KR102156113B1 - method to determine lateral collection length of charge carriers - Google Patents

Abstract

The method for measuring the horizontal collection distance of a charge carrier according to the present invention comprises: a light absorption layer; Measuring a photocurrent by using a target solar cell including a metal electrode positioned on the light absorbing layer, and irradiating light to the target solar cell; And deriving a horizontal collection distance of a charge carrier by using the photocurrent. The measuring method according to the present invention has the advantage of being able to measure the horizontal collection distance of a charge carrier with relatively simple and high accuracy.

Description

Method to determine lateral collection length of charge carriers

The present invention relates to a measuring method for easily measuring the horizontal collection distance of charge carriers in a solar cell.

As a transparent electrode provided on the light-receiving side of a solar cell, conductive metal oxides having high light transmittance and low sheet resistance such as indium tin oxide (ITO), ZnO:Al, and SnO ₂ are used. However, in order to overcome the low mechanical properties and high process cost of these conductive metal oxide-based transparent electrodes, recent metal oxide transparent electrodes are being replaced with network-based transparent electrodes such as silver nanowires, carbon nanotubes, and metal meshes. Research is actively being conducted.

As shown in the example shown in FIG. 1, photo-charge collection paths between the metal oxide-based transparent electrode and the network-based transparent electrode are different from each other. In the case of a metal oxide-based transparent electrode ((TCO film), as shown in FIG. 1(a) showing the charge transfer path, in a solar cell, the charge carrier moves vertically and the metal oxide-based transparent electrode (path 1 of FIG. 1(a)) ), and moves horizontally along the metal oxide-based transparent electrode to a metal grid connected to an external circuit (path 2 in Fig. 1(a)). On the other hand, in the case of a network-based transparent electrode (Network-TCE) As shown in Fig. 1(b) showing the charge transfer path, the photo-generated charge carrier moves vertically (path 1a in Fig. 1(b)) until it reaches the front of the solar cell, and then in the horizontal (horizontal) direction. After reaching the network by moving to (path 1b of FIG. 1(b)), it moves to a metal grid connected to an external circuit along the network (path 2 of FIG. 1(b)).

As shown in FIG. 1, in the case of a network-based transparent electrode, unlike a metal oxide-based transparent electrode, an additional horizontal (lateral) movement of the charge carrier (path 1b in FIG. 1(b)) is required in order for the charge carriers to be collected in the electrode. do.

Therefore, in order for the network-based transparent electrode to effectively collect photocurrent without loss of the generated charge carriers, the horizontal movement distance that the charge carriers must move to collect in the electrode (that is, the size of the empty space of the mesh electrode) is the capture of the charge carriers. Should be shorter than the distance.

When a network-based transparent electrode is to be used, in order to collect photocurrent without loss, a network-based transparent electrode must be designed in consideration of the horizontal collection distance of the charge carrier.

However, little is known how to directly measure the horizontal collection distance of charge carriers. However, for measuring the diffusion distance of minority charge carriers, U.S. Patent No. 9400306 discloses external quantum efficiency for measuring the diffusion distance. A method of measuring the diffusion distance of a charge carrier using (EQE, external quantum efficiency) is disclosed. However, in the case of using this method, if the diffusion distance of the charge carrier is larger than the thickness of the absorbing layer of the thin film, an error occurs, and the measurement of the external quantum efficiency itself requires precise equipment, making it difficult to easily measure the diffusion distance. Considering the collection distance can be inferred, but there is a limitation in that it cannot directly calculate the horizontal collection distance of the charge carrier.

Accordingly, in order to implement a network-based transparent electrode that can effectively collect photocurrent without loss of charge carriers, it is necessary to develop a method for measuring the horizontal collection distance of charge carriers of a solar cell with high reliability as a simpler method.

US Patent Publication No. 9400306

An object of the present invention is to provide a method capable of measuring the horizontal collection distance of a charge carrier by a simple method of measuring a photocurrent by irradiating light.

Another object of the present invention is to provide a design method of a network-based transparent electrode capable of effectively collecting a photocurrent by having a designed collection efficiency and a designed light transmittance.

The method for measuring the horizontal collection distance of a charge carrier according to the present invention comprises: a light absorption layer; Measuring a photocurrent by using a target solar cell including a metal electrode positioned on the light absorbing layer, and irradiating light to the target solar cell; And deriving a horizontal collection distance of a charge carrier by using the photocurrent.

In the measurement method according to an embodiment of the present invention, the absorption depth of light irradiated to the target solar cell for the light absorption layer may be within 150 nm.

In the measurement method according to an embodiment of the present invention, light irradiated to a target solar cell may be monochromatic light.

In the measurement method according to an embodiment of the present invention, the photocurrent may be a current obtained by irradiating a target solar cell with white light and then irradiating monochromatic light.

In the measuring method according to an embodiment of the present invention, the metal electrode may be in the shape of a disk, an elliptical plate, or a polygonal plate.

In the measurement method according to an embodiment of the present invention, based on the photocurrent value according to the radius of the metal electrode, the horizontal collection distance of the charge carrier may be calculated using Equation 1 below.

