JP2006237180A - Method of forming photovoltaic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a photovoltaic device which can prevent the degradation of characteristics with the passage of time due to the long-time film formation by a deposition film formation apparatus, can minimize the variation in characteristics at the time of mass-production, can manufacture a photovoltaic power device having a high photoelectric conversion efficiency stably with a high productivity. <P>SOLUTION: The photovoltaic device has a structure wherein a rear electrode 202, semiconductor layers 203, 204, and 205, and a transparent electrode 206 are stacked in order on a substrate 201. In forming the photovoltaic power device, the formation conditions for the transparent electrode are set based on the value of self-bias voltage generated at the time of forming the semiconductor layers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a photovoltaic element using a non-single crystal semiconductor such as amorphous silicon or microcrystalline silicon.

  Conventionally, as a photovoltaic element used as a solar cell or the like, an amorphous material typified by amorphous silicon (a-Si: H) or a non-single-crystal semiconductor material such as microcrystalline silicon is inexpensive, has a large area and It is attracting attention because it can be made thin, has a high degree of freedom in composition, and can control electrical and optical characteristics over a wide range. For the production of such an element, a deposited film forming apparatus for forming a thin film by a plasma CVD method under a reduced pressure condition is generally widely used and used in industry.

  It is fundamentally important that solar cells have sufficiently high photoelectric conversion efficiency, excellent characteristics stability, and can be mass-produced. Therefore, in the production of solar cells using non-single-crystal semiconductor layers, etc., the electrical, optical, photoconductive, mechanical properties, fatigue properties against repeated use, and resistance to usage environments are improved. In addition, a photovoltaic device having a larger area and a more uniform film thickness and film quality of the semiconductor layer constituting the solar cell can be formed and mass-produced by a reproducible method at high speed. It is requested to do.

In a solar cell, a semiconductor layer which is an important constituent element has a semiconductor junction such as a so-called pn junction or pin junction. When a thin-film semiconductor such as a-Si is used, a glow discharge is performed by mixing a gas containing an element serving as a dopant such as phosphine (PH ₃ ) or diborane (B ₂ H ₆ ) with silane (SiH ₄ ). The semiconductor layer having a desired conductivity type can be obtained by decomposing the source gas and growing it on a heated solid surface (plasma CVD method).

  Thus, it is known that these semiconductor films can be easily semiconductor-bonded by sequentially laminating semiconductor layers of a desired conductivity type on a desired substrate. Thus, as a method for manufacturing a solar cell obtained by stacking non-single-crystal semiconductor layers, an independent semiconductor layer manufacturing container for manufacturing each semiconductor layer is provided, and each of these semiconductor layer manufacturing containers is provided with There has been proposed a method of manufacturing a stacked body of semiconductor layers in which desired semiconductor junctions are formed by sequentially manufacturing the semiconductor layers.

  For example, generally, there is known a method in which the independent semiconductor layer manufacturing containers are connected by a load lock system via a gate valve, and a substrate is sequentially moved to each container to form various semiconductor layers.

  Furthermore, as a method for significantly improving mass productivity, Patent Document 1 discloses a continuous plasma CVD apparatus that employs a roll-to-roll method. This apparatus continuously forms a flexible substrate having a desired width and a sufficient length in a transport path provided with a plurality of glow discharge regions for performing glow discharge to form a semiconductor layer. It is an apparatus that continuously manufactures a device having a plurality of semiconductor layers semiconductor-bonded by sequentially transporting and depositing necessary conductive semiconductor layers on a substrate in each glow discharge region.

  However, in such a mass production apparatus for photovoltaic elements, there is a problem that a film is gradually deposited on the electrode surface by generating plasma over a long time in a large area, and the condition of power input changes. It was. This is because the impedance of the electrode changes as the deposited film thickness increases, and the film formation rate decreases.

  Regarding this problem, Patent Document 2 describes a film forming method characterized in that input power is adjusted so that a self-bias voltage (Vdc) generated in a high-frequency electrode becomes a constant value. This method is effective for film formation at the beginning of film formation or when the absolute value of the self-bias voltage is small.

  However, in film formation and mass production equipment that require higher power application or longer processing time to increase the processing speed of the substrate, the absolute value and change amount of the self-bias voltage become large and control is difficult. In other words, the characteristics deteriorated as the self-bias voltage changed and the film formation rate decreased. In particular, a decrease in film thickness accompanying a decrease in film formation rate during the formation of an i-type semiconductor layer causes a decrease in short circuit current (Isc), which is a solar cell characteristic, and greatly affects the decrease in conversion efficiency.

  Such a problem is caused by the fact that the i-type semiconductor layer, which is a photoactive layer, is responsible for light absorption, requires a large film thickness, and the film adheres to the electrode forming it extremely quickly and in large quantities. . That is, in an apparatus for forming an i-type semiconductor layer, it means that a change in film forming conditions such as electrode impedance and exhaust conductance is severe. Under such circumstances, there is a limit to a method that relies solely on the control at the time of forming the i-type semiconductor layer in order to finally produce a photovoltaic device having stable characteristics.

