystalline silicon grain surrounded by the hydrogenated amorphous silicon carbide (i-a-SiC:H).
When the source gas including the non-silicon based element such as germanium is supplied to the chamber, the first sub-layer 233A and the second sub-layer 233B include hydrogenated amorphous silicon germanium (i-a-SiGe:H). The second sub-layer 233B includes a crystalline silicon grain surrounded by the hydrogenated amorphous silicon germanium (i-a-SiGe:H).
Here, as shown in
In this case, the diameter of the crystalline silicon grain can be equal to or more than 3 nm and equal to or less than 10 nm. If the crystalline silicon grain has a diameter less than 3 nm, it is difficult to form the crystalline silicon grain and a degradation rate reduction effect of a solar cell is reduced. If the crystalline silicon grain has a diameter greater than 10 nm, the volume of grain boundary in the circumference of the crystalline silicon grain is excessively increased. As a result, the crystalline silicon grain is also increasingly recombined with each other, thereby reducing the efficiency.
As such, when the light absorbing layer 233 including a plurality of the sub-layers 233A and 233B is made, the degradation rate, i.e., a value which is obtained by dividing a difference between initial efficiency and stabilization efficiency by the initial efficiency, is reduced. Accordingly, the photovoltaic device according to the embodiment of the present invention can have high stabilization efficiency.
In other words, the first sub-layer 233A made of an amorphous silicon based material interrupts columnar growth of the crystalline silicon grain of the second sub-layer 233B. As shown in
Such a columnar growth of the crystalline silicon grain increases a recombination rate of carriers such as an electron hole and an electron at a grain boundary, thus the initial efficiency of a photovoltaic device is lowered.
However, in the case of the light absorbing layer 233 including a plurality of sub-layers 233A and 233B in the embodiment of the present invention, since a short-range-order (SRO) and a medium-range-order (MRO) in the silicon thin film matrix are improved, the degradation rate of the light absorbing layer 233 is lowered and the stabilization efficiency is increased. The amorphous silicon based material of the first sub-layer 233A interrupts the columnar growth of the crystalline silicon grain in the second sub-layer 233B, thereby reducing a diameter variation of the crystalline silicon grain. As a result, a time required for the efficiency of the photovoltaic device to reach the stabilization efficiency is reduced and high stabilization efficiency is obtained.
The crystalline silicon grains of the second sub-layer 233B are covered with amorphous silicon based material and isolated from each other. The isolated crystalline silicon grains act as radiative recombination centers of some of the captured carriers, and hence suppress photocreation of dangling bonds. As a result, the non-radiative recombination in the amorphous silicon based material, which surrounds the crystalline silicon grains of the second sub-layer 233B, is reduced.
Meanwhile, as shown in
Light with a short wavelength having a high energy density has a small penetration depth. A larger optical band gap is required to absorb light with a particular wavelength having a high energy density. Therefore, the closer the sub-layers 233A and 233B are to a side of incident light, the relatively larger optical band gap the sub-layers 223A and 233B have. As a result, light with a particular wavelength having a high energy density is absorbed as much as possible. The farther the sub-layers 233A and 233B are from a side of incident light, the relatively smaller optical band gap the sub-layers 233A and 233B have. As a result, light with a wavelength other than the particular wavelength mentioned above is absorbed as much as possible.
Here, the more the flow rate of the source gas including non-silicon based element such as oxygen or carbon is increased, the larger the optical band gap is. Therefore, in accordance with the elapsed deposition time T, reduced are the first flow rate value α and the second flow rate value β of the source gas including non-silicon based element such as oxygen or carbon, or reduced are a duration time t1 of the first flow rate value α and a duration time t2 of the second flow rate value β.
In addition, as shown in
In this case, the more the flow rate of the source gas including non-silicon based element such as germanium is increased, the smaller the optical band gap is. Therefore, in accordance with the elapsed deposition time T, increased are the first flow rate value α and the second flow rate value β of the source gas including non-silicon based element such as germanium, or reduced are a duration time t1 of the first flow rate value α and a duration time t2 of the second flow rate value β.
As described above light with a particular wavelength having a high energy density has a small penetration depth. A larger optical band gap is required to absorb light with a particular wavelength having a high energy density.
Therefore, the lower flow rate the source gas including non-silicon based element such as germanium has, the relatively larger optical band gap the sub-layers 233A and 233B closer to a side of incident light have. As a result, the sub-layers 233A and 233B closer to a side of incident light absorb light with a particular wavelength as much as possible.
Also, the larger flow rate the source gas including non-silicon based element such as germanium has, the relatively smaller optical band gap the sub-layers 233A and 233B farther from a side of incident light have. As a result, the sub-layers 233A and 23313 farther from a side of incident light absorb light with a wavelength other than the particular wavelength mentioned above as much as possible.
