JP2018004535A - Inspection method for compound thin film solar cell, inspection system of the same, and compound thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method for a compound thin film solar cell capable of easily managing an amount of a void contained in an optical absorption layer, an inspection system of the same, and the compound thin film solar cell.SOLUTION: An inspection method for a compound thin film solar cell includes a step in which a measurement unit measures frequency characteristics of impedance of the compound thin film solar cell under a state where a prescribed voltage is applied between a first electrode and a second electrode, and a step in which a determination unit determines whether a Nyquist diagram based on measurement results of the measurement unit includes an inductive semi-circle in a low frequency domain along with a capacitive semi-circle in a high frequency domain or not.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a compound thin film solar cell including a light absorption layer made of a compound semiconductor, a compound thin film solar cell inspection system, and a compound thin film solar cell inspection method.

The compound thin film solar cell includes a layer made of a compound semiconductor as a light absorption layer. Especially, the compound thin film solar cell using the I-III-VI ₂ group compound semiconductor and the I- (I-IV) -VI ₄ group compound semiconductor as a p-type compound semiconductor which comprises a light absorption layer is light absorption. The layer can be formed from a relatively inexpensive and readily available material, and its manufacture is also easy, and research and development is actively underway.

Among these, a solar cell including a light absorbing layer made of a chalcogenite-based I- (I-IV) -VI group ₄ compound semiconductor containing S, Se together with Cu, Zn, Sn is referred to as a CZTS-based compound thin film solar cell. Is done. The CZTS-based light absorption layer has a composition of Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , or Cu ₂ ZnSn (S, Se) ₄ .

  The CZTS-based compound thin film solar cell has a laminated structure in which a first electrode layer, a light absorption layer made of the above-described p-type compound semiconductor, a buffer layer made of an n-type compound semiconductor, and a second electrode layer are arranged in this order. ing. When light enters the solar cell from the second electrode layer side with respect to the light absorption layer, electric power is generated based on an electromotive force caused by a pn junction that is a junction between the light absorption layer and the buffer layer.

  In such a compound thin film solar cell, for example, various defects such as a defect in an interface forming a pn junction and a defect in a semiconductor constituting a light absorption layer or a buffer layer cause a decrease in power generation characteristics in the compound thin film solar cell. It is known to be a factor. Various inspection methods for inspecting the presence or absence of such defects have been proposed (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2015-188273

  Voids, which are voids generated in the light absorption layer, are a type of defect that hinders the enhancement of the power generation characteristics of the compound thin film solar cell. In the production of compound thin-film solar cells, in order to maintain its quality, in addition to suppressing the generation of voids that hinder the improvement of power generation characteristics, non-destructive inspection of the amount of voids that hinders the improvement of power generation characteristics A method to manage by is required.

  An object of the present invention is to provide a compound thin film solar cell inspection method, a compound thin film solar cell inspection system, and a compound thin film solar cell that can easily manage the amount of voids contained in the light absorption layer. To do.

  In the method for inspecting a compound thin film solar cell that solves the above problem, the compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, and an n-type compound semiconductor. A buffer layer, and an intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, The light absorption layer, the buffer layer, and the second electrode layer are arranged in this order, and the inspection method applies a predetermined voltage between the first electrode layer and the second electrode layer. In the applied state, the measurement unit measures the frequency characteristics of the impedance of the compound thin-film solar cell, and the Nyquist diagram based on the measurement result of the measurement unit induces the low frequency region along with the capacitive semicircle in the high frequency region. Whether a sex semicircle is included Tough; and a determining step.

  In the inspection system for a compound thin film solar cell that solves the above problem, the compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, and an n-type compound semiconductor. A buffer layer, and an intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, The light absorption layer, the buffer layer, and the second electrode layer are arranged in this order, and the inspection system applies a predetermined voltage between the first electrode layer and the second electrode layer. A measurement unit for measuring the frequency characteristics of impedance in the compound thin film solar cell in an applied state, and a Nyquist diagram based on the measurement result of the measurement unit, together with a capacitive semicircle in the high frequency region and an inductive half in the low frequency region. Yen included And a determination unit that not.

  When the amount of voids in the light absorption layer is so large that good power generation characteristics cannot be obtained, an inductive semicircle in the low frequency region appears in the Nyquist diagram. Therefore, according to the above inspection method and inspection system, whether the amount of voids in the light absorption layer is small enough to obtain good power generation characteristics, that is, the compound thin film solar cell has good power generation characteristics. It is possible to determine whether or not it exists. Since the frequency characteristic of the impedance can be measured without destroying the compound thin film solar cell, such inspection can easily manage the amount of voids included in the light absorption layer.

  In the method for inspecting a compound thin film solar cell that solves the above problem, the compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, and an n-type compound semiconductor. A buffer layer, and an intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, The light absorption layer, the buffer layer, and the second electrode layer are arranged in this order, and the inspection method applies a predetermined voltage between the first electrode layer and the second electrode layer. The step of measuring the frequency characteristics of the impedance of the compound thin film solar cell in the applied state, the first circuit block is a parallel circuit of the first resistor and the first CPE, and the second circuit block is the second Resistor in parallel with 2nd and 3rd CPE A circuit in which the third CPE is connected in reverse phase with respect to the first CPE and the second CPE, and a series circuit of a third resistor, the first circuit block, and the second circuit block is a circuit model. It is determined whether or not a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristic of the third CPE by fitting the measurement result of the measuring unit and the circuit model. A step of determining by the unit.

  In the inspection system for a compound thin film solar cell that solves the above problem, the compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, and an n-type compound semiconductor. A buffer layer, and an intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, The light absorption layer, the buffer layer, and the second electrode layer are arranged in this order, and the inspection system applies a predetermined voltage between the first electrode layer and the second electrode layer. A measurement unit that measures the frequency characteristics of the impedance of the compound thin film solar cell in an applied state, the first circuit block is a parallel circuit of a first resistor and a first CPE, and the second circuit block is a second resistor. Same as 2nd CPE and 3rd CPE A circuit in which the third CPE is connected in an opposite phase to the first CPE and the second CPE, and a series circuit of a third resistor, the first circuit block, and the second circuit block is a circuit model. It is determined whether or not a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristic of the third CPE by fitting the measurement result of the measuring unit and the circuit model. A determination unit.

