JP6411801B2 - Photocell evaluation method, photovoltaic cell evaluation apparatus, program, and photovoltaic cell manufacturing method - Google Patents

Description

  The present invention relates to a photovoltaic cell evaluation method, a photovoltaic cell evaluation apparatus, a program, and a photovoltaic cell manufacturing method.

  Technology development such as higher efficiency is being promoted for photovoltaic cells such as solar cells. The most successful method in the development of high efficiency solar cells is multijunction tandemization. However, the current development of multi-junction solar cells is largely based on trial and error. In order to enhance the feedback of fabrication and evaluation, a standard method for nondestructively evaluating the quality and characteristics of each subcell that is a constituent element is desired.

  In recent years, methods for analyzing current-voltage characteristics and open-circuit voltage Voc of each subcell based on electroluminescence (EL) intensity measurement have been proposed (see, for example, Non-Patent Document 1).

  However, in previous studies, 1) EL intensity was measured and formulated as an arbitrary unit or relative intensity, 2) the entire current-voltage characteristics were measured, and 3) the theoretical predictions agreed with the measurement results of the overall current-voltage characteristics. The method of estimating the current-voltage characteristics of each subcell by adjusting the parameters was adopted. Since this method includes a process of artificially adjusting parameters, it cannot be said that the current-voltage characteristics of each subcell are evaluated experimentally. In order to make a detailed diagnosis inside the solar cell, such as the current-voltage characteristics of each subcell, the breakdown of loss of each subcell, the size of luminescence coupling, and the quality of materials, an evaluation method that does not include the above assumptions is desirable. It is.

  The external quantum efficiency spectrum measurement method for solar cells using bias light is one of the standard evaluation methods for multi-junction solar cells. This is very important for evaluation of the individual carrier generation performance of each subcell, and is useful for diagnosing the short-circuit current Isc and current matching between the subcells (see, for example, Patent Document 2).

  Various evaluation methods are also desired for single-junction photovoltaic cells.

Raymond Hoheisel, Frank Dimroth, Andreas W. Bett, Scott R. Messenger, Phillip P. Jenkins, Robert J. Walters, Electroluminescence analysis of irradiated GaInP / GaInAs / Ge space solar cells, Solar Energy Materials and Solar Cells 108, 235 (2013 ). G. Siefer, C. Baur, A. W. Bett, External quantum efficiency measurements of germanium bottom subcells: Measurement artifacts and correction procedures, 35th Photovoltaic Specialists Conference (PVSC), 704-707 (2010).

  An object of the present invention is to provide a technique related to a novel evaluation method for a photovoltaic cell.

According to one aspect of the present invention,
(A) The photocell having the first subcell corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode, and is obtained from the first subcell as a function of the injected current density during operation of the light emitting diode. Providing a radiation recombination loss rate corresponding to light emission to
(B) For the first subcell, based on the balance between the net carrier generation rate and the net carrier loss rate, the relationship between the injection current density during light-emitting diode operation and the extraction current density during photocell operation is determined, From the radiation recombination loss rate obtained as a function of the injection current density during the operation of the light emitting diode in the step (a), the light from the first subcell to the outside of the photovoltaic cell as a function of the extraction current density during the operation of the photovoltaic cell Obtaining a radiation recombination loss rate corresponding to the emission is provided.

According to another aspect of the invention,
Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A photovoltaic cell evaluation device comprising a computing device configured to obtain a radiation recombination loss rate corresponding to light emission from the first subcell to the exterior of the photovoltaic cell as a function of extraction current density during photovoltaic cell operation. Provided.

According to yet another aspect of the invention,
Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A program is provided for causing a computer to execute a procedure for obtaining a radiation recombination loss rate corresponding to light emission from the first subcell to the outside of the photovoltaic cell as a function of the extraction current density during photovoltaic operation.

According to yet another aspect of the invention,
Forming a photovoltaic cell;
And evaluating the characteristics of the photovoltaic cell,
The step of evaluating the characteristics of the photovoltaic cell includes:
Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A method of manufacturing a photovoltaic cell is provided that includes obtaining a radiative recombination loss rate corresponding to light emission from the first subcell to the exterior of the photovoltaic cell as a function of extraction current density during photovoltaic cell operation.

  During the operation of the photovoltaic cell, based on the radiation recombination loss rate corresponding to the light emission from the first subcell to the outside of the photovoltaic cell, obtained as a function of the injection current density during the operation of the light emitting diode, corresponding to the absolute intensity of the electroluminescence By obtaining the radiation recombination loss rate corresponding to the light emission from the first subcell to the outside of the photovoltaic cell as a function of the extraction current density, it is possible to evaluate various characteristics of the photovoltaic cell.

FIG. 1A is a cross-sectional view showing a schematic structure of the photovoltaic cell 10, and FIG. 1B is a schematic view showing an example of a situation of EL absolute intensity measurement (and analysis). FIG. 2 is a graph showing the external light emission quantum efficiency when the light emitting diode of each subcell of the photovoltaic cell according to the example is operated. FIG. 3 is a graph showing the external quantum efficiency and the reflectance measured from the top surface of the photovoltaic cell during the photovoltaic cell operation of each subcell of the photovoltaic cell according to the example. FIG. 4 is a graph showing the external light emission quantum efficiency during the photovoltaic cell operation of each subcell of the photovoltaic cell according to the example. FIG. 5A and FIG. 5B are a table summarizing a graph and various characteristic values showing the current-voltage characteristics during the photovoltaic cell operation of the photovoltaic cell according to the example, respectively. 6 (A) and 6 (B) are power balance sheets under the maximum output conditions of the photovoltaic cell according to the example. 7 (A) and 7 (B) are carrier balance sheets under the open circuit conditions of the photovoltaic cell according to the example, and FIGS. 7 (C) and 7 (D) are those under the maximum output condition of the photovoltaic cell according to the example. It is a carrier balance sheet. FIG. 8A is a graph showing the internal emission quantum efficiency of each subcell of the photovoltaic cell according to the example, and FIG. 8B shows the external emission quantum efficiency and the internal emission quantum efficiency of each subcell of the photovoltaic cell according to the example. It is a summary table.

  Hereinafter, an evaluation method of a photovoltaic cell according to an embodiment of the present invention will be described along with an experiment (Example) performed as an example.

  First, a photovoltaic cell to be evaluated will be described. Here, an example in which a multi-junction photovoltaic cell is evaluated will be described. The multi-junction photovoltaic cell has a structure in which a plurality of subcells are stacked so that subcells having a wider band gap are arranged on the light incident side. Each subcell is configured as a semiconductor photovoltaic cell having a pn junction. The light incident side of the photovoltaic cell may be referred to as the upper side, the upper side, and the like, and the side opposite to the light incident side of the photovoltaic cell may be referred to as the light incident opposite side, the lower side, the lower side, and the like. The photovoltaic cell to be evaluated may be formed by any known method.

