Patent Application
20150287853
The present invention relates to a fabrication method of a semiconductor film, a solar cell and a chalcopyrite compound, particularly relates to a solar cell having high photoelectric conversion efficiency, a composition of an optical absorption layer thereof, and a fabrication method of a semiconductor film which is an optical absorption layer thereof.
The chalcopyrite compound is a compound semiconductor having a chemical formula XYZ2 including a 1B group element X (X is Cu or Ag), a 3B group element Y (Y is Al, Ga, or In), and a 6B group element Z (Z is S, Se, or Te). The chalcopyrite compound shows an optical absorption characteristic which differs by a chemical composition, in the compound, CuInSe2 shows optical absorption which is higher than that of silicon from infrared to ultraviolet wavelength region, and therefore, CuInSe2 attracts attention as a material of a solar cell.
A number of technologies are known concerning a fabrication method of a chalcopyrite compound, and the technologies are grossly classified to: A. a technology concerning a fabrication of a chalcopyrite compound thin film; and B. a technology concerning a film treatment after fabricating the film.
As publicly known literatures concerning A. the technology of film fabrication, there are Japanese Unexamined Patent Application Publication No. Hei 9(1997)-213977 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-503708. Japanese Unexamined Patent Application Publication No. Hei 9(1997)-213977 discloses a method of forming a CuInSe2-xSx thin film by controlling distributions of selenium and sulfur in a depth direction of the film, and giving a change in an optical band gap in the depth direction of the film. The literature shows that a solar cell having a high open voltage can be configured by using the CuInSe2-xSx thin film formed the method for an optical absorption layer. Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-503708 discloses a method of fabricating a semiconductor thin film configured by a chalcopyrite compound 4 elements alloy or 5 or more elements alloy.
Japanese Unexamined Patent Application Publication No. Hei 9(1997)-213977 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-503708 describe stoichiometric methods of fabricating a chalcopyrite compound thin films which do not include an atomic defect. However, as shown in Maeda, Wada, “CuInSe2 no Denshi Kozo to Koshi Kekkan (Electronic Structure and Lattice Defect of CuInSe2) ‘Recent Development of Thin Film Compound Semiconductor Photovoltaic Cells’”, CMC Publishing CO., LTD. Tokyo (2007), pp. 18-28, a stoichiometric chalcopyrite compound is more unstable than a non-stoichiometric chalcopyrite compound including a Z atomic defect. Therefore, in the methods of carrying out high temperature treatments at 500° C. or higher which are described in Japanese Unexamined Patent Application Publication No. Hei 9(1997)-213977 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-503708, the Z atomic defect is caused in the film after forming the film, and the stoichiometric chalcopyrite compound thin film as asserted by these structures is not obtained.
The Z atomic defect of the thin film in the chalcopyrite compound is operated as a recombination center of an electron and a hole. Therefore, it is preferable to repair the Z atomic defect in the film in order to obtain the chalcopyrite compound thin film having high photoelectric conversion efficiency.
B. The film treatment after forming the film is a technology for resolving the problem. There are Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 and Japanese Unexamined Patent Application Publication No. 2012-15328 as publicly known literatures concerning the technology B. Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 describes a method of repairing a selenium atomic defect in a film by annealing a thin film of CuInSe2 after a film fabricating process at a treatment temperature equal to or higher than 250° C. and equal to or lower than 550° C. under a hydrogen selenide (H2Se) gas atmosphere. Also, the literature describes that when the annealing process is carried out not under the H2Se atmosphere but under a hydrogen sulfide (H2S) gas atmosphere, a sulfur atom is brought into the selenium atomic defect in the film, and an optical band gap only at a film surface can also be changed.
Japanese Unexamined Patent Application Publication No. 2012-15328 describes a method of repairing a generated selenium atomic defect by diffusing a selenium atom in the film while reducing selenium atomic defect formation which is caused after forming the film by rapidly cooling the CuInSe2 film as crystallized down to 210° C. or lower and carrying out a selenium (Se) gas annealing.
Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 and Japanese Unexamined Patent Application Publication No. 2012-15328 describe the methods of repairing the Z atomic defect caused in the film after forming the chalcopyrite compound thin film including selenium as Z by the annealing treatment under the H2Se or Se gas atmosphere. However, there poses a problem that H2Se and Se gas are toxic.
