KR101283912B1 - One body light trapping apparatus having concentrator for increasing power conversion efficiency of photovoltaic cells - Google Patents

Abstract

PURPOSE: A light trapping device integrated with a concentrator for increasing the power conversion efficiency of a solar cell is provided to increase the power conversion efficiency of the solar cell without a daily light tracking apparatus by linearly arranging a compound parabolic trapper in one dimension. CONSTITUTION: An optical component has elements which are periodically arranged in one dimension. The optical component is installed in a preset space of a solar cell. The optical component improves the power conversion efficiency of the solar cell by trapping incident light in a space. The optical component includes a periodical one-dimensional array of a parabolic mold. A long axis of the parabolic mold is arranged from the east to the west.

Description

One Body Light Trapping Apparatus having Concentrator for Increasing Power Conversion Efficiency of Photovoltaic Cells}

The present invention relates to a light concentrator-integrated light confinement device for supplying light to a solar cell, and in particular, a one-dimensional linear arrangement of a CPT (Compound Parabolic Trapper), not a planar array, without a daily light tracking apparatus It can increase the power conversion efficiency (PV) of photovoltaic cells (PV), and also eliminates the need for an annual light tracking apparatus, but also allows for a smaller incident angle due to the annual light tracking apparatus. The present invention relates to a light concentrator integrated light confinement device which can reduce and further increase the light confinement effect.

Research into thin film solar cells is a global trend, and many companies are investing heavily in implementing high efficiency thin film solar cells. In the case of Korea, investment at the enterprise level is relatively low at present, but considering the global trend, the expansion of investment is inevitable, and competition for preoccupying high-efficiency thin-film solar cells is getting fiercer.

Solar cells are manufactured in bulk cell form using crystalline silicon (c-Si) or in thin film form using amorphous silicon (a-Si), organic materials, etc., as well as research on low cost, process simplification, and life extension, In order to improve absorbance in solar cells, various efforts have been made, including development of materials. Especially, light confinement technology can be an alternative, and light confinement devices using condensers show excellent power conversion efficiency due to effective light confinement. .

In 2008, Tvingstedt et al., In the light concentrator integrated light confinement device structure as shown in FIG. 5A, increases the light confinement effect to a thin-film solar cell using an MLA (Micro Lenses Array) in a one-dimensional or two-dimensional array. And increased short circuit current by 25%. In the MLA structure of the one-dimensional or two-dimensional array, such a light tracking device is required, there is a problem that can not be solved even with an annual light tracking apparatus (annual light tracking apparatus) is a situation that needs to be improved and requires a high cost. For more information, see the article "Trapping light with micro lenses in thin film organic photovoltaic cells," (Optics Express 16, 21608-21615, 2008).

Also, in 2000, Peumans et al. Proposed a light confinement method using a CPC (Compound Parabolic Concentrator) of a two-dimensional array in the light concentrator integrated light confinement device structure as shown in FIG. More information can be found in the article "Efficient photon harvesting at high optical intensities in ultrathin organic double-heterostructure photovoltaic diodes," (Applied Physics Letters 76, 2650-2652, 2000).

As described above, the light concentrator integrated light concentrator using MLA or CPC is very sensitive to the incident angle and therefore has a disadvantage that a daily light tracking apparatus must be accompanied. Given that most thin film solar cells are inexpensive, it is difficult to apply a costly light tracking device.

Accordingly, an object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a solar cell without a daily light tracking apparatus by arranging a CPT (Compound Parabolic Trapper) array instead of a planar one-dimensional linear array. It can increase the power conversion efficiency (PV) of photovoltaic cells (PV), and also eliminates the need for an annual light tracking apparatus, but also allows for a smaller incident angle due to the annual light tracking apparatus. The present invention provides a light concentrator integrated light concentrating device that can reduce the number and further increase the light confinement effect.