FIG. 1A is a cross-sectional view illustrating a schematic structure of the photovoltaic cell 10 and illustrates the structure of the photovoltaic cell (photovoltaic cell of the example) that is an evaluation target in the example. The photovoltaic cell (cell) 10 has a structure in which _three subcells SC _{1 to} SC ₃ are stacked. Most disposed on the light incident side (upper side) subcells (top subcell) SC ₁ is formed, for example by an indium gallium phosphide (InGaP). Top subcell (middle subcell) SC ₂ disposed immediately below the subcell SC ₁ is formed by, for example, gallium arsenide (GaAs). Middle subcell SC arranged subcell immediately below the ₂ (Botomusabuseru) SC ₃ is formed by, for example, germanium (Ge). The photovoltaic cell 10 of an Example is comprised as a solar cell utilized out of the atmosphere, and AM0 sunlight is assumed as incident light.

Top and subcell SC ₁ and the middle subcell SC ₂ are stacked via a tunnel junction _{TN 12.} A middle subcell SC ₂ and Botomusabuseru SC ₃ are stacked via a tunnel junction _{TN 23.} In each of the subcells SC _{1 to} SC ₃ , for example, a pn junction is formed in an arrangement in which the upper side is an n-type semiconductor layer and the lower side is a p-type semiconductor layer. Note that the structure of the photovoltaic cell may be a structure in which the stacking order of the p-type semiconductor layer and the n-type semiconductor layer is inverted up and down with respect to the illustrated photovoltaic cell.

_On the upper surface of the top subcell SC1, an upper electrode ELU is formed of, for example, silver (Ag). The outside of the upper electrode ELU forms a light incident region where light enters the photovoltaic cell from the outside. An antireflection layer (AR coating) ARC may be formed on the light incident region. _On the lower surface of the bottom subcell SC3, for example, a lower electrode ELL is formed over the entire surface with Ag. The lower electrode ELL forms a reflective electrode that reflects light upward.

Various physical quantities to be described later may be distinguished by attaching subscripts “1”, “2”, and “3” to those related to the top subcell SC ₁ , middle subcell SC ₂ , and bottom subcell SC _3. . In addition, the subscript “i” may be added when each subcell is generally represented. In addition, in order to indicate the outside of the photovoltaic cell (specifically, the upper air layer in the embodiment), the subscript “0” may be attached.

  Next, the photovoltaic cell evaluation method according to the embodiment will be described.

First, a photovoltaic cell to be operated as a light emitting diode by applying a forward voltage (LED), for measuring the absolute intensity of the electroluminescence (EL) from each subcell SC _i (EL absolute intensity). The forward bias current density (injection current density) J _LED injected into the photovoltaic cell is varied to obtain the EL absolute intensity of each subcell SC _i as a function of the injection current density J _LED .

EL absolute intensity of each subcell SC _i, in turn, is a radiative recombination loss rate corresponding to the light emitting _{R ext_i → 0} to photovoltaic outside from each subcell SC _i. Here, the subscript arrow “→” represents the direction from the radiation generation side to the destination side, and “i → 0” represents the subcell SC _i to the outside of the photovoltaic cell (specifically, the upper air layer in the embodiment). Represents the light emission to By measuring the EL absolute intensity for various injection current density _{J LED,} can be obtained radiative recombination losses as a function of _{J LED} rate _{R ext_i → 0.} In the following, for ease of explanation, EL absolute intensity and various rates are considered per unit area.

Based on the radiation recombination loss rate R _{ext — i → 0} , the external quantum efficiency of light emission during LED operation, that is, the external light emission quantum efficiency EQE _i ^LED can be obtained. The injection current density J _LED is converted into a carrier injection rate that is injected into the photovoltaic cell (to each subcell) by the current by dividing by the elementary charge q. By dividing the radiation recombination loss rate R _{ext — i → 0} by the carrier injection rate J _LED / q, the external light emission quantum efficiency EQE _i ^LED at the time of LED operation of each subcell SC _i is calculated. In general, quantum efficiency is sometimes referred to as quantum yield.

FIG. 1B is a schematic diagram showing an example of the situation of EL absolute intensity measurement (and analysis). Note that illustration of the tunnel junctions TN ₁₂ and TN ₂₃ and the antireflection layer ARC of the photovoltaic cell 10 is omitted to avoid the complexity of the illustration (see FIG. 1A). A forward bias is applied to the photovoltaic cell 10 by the power source 20 to cause EL emission, and the EL absolute intensity is measured by the measuring device 30. This measurement is preferably performed in a state where no light enters the photovoltaic cell 10 from the outside. The EL absolute intensity may be measured by any known method, and the measuring device 30 may have any known configuration capable of measuring the absolute intensity of EL emission.

The control device 40 controls the power supply 20 so as to perform measurement by changing the injection current density J _LED , and receives data corresponding to the measurement result from the measuring device 30. The control device 40 is configured as a control device that performs such measurement control, and is configured as a calculation device that performs various calculations (analysis) performed in the following description. And a storage device that stores programs and data for performing calculations and the like, and a CPU that reads and executes programs and the like from the storage devices. The control device (calculation device) 40 is constituted by a personal computer, for example. A photovoltaic device evaluation device is configured including at least the calculation device 40. The photovoltaic cell evaluation apparatus may include a power supply 20 and a measuring device 30. As will be described later, in the case of an embodiment in which measurement and analysis are performed separately, a control device and a calculation device can be prepared separately.

More specifically, the EL absolute intensity measurement method performed in the examples will be described. As a forward bias, a negative voltage and a positive voltage were applied to the upper electrode ELU and the lower electrode ELL of the photovoltaic cell 10, respectively. By applying the forward bias, the photovoltaic cell 10 generated red EL light emission. This EL emission was clearly observed with the naked eye. The measurement of EL absolute intensity was carried out separately for the top subcell SC ₁ and middle subcell SC ₂ and for the bottom subcell SC ₃ .

Measurements for the top subcell SC ₁ and the middle subcell SC ₂ will be described. The EL spectrum from the photovoltaic cell 10 was measured using a spectrometer that was previously calibrated for relative wavelength sensitivity using a standard light source. A spectrometer having a cooled silicon CCD detector and having sensitivity at wavelengths of 400 nm to 1100 nm was used. The EL spectra calibrated with relative wavelength sensitivity were obtained from the top subcell SC ₁ (InGaP) and the middle subcell SC ₂ (GaAs) having peaks at 685 nm (1.81 eV) and 882 nm (1.405 eV), respectively.

  Next, a photosensor comprising a silicon photodiode light-receiving element having a disc-shaped light-receiving surface of an optical power meter that has been subjected to absolute sensitivity calibration is placed in a close position parallel to the top surface of the photovoltaic cell 10 to set the wavelength of the optical power meter. The optical power was measured. The total photocurrent detected by the photosensor was calculated from the nominal optical power value of the set wavelength measured and the absolute wavelength sensitivity of the photosensor at the set wavelength.

  Then, an EL absolute intensity spectrum was obtained from the measured EL spectrum (relative wavelength sensitivity calibrated), the total photocurrent detected by the photosensor, and the absolute wavelength sensitivity curve of the silicon photodiode light receiving element. The EL absolute intensity of each subcell was determined from the EL absolute intensity spectrum, and the external emission quantum efficiency was determined.