  When the amount of voids in the light absorption layer is so large that good power generation characteristics cannot be obtained, a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristics of the third CPE. Therefore, according to the above inspection method and inspection system, whether the amount of voids in the light absorption layer is small enough to obtain good power generation characteristics, that is, the compound thin film solar cell has good power generation characteristics. It is possible to determine whether or not it exists. Since the frequency characteristic of the impedance can be measured without destroying the compound thin film solar cell, such inspection can easily manage the amount of voids included in the light absorption layer.

  A compound thin film solar cell that solves the above problems includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, An intermediate layer including an element constituting one electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, and the buffer. A thin film compound solar cell having a structure in which a layer and the second electrode layer are arranged in this order, and a predetermined AC voltage of 0.3 V or more is applied between the first electrode layer and the second electrode layer The Nyquist diagram representing the frequency characteristics of impedance in the compound thin film solar cell measured in the above state includes only the capacitive semicircle in the high frequency region.

  According to the said structure, the amount of voids which a light absorption layer has is small, and the compound thin film solar cell with which favorable electric power generation characteristics are acquired is realizable. And since the frequency characteristics of impedance can be measured without destroying the compound thin film solar cell, the light absorption layer is formed by using the presence or absence of an inductive semicircle in the low frequency region in the Nyquist diagram as an index. It is possible to easily manage the amount of voids to be included.

  A compound thin film solar cell that solves the above problems includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, An intermediate layer including an element constituting one electrode layer and a part of the element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, and the buffer. A compound thin film solar cell having a structure in which a layer and the second electrode layer are arranged in this order, wherein a parallel circuit of a first resistor and a first CPE is a first circuit block, and a second resistor and a second CPE The parallel circuit is a second circuit block, and a series circuit of a third resistor, the first circuit block, and the second circuit block is a circuit model, and is between the first electrode layer and the second electrode layer. Measured with a predetermined AC voltage of 0.3V or higher applied The said compound film equivalent circuit of the compound thin film solar cell conforming to the frequency characteristic of the impedance in a solar cell, which is the circuit model.

  According to the said structure, the amount of voids which a light absorption layer has is small, and the compound thin film solar cell with which favorable electric power generation characteristics are acquired is realizable. And since the frequency characteristic of impedance can be measured without destroying the compound thin film solar cell, it is related to the amount of voids included in the light absorption layer by using the configuration of an equivalent circuit suitable for the measurement result as an index. Management can be performed easily.

  According to the present invention, it is possible to easily manage the amount of voids in the light absorption layer.

Sectional drawing which shows the cross-sectional structure of a compound thin film solar cell about one Embodiment of a compound thin film solar cell. It is a figure which shows the frequency characteristic of the impedance in a compound thin film solar cell, Comprising: The figure which shows an example which represented the measurement result in case an applied voltage is very small as a Nyquist diagram. Compound thin film solar cell is a diagram showing the frequency characteristics of impedance in a compound thin film solar cell, the applied voltage is more than a predetermined value, and the amount of voids in the light absorption layer is so large that good power generation characteristics cannot be obtained The figure which shows an example which represented the measurement result of as a Nyquist diagram. The figure which shows the image which image | photographed the cross section of the light absorption layer of a compound thin film solar cell using the scanning electron microscope. The figure which shows the equivalent circuit model of the compound thin film solar cell in which the electrical property by the void which a light absorption layer has was considered. The figure which represented the measurement result of the frequency characteristic of the impedance in the compound thin film solar cell of the test example 1 as a Nyquist diagram. The figure which represented the measurement result of the frequency characteristic of the impedance in the compound thin film solar cell of Test Example 2 as a Nyquist diagram. The figure which represented the measurement result of the frequency characteristic of the impedance in the compound thin film solar cell of Test Example 3 as a Nyquist diagram. The figure which represented the measurement result of the frequency characteristic of the impedance in the compound thin film solar cell of Test Example 4 as a Nyquist diagram.

  With reference to FIG. 1, one Embodiment of a compound thin film solar cell, the test | inspection method and test | inspection system of a compound thin film solar cell is described.

[Configuration of Compound Thin Film Solar Cell]
As shown in FIG. 1, the compound thin film solar cell 10 includes a substrate 11, a first electrode layer 12, an intermediate layer 13, a light absorption layer 14, a buffer layer 15, and a second electrode layer 16. The first electrode layer 12, the intermediate layer 13, the light absorption layer 14, the buffer layer 15, and the second electrode layer 16 are arranged in this order from a position close to the substrate 11, and these layers are positioned on the substrate 11. Yes.

  As the substrate 11, for example, a glass substrate, a metal plate, a resin film, or the like is used. The first electrode layer 12 is made of, for example, Mo (molybdenum). The thickness of the first electrode layer 12 is not particularly limited, but is preferably 200 nm or more.

The light absorption layer 14 is composed of a CZTS-based compound semiconductor that is one of p-type compound semiconductors, that is, a CZTS semiconductor. The CZTS semiconductor is composed of at least one element of group VIB (group 16) S (sulfur) and group VIB (group 16) Se (selenium), group IB (group 11) Cu (copper), group IIB. This is a compound semiconductor containing three elements of (Group 12) Zn (zinc) and Group IVB (Group 14) Sn (tin). That, _{CZTS-semiconductors,} IB 2 - is (IIB-IVB) -VIB ₄ group compound semiconductor. Specifically, the light absorption layer 14 has a composition of Cu ₂ ZnSnS _x Se _4-x (0 ≦ x ≦ 4). The thickness of the light absorption layer 14 is not particularly limited, but considering the extinction coefficient of the material constituting the light absorption layer 14, it is preferable that the absorption coefficient of the light absorption layer 14 is good when it is 1 μm or more and 3 μm or less.