First, to summarize the features of the present invention, according to one aspect of the present invention, a light concentrator integrated light confinement device for delivering light to a solar cell (PV), an optical component having components of a periodic one-dimensional array The optical system includes, as the components, a periodic one-dimensional array of parabolic molds having parabolic cross-sections, the optical system having a predetermined space on the solar cell PV. It is installed on, to trap the incident light in the space is characterized in that for improving the power conversion efficiency in the solar cell (PV).

The molding is arranged such that its long axis is in the east-to-west direction, and the molding may be made of various materials such as glass or plastics.

An opening is provided at a lower portion of each of the paraboloids of the molding on the solar cell PV side, and a trapping mirror with metal coding on the lower portion for confining light incident through the opening to the space. It may further include. Here, each paraboloid of the molding is inclined at an angle as necessary according to design, and the opening portion is located at the focal point of the paraboloid of the molding on the opposite side.

The molding may be manufactured in a filled form, may be manufactured in an empty form, or may be manufactured in a metal-coated form on both sides of the parabolic shape.

The molded article having a parabolic cross section may be manufactured in an asymmetrical shape in which curved surfaces on both sides have curved surfaces having different inclination angles.

A molding further comprising a periodic second one-dimensional array of parabolic molds having a parabolic bilateral curved surface vertically over the one-dimensional array, or having a bilateral curved surface having a parabolic cross section at the long axis direction of the molding. It may further include a second periodic one-dimensional array of parabolic mold.

And, according to another aspect of the invention, the light collector integrated light confinement device for delivering light to the solar cell PV, includes an optical component having components of a periodic one-dimensional array, the optical system And a micro lens array (MLA) in a periodic one-dimensional array as the components, and the optical system is installed in a space on a solar cell PV to trap incident light in the space. In order to improve the power conversion efficiency in the solar cell (PV).

An opening may be provided at a predetermined width at a focal length of each lens of the MLA, and may further include a trapping mirror for confining light incident through the opening to the space.

The MLA of the second one-dimensional array may be further included at the end of the long axis direction of the MLA of the one-dimensional array.

The solar cell (PV) is usually a structure or inverted structure, the active layer is crystalline silicon (c-Si), organic material (for organic PV (OPV), polymers, small molecule compounds, etc.) or dye-sensitive polymer Material, amorphous silicon (a-Si), CdTe, or CIGS thin film type, or crystalline silicon (c-Si) may include a bulk cell type.

It may further include an annual light tracking apparatus for tracking the altitude of the sun during the year, operates without a daily light tracking apparatus, the light collector integrated under the control of the year-round light tracking apparatus Light Containment Device Allows the entire system to move in the direction of the sun.

The condensing magnification is n / sin (θ _a / 2) between the solar cell PV and the optical component (n ² / sin ² (θ _a / 2) is possible in _a parabolic CPT two-dimensional array), Here, θ _a is an allowance angle of light and n is a refractive index in the optical system.

It operates without a daily light tracking apparatus and the annual light tracking apparatus can be used at an allowable angle of incidence of 47 ° or more, but the components are designed to receive light with an allowable angle of incidence of 47 ° or less. When the light tracking device during the year can further increase the performance.

In addition, according to another aspect of the present invention, a method of manufacturing a light concentrator integrated light confinement device for delivering light to a solar cell (PV), to fabricate an optical component having components of a periodic one-dimensional array The optical system includes a periodic one-dimensional array of parabolic molds formed by pouring a molten liquid of a corresponding material for a molding into a metal mold and cooling the solid to solids. Producing a; And installing the manufactured optical system in a predetermined space on the solar cell PV, wherein the optical system confines incident light to the space to improve power conversion efficiency in the solar cell PV. It is characterized by.

According to the light concentrator integrated light trapping device according to the present invention, a CPT (Compound Parabolic Trapper) array or a MLA (Micro Lens Array) array is not a planar one-dimensional linear array to collect the light at a small entrance and to prevent it from escaping from below, The power conversion efficiency of the thin-film solar cell can be improved, and in some cases, by adding another one-dimensional array vertically or horizontally, there is an effect of maintaining the allowable incident angle while increasing performance compared to the one-dimensional array alone.