It will be described measurement on Botomusabuseru SC _3. Combining an InGaAs photodiode element having a sensitivity at a wavelength of 900 nm to 2100 nm and having a disc-shaped light receiving surface with a known absolute sensitivity with an optical filter that cuts the short wavelength side of 1500 nm or less, a parallel proximity position to the upper surface of the photovoltaic cell , The photocurrent was measured to determine the EL absolute intensity, and the external light emission quantum efficiency was determined.

  In the measurement of the total luminous flux per area of the flat light emitting element, such simple measurement at the parallel proximity position is approximately used. More generally, for example, it may be determined by measuring the total luminous flux using an integrating sphere or measuring the radiation angle distribution.

For each subcell SC _i , measurements as described above are performed for various forward bias currents J _LED , and as a function of J _LED , EL absolute intensity (radiation recombination loss rate R _{ext — i → 0} ) and external quantum efficiency EQE _i ^LED was determined.

FIG. 2 shows the external light emitting quantum efficiency EQE ^LED as a function of the injection current density J _LED during LED operation of the top subcell (Top), middle subcell (Mid), and bottom subcell (Bot) of the photovoltaic cell according to the example.

In addition to the radiation recombination loss rate R _{ext — i → 0} obtained as a function of J _LED as described above, a carrier generation rate R _{sun — i} by absorption of light incident on each subcell SC _i from the outside of the photovoltaic cell is prepared. . This carrier generation rate _{Rsun_i} is _referred to as an external light absorbing carrier generation rate. The external light absorbing carrier generation rate _{Rsun_i} can be obtained, for example, as follows.

First, for each subcell SC _i , the external quantum efficiency EQE _i ^PV as a photovoltaic cell during photovoltaic cell operation (PV operation) is obtained. Next, the external light absorption carrier generation rate R _{sun — i} is obtained by multiplying the external quantum efficiency EQE _i ^PV by the spectrum of incident light assumed when actually used as a photovoltaic cell. The external quantum efficiency EQE _i ^PV during PV operation may be obtained by any known method.

In the present embodiment, as will be described later, the external quantum efficiency y _ext of light emission during PV operation of the photovoltaic cell is calculated. In order to distinguish these “quantum efficiencies” during PV operation, the external quantum efficiency EQE ^PV as a photovoltaic cell during PV operation is simply referred to as “external quantum efficiency” during PV operation. The quantum efficiency y _ext will be referred to as “external light emission quantum efficiency”.

In the example, based on the method described in Non-Patent Document 2, the external quantum efficiency EQE _i ^PV during PV operation of each subcell SC _i was obtained. For each subcell SC _i , the external light absorption carrier generation rate R _{sun — i} was obtained by multiplying the external quantum efficiency EQE _i ^PV during PV operation by the sunlight spectrum of AM0. The outline of the method described in Non-Patent Document 2 is as follows. In a state in which bias light is incident on another subcell other than the subcell, a monochromatic light having a known intensity is incident on the subcell, and a current flowing through the photovoltaic cell is measured. Gives the external quantum efficiency, which is the rate at which the extracted current is converted to electrons.

FIG. 3 shows the external quantum efficiency EQE ^PV during PV operation of the top subcell (Top), middle subcell (Mid), and bottom subcell (Bot) of the photovoltaic cell according to the embodiment as a function of the photon energy of the wavelength of the incident light. . In addition, the reflectance (Reflectivity) measured from the upper surface of the photovoltaic cell is also shown in FIG.

As described above, a radiation recombination loss rate R _{ext — i → 0} corresponding to light emission to the outside of the photovoltaic cell during LED operation is prepared for each subcell SC _i by measuring the EL absolute intensity. For each subcell SC _i , an external light absorbing carrier generation rate R _{sun — i} during PV operation is prepared.

Next, for each subcell SC _{i, based} on the radiation recombination loss rate R _{ext — i → 0} corresponding to light emission to the outside of the photovoltaic cell during LED operation, the external light absorption carrier generation rate R _{sun — i,} etc. during PV operation, PV As a function of the extraction current density J _PV during operation, a radiation recombination loss rate R _{ext — i → 0} corresponding to light emission to the outside of the photovoltaic cell during PV operation is obtained.

In particular, based on the radiation recombination loss rate R _{ext — i → 0} corresponding to light emission to the outside of the photovoltaic cell during LED operation, as a function of the extraction current density J _PV during PV operation, the light to the outside of the photovoltaic cell during PV operation By _obtaining the radiation recombination loss rate R _{ext — i → 0} corresponding to the emission, various characteristics of the photovoltaic cell can be evaluated. Hereinafter, the details of the calculation method will be described according to the embodiment.

As described above, the subscripts “1”, “2”, and “3” are attached to the physical quantities and the like related to the top subcell SC ₁ , the middle subcell SC ₂ , and the bottom subcell SC ₃ . The subscript “i” is added when each subcell is generally represented. The subscript “0” is added to indicate the outside of the photovoltaic cell. Various rates are considered per unit area.

For a multi-junction photovoltaic cell having three subcells as in the example, the balance (carrier balance) between the net carrier generation rate and the net carrier loss rate in each subcell SC _i is expressed by the following equations (1) to (3 ).

Equations (1) to (3) indicate carrier balances in the top subcell SC ₁ , middle subcell SC ₂ , and bottom subcell SC ₃ , respectively. The left side shows the net carrier generation rate, the right side shows the net carrier loss rate, and the carrier balance shows the relationship that the net carrier generation rate is equal to the net carrier loss rate.

R _{sun — i} is a carrier generation rate (per unit area) due to absorption of light incident on the subcell SC _i from the outside (upper space) of the photovoltaic cell (external light absorption carrier generation rate).

J is an injection current density into the photovoltaic cell (to the subcell) or an extraction current density from the photovoltaic cell (from the subcell), and the forward direction of the pn junction is the positive direction. q is an elementary charge amount, and J / q is a carrier injection rate (per unit area) by injection current or a carrier extraction rate (per unit area) by extraction current. J at the time of LED operation becomes the injection current density J _{LED in the} positive direction, and J at the time of PV operation becomes the extraction current density J _{PV in the} negative direction.

R _{ext — i → 0} is a radiation recombination loss rate (per unit area) corresponding to light emission from the subcell SC _i to the outside (upper space) of the photovoltaic cell.

_{R ext_i → i + 1} to the carrier loss rate subcells SC _i appears (in the right side) is a subcell _{SC i +} corresponding to the light emission to ₁ (per unit area) radiative recombination loss rate just below the subcells SC _i. As carrier generation rate subcells SC _i appears (in the left-hand _{side) R ext_i-1 → i} is (per unit area) by luminescence coupled with the light incident from the subcells _{SC i-1} immediately above the subcells SC _i carriers generated Rate. _S in R _{ext — 3 → S} constituting the carrier loss rate of the bottom subcell SC ₃ indicates a substrate side member on the lower side from the pn junction.