Although the method of Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 using the H2S gas having less toxicity is worth paying attention, the repairing of the selenium atomic defect of the CuInSe2 film by H2S gas is limited to the surface of the film. This method aims to achieve high conversion efficiency by changing an optical band gap only at the surface of the film.
It is the object of the present invention to provide an optical absorption layer having the most pertinent optical band gap without using a gas having high toxicity in repairing a Z atomic defect caused in a film after forming a chalcopyrite compound thin film represented by CuInSe2.
First, an explanation will be given of a fabrication method.
(1) The object described above is achieved by subjecting a chalcopyrite compound film to an annealing treatment in a gas atmosphere including sulfur under a pressurized condition after forming the film.
A representative example of the chalcopyrite compound having a chemical formula of XYZ2, in which X is silver or copper, Y is gallium, indium, or aluminum, Z is sulfur, selenium, or a tellurium. The chalcopyrite compound may be configured not only by a ternary system, but a four or more elements system having two kinds of elements as Y.
Here, in comparison with a background art, in Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545, in a case of using H2S gas having less toxicity, only the Z atomic defect at a surface of the film is repaired by a sulfur atom. The fact shows that in Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545, only a Z atomic defect near to a surface of a crystal is repaired and the Z atomic defect existed at the inner portion of the crystal cannot be repaired. According to the method, since only the film surface is repaired, an annealing time period is believed to be about several seconds.
On the other hand, the present invention allows the Z atomic defect over a total of the film to be repaired by a sulfur atom by diffusing sulfur to an inner portion of a crystal by annealing a chalcopyrite thin film in a gas atmosphere including sulfur under a pressurized condition.
When a polycrystal chalcopyrite thin film is annealed by using a pressurized sulfur gas, in comparison with a case of no pressurization, more sulfur atoms per time can be supplied to a surface of a crystal grain of chalcopyrite configuring a thin film, and the Z atomic defect which exists at an inner portion of the crystal grain which cannot be treated in the case of no crystallization can be repaired by a sulfur atom by accelerating to diffuse the sulfur atom to the inner portion of the crystal grain. Specifically, in a case of using a sulfur gas at 10 atm, in comparison with a case of 1 atm, an amount of sulfur atoms supplied per unit time to a unit surface of the crystal grain can be made to be 10 times as much as that in the case of 1 atm.
Incidentally, the reason of repairing only the surface of film in Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 is as follows. First, an output voltage can be increased. A P/N junction of a CuInSe2 solar cell exists at a surface of CuInSe2 on a side on which a solar ray is incident. When S is introduced to the surface, an optical band gap at the junction can be increased, and an output can be increased by increasing an output voltage. Successively, efficiency of taking out a carrier is increased. When an optical band gap at a vicinity of the surface is increased by introducing S to the surface, a gradient can be attached to the optical band gap. When the gradient is attached to the optical band gap, a carrier (electron and hole) by optical absorption can efficiently be taken out to outside. As a result, an output is increased by increasing a current. In this way, it is an object of Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 to attach a gradient to an optical band gap by only repairing a surface of the film, which is quite different from a configuration in which a Z atom defect over a total of the film is repaired by a sulfur atom to provide an optical absorption layer having the most pertinent optical band gap as in the present application.
(2) A temperature of the annealing treatment is made to be lower than a melting point (217° C.) of selenium and higher than a melting point (112° C.) of sulfur in a case where Z=Se or S.
It is preferable that the annealing treatment temperature of the chalcopyrite compound after forming the film is made to be as low as possible from a view point of restraining a detachment of the Z atom from the film and reducing as much as possible the Z atomic defect in the film. On the other hand, when the film treatment temperature is lower than the melting point of Z, Z aggregates in the film, a chemical composition of the film is in excess of Z, which is not preferable.
Hence, the detachment of the Z atom is restrained as much as possible and at the same time the sulfur atom is prevented from aggregating in the film excessively by making the treatment temperature of the film lower that in the background art technology by making the treatment temperature of the chalcopyrite compound including selenium or sulfur as Z lower than the melting point (217° C.) of selenium and higher than the melting point (112° C.) of sulfur.