In addition, reducing the light-convergence magnification of the CPT can increase the allowable incident angle. When the allowable incident angle is ± 23.5 ° in a one-dimensional array, it is possible to collect about 3.8 times, which allows all changes in solar altitude during the year. Placing the one-dimensional concentrator array east-west allows the light confinement effect to be achieved without daily light tracking.

In addition, an annual light tracking apparatus may also be eliminated, but an allowable incident angle may be reduced by an annual light tracking apparatus, thereby increasing the light confinement effect.

In addition, the thin-film solar cell, which is in the spotlight as a next-generation energy source, is still in the research stage due to its low power conversion efficiency of about 10% despite the great commerciality and numerous applications. Although much research is currently focused on the synthesis of light absorbing materials that can increase power conversion efficiency, if the present invention draws an efficiency increase of about 20% for a given material, this will greatly accelerate the commercialization of thin film solar cells. .

1 is a view for explaining a light collector integrated light confinement device according to an embodiment of the present invention having an optical component, a space, a photovoltaic, and a back reflector.
Figure 2a is the expected degree of absorption in the active layer of normal polymer PV of the normal structure according to the decrease of escape probability P _esc , Figure 2b is the change of J _sc according to P _esc of the normal polymer PV according to the traveling angle in the substrate, Figure 2c Changes of J _sc according to P _esc in normal polymer PV, amorphous silicon PV, and inverted polymer PV, FIG. 2D shows thickness CuPc (6.5nm) / C ₆₀ (20nm), CuPc (10nm) / C ₆₀ (31nm), CuPc The change in J _sc with P _esc in small molecular PV for (14 nm) / C ₆₀ (38 nm).
3 is a graph showing the change in normalized J _sc for angles varying from 0 °, 30 ° and 60 ° per day in inverted and conventionally structured polymer PV.
4 is a change in normalized J _sc according to the annual incidence angle change using 1D MLA in the inverted structure and the conventional structure polymer PV, respectively.
5A and 5B show a conventional condenser integrated light confinement technique using MLA (Micro Lenses Array) and CPC, respectively.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings and the contents described in the accompanying drawings, but the present invention is not limited or limited to the embodiments.

<Absorption improvement>

1 is a view for explaining a light collector integrated light confinement device 100 according to an embodiment of the present invention having an optical component, a space, a photovoltaic, and a back reflector.

Referring to FIG. 1, the light concentrator integrated light confinement device 100 according to an embodiment of the present invention includes a space on a solar cell (PV, Photovoltaic) and a solar cell (PV) installed on a back reflector. It includes an optical component installed with a space.

The incident light causes internal reflection between the solar cell PV and the optical component, allowing more light to be absorbed in the active layer of the solar cell PV. The number of bounces (or condensation magnifications) reflected between the solar cell PV and the optical component N _ref uses an escape probability P _esc as shown in [Equation 1], where n is the refractive index. Can be represented.

[Equation 1]

For example, a textured cell with a Lambertian surface is P _esc = 1 / n ² , and N _ref = n ² . The maximum light path length (bounce number) in the bulk cell is known as the Yablonovitch limit, 4n ² . The path length of the maximum light in such a planar bulk cell can be obtained when considering the back reflection by the metal layer and the oblique light propagation. Thin film solar cells (PV) of the present invention for back reflection may be similar to metal layers. Oblique light propagation may affect absorption in thin film solar cells (PV). However, unlike the bulk cell, such a thin film solar cell (PV) can not be obtained geometrically simply the effect of improving the path length of the light according to the progress angle increases. In bulk cells, absorption can be increased from oblique light propagation by the active layer, whereas in thin film solar cells (PV), the front and back layers of optical components and solar cells (PV), which are composed of transparent electrodes and cause Fresnel reflections, The cavity effect due to the space between the thin films should be considered. Therefore, in the present invention, since the back reflection is always present in the thin film solar cell (PV), the path is improved by this, or the path is improved by considering the Fresnel reflection or cavity effect, which is complicated when the oblique light proceeds as described above. Rather than increasing, we want to base more on improving N _ref .