R _{nr — i} is the non-radiative recombination loss rate (per unit area) in subcell SC _i .

That is, the carrier generation rate (left side) of the net in the subcell SC _i is the external light absorption carrier generation rate R _{sun — i} , the carrier injection rate by the injection current, or J / q which is the carrier extraction rate by the extraction current, This is expressed as the sum of the carrier generation rate R _{ext — i−1 → i} due to luminescence coupling accompanying the light incidence from the subcell. In the top sub-cell SC _1, since subcell above is not arranged, the carrier generation rate by luminescence coupled with the light incident from the upper subcell is zero.

On the other hand, the carrier loss rate (right side) of the net in the subcell SC _i is the radiation recombination loss rate R _{ext — i → 0} corresponding to light emission to the outside (upper space) of the photovoltaic cell, and downward (on the opposite side of light incidence). _Is represented by the sum of the radiation recombination loss rate R _{ext — i → i + 1} (R _{ext — i → S} ) corresponding to the light emission and the non-radiation recombination loss rate R _{nr — i} .

Is another term for _{R Sun_i} and J / q in carrier _{balance, R ext_i → 0, R ext_i} → i + 1 (R ext_i → S, R ext_i-1 → i), and _{R Nr_i is, R sun_i} and J / It is determined by giving q. That is, these terms, as a function of J and _{R sun_1 ~R sun_3, R ext_i →} 0 [J, R sun_1, R sun_2, R sun_3] given as. Here, square brackets are used to indicate a function.

If the non-radiative recombination loss rate R _{nr_i} is all zero, the recombination loss of the photovoltaic cell coincides with the ideal case of only the radiative recombination loss (radiation limit). Is given in the paper. However, in reality, the non-radiative recombination loss rate R _{nr — i} is not zero and is an amount that varies depending on the current density J.

In the case of LED operation, the current of the current density J _LED is injected by applying a forward bias in a state where light is not incident on the photovoltaic cell (R _sun — _i = 0). At this time, for example, R _{ext — i → 0} [J, R _{sun — 1} , R _{sun — 2} , R _{sun — 3} ] is expressed as R _{ext — i → 0} [J _LED , 0, 0, 0]. This is simplified and expressed as R _{ext — i → 0} [J _LED ]. R _{ext_i → i + 1} (R _{ext_i → S} , R _{ext_i−1 → i} ) and R _{nr_i} have the same notation. In the LED operation, the above formulas (1) to (3) are expressed as the following formulas (1 _LED ) to (3 _LED ).

As described above, the radiation recombination loss rate R _{ext — i → 0} of each subcell SC _{i is} already obtained as a function of J _LED . The radiation recombination loss rate R _{ext — i → i + 1} can be calculated from the radiation recombination loss rate R _{ext — i → 0} . The radiation recombination loss rate R _{ext — i → S} can be determined according to the structure below the lowermost subcell (bottom subcell). Therefore, from the equations (1 _LED ) to (3 _LED ), the unknown non-radiative recombination loss rate R _{nr_i} can also be determined as a function of J _LED . In this way, all terms in the equations (1 _LED ) to (3 _LED ) are obtained as a function of J _LED .

Specifically, the radiation recombination loss rate R _{ext — i → i + 1} can be obtained as follows. As in the present embodiment, there is AR coating on the surface, close to the ratio 1 between the refractive index _{n i + 1} of the refractive index _{n i} and subcells _{SC i + 1} of the material of the material of the subcells SC _i, holds the _{n i} + 1> _{n i} In the case of such a typical multi-junction cell, it can be expressed as R _ext — _{i → i + 1} = n _i ² × R _{ext — i → 0} using the radiation recombination loss rate R _{ext — i → 0} and the refractive index n _i. . More generally,
It can be expressed as. Definitions and calculation methods such as a _{i + 1 → i} and a _{0 → i} will be described later.

Specifically, the radiation recombination loss rate R _{ext — i → S} can be obtained as follows. For example, in the case of a structure in which there is no absorptive substrate layer below the lowermost subcell (bottom subcell) and a total reflection mirror exists, it can be set to zero. More generally, the substrate layer is regarded as an (i + 1) layer, and the above expression of R _{ext — i → i + 1} can be applied according to the reflectance and the absorption coefficient.

In the case of PV operation, by making light incident on the photovoltaic cell (R _{sun — i} ≠ 0), an extraction current having a current density J _PV is generated in the negative direction, and light emission is also generated. In this case, for example, _{R ext_i → 0 [J, R} sun_1, R sun_2, R sun_3] _{is, R ext_i → 0 [J PV} , R sun_1, R sun_2, R sun_3] denoted. Simplified _this will be denoted as _{R ext_i → 0 [J PV]} . R _{ext_i → i + 1} (R _{ext_i → S} , R _{ext_i−1 → i} ) and R _{nr_i} have the same notation. In the PV operation, the above formulas (1) to (3) are expressed as the following formulas (1 _PV ) to (3 _PV ). Here, as described above, the external light absorbing carrier generation rate R _{sun — i} has already been obtained.

For each subcell, the net carrier generation rate (left side) of the equations (1 _LED ) to (3 _LED ) during LED operation and the net carrier generation rate of the equations (1 _PV ) to (3 _PV ) during PV operation ( by considering the above condition left) and are equal, the injected current density J _LED at LED operation and obtained current density J _PV during PV operation can correspond.

First, the top sub-cell SC _1, so as to satisfy the relationship of _{J LED / q = R sun_1 +} J PV / q, it is possible to correspond to _{J PV} and _{J LED.}

_{Then, R ext_1 →} 0 when the _{J LED} corresponding to _{J PV [J LED] (R} ext_i → 0 [J LED, 0,0,0]) by reference _{to, R ext_i} corresponding to _{J PV → 0 [J PV] (R ext_i} → 0 [J PV, R sun_1, R sun_2, R sun_3]) can be determined. Thus, the radiative recombination losses were obtained as a function of the injection current density _{J LED} at LED operation rate _{R ext_1 → 0,} the radiative recombination losses rate _{R ext_1 → 0} as a function of the obtained current density _{J PV} Can be obtained. Further, similarly, the radiation recombination loss rate R _{ext — 1 → 2} and the non-radiation recombination loss rate R _{nr — 1} can be obtained as a function of the extraction current density J _PV .

The middle sub-cell _{SC 2, J LED / q +} R ext_1 → 2 [J LED] = R sun_2 + J PV / q + R ext_1 → 2 so as to satisfy the relationship of _{[J PV],} can correspond to _{J PV} and _{J LED} . Here, as described above, R _{ext — 1 → 2} [J _LED ] and R _{ext — 1 → 2} [J _PV ], which are physical quantities for the top subcell SC ₁ , have already been obtained.

Also for the middle subcell SC ₂ , by obtaining the correspondence between J _PV and J _LED , the radiation recombination loss rate R _{ext — 2 → 0} and the radiation recombination loss rate R _{ext — 2 → 3} obtained as a function of J _LED are obtained. , and are obtained from the non-radiative recombination losses rate _{R Nr_2,} radiative recombination losses as a function of _{J PV} rate _{R ext_2 → 0,} radiative recombination losses rate _{R ext_2 → 3,} and the non-radiative recombination losses rate _{R Nr_2} be able to.