(Equation 1)

In Equation 1, i _p is the measured photocurrent, J _g is the photocurrent density, L _lc is the charge carrier horizontal capture distance, and r is the radius of the metal electrode.

In the measuring method according to an embodiment of the present invention, the measuring of photocurrent may include measuring the photocurrent by varying the radius of the metal electrode.

In the measurement method according to an embodiment of the present invention, the horizontal collection distance of the charge carrier may be derived by Equation 2 below.

(Equation 2)

In relational equation 2, L _lc is the charge carrier horizontal collection distance, h is the Franck constant, c is the luminous flux, λ is the wavelength of the irradiated light, i _p is the measured photocurrent, I ₀ is the intensity of the irradiated light, and L _peri is the The circumference length, e is the charge of the electron, and R _f is the light reflectance of the target solar cell.

In the measurement method according to an embodiment of the present invention, the target solar cell may further include a buffer layer positioned between the light absorbing layer and the metal electrode and positioned in contact with the light absorbing layer.

In the measurement method according to an embodiment of the present invention, light irradiated to the target solar cell may have a longer wavelength than light having a wavelength corresponding to the energy band gap of the buffer layer.

In the measurement method according to an embodiment of the present invention, light irradiated to a target solar cell may be light in a wavelength band of 550 to 700 nm.

The present invention includes a method for designing a transparent electrode using the method for measuring the horizontal collection distance of a charge carrier.

The method of designing a transparent electrode according to the present invention includes: calculating a horizontal charge carrier collection distance by the method for measuring a horizontal charge carrier collection distance; Setting horizontal collection efficiency and light transmittance of the network-based transparent electrode; And calculating the empty space size of the network-based transparent electrode that satisfies the set light transmittance and horizontal collection efficiency using Equation 3 below.

(Equation 3)

In Equation 3, η _l is the horizontal collection efficiency, Llc is the horizontal collection distance of the charge carrier, and L is the size of the empty space of the network-based transparent electrode.

The present invention includes a transparent electrode for a thin film solar cell designed according to the method for designing the transparent electrode described above.

The present invention has the advantage of measuring the horizontal collection distance of the charge carrier by using an extremely simple and easy method of irradiating light and measuring the photocurrent, and furthermore, the horizontal collection distance of the charge carrier with high accuracy regardless of the intensity of the applied light. Can be measured. In addition, the present invention has the advantage of designing a network-based transparent electrode having a designed horizontal collection efficiency and a designed light transmittance using the horizontal collection distance of the charge carrier.

1 is a collection path (movement path) of photo-generated charge carriers in a solar cell equipped with a metal oxide-based transparent electrode (Fig. 1(a)) and a solar cell equipped with a network-based transparent electrode (Fig. 1(b)) It is a diagram showing.
2 is a cross-sectional view (FIG. 2(a)) and a top bird's-eye view (FIG. 1(b))) of a solar cell used in a measuring method according to an embodiment of the present invention.
3 is a diagram illustrating measurement of a photocurrent of a target solar cell used in a measurement method according to an embodiment of the present invention.
FIG. 4 is a diagram showing a diameter of a silver nanowire forming a transparent electrode based on a conductive network and a horizontal collection efficiency at a set light transmittance in a method of designing a transparent electrode according to an embodiment of the present invention, and a blank space size of a conductive network .

Hereinafter, a method of measuring a horizontal collection distance of a charge carrier of a solar cell according to the present invention will be described in detail. At this time, unless there are other definitions in the technical and scientific terms used, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and unnecessarily obscure the subject matter of the present invention in the following description. Description of possible known functions and configurations will be omitted.

The present invention relates to a method for measuring the horizontal collection distance of charge carriers in a solar cell. In the present invention, the horizontal charge carrier collection distance corresponds to the charge carrier diffusion distance, and accordingly, the present invention may include a method of measuring the charge carrier diffusion distance in a solar cell.

In the method of measuring the horizontal collection distance of a charge carrier according to an embodiment of the present invention, the target solar cell may mean a solar cell used for measuring the horizontal collection distance of the charge carrier, and together with this, the horizontal collection distance of the charge carrier is measured. It can mean the solar cell you want to do. The target solar cell may be a silicon solar cell in which the material of the light absorption layer is crystalline or amorphous silicon, a compound semiconductor solar cell in which the material of the light absorption layer is a compound semiconductor, or an organic solar cell in which the material of the light absorption layer is an organic semiconductor material. In this case, the compound semiconductor solar cell may include a group III-V compound semiconductor solar cell, a group II-III-VI compound semiconductor solar cell, or a group II-VI compound semiconductor solar cell. Group III-V compound semiconductor solar cells may include GaAs or InGaP solar cells, and II-III-VI compound semiconductor solar cells are CIS (Cu-In-S, Se) or CIGS (Cu-In, Ga- S,Se) may include a solar cell, and the II-VI group solar cell may include a CdTe solar cell.

The method for measuring the horizontal collection distance of a charge carrier according to the present invention comprises: a light absorption layer; Measuring a photocurrent by using a target solar cell including a metal electrode positioned on the light absorbing layer, and irradiating light to the target solar cell; And deriving a horizontal collection distance of a charge carrier by using the photocurrent.