The intermediate layer 13 is sandwiched between the first electrode layer 12 and the light absorption layer 14 and is in contact with each of these layers. The intermediate layer 13 includes Mo and at least one element of S and Se that is included in the light absorption layer 14. Specifically, the intermediate layer 13 has a composition of MoS _y Se _2-y (0 ≦ y ≦ 2).

  The thickness of the intermediate layer 13 is preferably 10 nm or more and 300 nm or less. If the thickness of the intermediate layer 13 is 10 nm or more, it is possible to suppress the separation of the layers on the front and back of the intermediate layer 13 due to the temperature change. Specifically, if the thickness of the intermediate layer 13 is 10 nm or more, the intermediate layer 13 has resistance to withstand a thermal shock test specified by JIS standard (JIS C 60068-2-14: 2011). Moreover, if the thickness of the intermediate layer 13 is 300 nm or less, the intermediate layer 13 can be prevented from obstructing the extraction of current, so that the photoelectric conversion efficiency can be prevented from decreasing.

The buffer layer 15 is in contact with the light absorption layer 14 and is made of an n-type compound semiconductor. For example, the buffer layer 15 is made of CdS, In ₂ S ₃ , Zn (S, O, OH), or the like. That is, the light absorption layer 14 and the buffer layer 15 form a pn junction by heterojunction. The thickness of the buffer layer 15 is preferably 15 nm or more in order to form a good pn junction. On the other hand, when the thickness of the buffer layer 15 is increased, the buffer layer 15 absorbs light and the light reaching the light absorbing layer 14 is reduced. In order to suppress such loss, the thickness of the buffer layer 15 is: It is preferable that it is 300 nm or less.

  The second electrode layer 16 constitutes a pair of electrodes together with the first electrode layer 12 and functions as an electrode for taking out current from the compound thin film solar cell 10. The material for forming the second electrode layer 16 is not particularly limited as long as the second electrode layer 16 can function as such an electrode. For example, an n-type semiconductor such as ZnO to which Al (aluminum) is added is used. It is preferable that it is comprised from ZnO which is. The thickness of the second electrode layer 16 is not particularly limited, but is preferably 50 nm or more and 1 μm or less.

  A take-out electrode made of Al or Ag (silver) may be disposed on the second electrode layer 16. The extraction electrode makes it easier to extract the current. The thickness of the extraction electrode is not particularly limited, but is preferably 50 nm or more and 1 μm or less.

  In such a compound thin film solar cell 10, light is incident on the light absorption layer 14 from the second electrode layer 16 side, and an electromotive force generated due to a pn junction formed by the light absorption layer 14 and the buffer layer 15. Power is generated based on

  In addition to the above-described layers, the compound thin film solar cell 10 may include a member for increasing the strength of the compound thin film solar cell 10 such as a cover glass or a protective film.

[Analysis by AC impedance measurement]
The characteristic of the compound thin film solar cell 10 obtained by measuring and analyzing the frequency characteristic of the impedance of the compound thin film solar cell 10 described above by using an electrochemical impedance method (EIS: Electrochemical Impedance Spectroscopy) will be described.
The impedance is measured under the following conditions at room temperature in the dark.
Measurement device: Frequency characteristic analyzer (FRA: Frequency Response Analyzer) [Device name: FRA5087]
・ Measurement frequency: 0.1mHz to 1MHz
・ Applied voltage: AC10mV or AC0.3V

  FIG. 2 shows an example of measurement results of impedance frequency characteristics when the applied voltage is 10 mV, expressed as a Nyquist diagram with the real part of the impedance shown on the horizontal axis and the imaginary part shown on the vertical axis. In the Nyquist diagram, two capacitive semicircles appear, and in detail, in a region where the vertical axis, which is the imaginary axis, is negative, a relatively small semicircular arc A and a relatively large semicircle A curve having a shape in which the arc B is fused. Of these, the small arc A portion corresponds to the characteristics of the interface portion between the intermediate layer 13 and the light absorption layer 14, and the large arc B portion corresponds to the characteristics of the interface portion between the light absorption layer 14 and the buffer layer 15. Equivalent to. Further, the portion up to the end of the arc A on the horizontal axis, which is the real axis, corresponds to a resistance component including the wiring resistance of the measurement circuit, the resistance of the extraction electrode, the bulk resistance of each layer, and the like.

  It should be noted that each of the arc A portion and the arc B portion of the Nyquist diagram is attributed to either the interface between the intermediate layer 13 and the light absorption layer 14 or the interface between the light absorption layer 14 and the buffer layer 15. Whether it is a thing is judged by the measurement which applies a DC voltage to the compound thin film solar cell 10. FIG. That is, when the DC voltage applied to the compound thin-film solar cell 10 is gradually increased and the frequency characteristics of impedance are measured, the semicircular portion where the fluctuation of the resistance component increases is the light absorption layer 14 and the buffer layer that form a pn junction. 15 is determined to correspond to the interface portion.

  FIG. 3 is an example in which the measurement result of the frequency characteristics of impedance when the applied voltage is AC 0.3 V is represented as a Nyquist diagram, and the amount of voids in the light absorption layer 14 provides good power generation characteristics. The measurement result with respect to the compound thin film solar cell 10 so many that it cannot be shown is shown. In the Nyquist diagram, two capacitive semicircles and one inductive semicircle appear, that is, in addition to arc A and arc B, a semicircular arc C is formed in a lower frequency region than these arcs. appear. That is, the arc C appears in a region where the imaginary axis is positive following the arc B.

  The arc A and the arc B are smaller than when the applied voltage is AC 10 mV, and it may be difficult to identify the boundary visually. Since the interface between the light absorption layer 14 and the buffer layer 15 is a pn junction interface, the degree of decrease in the resistance component at this interface due to the increase in applied voltage is the resistance component at the interface between the intermediate layer 13 and the light absorption layer 14. Is greater than the degree of decrease.