Further, in the same manner for the other sub-cells, the physical quantity of each term can be determined as a function of J _PV.

As described above, for each sub-cell, based on the EL absolute intensity measurement of each injection current density J _LED at LED operation, each term in the carrier balance can be obtained as an amount corresponding to the J _LED. Then, based on each term in carrier balance obtained as an amount corresponding to the J _LED, as an amount corresponding to the obtained current density J _PV during PV operation, it is possible to obtain the terms in carrier balance.

For each subcell SC _i , when each term in the carrier balance is obtained as a function of the extraction current density J _PV , other various physical quantities, for example, the external light emission quantum efficiency y _{ext_i} at the time of PV operation can be obtained. Various characteristics of the photovoltaic cell can be evaluated.

The external light emission quantum efficiency y _{ext — i} is defined as the ratio of the radiation recombination loss rate R _{ext — i → 0} corresponding to the light emission to the outside of the photovoltaic cell with respect to the net carrier loss rate (= net carrier generation rate). That is, the external emission quantum efficiency _{y ext_i [J PV] (y} ext_i [J PV, R sun_1, R sun_2, R sun_3]) during PV operation of each subcell SC _i, the following equation ₍₁ y) like ~ It is represented by (3 _y ).

4, the top sub-cell of the photovoltaic cell according to Example (Top), a middle subcell (Mid), and Botomusabuseru the external light emission quantum efficiency _{y ext} at PV operation of (Bot), as a function of the obtained current density _{J PV.}

Here, in the derivation of the result shown in FIG. 4, assuming the boundary condition in which a total reflection mirror exists below the bottom subcell, R _{ext — 3 → S} = 0, that is, from the bottom subcell to the subcell immediately below It was assumed that there was no radiation recombination loss corresponding to light emission.

Hereinafter, as analysis examples for evaluating various characteristics of PV cells during PV operation, (A) evaluation of current-voltage characteristics of each subcell and all subcells (entire cell), (B) evaluation of loss breakdown of each subcell, (C ) Evaluation of carrier balance and luminescence coupling ratio, and (D) Evaluation of material quality (internal emission quantum efficiency y _{int — i} ) of each subcell will be described.

(A) Evaluation of current-voltage characteristics of each subcell and all subcells (entire cell) In the above formulas (1) to (3), in the ideal case where the non-radiative recombination loss rate _{Rnr_i} is zero (radiation limit) , external light emission quantum efficiency _{^y ext_i} rad _{[J PV]} and subcells SC _i, this time subcell SC _i voltage according to _V ⁱ rad _{[J PV]} to, is formulated by the prior research papers are given. Specifically, the external emission quantum efficiency _{^y ext_i} rad _{[J PV]} and the voltage _V ⁱ rad _{[J PV]} can be calculated based on the semiconductor basic equations detailed equilibrium expressions and Shockley.

An external light emission quantum efficiency _{^y ext_i} rad _{[J PV]} and the voltage _V ⁱ rad _{[J PV]} in radiation limits, the external light emission quantum efficiency _y Ext_i determined for the actual photovoltaic cell as described above _{[J PV]} used, subcell SC _i nonradiative recombination losses due to voltage deterioration [Delta] V _i of _{[J PV],} and the voltage according to the actual subcell SC _{i V i [J PV]} is determined by the following expression like The Here, k _B is a Boltzmann constant, and T is an absolute temperature.

FIG. 5A is a graph showing the current-voltage characteristics during PV operation of the photovoltaic cell according to the example. The vertical axis represents the magnitude | J _PV | of the extraction current density in units of mA / cm ² . The horizontal axis indicates the voltage applied to each subcell or all subcells (entire cell) in V units. Top subcell (Top), a middle subcell (Mid), current-voltage characteristics of Botomusabuseru entire current-voltage characteristics and cell (Bot) (Total), i.e., the voltage V applied to each subcell SC _i in accordance with the obtained current density _{J PV i} [ _JPV ] and the voltage V [ _JPV ] applied to the entire cell are indicated by solid lines. Voltage applied to the entire cell V _{[J PV]} is obtained as the sum of the voltage applied to each subcell _{SC i (V 1 [J PV} ] + V 2 [J PV] + V 3 [J PV]). The current-voltage characteristics of all subcells at the radiation limit are indicated by dotted lines. The current-voltage characteristics actually measured by the conduction measurement under the AM0 condition are shown by white circle plots.

  It can be seen that the current-voltage characteristics of the entire cell (Total) calculated as the sum of the current-voltage characteristics of the subcells (Top, Mid, Bot) agree very well with the measured current-voltage characteristics. Thus, according to the photovoltaic cell evaluation method of the present embodiment, the current-voltage characteristics of each subcell can be calculated, and further, the current-voltage characteristics of the entire cell can be calculated from the current-voltage characteristics of each subcell. .

Based on the current-voltage characteristics obtained as described above, the radiation open-circuit voltage Voc ^rad , the open-circuit voltage deviation ΔVoc from the radiation limit open-circuit voltage Voc ^rad , the open-circuit voltage Voc, the short-circuit current density Jsc, the current under the maximum output condition The density (maximum output operating current density) Jm, the voltage under the maximum output condition (maximum output operating voltage) Vm, the fill factor FF, and the efficiency ηsc were calculated.

  In the table of FIG. 5B, these values are shown together, and the peak energy (bandgap energy) Eem of the EL spectrum of each subcell and the external quantum efficiency EQE @ during PV operation at the peak energy of the EL spectrum are shown. em. For comparison, values obtained from current-voltage characteristics actually measured by conduction measurement under the AM0 condition are shown in the bottom row of the table.

  This analysis reveals the following, for example. The open-circuit voltage Voc of the entire cell is estimated to be 2.63V, and as a breakdown, the contributions of the top, middle, and bottom subcells are 1.36V, 1.01V, and 0.26V, respectively. The decrease ΔVoc of the open circuit voltage Voc due to the non-radiative recombination loss is estimated to be 0.46 V for the entire cell. As a breakdown, the contributions of the top, middle, and bottom subcells are 0.12 V,. 07V and 0.27V. In addition, the various values estimated by the evaluation method of the present embodiment are in good agreement with the actual measurement values.

  As described above, according to the photovoltaic cell evaluation method of the present embodiment, the current-voltage characteristics of the entire cell can be estimated from the current-voltage characteristics of the subcells. Therefore, it is not necessary to measure the current-voltage characteristics of the entire cell in advance. In addition, the current-voltage characteristics of the entire cell can be compared with the values estimated from the current-voltage characteristics of the subcells and the measured values, and the difference between the two can be analyzed. The difference between the two can be analyzed as the contribution of tunnel junctions and electrodes between subcells, series resistance of the circuit, voltage offset, and the like.