N _ref = n ² is 12 or more for surface textured silicon (n = 3.5) bulk cells, while the value is about 2.25 for thin film solar cells (PV) on glass (n = 1.5) substrates. This is not enough to significantly increase absorption in thin film solar cells (PV). In fact, it is possible to increase absorption through a narrow range of incidence of light. A theory which is known with respect to a limited incident angle, allows the angle of incidence of the incident light (acceptance angle) can be a _{^{n 2 / sin 2 (θ a}} / 2) of the theoretical limit value N _ref when the change in the θ _a. This limit is obtained using a two-dimensional CPC (compound parabolic concentrator) array as shown in FIG. 5B and an optical system (reflective undercoat / reflecting cathode) to guide incident light to the entrance and block light reflected from the floor. Can be.

Normally planar or textured cells have an acceptable acceptance angle of light of 180 °. However, not all of this range of incidence is necessary because the elevation of the sun in the north-south direction is within ± 23.5 ° per year. If the one-dimensional CPT array of the present invention is used as shown in FIG. 3 to reduce the acceptance angle as the optical component of the present invention, the escape probability P _esc is sin (θ _a / 2). ) / n. Therefore, although N _ref is n / sin (θ _a / 2), which is smaller than n ² / sin ² (θ _a / 2), there is an advantage that a light (sun) tracking device is unnecessary. For example, for a 47 ° acceptance angle, the value may be increased to 3.76. In addition to the CPT arrangement, there may be various optical component configurations that can increase N _ref without light (sun) tracking devices. Optical component configurations will be described to control the compromise between light trapping and acceptance angle as described below.

Through increased N _ref , absorption in the active layer of the solar cell PV is improved. For a specific propagation angle θ of a specific wavelength of light in the space, the degree of absorption A ' _act in the active layer of the solar cell PV can be expressed as shown in [Equation 2].

&Quot; (2) &quot;

Here, A _act is the absorption efficiency of the active layer having only a double pass (absorption by the first incident light inside the active layer and absorption by the reflected light), A _parasitic is absorption in other parasitic layers other than the active layer The efficiency, T _inc, is the transmittance in the optical component. P _esc should be close to zero for maximum absorption. As described above, the absorption efficiency A _act of the active layer with respect to _parasitic absorption efficiency A _parasitic per bounce determines the maximum absorption degree A ' _act in the active layer of the solar cell PV. Losses A _parasitic is usually small in the unit cell, but the loss of parasitic absorption increases when light absorption increases due to light confinement, so the overall parasitic absorption cannot be ignored. Equation 2 above represents the maximum absorption that can be obtained in a unit cell through a specific light propagation angle and a perfect light confinement scheme.

However, in practice the permissible acceptance angle is not zero and P _esc is not zero. Therefore, the absorbance degree A ' _act in the active layer of the solar cell PV needs to be modified as shown in [Equation 3].

&Quot; (3) &quot;

Here, A _ref is an amount of light loss in which light is internally reflected in an optical component. A _ref is zero on glass, but may not be zero when an optical component (eg, a metal material) of another reflective material is installed. For example, due to Fresnel reflections on a typical flat glass substrate, T _inc and P _esc are approximately 0.96 for typical incidence of light.

<Performance improvement>

Hereinafter, a solar cell (PV) including an active layer made of a polymer (normal structure / inverted structure), amorphous silicon (a-Si), a small molecule compound (small molecular weight organic material), and the like was analyzed. The basic structure of the light concentrator integrated light confinement device 100 including the solar cell PV is shown in the following table. Such examples will be described here, but the light concentrator integrated light trapping apparatus 100 of the present invention may include organic materials (a polymer, a small molecule compound, etc.) for amorphous silicon (a-Si) or OPV (Organic PV). , Thin-film solar cell (PV) made of polymer material for dye-sensitized solar cell (DSSC), crystalline silicon (c-Si), CdTe, CIGS, etc., or bulk cell solar cell (PV) made of crystalline silicon (c-Si) It can be applied to various solar cells (PV).