  When the amount of voids included in the light absorption layer 14 is small enough not to affect the power generation characteristics, the arc C does not appear in the Nyquist diagram even when the applied voltage is AC 0.3V.

  FIG. 4 shows an example of an image obtained by photographing a cross section of the light absorption layer 14 having voids with a scanning electron microscope. A void existing in the light absorption layer 14 is a void Vd. Such voids Vd are different in the movement tendency of each element in the precursor layer when the precursor layer of the light absorption layer 14 is heat-treated to form the light absorption layer 14, and each layer at the time of shrinkage after the heat treatment. This is caused by the difference in thermal expansion coefficient.

  Since the void Vd is a void, if the void Vd is present in the light absorption layer 14, the path of electrical carrier movement in the light absorption layer 14 is hindered by the void Vd portion. Specifically, the movement path of holes generated at the pn junction interface formed by the light absorption layer 14 and the buffer layer 15 and going to the first electrode layer 12 is obstructed. If the ratio of the void Vd in the light absorption layer 14 is equal to or greater than a certain value, the influence of the inhibition of carrier movement by the void Vd becomes large, and good characteristics as the power generation characteristics of the compound thin film solar cell 10 cannot be obtained. .

  As is generally known as the IV characteristic of a solar cell, in the compound thin film solar cell 10, it becomes difficult to extract current when the voltage increases. Therefore, in the compound thin film solar cell 10 with a lot of voids Vd, as the voltage increases, the influence of the inhibition of carrier movement by the voids Vd on the ease of current flow becomes easier to see, and a voltage higher than a predetermined value is applied. When this occurs, it becomes apparent and appears as an arc C in the Nyquist diagram. That is, the portion surrounding the void Vd in the light absorption layer 14 is regarded as an inductor component when viewed macroscopically.

  FIG. 5 shows an equivalent circuit of the compound thin-film solar cell 10 in which the arc C appears in the Nyquist diagram as shown in FIG. 3, that is, the amount of voids in the light absorption layer 14 is large.

  The equivalent circuit 100 is a series circuit in which a circuit resistance (Rs), a first circuit block CB1, and a second circuit block CB2 are connected in series. The first circuit block CB1 is a parallel circuit in which a first resistor (R1) and a first CPE (CPE1) are connected in parallel, and the second circuit block CB2 is a second resistor (R2) and a second CPE (CPE2). And a third CPE (CPE3) are connected in parallel.

  The first circuit block CB1 is an equivalent circuit corresponding to the portion of the arc A in the Nyquist diagram, that is, showing the characteristics of the interface between the intermediate layer 13 and the light absorption layer 14. Of the second circuit block CB2, the parallel circuit composed of the second resistor and the second CPE corresponds to the arc B portion in the Nyquist diagram, that is, exhibits the characteristics of the interface between the light absorption layer 14 and the buffer layer 15. It is an equivalent circuit. Of the second circuit block CB2, the third CPE is an equivalent circuit corresponding to the portion of the arc C in the Nyquist diagram, that is, an equivalent circuit showing characteristics due to voids in the light absorption layer. The circuit resistance Rs indicates a resistance component including the wiring resistance of the measurement circuit, the resistance of the extraction electrode, the bulk resistance of each layer, and the like.

Here, CPE (Constant Phase Element) is an element whose impedance is represented by “Z _CPE = 1 / (jω) ^p T” using a CPE index p and a CPE constant T. Note that j represents an imaginary unit, and ω = 2πf (f is the frequency [Hz] of the applied AC voltage). In the equivalent circuit 100, the third CPE is connected so as to have an opposite phase to the first CPE and the second CPE.

  The CPE index p is a value indicating how much the arc in the Nyquist diagram is deviated from the perfect semicircle, that is, how much the arc is inclined from the complete semicircle. In the first CPE and the second CPE, A positive value between 0 and 1, and a negative value between -1 and 0 in the third CPE. For example, in the first CPE and the second CPE, when the CPE index p is 1, the arc is a perfect semicircle, and as the CPE index p approaches 0, the arc becomes a collapsed semicircle. That is, when the CPE index p is 1, the CPE behaves as a capacitor, and the CPE constant T corresponds to the capacitance component of this ideal capacitor.

  When the amount of voids included in the light absorption layer 14 is small enough not to affect the power generation characteristics, or when the applied voltage is very small such as AC 10 mV, the equivalent circuit of the compound thin film solar cell 10 is the above equivalent circuit. A circuit in which the third CPE is deleted from 100, that is, the second circuit block CB2 is a circuit that is a parallel circuit of the second resistor and the second CPE.

  By performing fitting using the Nyquist diagram showing the measurement result of the frequency characteristics of the impedance of the compound thin film solar cell 10 and such an equivalent circuit, the structural characteristics of the compound thin film solar cell 10 can be analyzed.

  For example, when fitting is performed using a Nyquist diagram obtained when a very small applied voltage such as AC 10 mV is applied, and an equivalent circuit having no third CPE, the resistance value of the circuit resistance, The resistance value of the first resistor, the CPE index p and CPE constant T of the first CPE, the resistance value of the second resistor, the CPE index p and CPE constant T of the second CPE are calculated.

  The resistance value of the first resistance indicates the magnitude of resistance at the interface between the intermediate layer 13 and the light absorption layer 14 and in the vicinity of the interface. That this resistance is small suggests that the resistance in the compound thin film solar cell 10 resulting from the joining state of the intermediate | middle layer 13 and the light absorption layer 14 is small, and it becomes easy to take out an electric current, so that this resistance is small. The resistance value of the second resistance indicates the magnitude of resistance at the interface between the light absorption layer 14 and the buffer layer 15 and in the vicinity of the interface. A large resistance indicates that a good pn junction with few defects and little leakage current is formed in the semiconductor.