(B) Evaluation of Loss Breakdown of Each Subcell Based on the carrier balance during PV operation (formulas (1 _PV ) to (3 _PV )), all the recombination loss rates of carriers in each subcell can be obtained. Further, the current-voltage relationship can be obtained as described in the evaluation (A). Based on the recombination loss rate and the current-voltage relationship, a power balance sheet showing the balance of input, loss, and output can be created, and the contribution of each item can be analyzed and evaluated.

Here, as shown in FIG. 6 (A), it was created power balance sheet at the maximum output condition _(J PV = Jm and V = Vm). FIG. 6A shows the value of each item as an absolute value (mW / cm ² ).

  The loss (Loss) is shown in the table divided into items of “Thermalization”, “Emission to Air”, “Emission to Sub”, “Non-rad. Recombi”, and “Junction Loss”. As described above, the carrier recombination loss rate is divided into a radiative recombination loss rate and a non-radiative recombination loss rate, and the radiative recombination loss rate is the recombination loss related to light emission into the space above the photovoltaic cell. The rate and the recombination loss rate for light emission to the lower subcell. Recombination loss rate for light emission into the space above the photovoltaic cell, recombination loss rate for light emission to the lower subcell, and non-radiative recombination loss rate converted to power, respectively, "Emission to Air" , “Emission to Sub” and “Non-rad. Recombi”.

  “Thermalization” is a loss due to the fact that incident light having energy equal to or higher than the band gap energy is used with the energy lowered to the band gap energy. “Junction Loss” is a loss corresponding to the difference between the voltage corresponding to the band gap energy of each subcell and the maximum output operating voltage Vm.

  In the table, “Input” is divided into items “AM0 sun” and “Luminescent Coupling”. “AM0 sun” is obtained by converting the carrier generation rate by absorption of sunlight of AM0 into power. “Luminescent Coupling” is obtained by converting a carrier generation rate by luminescence coupling accompanying light incidence from an upper subcell into power.

The irradiation power of sunlight of AM0 is 135 mW / cm ² . The difference between the total irradiation power of sunlight and the input to all subcells is the so-called transmission loss (“Transmission Loss”).

  The output (Output) is shown in the item of “IV output” in the table, and is obtained by multiplying the maximum output operating voltage Vm applied to each subcell and the entire cell by the absolute value of the maximum output operating current density Jm. is there.

FIG. 6B shows the value of each item of the power balance sheet shown in FIG. 6A in a ratio where the AM0 sunlight irradiation power of 135 mW / cm ² is 1.

  This analysis reveals the following, for example. At maximum power conditions, the radiation recombination losses (“Emission to Air” and “Emission to Sub”) are negligibly small. Solar power ("AM0 sun") with 100% overall is 26.4% for transmission loss ("Thermalization") and 18.5% for thermal loss ("Thermalization"). Radiation recombination loss (“Non-rad. Recombi”) is 6.8%, junction loss (“Junction Loss”) is 19.6%, solar cell output (“IV output”) is 28.7%, etc. Allocated. That is, the overall solar cell efficiency ηsc is estimated to be 28.7%. As a breakdown of the overall solar cell efficiency of 28.7%, the contributions of the top, middle, and bottom subcells are 15.2%, 10.7%, and 2.8%, respectively.

(C) Evaluation of carrier balance and luminescence coupling ratio Based on the carrier balance at the time of PV operation (formulas (1 _PV ) to (3 _PV )), a carrier balance sheet indicating the balance between generation of carriers and loss can be created. It is possible to analyze and evaluate the contribution of each item.

Here, as shown in FIG. 7 (A) and FIG. 7 (B), the carrier balance sheet in the open circuit condition _{(J PV} = 0 and V = Voc), in FIG. 7 (C) and FIG. 7 (D) As shown, a carrier balance sheet under maximum output conditions (J _PV = Jm and V = Vm) was prepared. FIG. 7 (A) and FIG. 7 (C) show the value of each item as an absolute value (mA / cm ² ). Note that the carrier balance sheets in FIGS. 7A and 7C are expressed in units of current density by multiplying the elementary charge q, not the generation / loss rate itself for the number of carriers. FIG. 7B and FIG. 7D show the ratio of each item of the carrier balance sheet in FIG. 7A and FIG. 7C with 1 as the input by sunlight to each subcell. It is shown by.

  “AM0 sun” and “Luminescent Coupling” are carrier generation rates corresponding to the items of the same name described in the evaluation (B) above. “Emission to Air”, “Emission to Sub”, and “Non-rad. Recombi” are carrier loss rates corresponding to the items of the same name explained in the evaluation (B) above. “Current @ Voc” and “Current @ Vm” are extraction current densities under open circuit conditions and maximum output conditions, respectively.

  This analysis reveals the following, for example. Under open circuit conditions, the luminescence coupling from the top subcell to the middle subcell contributes about 1%, and the luminescence coupling from the middle subcell to the bottom subcell contributes about 10%. Under the maximum output condition, the luminescence coupling is as small as 0.1% or less, and most of the carriers that have not contributed to the current output disappear due to non-radiative recombination.

(D) Evaluation of material quality of each subcell (internal emission quantum efficiency y _{int — i} ) The external emission quantum efficiency y _{ext —} i reflects the magnitude of the non-radiative recombination loss of each sub cell. is not. This is because, even if the material quality is the same, y _{ext_i} will have a different value if the structural parameters such as the film thickness and surface reflectance of each subcell are different. In development aimed at improving the performance of photovoltaic cells such as solar cells, it is desirable to be able to quantify the quality of the material separately from the structural parameters.

In order to evaluate the material quality of each subcell, the internal light emission quantum efficiency y _{int —} i can be used as an index. The internal light emission quantum efficiency y _{int — i} is an amount per unit volume of the material, and is expressed by the sum of the radiation recombination loss rate and the non-radiation recombination loss rate inside each subcell, as shown in Equation (13) described later. It is defined as the ratio of the radiative recombination loss rate (it can also be expressed as an amount per unit area by multiplying each rate by the thickness of the film).

We have already obtained the external emission quantum efficiency y _{ext —} i of each subcell during PV operation as a function of the extraction current density J _PV . We propose to calculate the internal emission quantum efficiency y _{int —} i using y _{ext — i} and the EQE ^PV measurement result and the reflectance measurement result shown in FIG. 3. This makes it possible to quantify the material quality of each subcell.

In order to _{relate the} internal light emission quantum efficiency y _{int — i} and the external light emission quantum efficiency y _{ext —} i, the following general formula (4), (5), or (6) may be used.

In the formula (4) ~ (6), α i, l i, n i respectively represent the absorption coefficient of the i layer (subcells SC _i), the thickness, the refractive index. a _{0 → i} and a _{i + 1 → i} represent the angle-average absorption ratios on the air side and the (i + 1) layer side. The upper line represents the average value in the emission energy band. In addition, the average value in the emission energy band of α _i , a _{0 → i} , a _{i + 1 → i} is defined by equations (15) to (17) described later.