In the mean time, as described above, the hydrogen dilution ratio and the pressure in the chamber 310 in the embodiment of the present invention are constant. Since a flow rates of hydrogen and silane supplied to the inside of the chamber 310 are larger than the flow rate of the source gas including non-silicon based element, it is relatively more difficult to control the flow rates of hydrogen and silane than to control the flow rate of the source gas including non-silicon based element, and turbulence can be generated in the chamber 310 due to the flows of hydrogen and silane. Accordingly, if the flow rates of the hydrogen and the silane are constant, it is easy to control the source gas including non-silicon based element having low flow rates and possible to reduce the possibility of generating turbulency within the chamber 310, thereby improving a film quality of the light absorbing layer 233.
If the flow rate of hydrogen varies within a range between 0 and a certain value so as to form the first sub-layer 233A and the second sub-layer 233B, during a period of time during which the flow rate of hydrogen is equal to 0 as the flow rate of hydrogen varies cyclically, that is, a period of time during which hydrogen is not flown from the outside to the chamber, the hydrogen which remains in the chamber 310 increases in accordance with deposition time T, increasing crystallinity of the sub-layers. As a result, it is difficult to form sub-layers having a uniform crystal size and a uniform thickness.
On the other hand, in the embodiment of the present invention, since the flow rates of hydrogen and silane are constant and the flow rate of the source gas including non-silicon based element varies cyclically, an amount of hydrogen in the chamber 310 is maintained constant, making it easier to form the sub-layers 233A and 233B having a uniform crystal size and a uniform thickness.
As described above, in the embodiments of the present invention, plasma-enhanced chemical vapor deposition method is used instead of photo-CVD. The photo-CVD is not suitable for manufacturing a large area photovoltaic device. Also, as deposition is performed, a thin film is deposited on a quartz window of a photo-CVD device, reducing UV light penetrating through the quartz window.
For this reason, a deposition rate is gradually reduced and the thicknesses of the first sub-layer 233A and the second sub-layer 233B are gradually reduced. Contrarily, the plasma-enhanced chemical vapor deposition (PECVD) method can solve the shortcomings of the photo-CVD.
In the plasma-enhanced chemical vapor deposition method used in the embodiment of the present invention, a frequency of a voltage supplied from an electric power source E can be equal to or more than 13.56 MHz. When a frequency of a voltage supplied from an electric power source E is equal to or more than 27.12 MHz, a deposition rate is improved and a quantum dot caused by a crystalline silicon grain can be easily formed.
As mentioned above, the crystalline silicon grain having a uniform diameter reduces a time required for the efficiency of the photovoltaic device to reach the stabilization efficiency and improves the stabilization efficiency. To this end, in the embodiment of the present invention, the hydrogen dilution ratio of the chamber 310 is maintained constant while the second sub-layer 233B of the light absorbing layer 233 is repeatedly deposited. In other words, the hydrogen dilution ratio (within an allowable error range) of the second sub-layer 233B is maintained constant in every period that the first and second sub-layers 233A and 23313 are formed.
Even though it is explained referring to
By forming the light absorbing layer 233 as mentioned above, not only the high stabilization efficiency of a photovoltaic device but also short time and low cost for manufacturing thereof can be obtained. That is, the time and cost required for manufacturing the light absorbing layer 233 can be reduced by forming the light absorbing layer 233 including the second area of the hydrogenated amorphous silicon single layer or the hydrogenated amorphous silicon based material. Furthermore, the high stabilization efficiency can be obtained due to the lowered degradation rate by forming the light absorbing layer 233 including the first area of the First sub-layer 233A and the second sub-layer 233B alternately stacked.
Hereinafter, a light absorbing layer 233 refers to not only a case that the first sub-layer 233A and second sub-layer 233B are alternately stacked in the entire light absorbing layer 233 but also a case that the first sub-layer 233A and second sub-layer 233B are alternately stacked only in a part of the light absorbing layer 233.
When oxygen or carbon as a source gas including non-silicon based element is flown to the chamber 310, the thickness of the light absorbing layer 233 is equal to or more than 150 nm and is equal to or less than 300 nm. An average oxygen content of the light absorbing layer 233 can be equal to or more than 0 atomic % and is equal to or less than 3 atomic %. An optical band gap of the light absorbing layer 233 can be equal to or more than 1.85 eV and is equal to or less than 2.1 eV.
If the optical band gap of the light absorbing layer 233 formed by a flow of oxygen or carbon is equal to or more than 1.85 eV, the light absorbing layer 233 can absorb a lot of light with a short wavelength having a high energy density. If the optical band gap of the light absorbing layer 233 is greater than 2.1 eV, the light absorbing layer 233 including the plurality of sub-layers 233A and 233B is difficult to form and absorption of light is reduced. Therefore, the efficiency can be reduced by reduction of a short-circuit current.