  The value of the CPE index p of the first CPE is such that the closer the CPE index p is to 1, the smoother the surface shape of the interface between the intermediate layer 13 and the light absorbing layer 14 is. In each layer of the intermediate layer 13 and the light absorbing layer 14 It shows that the composition is uniform. The value of the CPE index p of the second CPE is such that the closer the CPE index p is to 1, the smoother the surface shape of the interface between the light absorption layer 14 and the buffer layer 15 is, and in each layer of the light absorption layer 14 and the buffer layer 15 It shows that the composition is uniform. The smoother the surface shape of the interface between the light absorption layer 14 and the buffer layer 15, and the more uniform the composition of each layer of the light absorption layer 14 and the buffer layer 15, the more the light absorption layer 14 and the buffer layer 15 As a result, a good pn junction is formed, so that the power generation characteristics of the compound thin-film solar cell 10 are improved.

  Further, fitting is performed using the Nyquist diagram obtained when a voltage of a predetermined value or more is applied and the equivalent circuit 100, and the CPE index p and CPE constant T of the third CPE calculated by this fitting are used. Is in an appropriate range indicating the presence of the third CPE, whether or not the amount of voids of the light absorption layer 14 is so large that good power generation characteristics cannot be obtained, that is, the compound thin film solar cell 10 It is possible to determine whether or not the battery has good power generation characteristics.

[Compound thin film solar cell inspection method and inspection system]
An inspection method and inspection system for the compound thin film solar cell 10 will be described. In the method for inspecting the compound thin film solar cell 10, the measurement unit included in the inspection system measures the frequency characteristics of the impedance in the compound thin film solar cell 10, and then the determination unit included in the inspection system uses the measurement result of the measurement unit. Analyze and judge. There are two types of inspection methods, the first inspection method and the second inspection method, for the inspection method of the compound thin film solar cell 10, and which inspection method is used depends on the required apparatus configuration and required inspection accuracy. It may be determined as appropriate in consideration of the above.

  The first inspection method of the compound thin film solar cell 10 is the frequency of the impedance of the compound thin film solar cell 10 in a state where a voltage of a predetermined value or more is applied between the first electrode layer 12 and the second electrode layer 16. Whether or not the characteristic measuring step and the Nyquist diagram based on the measurement result include the arc A and the arc B which are capacitive semicircles in the high frequency region and the arc C which is an inductive semicircle in the low frequency region Determining. The voltage to be applied may be a voltage at which an arc C appears in the Nyquist diagram obtained as a measurement result for the compound thin film solar cell 10 having a large amount of voids such that good power generation characteristics cannot be obtained. 3V or more. The applied voltage is preferably not more than the open circuit voltage. The reason is that when a voltage higher than the open circuit voltage is applied, a current in the direction opposite to the current that flows originally flows through the solar cell, and the solar cell is loaded, causing a failure.

  The conditions at the time of measuring the frequency characteristics of the impedance are based on the conditions described in the description of the analysis by the AC impedance measurement described above based on the electrochemical impedance method.

  When the arc C appears in the Nyquist diagram based on the measurement results, the amount of voids in the light absorption layer 14 is so large that good power generation characteristics cannot be obtained. It is judged that it does not have sufficient performance. On the other hand, when the arc C does not appear in the Nyquist diagram based on the measurement result, the amount of voids of the light absorption layer 14 is small enough to obtain good power generation characteristics, and the compound thin film solar cell 10 has sufficient power generation characteristics. It is judged that it has the performance.

  The second inspection method of the compound thin film solar cell 10 includes a step of measuring the frequency characteristics of the impedance of the compound thin film solar cell 10 in a state where a voltage having a magnitude greater than the predetermined value is applied, and the equivalent circuit 100 as a circuit model. And determining whether a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristic of the third CPE by fitting the measurement result of the frequency characteristic of the impedance and the circuit model. including. The numerical values indicating the characteristics of the third CPE are the CPE index p and the CPE constant T of the third CPE, and these numerical values are regions where the impedance spectrum corresponding to the third CPE is an arc C in the Nyquist diagram and the imaginary axis is positive. When the numerical value is a value appearing in the above, it is determined that the value is within a predetermined range indicating the presence of the third CPE.

  That is, the difference between the Nyquist diagram showing the measurement result of the frequency characteristic of the impedance and the Nyquist diagram obtained from the equivalent circuit 100 is fitted by an algorithm that makes the numerical value indicating the characteristic of each circuit element equal to or less than a predetermined value. If possible, it is determined that the third CPE exists.

  When the numerical value indicating the characteristic of the third CPE is within a predetermined range indicating the presence of the third CPE, that is, when it is determined that the equivalent circuit that matches the measurement result of the frequency characteristic of the impedance has the third CPE, the light absorption The amount of voids in the layer 14 is so large that good power generation characteristics cannot be obtained, and it is determined that the compound thin-film solar cell 10 does not have sufficient performance with respect to power generation characteristics. On the other hand, when the numerical value indicating the characteristic of the third CPE is not within the predetermined range indicating the presence of the third CPE, that is, it is determined that the equivalent circuit that matches the measurement result of the frequency characteristic of the impedance does not have the third CPE. When the amount of voids in the light absorption layer 14 is small enough to obtain good power generation characteristics, the compound thin-film solar cell 10 is determined to have sufficient performance with respect to power generation characteristics.

  In the first inspection method, the amount of voids can be inspected without fitting with an equivalent circuit, and in the second inspection method, based on the electrical analysis of the curve appearing in the Nyquist diagram. Thus, the amount of voids can be inspected.

  The inspection of the compound thin-film solar cell 10 is performed in cooperation with a measuring device such as a frequency characteristic analyzer and an arithmetic device, and an inspection system is configured from these devices. The arithmetic device is a computer that includes a control unit and a storage unit, and the control unit performs various arithmetic processes based on programs, data, and the like stored in the storage unit. Specifically, the measurement of the frequency characteristic of the impedance is performed by a measuring device. Then, using the data sent from the measuring device to the computing device, the computing device creates the Nyquist diagram in the first inspection method, determines whether or not the arc C appears in the Nyquist diagram, and The calculation of the numerical value indicating the characteristic of the third CPE in the second inspection method and the determination as to whether or not the numerical value is within a predetermined range indicating the presence of the third CPE. That is, the measurement device constitutes a measurement unit, and the arithmetic device constitutes a determination unit. The program stored in the storage unit includes a program for causing the control unit to execute such determination. Note that one inspection device may be configured by the measurement device and the arithmetic device.