The present invention is an extremely simple and easy method of measuring the current by irradiating light to a target solar cell to be measured. The horizontal collection distance of charge carriers (small number of carriers), that is, the diffusion distance of the charge carriers can be accurately measured. There is an advantage.

Specifically, the conventional method of measuring the diffusion distance of charge carriers has been conventionally measured using an external quantum efficiency (EQE). However, it is difficult to measure the external quantum efficiency because it requires the use of highly specialized measuring equipment. In addition, when measuring the charge carrier diffusion distance using this external quantum efficiency, the intensity of the irradiated light is 0.1 to 1 mW. /cm ^{2, which} is very different from the actual operating conditions of the solar cell, and if the length of the measured charge carrier diffusion distance is greater than the thickness of the thin film, there is a problem that an error of the measured value occurs, and only in the wavelength band where the external quantum efficiency change is large. There is a problem that can be measured.

However, when measuring the horizontal collection distance (diffusion distance) of the charge carrier using the method of the present invention, it is not necessary to measure the external quantum efficiency, and a simple method of irradiating light to the target solar cell and measuring the current is high. It has the advantage of being able to measure the charge carrier diffusion distance with accuracy.

The absorption depth of the irradiated light to the light absorbing layer that absorbs the light irradiated to the target solar cell and generates photoelectrons and photoholes is preferably within 150nm, more preferably within 100nm. That is, it is preferable that light having an absorption depth of 150 nm, more preferably within 100 nm, is irradiated in the light absorption layer. The absorption depth of light irradiated to the target solar cell means how deeply the light penetrates into the absorber before the light is absorbed, and the absorption depth varies according to the wavelength of light even with the same light absorber (light absorbing layer material). As is known, the absorption depth is given by the reciprocal of the absorption coefficient (α ^-1 ), and means the distance at which the intensity of irradiated light is reduced to about 36% (1/e).

When the absorption depth of the irradiated light is 150 nm, more preferably within 100 nm, the photocharge may be generated by being limited to a thin surface area (surface area on the light-receiving surface side) not inside the light absorption layer. At this absorption depth, the vertical (thickness direction of the light-absorbing layer) movement of the photo-charge carriers can be neglected and photocurrent by collection of the photo-charge carriers into the metal electrode by horizontal (direction parallel to the surface of the light-absorbing layer) movement. Can be created.

In addition, it is preferable that the irradiated light is monochromatic light. When the irradiated light is monochromatic light, it is advantageous because it is limited to a thinner surface area of the light absorbing layer to generate photocharges, and it is also advantageous because the current density can be calculated. In this case, the half-width (FWHM) of the monochromatic light in the optical spectrum (light intensity-wavelength spectrum) may be 100 nm, specifically 50 nm or less, but is not limited thereto.

In the measuring method of the present invention, since the accuracy of the horizontal distance of the charge carrier calculated according to the intensity of the irradiated light does not vary, the intensity of the light irradiated to the target solar cell may be an intensity suitable for photocurrent measurement. As a practical example, the strength of the irradiated steel may be 10 to 200W/m ² , but is not limited thereto.

In the measurement method according to an embodiment of the present invention, the photocurrent may be a current obtained by irradiating white light to a target solar cell, stopping the irradiation of white light, and irradiating monochromatic light.

When the target solar cell is irradiated with white light, photoelectron-hole pairs may be generated by high-energy photons, and these photocharges may neutralize defects present at the interface of the light absorption layer. When the target solar cell is irradiated with white light due to such defect neutralization, a gradual increase in photocurrent occurs, and the photocurrent tends to saturate to a certain value after a certain time.

As the conditions under which the solar cell operates normally is a state in which defects present at the interface of the light absorption layer are neutralized, as described above, photocurrent (horizontal photocurrent) used for measuring the horizontal collection distance of the charge carrier by irradiating monochromatic light after irradiation with white light. By measuring, it is advantageous to more accurately calculate the horizontal collection distance under actual solar cell operating conditions.

The intensity of the irradiated white light may be similar to the intensity in consideration of the intensity of the irradiated sunlight during normal operation of the solar cell. For example, the intensity of white light irradiated may be 0.8 to 1.2 sun, but is not limited thereto.

The metal electrode may have any shape as long as the metal electrode does not cover all of the light absorbing layer, but only partially, on a projection image viewed from the metal electrode side toward the light absorbing layer. As a specific example, the metal electrode may be in the shape of a disk, an elliptical plate, or a polygonal (triangle to dodecagonal) plate. In this case, when the metal electrode is not circular, it goes without saying that the size or radius of the metal electrode may mean the size or radius when converted to a circle having the same area.

As described later, even if the metal electrode has a very small size in the order of several micrometers, the horizontal collection distance can be measured by measuring the photocurrent according to the size of the metal electrode by changing the size of the metal electrode, thereby ensuring stable current movement. As far as possible, the size of the metal electrode is not largely limited.

However, as will be described later, in the case of calculating the horizontal collection distance by measuring the ease of formation of the metal electrode and single light irradiation and photocurrent measurement, the radius of the metal electrode is 100 μm or more, specifically, the radius of the metal electrode is 100 to 3000. It is advantageous that the µm, more specifically 500 to 3000 µm or more.