According to the methods of Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 and Japanese Unexamined Patent Application Publication No. 2012-15328 using H2Se or Se gas, the treatment temperature of the film cannot be made to be lower than the melting point of selenium in order to prevent the aggregation of selenium into the film. In contrast thereto, according to the method of the present invention using a gas including S of H2S or the like, the treatment temperature of the film can be made to be lower than the melting point of selenium.
As a result, the detachment of selenium from inside of the film can substantially be restrained in a case of treating the chalcopyrite compound thin film having selenium as Z by the present invention.
(3) A temperature in the annealing treatment described above is made to be lower than the melting point (449° C.) of tellurium and higher than the melting point (112° C.) of sulfur in a case of Z=Te. Thereby, the detachment of the tellurium atom from the film is restrained as much as possible, and at the same time, the sulfur atom is prevented from aggregating into the film excessively.
According to the background art using hydrogen telluride (H2Te), the treatment temperature of the film cannot be made to be lower than the melting point of tellurium, in order to prevent aggregation of tellurium into the film. In contrast thereto, according to the method of the present invention using a gas including S of H2S or the like, the treatment temperature of the film can be made to be lower than the melting point of tellurium, and the detachment of the tellurium from inside of the film can be restrained.
(4) The annealing treatment is made to be carried out by making the pressure of the gas including S as from 2 atm to 100 atm. Thereby, the Z atomic defect of the polycrystal chalcopyrite thin film having the film thickness becomes able to be repaired by the sulfur atom.
It is preferable that the pressure of the gas including S is high from a view point of repairing the Z atom in the chalcopyrite compound thin film, and therefore, it is preferable that the pressure of the gas is equal to or higher than 10 atm. On the other hand, the higher the pressure of the gas, the more complicated the device for the treatment, and therefore, it is preferable for mass production to repair the Z atom in the chalcopyrite thin film by using the gas including S at a comparatively low pressure.
(5) H2S is preferable as the gas including sulfur. A molecular weight of H2S gas is the smallest as the molecule including sulfur, and H2S gas is excellent in diffusivity, and suitable for the annealing treatment of the polycrystal chalcopyrite compound thin film. Further, a product in a case where H2S is decomposed at the surface of the chalcopyrite compound is only H2 which is detached easily from the surface and S which is necessary for repairing the Z atom defect, and H2S has an advantage in which a chemical residue of contaminating the surface is not produced.
Successively, an explanation will be given of the chalcopyrite compound film.
(6) A chalcopyrite compound is made to have a chemical composition of XYSexSy or XYTexSy, where a value of x+y is equal to or more than 1.95 and equal to or less than 2. Here, X is silver or copper, Y is gallium, indium, or aluminum, Z is sulfur, selenium or tellurium.
According to Japanese Unexamined Patent Application Publication No. Hei 6(1994)-120545 and Japanese Unexamined Patent Application Publication No. 2012-15328, the defect over the total of the film cannot be repaired, and therefore, x+y is believed to be equal to or less than 1.90. On the other hand, according to the present application, the defect of the total of the film is repaired, and therefore, a value of x+y is equal to or more than 1.95 and equal to or less than 2.
Explaining in details by using a specific example, when an annealing treatment of a thin film of a chalcopyrite compound XYSexVz having a selenium atom and a selenium atomic defect V is carried out, a sulfur atom is introduced to V, and a thin film having a chemical composition of XYSexSyVz-y is obtained. Here, y≦z and 1.95<x+y<x+z=2.
As in (1) described above, when the polycrystal CuInSex thin film is treated, the sulfur atom is introduced into the selenium atomic defect in the film, and the chalcopyrite compound thin film having the chemical composition of CuInSexSy is obtained. A range of x+y is equal to or more than 1.95 and equal to or less than 2, and in comparison with the case where the treatment is not carried out, the Z atomic defect density in the film can be lowered. Thus, the CuInSe2 film having less carrier recombination by the Z atomic defect can be obtained.
Further, the CuInSexSy thin film obtained by the treatment has an optical band gap larger than that of the CuInSexS thin film before the treatment, and the optical band gap of the film is near to the optical band gap of 1.45 eV at which a solar ray can be converted into an electric energy the most efficiently by the treatment.