US Patent No. 4,400,409 Patent Specification Japanese Patent Laid-Open No. 11-233443

  The present invention provides a photovoltaic device having high photoelectric conversion efficiency by preventing deterioration of characteristics over time due to long-time film formation in the deposited film forming apparatus as described above, and minimizing variation in characteristics during mass production. It is an object of the present invention to provide a method for forming a photovoltaic element with high productivity that can be stably manufactured.

In order to achieve the above object, in the present invention, in the method of forming a photovoltaic device having a structure in which a back electrode, a semiconductor layer, and a transparent electrode are laminated in this order on a substrate, self-generated when the semiconductor layer is formed. The transparent electrode forming condition is set based on a bias voltage value.
In the present invention, in a method of forming at least two photovoltaic elements having a structure in which a transparent electrode, a semiconductor layer, and a back electrode are laminated in this order on a substrate, the nth (n is an integer of 1 or more) The formation conditions of the transparent electrode formed on the (n + 1) th substrate are set based on the self-bias voltage value generated when the semiconductor layer is formed on the th substrate.
Further, in the method for forming a photovoltaic device of the present invention, the formation condition of the transparent electrode is selected from applied power, applied voltage, applied current, formation time, gas flow rate, formation temperature, deposition rate, or baking time. It is characterized by being at least one or more.

  According to the present invention, in the method for forming a photovoltaic device having a structure in which a back electrode, a semiconductor layer, and a transparent electrode are stacked in this order on a substrate, based on a self-bias voltage value generated when the semiconductor layer is formed. The film thickness or transmittance of the transparent electrode is set.

  In the present invention, in a method of forming at least two photovoltaic elements having a structure in which a transparent electrode, a semiconductor layer, and a back electrode are laminated in this order on a substrate, the nth (n is an integer of 1 or more) The film thickness or transmittance of the transparent electrode formed on the (n + 1) th substrate is set based on the self-bias voltage value generated when the semiconductor layer is formed on the th substrate.

  Further, in the method for forming a photovoltaic element of the present invention, based on the relationship between the self-bias voltage value generated when forming the semiconductor layer and the short-circuit current of the photovoltaic element, the formation conditions of the transparent electrode or The film thickness or transmittance is set.

  According to the method for forming a photovoltaic element of the present invention, for example, it is possible to prevent deterioration of characteristics over time due to long-time film formation in a deposited film forming apparatus, and to minimize variation in characteristics during mass production. A photovoltaic element with high photoelectric conversion efficiency can be stably produced with high productivity.

  Hereinafter, the present invention will be described in detail with reference to the drawings. However, the photovoltaic element forming method of the present invention is not limited thereto.

  FIG. 1 is a schematic view schematically showing an example of a deposited film forming apparatus for forming a semiconductor layer of a photovoltaic element of the present invention.

  In FIG. 1, an inner reaction vessel 100, which is a discharge space, is installed inside an outer reaction vessel 110. The substrate 101 is installed so as to be in close contact with the heater 102 installed in the outer reaction vessel 110, and after evacuating from the exhaust pipe 109 using an exhaust device (not shown), the substrate 101 is heated to a desired temperature. When the substrate temperature is stabilized, the gas introduction valve 107 is opened, the flow rate is adjusted by the mass flow controller 108, and the source gas containing silicon atoms is introduced into the inner reaction vessel 100 (discharge space) through the gas introduction tube 106.

  Next, high frequency power is applied to the cathode electrode 103 from the high frequency power source 104 to generate plasma. At that time, since the vessel wall and the substrate are both grounded, the plasma spreads uniformly in the reaction vessel. The self-bias voltage generated at the cathode electrode is constantly monitored by a self-bias voltage reader 105.

  This self-bias voltage gradually changes as the amount of film deposition on the cathode electrode increases. In particular, in the case of a mass production apparatus, a processing substrate is continuously put into a reaction vessel and a film is formed over a long period of time. Therefore, in the case of a substrate processed in the latter half, the cathode electrode is compared to the substrate at the start of film formation. The film is deposited in a large amount, and the self-bias voltage value is greatly changed.

  Specifically, it is considered that the impedance of the electrode changes due to an increase in the amount of film deposition, and the film formation rate decreases as the self-bias voltage value changes. Therefore, there is a difference in the film thickness of the semiconductor layer between the substrate processed immediately after cleaning the reaction vessel and the substrate processed after repeating the film formation, and particularly in the case of a non-single crystal solar cell, the film of the i-type semiconductor layer The decrease in short circuit current (Isc) in the latter half of the film formation caused by the decrease in thickness was significant.

  Therefore, in the photovoltaic element forming method of the present invention, based on this self-bias voltage value, a short-circuit current due to the film thickness reduction is estimated, and a transparent electrode having an optimal film thickness or transmittance is formed for the formed semiconductor layer. By forming, the deterioration of characteristics is prevented, and finally a good state as a photovoltaic element is maintained.

  Hereinafter, the case where a non-single-crystal solar cell is produced by the photovoltaic element forming method of the present invention will be described.