  As described above, the light absorption layer 14 is determined by determining the presence or absence of the arc C in the Nyquist diagram or the presence or absence of the third CPE in the equivalent circuit compatible with the Nyquist diagram using the measurement result of the frequency characteristic of the impedance. It is possible to inspect whether or not the amount of voids of the battery satisfies the criteria for obtaining good power generation characteristics. Since the frequency characteristics of the impedance can be measured without destroying the compound thin film solar cell 10, management regarding the amount of voids included in the light absorption layer 14 can be easily performed by such inspection.

[Method for producing compound thin-film solar cell]
A method for producing the above-described compound thin film solar cell 10 will be described.
First, the first electrode layer 12 is formed on the upper surface of the substrate 11. The first electrode layer 12 is formed using, for example, sputtering, vapor deposition, and CVD (Chemical Vapor Deposition).

  Subsequently, a precursor layer of the light absorption layer 14 is formed on the upper surface of the first electrode layer 12. The precursor layer is a layer containing at least Cu, Zn, and Sn among the elements constituting the light absorption layer 14, and is formed by, for example, a solution coating method, sputtering, electron beam evaporation, or the like. As an example of the solution coating method, there is a method of forming a precursor layer by applying an ink containing nanoparticles.

  When the precursor layer is formed by applying the ink containing the nanoparticles, first, the light absorbing layer forming ink containing the nano-sized particles composed of the constituent elements of the light absorbing layer 14 is prepared. Then, the light absorbing layer forming ink is applied on the upper surface of the first electrode layer 12 to form a film containing nanoparticles, and this film is dried to be included in the applied film. The solvent is removed. Thereby, the coating film as a precursor layer is formed.

  When sputtering or electron beam evaporation is used, a layer containing Cu, Zn, and Sn is formed on the upper surface of the first electrode layer 12 as a precursor layer. A precursor layer having such a composition may be formed by a solution coating method.

  Subsequently, the precursor layer is heated in an atmosphere containing at least one element of S and Se, whereby sulfidation and selenization are performed, and the light absorption layer 14 is formed. In the heating step, crystallization of the precursor layer proceeds by applying heat to the precursor layer.

  The precursor layer is heated by annealing using a heating furnace or rapid thermal annealing (RTA), and the maximum temperature of the heat treatment is, for example, a predetermined temperature within a range of 400 ° C. or more and 660 ° C. or less. During this heat treatment, the intermediate layer 13 is formed by the reaction of the elements contained in the first electrode layer 12 with the elements contained in the precursor layer of the light absorption layer 14 and the atmosphere of the heat treatment. Properties such as thickness and composition distribution of each of the intermediate layer 13 and the light absorption layer 14 can be adjusted by the temperature and time of heat treatment, the concentration of elements contained in the atmosphere of the heat treatment, and the like.

  The buffer layer 15 is formed on the upper surface of the light absorption layer 14 using, for example, a CBD (Chemical Bath Deposition) method or the like. The second electrode layer 16 is formed on the upper surface of the buffer layer 15 by, for example, CVD or sputtering.

[Example]
The compound thin-film solar cell, the inspection method, and the inspection system described above will be described using specific examples.
<Manufacture of compound thin film solar cells>
Samples of four compound thin film solar cells of Test Example 1 to Test Example 4 were produced by the following manufacturing method.
[Formation of first electrode layer]
A first electrode layer made of Mo was formed on the upper surface of the soda lime glass substrate by sputtering.

[Adjustment of light absorbing layer forming ink]
A first solution was prepared by dissolving CuI (0.405 g), ZnI ₂ (0.447 g), and SnI ₄ (0.877 g) in 500 ml of pyridine. In addition, a _second solution was prepared by dissolving Na ₂ Se (0.658 g) in 125 ml of methanol. The first solution and the second solution were mixed, and this mixed solution was reacted at 0 ° C. in a nitrogen atmosphere to generate Cu—Zn—Sn—Se nanoparticles. The reaction mixture was filtered to remove Cu—Zn—Sn—Se nanoparticles and washed with methanol. Cu-Zn-Sn-Se nanoparticles after washing and thiourea are mixed so that the mass ratio of the nanoparticles to thiourea is 3: 2, and pyridine and methanol are added to the mixture, and Cu- A light absorbing layer forming ink containing Zn—Sn—Se nanoparticles was prepared.

[Formation of light absorption layer and intermediate layer]
A light absorbing layer forming ink was applied to the upper surface of the first electrode layer using a spray method, and the solvent contained in the light absorbing layer forming ink was evaporated to form a coating film as a precursor layer. And the laminated body comprised from a board | substrate, a 1st electrode layer, and a precursor layer was put into the heat processing furnace with the sulfur powder, and it heated at 580 degreeC for 20 minutes in S atmosphere. As a result, the precursor layer was subjected to sulfurization treatment, and a light absorption layer and an intermediate layer sandwiched between the first electrode layer and the light absorption layer were formed. The light absorption layer mainly contains Cu, Zn, Sn, and S, and the intermediate layer mainly contains Mo and S. The light absorption layer contains a small amount of Se derived from nanoparticles contained in the light absorption layer forming ink. The thickness of the light absorption layer is 2 μm.

[Formation of buffer layer]
A mixture containing 0.0015 M cadmium sulfate (CdSO ₄ ), 0.0075 M thiourea (NH ₂ CSNH ₂ ), and 1.5 M aqueous ammonia (NH ₄ OH) was heated to 67 ° C. And the buffer layer which consists of CdS was formed in the upper surface of a light absorption layer by immersing the laminated body provided with the light absorption layer mentioned above in a liquid mixture. The thickness of the buffer layer is 100 nm.