Incidentally, even in other material of a polycrystal CuGaSex, AgInSx, CuGaSex thin film or the like, the same goes with the case of the CuInSexSy thin film.
(7) A relationship between an atm and a chemical composition of a compound is as follows. A change in x+y (t) (x is a constant) in annealing of the compound XYZxSy(t) is represented as
y(t)=(2−x)−(2−x−y(0))exp(−kPt)
k: coefficient depending on substance
P: pressure.
Here, time t at which x+y≧1.95 becomes as t≧ln(0.05/2−x−y(0))kP by
2−(2−x−y(0))exp(−kPt)≧1.95.
Therefore, annealing may be carried out for time equal to or longer than −ln(0.05/2−x−y(0))/kP.
The Z atomic defect in the chalcopyrite compound thin film can be repaired by the sulfur atom. As a result, the optical band gap of the optical absorption film can be made to be near to an optimum value of a solar cell.
Thus, the chalcopyrite thin film in the polycrystal state having the film thickness of 1 through 2 micrometers is formed.
An explanation will be given of a method of carrying out a treatment of a fabrication method of a semiconductor thin film of the present invention by using the device of
At the step 14, the CuInSe2 thin film is formed above the substrate by using ternary simultaneous vapor deposition method, a sputtering method, a roll-to-roll process which are publicly-known technologies, or the methods of Japanese Unexamined Patent Application Publication No. Hei 9(1997)-213977 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-503708. At the step 15, the thin film is crystallized by treating the CuInSe2 thin film at a condition of 500° C. or higher in a H2Se gas atmosphere by using the publicly-known technologies. By the treatment of the step 15, the polycrystal CuInSe2 thin film is obtained. At the step 16, the CuInSe2 thin film fabricated above the substrate is arranged above the thin film stage 9 which is present in the pressure chamber. The CuInSe2 thin film corresponds to numeral 7 of
At the step 18, the pressurized H2S gas is introduced into the pressure chamber by using the pressure pump 4 and the H2S gas bomb 5. The pressure of H2S gas is 10 atm through 100 atm. At the step 19, electricity is supplied by using the power source cable 12 from the outside power source 11 to the electric heater, and the CuInSe2 arranged above the thin film stage is subjected to a heating treatment. The temperature of the thin film is adjusted to be equal to or higher than 112° C. and less than 217° C. by using the electric switch 13. At the step 20, the CuInSe2 thin film finished with the treatment is taken out of the pressure chamber 1.
The CuInSe2 thin film is formed on a glass substrate by using a publicly-known ternary simultaneous vapor deposition method. The film thickness is 1 μm, and the film is brought into a polycrystal state. The thin film is treated by using the device of
Table 1 shows the chemical compositions and the optical band gaps of the CuInSe2 thin films as treated. The chemical compositions are indicated by coefficients of respective elements of the chemical formula of the film.
Table 1 shows a chemical composition of the CuInSe2 thin film before the treatment for comparison. The composition of the film before the treatment is Cu0.8In1.14Se1.75, and the film includes a selenium atomic defect. When the film is treated under H2S gas atmosphere at 1 atm by a method of the publicly-known technology, the Se defect at a vicinity of a surface of the crystal grain is repaired by the sulfur atom, and the composition of the film becomes Cu0.8In1.14Se1.75S0.05. However, the selenium atomic defect at the inner portion of the crystal grain remains unrepaired, and a sum of the coefficients of Se and S of the chemical formula of the film becomes 1.80.
On the other hand, in a case where the film is treated by setting the pressure of the H2S gas to 10 atm, 50 atm, and 100 atm by the present invention, the sulfur atom is introduced also to the selenium atomic defect at the inner portion of the CuInSe2 crystal grain, and the composition of the film becomes Cu0.8In1.14Se1.75SexSy, and a value of x+y is made to be equal to or more than 1.95 and equal to or less than 2. In this way, the CuInSeS film having few defects and is near to a stoichiometric composition can be obtained by repairing the selenium defect in the CuInSe2 crystal by the sulfur atom by the present invention.