When an average oxygen content or an average carbon content of the light absorbing layer 233 formed by a flow of oxygen or carbon is greater than 3 atomic %, the optical band gap of the light absorbing layer 233 is rapidly increased and a dangling bond density is suddenly increased. As a result, the short-circuit current and a fill factor (FF) are reduced, so that the efficiency is degraded.
Thus, the light absorbing layer 233 formed by a flow of oxygen or carbon can be included in a top cell of a multiple junction photovoltaic device so as to absorb a lot of light with a short wavelength. The top cell corresponds to a photoelectric transformation layer on which light is first incident, among a plurality of photoelectric transformation layers 230.
When germanium as a source gas including non-silicon based element is flown to the chamber 310, the thickness of the light absorbing layer 233 is equal to or more than 300 nm and is equal to or less than 1000 nm. An average germanium content of the light absorbing layer 233 can be equal to or more than 0 atomic % and is equal to or less than 20 atomic %. An optical band gap of the light absorbing layer 233 can be equal to or more than 1.3 eV and is equal to or less than 1.7 eV. If the optical band gap of the light absorbing layer 233 formed by a flow of germanium is equal to or more than 1.3 eV and is equal to or less than 1.7 eV, the deposition rate of the light absorbing layer 233 is prevented from being rapidly reduced and the dangling bond density and a recombination are reduced. Therefore, the efficiency is prevented from being degraded.
If an average germanium content of the light absorbing layer 233 formed by a flow of germanium is greater than 20 atomic %, the deposition rate of the light absorbing layer 233 is rapidly reduced and a recombination is increased by the increase of the dangling bond density. Consequently, the short-circuit current, the fill factor (FF) and the efficiency are reduced.
Meanwhile, when the light absorbing layer 233 is formed by a flow of oxygen, carbon or germanium, the average hydrogen content of the light absorbing layer 233 can be equal to or more than 15 atomic % and is equal to or less than 25 atomic %. If the average hydrogen content of the light absorbing layer 233 is less than 15 atomic %, the size and density of the quantum dot are reduced, and then the optical band gap of the light absorbing layer 233 can be reduced and the degradation rate of the light absorbing layer 233 can be increased. If the average hydrogen content of the light absorbing layer 233 is greater than 25 atomic %, the diameter of the crystalline silicon grain is excessively increased so that a volume of unstable amorphous silicon is also increased. Accordingly, the degradation rate can be increased.
Thus, the light absorbing layer 233 formed by a flow of germanium can be included in either a bottom cell of a double junction photovoltaic device including two photoelectric transformation layers 230 or a middle cell of a triple junction photovoltaic device including three photoelectric transformation layers 230. The bottom cell is adjacent to the top cell on which light is first incident among two photoelectric transformation layers 230. The middle cell is adjacent to the top cell on which light is first incident among three photoelectric transformation layers 230.
That is to say, since the optical hand gap of the light absorbing layer 233 formed by a flow of germanium is equal to or more than 1.3 eV and is equal to or less than 1.7 eV, and thus, is less than an optical band gap, which is equal to or more than 1.85 eV and equal to or less than 2.1 eV, of the light absorbing layer 233 used in the top cell. Accordingly, the light absorbing layer 233 formed by a flow of germanium can be used in either the bottom cell of the double junction photovoltaic device or the middle cell of the triple junction photovoltaic device including three photoelectric transformation layers 230.
While the first sub-layer 233A is formed first in the embodiments of the present invention, the second sub-layer 233B can be also formed before the first sub-layer 233A is formed.
A warming-up period WU can be provided before starting to deposit the light absorbing layer 233. In other words, as shown in
Because a voltage is not supplied to the chamber during the warming-up period, plasma is not generated. Since the chamber 310 is in a vacuum state, a condition inside the chamber 310 may not satisfy the deposition condition of the light absorbing layer 233 even though source gas for forming the light absorbing layer 233 is supplied to the chamber.
Therefore, in the case where a deposition is not performed due to no generation of plasma during the warming-up period WU and where a deposition is performed by generation of plasma when a condition inside the chamber 310 satisfies the deposition condition of the light absorbing layer 233 after the warming-up period WU, the light absorbing layer 233 can be stably formed.
As shown in
Accordingly, the second sub-layer 233B is made of hydrogenated micro-crystalline silicon (μc-Si:H) including a crystalline silicon grain. The first sub-layer 233A is made of hydrogenated micro-crystalline silicon germanium (μc-SiGe:H). As explained before, a light absorbing layer 233 according to this embodiment of the present invention may include a first area in which the first sub-layer 233A and second sub-layer 233B are alternately stacked and a second area other than the first area. Here, the second area may not have a structure in which the first sub-layer 233A and the second sub-layer 233B are alternately stacked and have a single layer. In this case, the second area may include hydrogenated micro-crystalline silicon, or a hydrogenated micro-crystalline silicon germanium which comprises relatively small amount of the germanium.