The angle average a _{0 → i} of the absorptance for the air side hemisphere and the angle average a _{i + 1 → i} of the absorptance for the (i + 1) layer side hemisphere are the absorptance a _{0 → i} [θ] depending on the incident angle θ. Using a _{i + 1 → i} [θ],
It is expressed. Note that the (i + 1) layer side hemispherical angle average is a _{i + 1 → i} [θ] = 0 at the time of total reflection.

a _{0 → i} [θ], a _{i + 1 → i} [θ] are obtained by the theory of the absorption rate of a normal thin film,
It is expressed. Here, r _{0 → i} [θ] and r _{i + 1 → i} [θ] represent the reflectance as viewed from the air side and the (i + 1) layer side.

  The general formulas (4) to (6) are derived as follows.

y _{int_i} is
It is expressed. R _{int — i} is the radiation recombination loss rate inside each subcell SC _i . Note that tilde (˜) indicates an amount per unit volume.

y _{ext_i} is defined as
It is expressed.

R _int is expressed by the Van Roosbroeck equation (15).

R _ext is expressed by Planck's formulas (16) and (17).

From the equations (15) to (17),
And
From equations (13) and (14),
It is.

From equations (18) and (19),
Is obtained, and equations (4) to (6) are obtained.

Next, a specific method for obtaining the internal light emission quantum efficiency y _{int — i} from the external light emission quantum efficiency y _{ext — i} will be described. If structural parameters such as α _i , l _i , n _i , r _{0 → i} [θ], r _{i + 1 → i} [θ] are all known, the equations (7) to (12) are used. Then, a _{0 → i} and a _{i + 1 → i} are first calculated, and y _int — _i is calculated from y _ext — _i using equations (4) to (6).

On the other hand, when these structural parameters are not known, the parameters can be determined as follows. By determining the band gap energy Eem _i of each subcell from the EL spectrum measurement, the composition of the material of each subcell is estimated and the corresponding n _i is determined. From n _i and n _{i + 1} , r _{i + 1 → i} [θ] can be determined. A _{0 → i} [θ = 0] is obtained from the EQE ^PV measurement, r _{0 → i} [θ = 0] is determined by the reflectance measurement from the air side, and α _i and l _i are determined from the equation (9). Estimate the value of α _i l _i which is the product. r _{0 → i} [θ] is obtained by measurement or estimation based on r _{0 → i} [θ = 0], and a _{0 → i} [θ] and a _{i + 1 → i} [θ] are calculated. From here, a0 _{→ i} and _{ai + 1 → i} are calculated. Y _{int —} i can be calculated from y _{ext —} i using the parameters obtained in this way in equations (4) to (6).

Incidentally, regarded as _{n i} and _{n r} for the _{i + 1} and has a value close _{i + 1 → i [θ]} = 0, also regarded as _{r 0 → i [θ] =} 0 with a surface anti-reflection coating, thick film alpha _i When the product of the average value and l _i in the emission energy band is >> 1, and n _i <n _{i + 1} corresponding to Eem _i > Eem _{i + 1} , the equation (4) is
It is simplified as follows.

The graph in FIG. 8A shows the absolute value of the internal light emission quantum efficiency y _{int —} i of each subcell during LED operation and PV operation, calculated using the above method. In the low injection current region of the LED operation, all the subcells showed low internal light emission quantum efficiency y _{int_i} , but in the high injection current region, y _{int_i} of the top, middle, and bottom sub _cells was 5%, 56%, and 0, respectively. A value of about 3% was shown.

The table of FIG. 8B shows the external light emission quanta when J _PV = 0 and V = Voc (open circuit condition) and when J _PV = Jm and V = Vm (maximum output condition) during PV operation. The absolute values of the efficiency y _{ext — i} and the internal light emission quantum efficiency y _{int —} i are shown. The open circuit condition (shown as @Voc) was close to the high injection current region during LED operation, and y _{int_i} of the top, middle, and bottom subcells showed values of about 5%, 56%, and 0.3%, respectively. . Particularly, _{yint_i} of the GaAs material of the middle subcell is a high value of 56%. However, the maximum output condition (shown as @Vm) is close to the low injection current region during LED operation. At this time, it was found that y _{int —} i of the top, middle, and bottom subcells were low values of about 1.4%, 5.6%, and 0.3%, respectively. This means that there is room for improvement in solar cell efficiency due to improvement in crystal quality of the material.

  As described above, according to the photovoltaic cell evaluation method of the present embodiment, for example, for a multi-junction photovoltaic cell, based on the EL absolute intensity measured for each subcell, various characteristics of each subcell and the entire cell, etc. Can be analyzed and evaluated.

  In the above-described embodiment, the evaluation of a photovoltaic cell having three subcells, that is, a three-junction photovoltaic cell is illustrated. However, the photovoltaic cell to be evaluated is not limited to 3 junctions, and may be, for example, 2 junctions or 4 junctions or more. For cases other than three junctions, the carrier balance equations (1) to (N) corresponding to the number N of subcells are the same as the analysis performed using the above equations (1) to (3) for the three junction case. ).

  In the above-described example, the evaluation of the multi-junction photovoltaic cell is illustrated, but the photovoltaic cell to be evaluated by the evaluation method according to the present embodiment may be a single junction photovoltaic cell. Here, the single junction photovoltaic cell can be regarded as a photovoltaic cell having only one subcell. That is, it can be said that the photovoltaic cell evaluation method according to the present embodiment can be applied to an N-junction type (N is 1 or more) photovoltaic cell having at least one subcell.

When evaluating a single-junction photovoltaic cell, since there is one subcell, the analysis may be performed using the equation (1) corresponding to the top subcell in the case of the three junctions illustrated. Note that the radiation recombination loss rate R _{ext1 → 2} corresponding to the light emission to the lower side of the subcell may be handled as R _{ext1 → S.}

  Since the single junction type photovoltaic cell includes only one subcell, the current-voltage characteristic of the subcell can be measured by conduction measurement. However, the current-voltage characteristics obtained by the conduction measurement include effects of electrodes, series resistance of the circuit, voltage offset, and the like, and it is difficult to appropriately evaluate the quality of the semiconductor layer constituting the subcell. On the other hand, according to the current-voltage characteristics (see Analysis Example (A)) obtained by the evaluation method of the present embodiment based on the EL absolute intensity, the quality of the semiconductor layer of the subcell can be more appropriately evaluated. It is also possible to analyze the difference between the current voltage characteristics estimated by the evaluation method of the present embodiment and the current voltage characteristics obtained by conduction measurement. Furthermore, according to the evaluation method of the present embodiment, a carrier balance sheet (see Analysis Example (C)) or the like can be obtained for a single junction type photovoltaic cell.

  In addition, although the solar cell was illustrated as a photovoltaic cell in the above-mentioned Example, the evaluation method by this embodiment can also be used for evaluation of the photovoltaic cell using light sources other than the sun.