First, in the i-type semiconductor layer forming step, the i-type semiconductor layer is continuously formed without performing chamber cleaning, and the change in the self-bias voltage value at that time is recorded. Next, a transparent electrode of ITO (In ₂ O ₃ + SnO ₂ ) is formed on each element under the same conditions by a DC sputtering apparatus. The short-circuit current (Isc) of the manufactured non-single-crystal solar cell is measured to determine the relationship between the self-bias voltage and the short-circuit current (Isc) when forming the i-type semiconductor layer. Further, this process is performed a plurality of times while changing the formation conditions of the transparent electrode so as to increase the light transmission amount of the transparent electrode, and the self-bias voltage and the short-circuit current (when forming the i-type semiconductor layer) using the transparent electrode formation conditions as parameters. A data set of a combination of the relationship with Isc) is completed. A transparent electrode that detects and records the self-bias voltage during the formation of the i-type semiconductor layer in the actual photovoltaic element formation step, and obtains a desired short-circuit current (Isc) from the self-bias voltage value data and the previous data set. A solar cell having a short-circuit current (Isc) in which a decrease in the film thickness of the i-type semiconductor layer due to a change in self-bias is compensated can be obtained by selecting the formation conditions of and forming a transparent electrode according to the conditions.

  Further, in a photovoltaic device having a configuration in which the transparent electrode is formed before the i-type semiconductor layer, the transparent electrode formation condition obtained from the self-bias value at the time of film formation of the i-type semiconductor layer of a lot is set to the next lot. The same effect can be obtained by applying at the time of forming the transparent electrode.

As other transparent electrode materials that can be used in the present invention, an oxide metal such as SnO ₂ , In ₂ O ₃ , ZnO, CdO, and CdSnO ₄ and a metal such as Au, Al, and Cu are formed in a very thin and translucent form. The metal thin film etc. which were made are mentioned. As these forming methods, resistance heating vapor deposition, electron beam heating vapor deposition, spraying, and the like can also be used, and they are appropriately selected as desired.

  Here, the transparent electrode forming conditions to be adjusted will be described. As described above, a change in the self-bias voltage value during the formation of the i-type semiconductor layer indicates a decrease in the film formation rate. That is, since the thickness of the photoactive layer is reduced and the light absorption efficiency is reduced, the short-circuit current (Isc) is reduced, so that the light transmission amount of the transparent electrode may be increased. For this purpose, the film thickness of the transparent electrode is made thin and the transmittance (the transmittance in the present invention is the transmittance per unit film thickness in the same way as the absorption rate) may be increased.

  A method of reducing the film formation rate is suitable for reducing the film thickness. For this, in the sputtering method, the voltage and current of input power may be lowered. In the vapor deposition method, the film formation rate can be lowered by lowering the voltage and current of the heating power. Furthermore, the film formation time may be shortened without changing the film formation speed. Of course, the film thickness may be reduced by combining both speed and time.

In the case of metal oxide, the transmittance can be controlled by changing various film formation conditions during film formation. First, a change from an amorphous phase to a crystalline phase occurs when the film formation temperature is raised. Therefore, when the film formation temperature is raised, the transmittance increases. Further, by increasing the supply of oxygen atoms, oxygen vacancies are reduced, so that free carriers are reduced and the transmittance is increased. As a method for supplying oxygen atoms, introduction of O ₂ gas or H ₂ O is suitable. That is, the transmittance can be increased by increasing the amount of O ₂ gas and H ₂ O introduced. Usually, after maintenance of the film forming apparatus, moisture is adsorbed on the wall surface in the apparatus, so that the amount of H ₂ O introduced into the film can be changed by changing the baking time after the maintenance. That is, the transmittance can be increased by shortening the baking time.

  In this way, by changing the transparent electrode formation conditions according to the self-bias voltage at the time of film formation of the i-type semiconductor layer, the deposited film forming apparatus for long-time film formation without directly measuring the film thickness reduction amount of the photoactive layer It is possible to prevent deterioration of device characteristics over time due to a change in state and to minimize variations in device characteristics during mass production.

  FIG. 2 schematically shows a pin-type non-single crystal solar cell that can be produced by the above-described forming method of the present invention. FIG. 2 shows a solar cell having a structure in which light enters from the upper part of the figure. In the figure, 201 is a substrate, 202 is a back electrode, 203 is an n-type semiconductor layer, 204 is an i-type semiconductor layer, and 205 is a p-type semiconductor. Reference numeral 206 denotes a transparent electrode, and 207 denotes a collecting electrode.

Example 1
A method for continuously producing the non-single crystal solar cell of FIG. 2 using the apparatus shown in FIG. 3 will be described below.

  FIG. 3 is a schematic view showing an example of a deposited film forming apparatus for continuously producing non-single-crystal solar cells used in the present invention, including a substrate delivery chamber 301, an n-type semiconductor layer production container 302, and an i-type. The semiconductor layer preparation container 303, the p-type semiconductor layer preparation container 304, and the substrate winding chamber 305 are constituted by devices connected via a gas gate. Reference numerals 307, 312, 317, 322, and 323 denote exhaust pumps, and 311, 316, and 321 denote cathode electrodes, which are connected to power sources 310, 315, and 320, respectively. Further, the self-bias voltage generated at the electrodes can be read by the self-bias voltage readers 309, 314, and 319.

  Each reaction vessel 302, 303, 304 has an inner reaction vessel of 308, 313, 318, respectively, and infrared lamp heaters 324, 325, 326 are provided in a space opposite to the film formation space with the belt-like substrate 306 interposed therebetween. The temperature is controlled to a desired temperature by a temperature control system (not shown).