Since the first and the second sub-layers 233A and 233B have less optical band gaps than those of the sub-layers made of amorphous silicon germanium, the first and the second sub-layers 233A and 233B can easily absorb light with a longer wavelength. Accordingly, the light absorbing layer of the bottom cell of the double or triple junction photovoltaic device can include both the second sub-layer 233B including hydrogenated micro-crystalline silicon including a crystalline silicon grain and the first sub-layer 233A including hydrogenated micro-crystalline silicon germanium.
In order to absorb light with a long wavelength, an optical band gap of the light absorbing layer 233 made of hydrogenated micro-crystalline silicon germanium and hydrogenated micro-crystalline silicon can be equal to or more than 0.9 eV and equal to or less than 1.3 eV. An average germanium content of the light absorbing layer 233 can be is greater than 0 atomic % and equal to or less than 15 atomic %.
A thickness of the light absorbing layer 233 made of hydrogenated micro-crystalline silicon germanium and hydrogenated micro-crystalline silicon can be equal to or more than 0.5 μm and equal to or less than 1.0 μm. If the thickness of the, light absorbing layer 233 is less than 0.5 μm, the light absorbing layer 233 cannot perform its functions. If more than 1.0 μm, the thickness is so large that its efficiency is reduced.
A thickness of the second sub-layer 233B, which includes a crystalline silicon grain, made of hydrogenated micro-crystalline silicon can be equal to or more than 20 nm. If the thickness of the second sub-layer 23313 is less than 20 nm, it is difficult to form a crystalline silicon grain. Thus, it is hard to obtain the effect of the light absorbing layer 233 including the first and the second sub-layers 233A and 233B.
As described above, the thickness of the light absorbing layer 233 can be equal to or more than 0.5 μm and equal to or less than 1.0 μm. Also, a period of time equal to or more than 5 cycles P and equal to or less than 10 cycles P may be required in order that the light absorbing layer 233 including the first and the second sub-layers 233A and 23313 can fully perform its functions. Therefore, when germanium with the first flow rate value α and the second flow rate value β (equal to 0) is supplied to the chamber during one cycle P, a sum of the thickness of the first sub-layer 233A and the thickness of the sub-layer 233B can be equal to or more than 50 nm and equal to or less than 100 nm.
An average crystal volume fraction of the light absorbing layer 233 made of hydrogenated micro-crystalline silicon germanium and hydrogenated micro-crystalline silicon can be equal to or more than 30% and equal to or less than 60%. If the average crystal volume fraction is less than 30%, amorphous silicon is generated a lot and carriers are increasingly recombined with each other, thereby reducing the efficiency. If the average crystal volume fraction is more than 60%, a volume of grain boundary in a crystalline material is increased and a crystal defect is increased, thereby increasing the recombination of carriers.
An average oxygen content of the light absorbing layer 233 made of hydrogenated micro-crystalline silicon germanium and hydrogenated micro-crystalline silicon can be equal to or less than 1.0×1020 atoms/cm3. If the average oxygen content of the light absorbing layer 233 is more than 1.0×1020 atoms/cm3, conversion efficiency is reduced. While the first sub-layer 233A is formed first in the embodiment of the present invention, the second sub-layer 233B can be formed prior to the first sub-layer 233A.
Here, the thicknesses of the first and second sub-layers 233A and 233B and the absorbing layer 233 not be entirely uniform due to the uncertainty of the process conditions and parameters. A uniformity degree of each thickness of the first and second sub-layers 233A and 233B, and the absorbing layer 233 may be in a range that the deviation from the mean value of the each thickness is equal to or less than 10%. By maintaining the degree of thickness uniformity of each of the first and second sub-layers 233A and 233B, and the absorbing layer 233 in the above mentioned range, it is possible to prevent the properties of the light absorbing layer 233 from being deteriorated.
The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing embodiments is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Moreover, unless the term “means” is explicitly recited in a limitation of the claims, such limitation is not intended to be interpreted under 35 USC §112(6).
Number | Date | Country | Kind |
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10-2009-0060742 | Jul 2009 | KR | national |
This present application is a continuation-in-part application of U.S. patent application Ser. No. 12/762,946 filed on Apr. 19, 2010, which claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2009-0060742 filed on Jul. 3, 2009, the entireties of which are hereby incorporated by reference.
Number | Date | Country | |
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Parent | 12762946 | Apr 2010 | US |
Child | 13326445 | US |