[Formation of second electrode layer]
A second electrode layer made of ZnO was formed on the upper surface of the buffer layer. The thickness of the second electrode layer is 50 nm. Further, an extraction electrode made of Al was formed on the upper surface of the second electrode layer by vapor deposition. The thickness of the extraction electrode is 200 nm, and the area is 1.5 mm × 1.5 mm.

<Impedance measurement and analysis of measurement results>
For the compound thin-film solar cell of each test example, the frequency characteristic of impedance is measured, and the measurement result is represented in a Nyquist diagram, and the CPE index p of the third CPE is calculated by fitting the Nyquist diagram with the equivalent circuit 100. This confirmed the presence or absence of the third CPE.
The frequency characteristic of the impedance is measured by using a frequency characteristic analyzer [device name: FRA5087] and applying AC 0.3V using a frequency of 0.1 mHz (millihertz) to 1 MHz (megahertz) in the dark and at room temperature. I went.

<Calculation of void fraction>
About the compound thin film solar cell of each test example, the cross section of the light absorption layer was observed using the scanning electron microscope, and the void rate which is a parameter which shows the quantity of the void in a light absorption layer was computed. In order to easily observe the cross section of the light absorption layer, the cross section was polished flat using an ion milling method.

  The void ratio was calculated by the following method. That is, a plurality of analysis regions having a size including the entire light absorption layer in the thickness direction are set in the cross section, and the area occupied by the void in the analysis region is measured by image analysis for each analysis region. And about each analysis area | region, the area ratio which represented the ratio of the occupation area of the void with respect to the area of the whole light absorption layer in percentage is calculated. A value obtained by averaging the area ratios of all analysis regions is the void ratio. The analysis region is, for example, a rectangular region of 3 μm in the thickness direction of the light absorption layer and 5 μm in a direction perpendicular to the thickness direction, and three analysis regions are set in the cross section of the light absorption layer.

<Evaluation of power generation characteristics>
About the compound thin film solar cell of each Example and each comparative example, using a standard solar simulator, short-circuit current density, open-circuit voltage at the time of irradiation with simulated sunlight (light intensity: 100 mW / cm ² , air mass: 1.5), The fill factor and photoelectric conversion efficiency were measured and calculated.

<Result>
6 to 9 are Nyquist diagrams showing the measurement results of impedance frequency characteristics for the compound thin film solar cells of each test example, FIG. 6 is a Nyquist diagram of Test Example 1, and FIG. 7 is a test example. 8 shows a Nyquist diagram of Test Example 3, FIG. 8 shows a Nyquist diagram of Test Example 4, and FIG. Table 1 shows the measurement results of photoelectric conversion efficiency, short-circuit current density, open-circuit voltage, and fill factor as power generation characteristics for each test example, along with the void ratio and presence / absence of the third CPE determined as a result of the fitting. Indicates.

  As shown in FIGS. 6 to 9 and Table 1, the Nyquist diagrams of Test Examples 1 and 2 do not show the arc C, which is an inductive semicircle in the low frequency region, and the fitting result includes the third CPE. Indicates that no. On the other hand, in the Nyquist diagrams of Test Examples 3 and 4, an arc C which is an inductive semicircle in the low frequency region appears, and the fitting result indicates that the third CPE exists.

  Test Examples 1 and 2 have a lower void ratio and higher power generation characteristics such as short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency than Test Examples 3 and 4. In particular, with respect to photoelectric conversion efficiency, Test Examples 1 and 2 are significantly higher than Test Examples 3 and 4.

  From these results, a phenomenon in which the void inhibits carrier movement between the void ratios of Test Examples 1 and 2 and Test Examples 3 and 4 is observed as an inductor component that appears as an arc C in the Nyquist diagram. It is suggested that there is a void ratio that starts to be generated, and that a compound thin film solar cell having a void ratio higher than this void ratio cannot obtain good power generation characteristics.

  Therefore, the amount of voids in the light absorption layer is evaluated according to the presence or absence of the arc C in the Nyquist diagram or the presence or absence of the third CPE indicated by the fitting result, and the compound thin film solar cell has the performance of obtaining good power generation characteristics. It can be inspected whether or not. And if it is a compound thin film solar cell whose Nyquist diagram does not have the arc C, that is, a compound thin film solar cell whose fitting result indicates that the third CPE does not exist, good power generation characteristics can be obtained.

The light absorption layer is not limited to the case where the light absorption layer is formed of a CZTS semiconductor, and for example, even if the light absorption layer is formed of another p-type compound semiconductor such as a CIGS compound semiconductor, the compound thin film Since the solar cell has the same structure and power generation mechanism as the CZTS-based compound thin film solar cell, the relationship between the measurement result of the impedance frequency characteristics, the void ratio, and the power generation characteristics may be the same as described above. It is suggested. When the light absorption layer is composed of a CIGS semiconductor, the light absorption layer has a composition of CuIn _x Ga _1-x Se ₂ (0 <x <1) and includes a precursor layer containing an element included in the light absorption layer. However, by heating in an atmosphere containing Se, the light absorption layer and the intermediate layer are formed. In addition, voids can be formed during such heat treatment, as in the case of CZTS-based compound thin film solar cells.

As described above, according to the embodiment, the effects listed below can be obtained as described with reference to the examples.
(1) Impedance frequency characteristics of the compound thin-film solar cell 10 are measured in a state where a predetermined voltage is applied and expressed in a Nyquist diagram, and whether or not an inductive semicircle in a low frequency region appears in the Nyquist diagram By determining, whether or not the amount of voids of the light absorption layer 14 is so large that good power generation characteristics cannot be obtained, that is, whether or not the compound thin film solar cell 10 has good power generation characteristics. Judgment is possible. Since the frequency characteristics of the impedance can be measured without destroying the compound thin film solar cell 10, management regarding the amount of voids included in the light absorption layer 14 can be easily performed by such inspection. In the compound thin-film solar cell 10 in which the Nyquist diagram includes only the capacitive semicircle in the high frequency region, good power generation characteristics are obtained.