The metal electrode is light opaque and can be used without limitation if it is a metal having conductivity. As a specific and non-limiting example, the metal electrode is Al, Zn, Ti, Hf, Mg, Cu, Zr, Ca, Li, Sr, Ba, Sc, Y, Nb, Cr, Fe, Ru, Co, Rh, V , Ir, Ni, Pd, Pt, Ag, Cd, B, Ga, Mo, W, Mn, In, Ge, Sn, Sb, and may include one or more selected from Bi.

Hereinafter, the present invention will be described in detail based on a compound semiconductor solar cell in which a buffer layer, which is a layer of another heterogeneous material, is provided between the light absorbing layer and the electrode (light receiving electrode located on the light-receiving surface), and the metal electrode has a disk shape for clear understanding. . However, when a layer of heterogeneous material between the light absorbing layer and the electrode is provided, the light irradiation conditions described later are more advantageous, and as the horizontal collection distance of the charge carrier can be measured in the same or similar method as described below, the present invention The target solar cell in is not limited to compound semiconductor solar cells. In addition, even if the metal electrode is not in the shape of a disk, the shape of the metal electrode is not limited to the shape of a disk in the present invention, as the charge carrier horizontal collection distance is calculated equally by the circumference of the metal electrode instead of the circumference of the disk. .

Specifically, light irradiated to the target solar cell may have a longer wavelength than light having a wavelength corresponding to the energy band gap of the buffer layer. For example, when the band gap energy of the buffer layer is Eg1 (eV), the wavelength corresponding to Eg1 (eV) λ1 = hc/Eg1 (h = Frank's constant, c luminous flux) = 1240 (eV·nm)/Eg1 (eV) And, λ2, which is the wavelength of irradiated light, is preferably a longer wavelength than λ1. That is, it is preferable that λ1 <λ2. Light irradiation under these conditions is advantageous because it can fundamentally prevent the generation of charge carriers by the buffer layer.

A light absorption layer that is a compound semiconductor; A buffer layer positioned on the light absorption layer; In the case of a target solar cell including; and a metal electrode positioned on the buffer layer, it is preferable that light having a wavelength not absorbed by the buffer layer is irradiated together with the above-described light irradiation conditions.

Specifically, light irradiated to the target solar cell may have a longer wavelength than light having a wavelength corresponding to the energy band gap of the buffer layer. For example, when the bandgap energy of the buffer layer is Eg1 (eV), the wavelength corresponding to Eg1 (eV) λ1 = hc/Eg1 (h = Frank's constant, c luminous flux) = 1240 (eV·nm)/Eg1 (eV) And, λ2, which is the wavelength of irradiated light, is preferably a longer wavelength than λ1. That is, it is preferable that λ1 <λ2. Light irradiation under these conditions is advantageous because it can fundamentally prevent the generation of charge carriers by the buffer layer.

Light absorption by the buffer layer is prevented and a practical example of irradiation light having a light absorption depth of 150 nm, more preferably within 100 nm.When the target solar cell is a compound semiconductor solar cell, the wavelength of the irradiated light is 550 to 700 nm, specifically 550 To 650nm, but the present invention is not limited to these specific wavelength conditions.

In addition, when measuring the horizontal charge carrier collection distance in the target solar cell provided with the buffer layer, it is very advantageous to irradiate the target solar cell with white light and then monochromatic light. In this way, high energy photons generate photoelectron-hole pairs in the buffer layer, and these photocharges can neutralize defects present in the buffer layer as well as the interface between the light absorption layer and the buffer layer. Accordingly, when measuring the horizontal charge carrier collection distance by irradiation with white light, the effect of defects present at the buffer layer itself and the interface can be very effectively excluded, which is advantageous.

FIG. 2 is a diagram showing an example of a target solar cell used for measuring a horizontal collection distance of a charge carrier, and is a cross-sectional view (FIG. 2(a)) and an upper bird's-eye view (FIG. 2(b)). In this case, the black dots in FIG. 2 denote photo-charge carriers generated by light.

2, the target solar cell may include a lower electrode 100, a light absorption layer 200, a buffer layer 300, and a disk-shaped metal electrode 400, and the light absorption layer 200 And the buffer layer 300, and the buffer layer 300 and the metal electrode 400 (radius = r) may be positioned in contact with each other.

The photocurrent (i _p ) measured in FIG. 2 can be represented by Equation 4 below.

(Equation 4)

In Equation 4, i _p is a photocurrent measured by light irradiation, as shown in Fig. 2(a), and di _g is a ring area with a radius of R and a width of dR as shown in Fig. 2(b). It means the current generated by light in, and η _R is according to Equation 5 below.

(Equation 5)

In Equation 5, R is the radius of the ring in the arbitrary ring region shown in Fig. 2(b), r is the radius of the metal electrode, and L _lc is the horizontal collection distance. Accordingly, Rr corresponds to the horizontal movement distance of the charge carriers generated in the ring region.

If di _g is expressed as the current density (J _g ), as di _g =J _g 2πRdR, Equation 1 can be derived by substituting Equation 5 into Equation 4 and performing the integral in the metal radius r to an infinite range. .

(Equation 1)

In Equation 1, i _p is the measured photocurrent, J _g is the photocurrent density, L _lc is the charge carrier horizontal capture distance, and r is the radius of the metal electrode.