Incidentally, even when the CuInSe2 film is treated, composition ratios of Cu, In, and Se remain unchanged by the present invention. In this way, only the selenium atom defect can be repaired by the sulfur atom without influencing the atoms.
When the CuInSe2 film is treated, the sulfur atom is introduced to the selenium atom defect in the film, and therefore, the optical band gap of the film is increased by the present invention. The optical band gap of the CuInSe2 treated by the method of the present invention is about 1.10 eV and is near to an optimum value 1.45 eV of the optical band gap of the solar cell in comparison with the optical band gap (1.02 eV) before the treatment. In this way, the optical band gap of the CuInSe2 film can be brought near to an optimum value by the present invention.
A polycrystal CuInSe2 thin film having a film thickness of 1 μm is formed by using the publicly-known ternary simultaneous vapor deposition method and the thin film is treated by using the device of
In a case where the film is treated under the H2S gas atmosphere at 1 atm by using the publicly-known technology, a significant change over time is not observed in the x+y value. This is because the sulfur atom is introduced only to the selenium atomic defect near to the surface of the crystal grain, and the sulfur atom is not introduced to the selenium defect at the inner portion of the crystal grain.
On the other hand, in a case where the film is treated under the pressurized H2S gas atmosphere by using the method of the present invention, the x+y value is increased along with time, and the x+y value becomes equal to or more than 1.95 after 1 hour even at any pressure of 10 atm, 50 atm, and 100 atm. It is found that, by the method of the present invention using the pressurized gas, the selenium atomic defect at the inner portion of the crystal grain is effectively repaired by the sulfur atom. As described in the first embodiment, even in a case where the treatment is carried out for 1 hour, the detachment of the selenium atom from the film is not observed.
Time until the x+y value becomes equal to or more than 1.95 is about 50 minutes in a case where the pressure of the H2S gas is 10 atm, 30 minutes in a case of 50 atm, and about 10 minutes in a case of 100 atm. The higher the pressure of the H2S gas, the shorter the time required for repairing the selenium atomic defect, and the effect of the present invention using the pressurized gas can be confirmed.
Actually, in a case of fabricating a solar cell which uses the CuInSe2 thin film, it is preferable that the treatment time of the film is short in view of fabrication. The present invention can repair the selenium atomic defect in the film by the sulfur atom in comparatively short time, which is suitable for fabricating the CuInSe2 solar cell.
A CuGaSe2 thin film is fabricated on a glass substrate by using the publicly-known ternary simultaneous vapor deposition method. The film thickness is 1.1 μm, and the film is brought into the polycrystal state. The thin film is treated by using the device of
Table 2 shows chemical compositions and optical band gaps of the CuGaSe2 thin film as treated. The chemical compositions are indicated by coefficients of respective elements of chemical formula of the films.
Table 2 shows a chemical composition of the CuGaSe2 before treatment for comparison. The composition of the film before treatment is Cu0.92Ga1.06Se1.70, and the film includes a selenium atomic defect. When the film is treated under the H2S gas atmosphere at 1 atm by the method of the publicly-known technology, the selenium atomic defect at a vicinity of the surface of the crystal grain is repaired by the sulfur atom, and the composition of the film becomes Cu0.92Ga1.06Se1.70S0.10. However, the selenium atomic defect at the inner portion of the crystal grain remains unrepaired, and a sum of coefficients of Se and S of the chemical formula of the film becomes 1.80.
On the other hand, in a case of carrying out a treatment of the film by setting the pressure of the H2S gas to 10 atm, 50 atm, and 100 atm by the present invention, the sulfur atom is introduced also to the selenium atomic defect at the inner portion of the crystal grain, the composition of the film becomes Cu0.92Ga1.06SexSy, and the value of x+y can be made to be equal to or more than 1.95 and equal to or less than 2. In this way, the CuGaSeS thin film having few defects near to the stoichiometric composition can be obtained by repairing the selenium atomic defect in the CuGaSe2 crystal by the sulfur atom by the present invention.
Incidentally, the composition ratios of Cu, Ga, and Se of the film remain unchanged even when the CuGaSe2 film is treated by the present invention. In this way, only the selenium atomic defect can be repaired by the sulfur atom without influencing these atoms.