  (2) The frequency characteristic of the impedance of the compound thin film solar cell 10 is measured in a state where a predetermined voltage is applied, and the numerical result indicating the characteristic of the third CPE is obtained by fitting the measurement result with the circuit model which is the equivalent circuit 100. By determining whether or not a numerical value within a predetermined range indicating the presence of the third CPE is calculated, whether or not the amount of voids in the light absorption layer 14 is so large that good power generation characteristics cannot be obtained, That is, it is possible to determine whether or not the compound thin-film solar cell 10 has good power generation characteristics. Since the frequency characteristics of the impedance can be measured without destroying the compound thin film solar cell 10, management regarding the amount of voids included in the light absorption layer 14 can be easily performed by such inspection. As the numerical value indicating the characteristic of the third CPE, the compound thin-film solar cell 10 in which the numerical value within the predetermined range indicating the presence of the third CPE is not calculated, that is, the equivalent circuit suitable for the frequency characteristic of the impedance has the third CPE. In the compound thin film solar cell 10 without, good power generation characteristics can be obtained.

  DESCRIPTION OF SYMBOLS 10 ... Compound thin film solar cell, 11 ... Board | substrate, 12 ... 1st electrode layer, 13 ... Intermediate | middle layer, 14 ... Light absorption layer, 15 ... Buffer layer, 16 ... 2nd electrode layer, 100 ... Equivalent circuit, CB1 ... 1st Circuit block, CB2 ... second circuit block, R1 ... first resistor, R2 ... second resistor, Rs ... circuit resistance, CPE1 ... first CPE, CPE2 ... second CPE, CPE3 ... third CPE.

Claims (6)

A method for inspecting a compound thin film solar cell,
The compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, and the first electrode layer. An intermediate layer including a constituent element and a part of an element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second layer. The electrode layer has a structure arranged in this order,
A step of measuring a frequency characteristic of impedance of the compound thin-film solar cell in a state where a predetermined voltage is applied between the first electrode layer and the second electrode layer;
The determination unit determines whether or not the Nyquist diagram based on the measurement result of the measurement unit includes a capacitive semicircle in the high frequency region and an inductive semicircle in the low frequency region. Battery inspection method. A method for inspecting a compound thin film solar cell,
The compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, and the first electrode layer. An intermediate layer including a constituent element and a part of an element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second layer. The electrode layer has a structure arranged in this order,
A step of measuring a frequency characteristic of impedance of the compound thin-film solar cell in a state where a predetermined voltage is applied between the first electrode layer and the second electrode layer;
The first circuit block is a parallel circuit of a first resistor and a first CPE, and the second circuit block is a parallel circuit of a second resistor, a second CPE, and a third CPE, and the first CPE and the second CPE The third CPE is connected in reverse phase, and a series circuit of a third resistor, the first circuit block, and the second circuit block is a circuit model, and the measurement result of the measurement unit and the circuit model And a step of determining whether or not a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristic of the third CPE by fitting with the compound thin film solar cell Inspection method. An inspection system for a compound thin film solar cell,
The compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, and the first electrode layer. An intermediate layer including a constituent element and a part of an element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second layer. The electrode layer has a structure arranged in this order,
A measurement unit that measures frequency characteristics of impedance in the compound thin-film solar cell in a state where a predetermined voltage is applied between the first electrode layer and the second electrode layer;
A determination unit that determines whether the Nyquist diagram based on the measurement result of the measurement unit includes a capacitive semicircle in a high frequency region and an inductive semicircle in a low frequency region. Inspection system. An inspection system for a compound thin film solar cell,
The compound thin film solar cell includes a first electrode layer, a second electrode layer, a light absorption layer composed of a p-type compound semiconductor, a buffer layer composed of an n-type compound semiconductor, and the first electrode layer. An intermediate layer including a constituent element and a part of an element constituting the light absorption layer, the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second layer. The electrode layer has a structure arranged in this order,
A measurement unit that measures frequency characteristics of impedance of the compound thin-film solar cell in a state where a predetermined voltage is applied between the first electrode layer and the second electrode layer;
The first circuit block is a parallel circuit of a first resistor and a first CPE, and the second circuit block is a parallel circuit of a second resistor, a second CPE, and a third CPE, and the first CPE and the second CPE The third CPE is connected in reverse phase, and a series circuit of a third resistor, the first circuit block, and the second circuit block is a circuit model, and the measurement result of the measurement unit and the circuit model A determination unit that determines whether or not a numerical value within a predetermined range indicating the presence of the third CPE is calculated as a numerical value indicating the characteristic of the third CPE by fitting with system. A first electrode layer;
A second electrode layer;
a light absorbing layer composed of a p-type compound semiconductor;
a buffer layer composed of an n-type compound semiconductor;
An intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer;
The compound thin-film solar cell having a structure in which the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second electrode layer are arranged in this order,
A Nyquist diagram representing a frequency characteristic of impedance in the compound thin film solar cell measured in a state where a predetermined alternating voltage of 0.3 V or more is applied between the first electrode layer and the second electrode layer. Compound thin-film solar cells that contain only capacitive semicircles in the frequency domain. A first electrode layer;
A second electrode layer;
a light absorbing layer composed of a p-type compound semiconductor;
a buffer layer composed of an n-type compound semiconductor;
An intermediate layer including an element constituting the first electrode layer and a part of the element constituting the light absorption layer;
The compound thin-film solar cell having a structure in which the first electrode layer, the intermediate layer, the light absorption layer, the buffer layer, and the second electrode layer are arranged in this order,
A parallel circuit of the first resistor and the first CPE is a first circuit block, a parallel circuit of the second resistor and the second CPE is a second circuit block, and a third resistor, the first circuit block, and the second circuit. A series circuit with a block is a circuit model,
The compound thin film solar cell that matches the frequency characteristics of impedance in the compound thin film solar cell measured with a predetermined AC voltage of 0.3 V or more applied between the first electrode layer and the second electrode layer An equivalent circuit of is a circuit model of the compound thin film solar cell.