Accordingly, as a simple method of measuring the photocurrent in two or more metal electrodes having different radii from each other, the charge carrier horizontal collection distance (L _lc ) can be calculated.

As can be seen from Equation 1, the measurement method according to an embodiment of the present invention has the advantage of measuring the horizontal collection distance of the charge carrier using only the size, photocurrent, and current density of the metal electrode. This advantage prevents the occurrence of errors that may occur when measuring the diffusion distance using external quantum efficiency, and has the advantage of being able to measure the horizontal collection distance of the charge carrier by a simple method regardless of the intensity of applied light.

Furthermore, according to an embodiment of the present invention, when calculating the charge carrier collection distance using Equation 1, by measuring the photocurrent several times by varying the radius of the metal electrode, the charge carrier horizontal collection distance without any information on the photocurrent density There is an advantage of being able to calculate (L _lc ). That is, the method for measuring the horizontal collection distance of the charge carrier according to an embodiment of the present invention has the advantage of deriving the horizontal collection distance of the charge carrier only with the radius of the photocurrent and the metal electrode.

Accordingly, the measurement method according to an embodiment of the present invention is a target solar cell provided with metal electrodes having different sizes (radius) or a target solar cell in which metal electrodes having different sizes (radius) are separated from each other on one buffer layer. Measuring a photocurrent for each size (radius) of a metal electrode by irradiating light to a target solar cell using a cell; And calculating the charge carrier horizontal collection distance using Equation 1, based on the photocurrent values measured at metal electrodes having different sizes.

(Equation 1)

In Equation 1, i _p is the measured photocurrent, J _g is the photocurrent density, L _lc is the charge carrier horizontal capture distance, and r is the radius of the metal electrode.

At this time, in the case where the target solar cell is a solar cell in which metal electrodes having different sizes (radius) are separated from each other on one buffer layer, two or more metal electrodes having different sizes are formed by different metal electrodes. It goes without saying that, for example, the collected photocurrent) may be in a state separated by a distance that may not be affected. As a specific and non-limiting example, the distance between two adjacent metal electrodes may be in the order of several to tens of centimeters.

In addition, in the method for measuring the horizontal collection distance of a charge carrier according to an embodiment of the present invention, when the radius of the metal electrode is 100 µm or more, according to L _lc << r in Equation 1, the horizontal collection distance of the charge carrier is derived by Equation 6. Can be. That is, when the radius of the metal electrode is 100 μm or more, the horizontal collection distance of the charge carrier can be derived by Equation 6.

(Equation 6)

At this time, in Equation 6, L _peri is the circumferential length of the metal electrode.

That is, in the method of measuring the horizontal collection distance of the charge carrier according to an embodiment of the present invention, when the size of the metal electrode is 100 µm or more, and when the size of the metal electrode is larger than a certain level, the y-axis is the photocurrent, and the x-axis is the radius of the metal electrode. There is an advantage of being able to measure the charge carrier diffusion distance by using the slope of.

When the light irradiated to the solar cell is monochromatic light, the current density (J _g ) is according to Equation 7 below.

(Equation 7)

In Equation 7, J _g is the current density, e is the electron charge, I _ab is the intensity of light absorbed by the light absorbing layer, h is the Frank's constant, c is the luminous flux, and λ is the wavelength of the irradiated light.

According to Equation 8, the intensity of light absorbed by the light absorption layer I _ab , Equation 6 can be derived from Equation 2 below.

(Equation 8)

In Equation 8, I _ab is the intensity of light absorbed by the light absorbing layer, I ₀ is the intensity of light irradiated to the target solar cell, and R _f is the light reflectance of the target solar cell, that is, on the light-receiving surface on the side where the metal electrode is formed in the target solar cell. Is the light reflectance of

(Equation 2)

In Equation 2, L _lc is the horizontal capture distance of the charge carrier, h is the Franck constant, c is the luminous flux, λ is the wavelength of the irradiated light, i _p is the measured photocurrent, I ₀ is the intensity of the irradiated light, and L _peri is the The circumference length, e is the charge of the electron, and R _f is the light reflectance of the target solar cell.

As can be seen from Equation 2, the measurement method according to an embodiment of the present invention has the advantage of measuring the horizontal collection distance of the charge carrier using only the size of the metal electrode and the photocurrent, and the metal electrode of a single size There is an advantage in that the horizontal collection distance of the charge carrier can be measured by a simple and simple measurement that irradiates light to the equipped target solar cell and measures the photocurrent only once.