When the CuGaSe2 film is treated by the present invention, the sulfur atom is introduced to the selenium atomic defect in the film, and therefore, the optical band gap of the film is increased. The optical band gap of the CuGaSe2 film treated by the method of the present invention is about 1.78 eV, and is a value larger than an optical band gap (1.65 eV) of the film before treatment.
An AgInSe2 thin film is formed on a glass substrate by the publicly-known ternary simultaneous vapor deposition method. The film thickness is 2 μm, and the film is brought into a polycrystal state. The film is treated by using the device of
Table 3 shows a chemical composition and an optical band gap of the AgInS2 thin film as treated. The chemical composition is indicated by coefficients of respective elements in the chemical formula of the film.
Table 3 shows a chemical composition of an AgInS2 thin film before treatment for comparison. A composition of the film before treatment is Ag0.90In0.98S1.50, and the film includes the sulfur atom defect. When the film is treated under the H2S gas atmosphere at 1 atm by the publicly-known technologies, the sulfur atomic defect at a vicinity of the surface of the crystal grain is repaired by the sulfur atom, and the composition of the film becomes Ag0.90In0.98S1.65. The sulfur atomic defect at the inner portion of the crystal grain remains unrepaired, and the coefficient S of the chemical formula of the film becomes 1.65.
On the other hand, in a case of treating the film by setting the pressure of the H2S gas to 10 atm, 50 atm, and 100 atm by the present invention, the sulfur atom is introduced also to the sulfur atom defect at the inner portion of the crystal grain, a composition of the film becomes Ag0.90In0.98Sx+y, and the value of x+y can be made to be equal to or more than 1.95 and equal to or less than 2. In this way, the sulfur atomic defect in the AgInS2 crystal can be repaired by the sulfur atom by the present invention.
Incidentally, even when the AgInS2 film is treated, composition ratios of Ag and In are not changed and it is not observed that the composition ratio of S is reduced by the present invention. In this way, according to the present invention, only the sulfur atomic defect in the film can be repaired by the sulfur atom without influencing the atom which is present in the film before treatment.
When the AgInS2 film is treated by the present invention, the sulfur atom is introduced into the sulfur atom defect in the film, and therefore, the optical band gap of the film is increased. The optical band gap of the AgInS2 film treated by the method of the present invention is 1.83 through 1.85 eV, and is a value larger than the optical band gap (1.79 eV) of the film before treatment. The optical band gap of the treated film becomes a value extremely near to 1.87 eV which is an optical band gap of an AgInS2 single crystal.
In this way, the AgInS2 film with an electronic property near to that of the stoichiometric AgInS2 is obtained by the present invention.
A CuGaTe2 thin film is formed on a glass substrate by using the publicly-known ternary simultaneous vapor deposition method. The film thickness is 2 μm, and the film is brought into a polycrystal state. The thin film is treated by using the device of
Table 4 shows chemical compositions and optical band gaps of the CuGaTe2 thin film as treated. The chemical compositions are indicated by coefficients of the respective elements of the chemical formula of the film.
Table 4 shows the chemical composition of the AgInS2 thin film before treatment for comparison. The composition of the film of the treatment is
Cu0.89Ga11.04Te1.65, and the film includes the sulfur atomic defect. When the film is treated under the H2S gas atmosphere at 1 atm by the method of the publicly-known technology, a tellurium atomic defect at a vicinity of the crystal grain surface is repaired by the sulfur atom, and the composition of the film becomes Cu0.89Ga1.04Te1.65S0.12.
On the other hand, in a case where the film is treated by setting a pressure of the H2S gas to 10 atm, 50 atm, and 100 atm by the present invention, the sulfur atom is introduced also to the tellurium atomic defect at the inner portion of the crystal grain, the composition of the film becomes Cu0.89Ga1.04Sx+y, and a value of x+y can be made to be equal to or more than 1.95 and equal to or less than 2. In this way, the tellurium atomic defect in the CuGaTe2 crystal can be repaired by the sulfur atom. A gas including toxic Te may not be used by repairing the Te atomic defect by the gas including S.