  First, a vacuum vessel 301 having a substrate delivery mechanism of this manufacturing apparatus is degreased and cleaned, and a SUS430BA belt-like substrate 306 (width 300 mm × width) in which a silver thin film is deposited by 100 nm and a ZnO thin film is deposited by 1 μm by sputtering as a back electrode. A bobbin wound with a thickness of 0.2 mm) is set, and the belt-like substrate 306 is formed into an n-type semiconductor layer deposition container 302, an i-type semiconductor layer deposition container 303, a p-type semiconductor layer deposition container 304, and a strip shape. The tension was adjusted to the extent that there was no sagging through a vacuum vessel 305 having a substrate winding mechanism. At this time, the distance between the substrate and the cathode electrode is set to 20 mm.

Next, each vacuum vessel 301, 302, 303, 304, 305 was evacuated to 1 × 10 ⁻⁴ Pa or less by exhaust pumps 307, 312, 317, 322, 323. As a heat treatment before film formation, 500 sccm of He is introduced into each of the vacuum containers 302, 303, 304 from a gas introduction pipe (not shown), and the internal pressure of the vacuum containers 301, 302, 303, 304, 305 is adjusted to 130 Pa. Each vacuum vessel was evacuated with an exhaust pump with the opening degree adjusted. Here, sccm is a unit of flow rate, which is 1 sccm = 1 cm ³ / min (standard state), and hereinafter, the unit of flow rate is represented by sccm. Thereafter, the belt-shaped substrate and the vacuum vessel inner member were heated to 400 ° C. by the heating lamp heaters 324, 325, and 326, and left in this state for 1 hour.

Next, as a preparation for forming the n-type semiconductor layer, a temperature controller (not shown) was set so that the temperature indication value was 270 ° C., and the strip substrate 306 was heated by the infrared lamp heater 324. SiH ₄ gas was introduced into the inner reaction vessel 308 at 100 sccm, PH ₃ / H ₂ (1%) gas at 500 sccm, and H ₂ gas at 700 sccm from a gas introduction port (not shown). The opening of a conductance adjustment valve (not shown) was adjusted so that the pressure in the discharge chamber was 130 Pa, and the vacuum pump 312 was evacuated. The output value of the RF (13.56 MHz) power supply 310 was set to 100 W, and discharge was generated in the inner reaction vessel 308 through the electrode 311.

In preparation for forming the i-type semiconductor layer, a temperature control device (not shown) was set so that the temperature indication value was 300 ° C., and the strip substrate 306 was heated by the infrared lamp heater 325. From a gas introduction port (not shown), 800 sccm of SiH ₄ gas, 900 sccm of GeH ₄ gas, and 3000 sccm of H ₂ gas were introduced into the inner reaction vessel 313. The opening of the conductance adjustment valve was adjusted so that the pressure in the discharge chamber was 130 Pa, and the vacuum pump 317 was evacuated. The output value of the RF power source 315 was set to 1000 W, and discharge was generated in the inner reaction vessel 313 through the electrode 316. The self-bias voltage generated at the electrode 316 was monitored by a self-bias voltage reader 314.

As preparation for forming the p-type semiconductor layer, a temperature control device (not shown) was set so that the temperature indication value was 150 ° C., and the strip substrate 306 was heated by the infrared lamp heater 326. From a gas inlet port (not shown), 10 sccm of SiH ₄ gas, 500 sccm of BF ₃ / H ₂ (1%) gas, and 5000 sccm of H ₂ gas were introduced into the inner reaction vessel 318. The opening of the conductance adjustment valve was adjusted so that the pressure in the discharge chamber was 130 Pa, and the vacuum pump 322 was used to evacuate. The output value of the RF power source 320 was set to 2000 W, and discharge was generated in the inner reaction vessel 318 through the electrode 321.

  Subsequently, after preparation of each layer, the strip substrate 306 was transported at a speed of 1000 mm / min, and an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer were produced on the strip substrate. Here, the self-bias voltage value generated in the electrode 316 when forming the i-type semiconductor layer 30 minutes after the start of film formation was -0.2V. About 10 hours thereafter, the self-bias voltage value generated at the electrode 316 became −1.6 V. Finally, about 20 hours later, the film formation was completed at −2.45 V. FIG. 4 shows a graph of the time change of the self-bias voltage value generated at the electrode 316.

After one roll of the belt-shaped substrate was transported, all plasma excitation, all gas supply, energization of all lamp heaters, and transport of the belt-shaped substrate were stopped. Next, N ₂ gas for chamber leakage was introduced into the chamber (introducing member is not shown), the pressure was returned to atmospheric pressure, and the strip substrate in the vacuum vessel 305 was taken out.

Then, a transparent conductive film made of ITO (In ₂ O ₃ + SnO ₂ ) is continuously formed on the p-type semiconductor layer of the strip substrate by the following procedure under the conditions shown in Table 1 using the DC sputtering apparatus shown in FIG. A transparent electrode was formed.