In the case of a compound semiconductor solar cell, the light absorbing layer may be a chalcogen compound of copper and one or more elements selected from groups 12 to 14. Specifically, the compound semiconductor may include a copper-indium-chalcogen compound, a copper-indium-gallium-chalcogen compound, or a copper-zinc-tin-chalcogen compound. More specifically, the compound semiconductor is CIS (Cu-In-Se or Cu-In-S), CIGS (Cu-In-Ga-Se or Cu-In-Ga-S), CIGSS (Cu-In-Ga-Se -S), CZTS (Cu-Zn-Sn-Se or Cu-Zn-Sn-S) or CZTSS (Cu-Zn-Sn-Se-S). More specifically, the compound semiconductor is CuIn _x Ga _1-x Se ₂ (real number 0<x<1), CuIn _x Ga _1-x S ₂ (real number 0<x<1), CuIn _x Ga _1-x (Se _y S _1-y ) ₂ (real number 0<x<1, real number 0<y<1), Cu ₂ Zn _x Sn _1-x Se ₄ (real number 0<x<1), Cu ₂ Zn _x Sn _1-x S ₄ (real number 0<x<1) or Cu ₂ Zn _x Sn _1-x (Se _y S _1-y ) ₄ (real number 0<x<1, real number 0<y<1) ), but is not limited thereto, and a chalcogen compound is sufficient as a light absorbing layer used in a conventional compound semiconductor-based solar cell.

The thickness of the light absorbing layer is sufficient as long as it is used in a conventional compound semiconductor solar cell, and a specific and non-limiting example may be 1 to 5 μm, but the present invention cannot be limited by the thickness of the light absorbing layer. to be.

The buffer layer provided on the light absorption layer forms a light absorption layer and a built-in potential (pn junction, depletion layer), so that photoelectrons can selectively and spontaneously move from the light absorption layer to the buffer layer, and the lattice constant of the compound semiconductor forming the light absorption layer Any material that has a similar lattice constant and can form a high-quality interface can be used. As a specific example, when the compound semiconductor is a chalcogen compound of one or two or more selected elements from copper and groups 12 to 14, the buffer layer may include a buffer material used as a buffer layer in a conventional compound semiconductor solar cell.

Specifically, the buffer layer is doped with an n-type dopant or not doped with an n-type dopant, ZnS, CdS, Zn _x Cd _1-x S (real number of 0<x<1), In ₂ S ₃ , SnS ₂ , CdSe And one or two or more materials selected from ZnSe, but are not limited thereto. Hereinafter, a case doped with an n-type dopant is referred to as extrinsic, and a case not doped with a dopant is referred to as intrinsic. In more detail, the buffer layer is Extrinsic ZnS, Extrinsic CdS, Extrinsic Zn _x Cd _1-x S (real number of 0<x<1), Extrinsic In ₂ S ₃ , Extrinsic SnS ₂ , Extrinsic CdSe, Extrinsic ZnSe, Intrinsic ZnS, Intrinsic CdS, Intrinsic Zn _x Cd _1-x S (0<x<1), Intrinsic In ₂ S ₃ , Intrinsic SnS ₂ , Ste One or two or more of linzic CdSe and intrinsic ZnSe may be selected.

In this case, when the buffer layer contains an n-type dopant (when it contains an extrinsic semiconductor material), this means that at least a portion of the buffer layer is doped with an n-type dopant. When the buffer layer is doped with an n-type dopant, the concentration of the n-type dopant may be changed in a thickness direction that is a direction from a surface in contact with the light absorbing layer of the buffer layer toward the opposite surface. In detail, the concentration of the n-type dopant may continuously or discontinuously increase in the thickness direction of the buffer layer in a direction from a surface in contact with the light absorbing layer to an opposite surface thereof. In this case, the discontinuous increase also includes a structure in which an extrinsic region doped with an n-type dopant is located above an intrinsic region not doped with an n-type dopant, and the doping profile of the n-type dopant in the extrinsic region (thickness It goes without saying that the doping profile in the direction) may increase continuously or discontinuously. Intrinsic ZnS, Intrinsic CdS, Intrinsic Zn _x Cd _1-x S (0<x<1), Intrinsic In ₂ S ₃ , Intrinsic SnS ₂ , Intrinsic CdSe and Intrinsic ZnSe It may contain one or more materials selected from, and the extrinsic region is Extrinsic ZnS, Extrinsic CdS, Extrinsic Zn _x Cd _1-x S (real number where 0<x<1), Extrinsic It may include one or more materials selected from direct In ₂ S ₃ , Extrinsic SnS ₂ , Extrinsic CdSe and Extrinsic ZnSe. In this case, the buffer layer may have a structure in which the intrinsic region and the extrinsic region are sequentially formed in the thickness direction, or the n-type dopant may have a profile that continuously or discontinuously increases in the thickness direction (from the light absorbing layer to the front electrode). . At this time, the n-type dopant is an element selected from one or two or more of Al, Ga, B, Sn, Sb, F, Cl, Mn, Co, Ni, Fe, Ti, Mo, Nb, P, O, In, Cr, and Zn , More specifically, one or more elements selected from Ga, Al, B In, F, Cr, and Zn may be mentioned.

Since the buffer layer contains an n-type dopant and the n-type dopant has a concentration profile that continuously or discontinuously increases in the thickness direction of the buffer layer, a stable and wide depletion layer can be formed between the light absorbing layer and the buffer layer, thereby effectively separating photoelectrons. And can be moved.

The thickness of the buffer layer is sufficient as long as it is the thickness used in a conventional compound semiconductor solar cell, and a specific and non-limiting example may be 10 to 100 nm, but it is a matter of course that the present invention cannot be limited by the thickness of the buffer layer.

The target solar cell may further include a rear electrode formed under the light absorption layer and a substrate formed under the rear electrode, but is not limited thereto.