Incidentally, composition ratios of Cu, Ga, and Te of the film remain unchanged even when the CuGaTe2 film is treated by the present invention. In this way, according to the present invention, only the tellurium atomic defect in the film can be repaired by the sulfur atom without influencing atoms in the film before treatment.
When the CuGaTe2 film is treated by the present invention, the sulfur atom is introduced to the tellurium atomic defect in the film, and therefore, the optical band gap of the film is increased. The CuGaTe2 film treated by the method of the present invention has an optical band gap larger than that of the CuGaTe2 film before treatment, and a value thereof is 1.42 through 1.43 eV. The optical band gap is extremely near to the optical band gap of 1.45 eV which can convert a solar ray into electric energy most efficiently.
In this way, according to the present invention, the CuGaTe2 thin film having an ideal optical band gap can be obtained as the optical absorption layer of the solar cell by the present invention. The CuGaTe2 thin film treated by the present invention has an advantage that In which is a premium grade element is not included, and is excellent in view of an element strategy.
A CuAlSe2 thin film is formed on a glass substrate by using the publicly-known ternary simultaneous vapor deposition method. The film thickness is 2 μm, and the film is in a polycrystal state. The thin film is treated by using the device of
Table 5 shows chemical compositions and optical band gaps of the CuGaTe2 thin films as treated. The chemical composition is indicated by coefficients of respective elements of the chemical formula of the film.
The table shows a chemical composition of the CuAlSe2 thin film before treatment for comparison. The composition of the film of the treatment is Cu0.81Al1.04Se1.73, and the film includes the sulfur atomic defect. When the film is treated under the H2S gas atmosphere at 1 atm by the method of the publicly-known technologies, the selenium atomic defect at a vicinity of the surface of the crystal grain is repaired by the sulfur atom, and the composition of the film becomes Cu0.81Al1.04Se1.73S0.15.
On the other hand, in a case where the film is treated by setting the pressure of the H2S to 10 atm, 50 atm, and 100 atm by the present invention, the sulfur atom is introduced into the tellurium atomic defect at the inner portion of the crystal grain, the composition of the film becomes Cu0.81Al1.04SexSy, and a value of x+y can be made to be equal to or more than 1.95 and equal to or less than 2. In this way, the sulfur atomic defect in the CuAlSe2 crystal can be repaired by the sulfur atom.
Incidentally, even when the CuAlSe2 film is treated by the present invention, composition ratios of Cu, Al, and Se of the film remain unchanged. In this way, the present invention can repair only the selenium atomic defect in the film by the sulfur atom without influencing on the atom which exists in the film before the treatment.
When the CuAlSe2 film is treated by the present invention, the sulfur atom is introduced to the selenium atomic defect in the film, and therefore, optical band gap of the film is increased. The CuAlSe2 film treated by the method of the present invention has the optical band gap which is larger than that of the CuAlSe2 film before treatment, and the value is from 2.76 through 2.77 eV.
As shown in the above embodiments, the chalcopyrite compound thin film defect can effectively be repaired by the sulfur atom by the present invention. Incidentally, although according to the embodiments described above, examples of repairing the selenium and the sulfur atomic defects in CuInSe2, CuGaSe2, AgInS2 and CuAlSe2 thin films and repairing the tellurium atomic defect in the CuGaTe2 thin film have been described, a similar effect is achieved also for other chalcopyrite compound thin films having the different composition.
Incidentally, although according to the embodiments described above, the explanation has been given of the ternary elements compound, a similar effect is achieved also for four-element compounds of, for example, CuInAlSe2 including In, Al as Y.
Also, although according to the explanation described above, the pressure of the pressurized sulfur gas is made to be equal to or more than 10 atm and equal to or less than 100 atm, a similar effect is achieved even when the pressure of the gas is made to be equal to or more than 2 atm and less than 10 atm. However, in this case, an annealing time period which is necessary for obtaining a chalcopyrite compound thin film having a prescribed chemical composition is prolonged. On the other hand, a chalcopyrite compound thin film having a prescribed chemical composition can be obtained by annealing for comparatively short time by making the pressure of the pressurized sulfur gas equal to or more than 10 atm and equal to or less than 100 atm.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2012/077675 | 10/26/2012 | WO | 00 |