  After the apparatus is opened to the atmosphere for maintenance or the like, a belt-like substrate roll 502 is set in the substrate delivery chamber 501 and the transparent conductive film deposition chambers 506, 507, 508, 509, 510 and 511 are penetrated through the belt-like substrate 504. And fixed to the roll 514 of the substrate winding chamber 516. Then, it exhausted until the pressure in an apparatus became 0.1 Pa or less. Thereafter, argon gas as an inert gas was supplied to the transparent conductive film forming chambers 506, 507, 508, 509, 510, and 511 from the gas supply pipes 551, 552, 553, 554, 555, and 556 as shown in Table 1. Also, 30 sccm of argon gas was supplied to the gate 515. In this state, the opening of an exhaust valve (not shown) was adjusted to maintain the pressure in the apparatus at the pressure shown in Table 1. Heater units 541, 542, 543, 544, 545, and 546 with six 100 W infrared lamps provided in each of the transparent conductive film forming chambers 506, 507, 508, 509, 510, and 511 and stainless steel reflections Heating was performed while controlling the temperature as shown in Table 1 using a thermocouple brought into contact with the back surface of the substrate deposition surface by a plate. Subsequently, the servo motor was operated to rotate the take-up roll 514, and the conveyance of the belt-like substrate 504 was started.

  The belt-like substrate 504 was transferred to the transparent conductive film deposition chambers 506, 507, 508, 509, 510, and 511. DC voltage is applied to ITO targets 521, 522, 523, 524, 525, and 526 having a purity of 99.99% by weight and a size of 25 cm × 25 cm using DC power sources 531, 532, 533, 534, 535, and 536. An argon plasma was generated while performing control so that the power shown in FIG.

  Here, in order to adjust the film thickness of the transparent conductive film, the transport speed shown in Table 1 was not set to a constant value of 2500 mm / min, but the film was formed by changing the transparent electrode formation time by changing it. Specifically, the conveyance speed was changed from 2950 mm / min to 2500 mm / min in accordance with the self-bias voltage value at the time of film formation of the i-type semiconductor layer shown in FIG. This is because, since the strip-shaped substrate 504 is wound up in a roll shape, the portion where the transparent conductive film is first formed is the last portion where the self-bias is lowered during the formation of the i-type semiconductor layer. Is thinner. Therefore, the transport speed of the transparent conductive film is increased to reduce the film thickness of the transparent conductive film. In addition, the last part of the transparent conductive film formation is the first part when the i-type semiconductor layer is formed, and the i-type semiconductor layer is a normal film thickness. I'm speeding up.

  The belt-like substrate 504 on which the transparent electrode was formed was wound up in a winding chamber 516. In order to prevent the surface of the transparent conductive film from being damaged, a polyester film interleaf 513 was sandwiched between the substrates during winding.

  Furthermore, a non-single crystal solar cell was manufactured by forming Al as a current collecting electrode by vacuum deposition to a thickness of 1 μm.

(Comparative Example 1)
A non-single-crystal solar cell was produced in the same manner as in Example 1 except that the film formation was performed while keeping the transport speed constant at 2500 mm / min when forming the transparent electrode.

As an evaluation, the samples of Example 1 and Comparative Example 1 were irradiated with light of the sunlight spectrum of AM-1.5 at an intensity of 100 mW / cm ² using a solar simulator, and a voltage-current curve was obtained. Initial conversion efficiency was measured.

  FIG. 6 is a graph in which the solar cells obtained in Example 1 and Comparative Example 1 are extracted every certain film formation time and the short-circuit current (Isc) is plotted. The short-circuit current (Isc) is plotted on the vertical axis. The membrane time is shown on the horizontal axis. Here, the short-circuit current Isc (normalized) is expressed by standardizing the short-circuit current 30 minutes after the start of film formation in Example 1 as 1.

  The short-circuit current of the solar cell produced in Comparative Example 1 decreased by 4.1% as the film formation time elapses, whereas the short-circuit current of the solar cell produced in Example 1 lasted from the start of film formation. Almost no reduction was observed during 20 hours, and the reduction rate was all within 0.74%, and a remarkable effect was observed in maintaining device characteristics as compared with Comparative Example 1.

(Example 2)
In this example, a non-single crystal solar cell was produced in the same manner as in Example 1 except that the conditions for forming the transparent electrode were changed as follows.

In this example, in order to adjust the film thickness of the transparent electrode, the deposition power was controlled by changing the input power, and the film was formed at a constant transfer speed. The applied power shown in Table 1 is adjusted from 1.0345 W / cm ² to 1.2 W by adjusting the DC applied voltage in accordance with the change in the self-bias voltage value from the start to the end of film formation during the formation of the i-type semiconductor layer. A transparent conductive film of ITO (In ₂ O ₃ + SnO ₂ ) was formed according to the conditions in Table 1 except that the film thickness was increased to / cm ² . After film formation for one roll was completed, a collecting electrode was formed in the same manner as in Example 1 to produce a solar cell.

  As a result of evaluating this solar cell in the same manner as in Example 1, the short-circuit current of the solar cell produced in Example 2 hardly decreased during the last 20 hours from the start of film formation, and the rate of decrease was All were within 1.02%, and a remarkable effect was observed in maintaining device characteristics as compared with Comparative Example 1.

(Example 3)
In this example, a non-single crystal solar cell was produced in the same manner as in Example 1 except that the conditions for forming the transparent electrode were changed as follows.