  In the above-described embodiment, prior to analysis using carrier balance, EL absolute intensity measurement for preparing (obtaining) a radiation recombination loss rate corresponding to light emission to the outside of the photovoltaic cell during LED operation is also performed (analysis). Explained the example). However, the data (information) to be used for the analysis, such as the radiation recombination loss rate based on the EL absolute intensity measurement, may be prepared (if obtained) by some means, for example, the person who performs the analysis It may be provided by other measurement. Further, for example, the time and place where the measurement for obtaining data necessary for the analysis is performed may be different from the time and place where the analysis is performed. Note that an embodiment in which measurement and analysis can be performed simultaneously is efficient.

  The photovoltaic cell evaluation method according to the present embodiment can also be implemented as one step of the photovoltaic cell manufacturing process. By forming the photovoltaic cell and then performing the evaluation according to the above-described embodiment, for example, it can be determined whether or not the photovoltaic cell having desired characteristics is formed. Here, the method for forming the photovoltaic cell may be any known method.

  As mentioned above, although this invention was demonstrated along embodiment and an Example, this invention is not restrict | limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

SC ₁ , SC ₂ , SC ₃ , SC _i subcell TN ₁₂ , TN ₂₃ tunnel junction ELU, ELL electrode ARC antireflection layer 10 photovoltaic cell 20 power supply 30 measuring instrument 40 control device

Claims (14)

(A) The photocell having the first subcell corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode, and is obtained from the first subcell as a function of the injected current density during operation of the light emitting diode. Providing a radiation recombination loss rate corresponding to light emission to
(B) For the first subcell, based on the balance between the net carrier generation rate and the net carrier loss rate, the relationship between the injection current density during light-emitting diode operation and the extraction current density during photocell operation is determined, From the radiation recombination loss rate obtained as a function of the injection current density during the operation of the light emitting diode in the step (a), the light from the first subcell to the outside of the photovoltaic cell as a function of the extraction current density during the operation of the photovoltaic cell Obtaining a radiation recombination loss rate corresponding to the emission. In the step (a), a voltage is applied to a photovoltaic cell having a first subcell to operate as a light emitting diode, and an absolute intensity of electroluminescence from the first subcell is measured, whereby an injection current during operation of the light emitting diode is measured. Obtaining a radiation recombination loss rate corresponding to light emission from the first subcell to the exterior of the photovoltaic cell as a function of density;
The method for evaluating a photovoltaic cell according to claim 1. The photovoltaic cell further includes a second subcell stacked on the first subcell,
The step (a) corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the second subcell, and is obtained as a function of the injected current density during operation of the light emitting diode. Providing a radiation recombination loss rate corresponding to light emission from the subcell to the outside of the photovoltaic cell,
In the step (b), for the second subcell, based on the balance between the net carrier generation rate and the net carrier loss rate, the relationship between the injected current density during light-emitting diode operation and the extraction current density during photocell operation From the radiation recombination loss rate obtained as a function of the injection current density during the operation of the light emitting diode in the step (a), the function of the extraction current density during the operation of the photovoltaic cell as a function of the photovoltaic cell from the second subcell. Obtaining a radiative recombination loss rate corresponding to the light emission to the outside,
The method for evaluating a photovoltaic cell according to claim 1. further,
(C) For at least one subcell of the photovoltaic cell, the characteristics of the photovoltaic cell during operation of the photovoltaic cell are shown based on the radiation recombination loss rate obtained as a function of the extraction current density during operation of the photovoltaic cell in the step (b). The method for evaluating a photovoltaic cell according to claim 1, further comprising a step of calculating at least one physical quantity.   The physical quantities calculated in the step (c) are transmission loss in the photovoltaic cell, voltage applied to the subcell, thermalization loss in the subcell, radiation recombination loss in the subcell, non-radiative recombination loss in the subcell, junction loss in the subcell, and The method for evaluating a photovoltaic cell according to claim 4, comprising at least one of outputs from the subcell.   In the step (c), the external light emission quantum efficiency during the photovoltaic cell operation of the subcell is calculated based on the radiation recombination loss rate obtained as a function of the extraction current density during the photovoltaic cell operation in the step (b). Item 6. The method for evaluating a photovoltaic cell according to Item 4 or 5.   In the step (c), the voltage applied to the subcell is calculated based on the external light emission quantum efficiency, the ideal external light emission quantum efficiency under the radiation limit condition, and the ideal voltage applied to the subcell under the radiation limit condition. The method for evaluating a photovoltaic cell according to claim 6.   The method for evaluating a photovoltaic cell according to claim 6, wherein in the step (c), the internal light emission quantum efficiency of the subcell is calculated based on the external light emission quantum efficiency. As an item constituting the net carrier loss rate of the balance between the net carrier generation rate and the net carrier loss rate in the subcell used in the step (b),
(R1) a radiation recombination loss rate corresponding to light emission from the subcell to the outside of the photovoltaic cell;
(R2) includes a non-radiative recombination loss rate in the subcell,
In the step (b), for the subcell,
Based on the radiation recombination loss rate of the item (R1) obtained in the step (a), the non-radiative recombination loss rate of the item (R2) is obtained as a function of the injection current density during the operation of the light emitting diode.
further,
From the non-radiative recombination loss rate of the item (R2) obtained as a function of the injection current density during operation of the light emitting diode, the non-radiative recombination loss of the item (R2) as a function of the extraction current density during operation of the photovoltaic cell. The method for evaluating a photovoltaic cell according to claim 1, wherein a rate is obtained. Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A method for evaluating a photovoltaic cell, comprising: obtaining a radiation recombination loss rate corresponding to light emission from the first subcell to the outside of the photovoltaic cell as a function of an extraction current density during photovoltaic cell operation. Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A photovoltaic evaluation device, comprising: a computing device configured to obtain a radiation recombination loss rate corresponding to light emission from the first subcell to the exterior of the photovoltaic cell as a function of extraction current density during photovoltaic operation. further,
A power supply for applying a forward bias to the photovoltaic cell;
The evaluation apparatus for a photovoltaic cell according to claim 11, further comprising a measuring device that measures an absolute intensity of electroluminescence of the photovoltaic cell. Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A program for causing a computer to execute a procedure for obtaining a radiation recombination loss rate corresponding to light emission from the first subcell to the outside of the photovoltaic cell as a function of an extraction current density during photovoltaic cell operation. Forming a photovoltaic cell;
And evaluating the characteristics of the photovoltaic cell,
The step of evaluating the characteristics of the photovoltaic cell includes:
Light from the first subcell to the outside of the photovoltaic cell, which corresponds to the absolute intensity of electroluminescence during operation of the light emitting diode of the photovoltaic cell having the first subcell, obtained as a function of the injected current density during operation of the light emitting diode Radiation recombination loss rate corresponding to emission,
Based on the relationship between the injection current density during the operation of the light emitting diode and the extraction current density during the operation of the photovoltaic cell, which is obtained based on the balance between the net carrier generation rate and the net carrier loss rate for the first subcell. And
A method of manufacturing a photovoltaic cell comprising the step of obtaining a radiation recombination loss rate corresponding to light emission from the first subcell to the outside of the photovoltaic cell as a function of an extraction current density during photovoltaic cell operation.