Substrate (can serve as a support, and may include a rigid substrate or a flexible substrate. A specific example of a rigid substrate is a glass substrate including soda lime glass, a ceramic substrate such as alumina, stainless steel, and copper. As a specific example of the flexible substrate, a polymer substrate such as polyimide, a metal foil such as stainless steel foil, etc. may be mentioned, but the present invention cannot be limited by the material of the substrate. Of course.

The rear electrode has high electrical conductivity, can make ohmic contact with the compound semiconductor of the light absorbing layer, and any material that is stable in a chalcogen atmosphere can be used as a material used as a rear electrode in conventional compound semiconductor-based solar cells. This is enough. As an example of a specific rear electrode, molybdenum (Mo) may be mentioned, but it goes without saying that the present invention cannot be limited by the material of the rear electrode (back electrode). The thickness of the rear electrode is sufficient as long as it is used in a conventional compound semiconductor-based solar cell, and as a specific and non-limiting example, 0.5 to 2 μm may be mentioned, but the present invention is limited by the thickness of the rear electrode (back electrode). Of course it cannot be.

The present invention includes a method of designing a transparent electrode for a solar cell, specifically a network-based transparent electrode for a solar cell, using the method for measuring the horizontal collection distance of the charge carrier described above. The network-based transparent electrode may mean a metal mesh-type transparent electrode or a conductive one-dimensional nanostructure network-based transparent electrode, and a conductive one-dimensional nanostructure network-based transparent electrode is a continuous current as conductive one-dimensional nanostructures form contacts with each other. It may mean a transparent electrode forming a network that is a moving path. In this case, the conductive one-dimensional nanostructure may include nanotubes or nanowires made of conductive materials such as carbon nanotubes and silver nanowires, but is not limited thereto.

The method of designing a transparent electrode according to the present invention includes the steps of calculating a horizontal charge carrier collection distance by the method for measuring a horizontal charge carrier collection distance; Setting horizontal collection efficiency and light transmittance of the network-based transparent electrode; And calculating an empty space size of the network-based transparent electrode that satisfies the light transmittance and horizontal collection efficiency set using Equation 3 below.

In this case, the size of the empty space of the network-based transparent electrode may mean the size of the network in the case of a metal mesh-type transparent electrode, and in the case of a conductive one-dimensional nanostructure network-based transparent electrode, a closed curve formed by contacting one-dimensional nanostructures with each other It can mean the average size (diameter) when the closed curves are converted into circles of the same area based on the (minimum closed curve standard).

(Equation 3)

In Equation 3, η _l is the horizontal collection efficiency, L _lc is the horizontal collection distance of the charge carrier, and L is the empty space size of the network-based transparent electrode.

Further, when the network-based transparent electrode is a metal mesh type transparent electrode, the step of calculating the width of the conductive mesh using Equation 9 below may be further performed.

(Equation 9)

In Equation 9, D is the width of the conductive mesh in the transparent electrode (network-based transparent electrode), and T is the light transmittance of the transparent electrode.

The method of designing a transparent electrode according to the present invention is, when appropriately setting the horizontal collection efficiency and light transmittance of the transparent electrode according to the specific use of the solar cell, the horizontal collection efficiency and light transmittance set using only the measured charge carrier horizontal collection distance. There is an advantage of calculating the size of an empty space of a transparent electrode in which a transparent electrode satisfying can be manufactured, and further, there is an advantage of calculating the width of a conductive mesh.

At this time, it goes without saying that it is possible to manufacture a transparent electrode based on a conductive one-dimensional nanostructure network having a blank space size of the designed transparent electrode by controlling the density of the conductive one-dimensional nanostructure applied to form the transparent electrode.

3 is a diagram showing the measurement of the photocurrent of a target solar cell manufactured during light irradiation. Specifically, the target solar cell forms a 2000 nm-thick CuIn _x Ga _1-x S ₂ light absorbing layer by using co-evaporation on the Mo rear electrode on a soda-lime glass plate, and 60 nm-thick CdS on the light absorbing layer. After forming the buffer layer, an Al/Ni metal electrode was formed in the form of a disk having a radius of 1 mm using an electron beam evaporation method.

Light irradiation was performed using monochromatic light with a center wavelength of 600 nm (FHWM=50 nm). The absorption depth in the light absorption layer of the manufactured target solar cell of 600 nm monochromatic light was within 100 nm. The intensity of the irradiated monochromatic light was 66.2 W/m ^2, and the R _f of the monochromatic light (600 nm) for the manufactured target solar cell was 0.09. When the light of FIG. 3 is irradiated, a 600nm monochromatic light is generated and irradiated by passing 1sun white light through a 600nm bandpass filter (FHWM=50nm).

The photocurrent of FIG. 3 is a photocurrent measured by irradiating 600nm monochromatic light, then irradiating white light (1sun), stopping the irradiation of white light when the photocurrent is saturated, and irradiating 600nm monochromatic light again.