In this example, in order to adjust the transmittance of the transparent electrode, the substrate temperature was changed to control the crystallinity, and the film thickness was kept constant. By adjusting the number of infrared lamps used by the heater units 541, 542, 543, 544, 545, and 546 according to the change in the self-bias voltage value from the start to the end of film formation during the formation of the i-type semiconductor layer, A transparent conductive film of ITO (In ₂ O ₃ + SnO ₂ ) was formed according to the conditions in Table 1 except that the substrate temperature shown in 1 was lowered from 235 ° C. to 200 ° C. After film formation for one roll was completed, a collecting electrode was formed in the same manner as in Example 1 to produce a solar cell.

  As a result of evaluating this solar cell by the same method as in Example 1, the short-circuit current of the solar cell produced in Example 3 hardly decreased during the last 20 hours from the start of film formation, and the rate of decrease was All were within 0.89%, and a remarkable effect was observed in maintaining device characteristics as compared with Comparative Example 1.

Example 4
In this example, a non-single crystal solar cell was produced in the same manner as in Example 1 except that the conditions for forming the transparent electrode were changed as follows.

In this example, in order to adjust the transmittance of the transparent electrode, the oxygen flow rate was changed to control the oxygen concentration in the film, and the film thickness was kept constant. The conditions in Table 1 except that the oxygen flow rate shown in Table 1 is increased from 0.32 sccm to 0.4 sccm in accordance with the change in the self-bias voltage value from the start to the end of film formation when forming the i-type semiconductor layer. According to this, a transparent conductive film of ITO (In ₂ O ₃ + SnO ₂ ) was formed. After film formation for one roll was completed, a collecting electrode was formed in the same manner as in Example 1 to produce a solar cell.

  As a result of evaluating this solar cell in the same manner as in Example 1, the short-circuit current of the solar cell produced in Example 4 hardly decreased during the last 20 hours from the start of film formation, and the rate of decrease was All of them were within 0.61%, and a remarkable effect was observed in maintaining device characteristics as compared with Comparative Example 1.

(Example 5)
In this example, the production of a pin-type non-single-crystal solar cell in which light is incident from the substrate side shown in FIG. 7 will be described. FIG. 7 shows a solar cell having a structure in which light enters from the lower part of the figure. In the figure, 701 is a light-transmitting substrate, 702 is a back electrode, 703 is an n-type semiconductor layer, 704 is an i-type semiconductor layer, and 705 is A p-type semiconductor layer 706 represents a transparent electrode.

A transparent glass substrate having a size of 150 × 150 mm and a thickness of 2 mm is used as the translucent substrate 701, and a transparent conductive film made of ITO (In ₂ O ₃ + SnO ₂ ) is formed as a transparent electrode in the badge type DC sputtering apparatus shown in FIG. Membrane was performed. In FIG. 8, 701 is a translucent substrate, 801 is a substrate holder, 802 is a gas introduction means, 803 is a heater, 804 is an ITO target, and 805 is a DC sputtering power source.

First, the translucent substrate 701 was set in the substrate holder 801, and the inside of the apparatus was evacuated to a pressure of 0.1 Pa or less by a pump (not shown). Next, Ar gas (3.0 sccm) and O ₂ gas (0.01 sccm) were introduced into the apparatus through the gas introduction means 802 using a mass flow controller (not shown), and the pressure was maintained at 0.53 Pa using a pressure controller (not shown). . Thereafter, the translucent substrate 701 was heated to 200 ° C. by the heater 803. When the temperature was stabilized, a voltage was applied from the DC sputtering power source 805 to the ITO target 804 to generate plasma, and a transparent conductive film of ITO (In ₂ O ₃ + SnO ₂ ) was formed on the translucent substrate 701 for 120 seconds. At that time, the applied voltage was adjusted so that the input power density was 1.2 W / cm ² .

  A pin semiconductor junction was formed on the formed transparent electrode 706 using the semiconductor deposited film forming apparatus shown in FIG.

  FIG. 9 is a schematic view showing an example of a deposited film forming apparatus for producing a non-single crystal pin semiconductor junction used in the present invention. In FIG. 9, the deposited film forming apparatus includes a load chamber 901, a p-layer RF chamber 902, An amorphous silicon i-layer RF chamber 903, an n-layer RF chamber 904, and an unload chamber 905 are configured. The chambers are separated by gate valves 906, 907, 908, and 909 so that the source gases are not mixed.

  The RF chamber 902 is a p-type layer heater 910 and a p-type layer deposition chamber 911, the RF chamber 903 is an i-type layer heater 912 and an i-type layer deposition chamber 913, and the RF chamber 904 is an n-type layer heating. A heater 914 and an n-type layer deposition chamber 915 are provided. The translucent substrate 701 on which the transparent conductive film is formed is attached to a substrate holder 917, and moves on the transport rail 916 from the outside by a driving roller (not shown).

  Using this deposited film forming apparatus, each semiconductor layer was formed by the following procedure under the film forming conditions shown in Table 2.

  The translucent substrate 701 was set on the substrate holder 917 and set on the rail 916 of the load chamber 901. Then, the inside of the load chamber 901 was evacuated to a degree of vacuum of several hundred mPa or less by a vacuum pump (not shown).