As can be seen from FIG. 3, a photocurrent of 6.7x10 ^-7 A was measured in 600nm monochromatic light irradiation, and the photocurrent increased to 1.8x10 ^-5 A immediately after 600nm monochromatic light irradiation was stopped, and white light irradiation continued. It can be seen that the photocurrent is saturated to 2.5x10 ^-5 A at the time of 15 minutes of white light irradiation. After the photocurrent saturation was achieved by white light irradiation, the irradiation of white light was stopped again, and 600nm monochromatic light was irradiated. After the defect was neutralized by white light, the photocurrent by 600nm monochromatic irradiation was 4.8 x 10 ^-6 A. Substituting the values of I _p =4.8 x 10 ^-6 A, λ=600nm, R _f =0.09, I ₀ =66.2W/m ² and r=1mm into Equation 2, the result of calculating the horizontal collection distance of the charge carrier, The charge carrier horizontal capture distance (L _lc ) was 26.2 μm.

4 shows a transparent electrode based on a silver nanowire network as a design target electrode, using the calculated charge carrier horizontal collection distance and Equations 3 and 4, designing a light transmittance of 90%, and then horizontal collection efficiency (η _l ) And is a diagram showing the relationship between the diameter of the nanowire and the size of the empty space of the network-based transparent electrode.

As can be seen from FIG. 4, when setting the horizontal collection efficiency of the network-based transparent electrode, it is understood that the size of the empty space of the transparent electrode or the diameter of the silver nanowire in which the transparent electrode having the set horizontal collection efficiency and the set transparency is manufactured is determined. I can.

The present invention includes a transparent electrode for a solar cell designed (manufactured) according to the method of designing a network-based transparent electrode described above.

The present invention includes a solar cell including a transparent electrode manufactured according to the method for designing a network-based transparent electrode described above. In this case, the solar cell provided with the transparent electrode may be one provided with a transparent electrode for a thin film solar cell designed and manufactured according to the design method of the present invention instead of a metal electrode in the target solar cell described above.

As described above, the present invention has been described by the specific matters and limited embodiments and drawings, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is Those of ordinary skill in the relevant field can make various modifications and variations from this description.

Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all things that are equivalent or equivalent to the claims as well as the claims to be described later belong to the scope of the spirit of the present invention. .

Claims (14)

Light absorbing layer; And
A metal electrode positioned on the light absorbing layer;
Using the target solar cell including,
Measuring a photocurrent by irradiating light to the target solar cell; And
Including; deriving a charge carrier horizontal collection distance using the photocurrent,
Based on the photocurrent value according to the radius of the metal electrode, a charge carrier horizontal collection distance measurement method for calculating a charge carrier horizontal collection distance using Equation 1 below.
(Equation 1)

(In Equation 1, ip is the measured photocurrent, J _g is the photocurrent density, L _lc is the charge carrier horizontal collection distance, and r is the radius of the metal electrode) Light absorbing layer; And
A metal electrode positioned on the light absorbing layer and having a radius of 100 μm or more;
Using the target solar cell including,
Measuring a photocurrent by irradiating light to the target solar cell; And
Including; deriving a charge carrier horizontal collection distance using the photocurrent,
The charge carrier horizontal collection distance is calculated by the following equation (2).
(Equation 2)

(In relational equation 2, L _lc is the horizontal capture distance of the charge carrier, h is the Franck constant, c is the light flux, λ is the wavelength of the irradiated light, i _p is the measured photocurrent, I ₀ is the intensity of the irradiated light, and L _peri is the metal electrode. Circumference length of, e is the charge of the electron, R _f is the light reflectance of the target solar cell) The method according to claim 1 or 2,
The light irradiated to the target solar cell is a monochromatic light, which is a method of measuring a horizontal collection distance of a charge carrier. The method according to claim 1 or 2,
The photocurrent is a current obtained by irradiating white light to the target solar cell and then irradiating monochromatic light. The method according to claim 1 or 2,
The metal electrode is a method for measuring the horizontal collection distance of charge carriers in the shape of a disk, an elliptical plate, or a polygonal plate. delete The method of claim 1,
A method of measuring a horizontal collection distance of a charge carrier in which the step of measuring the photocurrent by varying the radius of the metal electrode is performed. delete The method according to claim 1 or 2,
The target solar cell further comprises a buffer layer positioned between the light absorbing layer and the metal electrode, and positioned in contact with the light absorbing layer. The method of claim 9,
Light irradiated to the target solar cell has a longer wavelength than light having a wavelength corresponding to the energy band gap of the buffer layer. The method of claim 9,
The light irradiated to the target solar cell is light in a wavelength band of 550 to 700 nm. The method of claim 1, 2, and 7 according to any one of the steps of calculating the horizontal collection distance of the charge carriers;
Setting horizontal collection efficiency and light transmittance of the network-based transparent electrode;
Calculating an empty space size of a network-based transparent electrode that satisfies a set light transmittance and a horizontal collection efficiency using Equation 3 below;
Design method of a transparent electrode for a solar cell comprising a.
(Equation 3)

(In Equation 3, η _l is the horizontal collection efficiency, L _lc is the horizontal collection distance of the charge carrier, and L is the empty space size of the network-based transparent electrode) A transparent electrode for a thin film solar cell designed according to claim 12.
The method according to claim 1 or 2,
A method of measuring a horizontal collection distance of a charge carrier in which the absorption depth of light irradiated to the target solar cell for the light absorption layer is within 150 nm.

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