  Next, the gate valve 906 is opened, and the substrate holder 917 is moved to the p-type layer deposition chamber 911 in the chamber 902. With the gate valves 906, 907, 908, and 909 closed, the source gas shown in the p layer in Table 2 is introduced into the p-type layer deposition chamber 911 by a gas introduction means (not shown) and is expressed by a pressure controller (not shown). It adjusted so that it might become the pressure shown in p layer of 2. The translucent substrate 701 was heated by the p-type layer heater 910 so that the substrate temperature shown in the p layer in Table 2 was reached. When the temperature was stabilized, RF having a power density shown in the p layer in Table 2 was applied from an RF power source (not shown) to generate plasma, and a p-type layer having a thickness shown in the p layer in Table 2 was deposited.

  After exhausting the deposition chamber 902 sufficiently, the gate valve 907 was opened, the substrate holder 917 was moved to the i-type layer deposition chamber 913 of the deposition chamber 903, and the gate valve 907 was closed.

  With the gate valves 906, 907, 908, 909 closed, the source gas shown in the i layer in Table 2 is introduced into the i-type layer deposition chamber 913 by a gas introduction means (not shown), and is displayed by a pressure controller (not shown). It adjusted so that it might become the pressure shown to i layer of 2. The translucent substrate 701 was heated by the i-type layer heater 912 so that the substrate temperature shown in the i layer in Table 2 was reached. When the temperature was stabilized, RF having a power density shown in the i layer in Table 2 was applied from an RF power source (not shown) to generate plasma, and an i-type layer having a thickness shown in the i layer in Table 2 was deposited. At this time, the self-bias voltage value was -0.230 V at the start of film formation and -0.237 V at the end.

  After exhausting the deposition chamber 903 sufficiently, the gate valve 908 was opened, the substrate holder 917 was moved to the n-type layer deposition chamber 915 of the deposition chamber 904, and the gate valve 908 was closed.

  With each gate valve 906, 907, 908, 909 closed, the source gas shown in the n layer of Table 2 is introduced into the n-type layer deposition chamber 915 by a gas introduction means (not shown) and is expressed by a pressure controller (not shown). It adjusted so that it might become the pressure shown to 2 n layer. The translucent substrate 701 was heated by the n-type layer heater 914 so that the substrate temperature shown in the n layer of Table 2 was reached. When the temperature was stabilized, RF having a power density shown in the n layer in Table 2 was applied from an RF power source (not shown) to generate plasma, and an n-type layer having a thickness shown in the n layer in Table 2 was deposited.

  After the deposition chamber 904 was sufficiently evacuated in the same manner as described above, the gate valve 909 was opened and the substrate holder 917 was moved to the unload chamber 905.

  All the gate valves are closed, nitrogen gas is sealed in the unload chamber 905, and the substrate is cooled. Thereafter, the takeout door of the unload chamber 905 was opened, and the substrate holder 917 was taken out.

  A solar cell was fabricated by forming a film of ZnO 2 μm and Al 1 μm in this order on a transparent substrate 701 on which a transparent electrode and a pin semiconductor junction were formed as described above, using a DC sputtering apparatus (not shown) in this order. . This solar cell is designated as Lot No. It was set to 1.

Next, lot no. 2 and subsequent solar cells were manufactured continuously. At that time, when the self-bias voltage value decreased by 3.56 V during the film formation of the i-type semiconductor from the previous experiment, the thickness of the transparent electrode was reduced by 15.2%. Since the short-circuit current (Isc) of the battery is known to be the same as the initial short-circuit current, the film formation time T (n) was adjusted according to the following formula when forming the transparent electrode.
T (n + 1) = ((− 0.152) × (| Vs ₀ −Vs (n) | /3.56) +1) × 120 [seconds]
Here, T (n + 1) is the lot number. n + 1 transparent electrode deposition time, Vs ₀ is lot no. 1 is a self-bias voltage value at the start of film formation of the i-type semiconductor layer, and Vs (n) is a lot number. The self-bias voltage value at the end of n-type i-type semiconductor layer deposition is represented. The film formation time was adjusted in units of 1 second and rounded up to the nearest 1 second.

Lot no. The transparent electrode deposition time T (2) of 2 is calculated, and T (2) = ((− 0.152) × (| −0.230 − (− 0.237) | /3.56) +1) × 120 = 119.96
Therefore, the film formation time was 120 seconds.

In this way, lot no. Lot no. Since the self-bias voltage value at the end of 499 i-type semiconductor layer deposition was −3.54 V, T (500) = ((− 0.152) × (| −0.230 − (− 3.54) | /3.56) +1) × 120 = 103.05
To lot no. The film formation time for 500 transparent electrodes was 104 seconds.

(Comparative Example 2)
All lot numbers The transparent electrode formation time of the transparent electrode was fixed at 120 seconds and lot no. Solar cells were made up to 500.

As an evaluation, the sample of Example 5 and Comparative Example 2 was irradiated with light of the sunlight spectrum of AM-1.5 with an intensity of 100 mW / cm ² using a solar simulator, and a voltage-current curve was obtained. Initial conversion efficiency was measured.

  The short circuit current of the solar cell produced in Comparative Example 2 is the lot no. 1 for the short-circuit current of 1. While the short circuit current of 500 decreased by 4.7%, the short circuit current of the solar cell manufactured in Example 5 hardly decreased in all lots, and the decrease rate was all within 0.68%. As compared with Comparative Example 2, a remarkable effect was observed in maintaining the device characteristics.

It is the schematic which shows typically an example of the deposited film formation apparatus for forming the semiconductor layer of the photovoltaic element of this invention. It is explanatory drawing which shows typically the structure of the pin type non-single-crystal solar cell which injects light from the other side of the board | substrate produced by the formation method of this invention. It is the schematic which shows an example of the semiconductor film formation apparatus used in the photovoltaic element formation method of this invention. It is the figure which plotted the transition of the self-bias voltage value at the time of film-forming of i-type semiconductor layer for every fixed film-forming time in Example 1 of this invention. It is the schematic which shows an example of the transparent conductive film formation apparatus used in the photovoltaic element formation method of this invention. It is the figure which extracted the photovoltaic cell produced in Example 1 of this invention, and the comparative example 1 for every fixed film-forming time, and plotted the value which normalized the short circuit current Isc. It is explanatory drawing which shows typically the structure of the pin type non-single-crystal solar cell which injects light from the substrate side produced by the formation method of this invention. It is the schematic which shows an example of the transparent conductive film formation apparatus used in the formation method of this invention. It is the schematic which shows an example of the deposited film formation apparatus which produces the batch type non-single-crystal pin semiconductor junction used in the photovoltaic element formation method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Reaction container 101 Substrate 102 Heater 103 Cathode electrode 104 High frequency power supply 105 Self-bias voltage reader 106 Gas introduction pipe 107 Gas introduction valve 108 Mass flow controller 109 Exhaust pipe 110 Outer reaction container 201 Substrate 202 Back electrode 203 N-type semiconductor layer 204 i Type semiconductor layer 205 p type semiconductor layer 206 transparent electrode 207 current collecting electrode 208 light incident direction 301 substrate delivery chamber 302 n type semiconductor layer preparation container 303 i type semiconductor layer preparation container 304 p type semiconductor layer preparation container 305 substrate Winding chamber 306 Strip substrate 307, 312, 317, 322, 323 Exhaust pump 308, 313, 318 Inner reaction vessel 309, 314, 319 Self-bias voltage reader 310, 315, 320 RF power source 311, 3 16, 321 Cathode electrodes 324, 325, 326 Heater 501 Substrate delivery chamber 502 Strip substrate roll 503 Roller 504 Strip substrate 506-511 Transparent conductive film deposition chamber 512 Steering roller 513 Interleaf 514 Strip substrate roll 515 Gate 516 Substrate take-up chamber 517 Magnet roller 521-526 ITO target 531-536 DC power source 541-546 Heater 551-556 Gas supply pipe 560 Vacuum pump 701 Translucent substrate 702 Back electrode 703 n-type semiconductor layer 704 i-type semiconductor layer 705 p-type semiconductor layer 706 Transparent electrode 707 Light incident direction 801 Substrate holder 802 Gas introduction means 803 Heater 804 ITO target 805 DC sputtering power supply 901 Load chamber 90 p-layer RF chamber 903 amorphous silicon i-layer RF chamber 904 n-layer RF chamber 905 unload chamber 906 to 909 gate valve 910 heater for p-type layer 911 RF plasma CVD p-layer deposition chamber 912 heating for amorphous i-type layer Heater 913 RF plasma CVD amorphous i-type layer deposition chamber 914 Heater for n-type layer 915 RF plasma CVD n-type layer deposition chamber 916 Holder transport rail 917 Substrate holder

Claims (6)

  In a method for forming a photovoltaic device having a structure in which a back electrode, a semiconductor layer, and a transparent electrode are stacked in this order on a substrate, based on a self-bias voltage value generated when the semiconductor layer is formed, A method for forming a photovoltaic element, characterized in that formation conditions are set.   In a method of forming at least two photovoltaic elements having a structure in which a transparent electrode, a semiconductor layer, and a back electrode are stacked in this order on a substrate, the semiconductor is formed on the nth (n is an integer of 1 or more) substrate. A method for forming a photovoltaic element, comprising setting conditions for forming a transparent electrode formed on an (n + 1) th substrate based on a self-bias voltage value generated when forming a layer.   The formation condition of the transparent electrode is at least one selected from application power, application voltage, application current, formation time, gas flow rate, formation temperature, deposition rate, and baking time. A method for forming a photovoltaic element according to 1 or 2.   In a method for forming a photovoltaic device having a structure in which a back electrode, a semiconductor layer, and a transparent electrode are stacked in this order on a substrate, based on a self-bias voltage value generated when the semiconductor layer is formed, A method for forming a photovoltaic element, characterized by setting a film thickness or transmittance.   In a method of forming at least two photovoltaic elements having a structure in which a transparent electrode, a semiconductor layer, and a back electrode are stacked in this order on a substrate, the semiconductor is formed on the nth (n is an integer of 1 or more) substrate. A method for forming a photovoltaic element, comprising setting a film thickness or a transmittance of a transparent electrode formed on an (n + 1) th substrate based on a self-bias voltage value generated when forming a layer.   The formation condition, film thickness, or transmittance of the transparent electrode is set based on a relationship between a self-bias voltage value generated when forming the semiconductor layer and a short-circuit current of the photovoltaic element. Item 6. A method for forming a photovoltaic device according to any one of Items 1 to 5.

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