A _ref was assumed to be zero, and T _inc was assumed to be 0.96 (transmittance between glass and air for typical light incident). In the simulation for the unit cell, absorbance is obtained by transfer-matrix formalism (TMF). In order to calculate short-circuit current densities (J _sc ), IQE was assumed to be 0.9 in polymer (normal / inverted) and amorphous silicon (a-Si) structures. In particular, IQE in the small molecule compound structure is calculated from the exciton diffusion equation, where the diffusion length is assumed to be 10 nm for CuPc and 20 nm for C ₆₀ . CuPc, C ₆₀ , ITO, PEDOT: PSS, TiO _x The refractive index is obtained by ellipsometry and the glass substrate is assumed to be 1.52. Refractive indices of PCDTBT: PCBM, a-Si, cathode materials (Ag, Al, etc.) are well known.

[table]

Figure 2a is the expected degree of absorption in the active layer of the normal polymer PV (normal parasitic absorption efficiency P _esc = 1 only) with a decrease in escape probability P _esc , Figure 2b is a normal polymer according to the traveling angle in the substrate changes in J _sc according to _esc P of PV, 2c is normal PV polymer, an amorphous silicon PV, in the inverted structure polymer PV changes in J _sc of the P _esc, Figure 2d is thick _{CuPc (6.5nm) / C 60 (} 20nm ), The change of J _sc with P _esc in small molecular PV for CuPc (10nm) / C ₆₀ (31nm) and CuPc (14nm) / C ₆₀ (38nm). In FIG. 2B, FIG. 2C, and FIG. 2D, the position P _esc = 0.266 is indicated.

As shown in Figure 2a, from the degree of absorption for the normal angle of incidence in the normal polymer PV structure, it was confirmed that the degree of absorption increases with decreasing P _esc . However, due to parasitic absorption loss caused by other layers such as PEDOT: PSS and metal layers (Ag, Al, etc.), the back reflector did not reach T _inc . Since the light absorption of the unit cell is very high near the wavelength of 500 nm, the degree of improvement in absorbance at this wavelength (see Equation 3) is relatively small. In addition, since the absorption is small even at a wavelength of 700 nm or more and the loss is large due to parasitic absorption rather than being absorbed in the active layer, the degree of absorption (see Equation 3) cannot be greatly increased. Therefore, in order to improve light confinement in PV structures, it is preferable that the active layer material exhibits an appropriate absorption in a certain wavelength band rather than a high absorption for a wide range of wavelengths.

As also described above, the absorption spectrum depends on the propagation angle θ of the light. As shown in FIG. 2B, J _sc for P _esc is shown for various propagation angles θ, which can be obtained by integration of the absorption spectrum. Light propagation in space improves the absorption rate when the propagation angle θ is small. However, due to the increase in Fresnel reflection in the transparent electrode ITO of the optical component as the angle increases, the total absorption decreases. Therefore, the advancing angle θ must be appropriate for effective light confinement. J _sc difference according to the big and small of advancing angle (theta) decreases with decreasing of P _esc . This is because the light reflected back from the transparent electrode ITO of the optical component can be effectively confined to the space.

In FIG. 2C, the change of J _sc according to P _esc in the normal polymer PV, amorphous silicon PV, and inverted structure polymer PV is shown. In the figure a vertical line representing P _esc = n / sin 23.5 ° (P _esc = 0.266) position with respect to an acceptable angle of acceptance of 47 ° in the glass of the optical component is indicated. Compared to the unit cell (plane cell with P _esc = 0.96) at this position, the increase of 16.5% and 31.1% in the normal polymer and a-Si structures, respectively. At P _esc = 0 and acceptance angle = 0, the maximum increases for each show 25.7% and 53.1%. As described above, the parasitic absorption loss in the metal layer (Ag / Al) significantly affects the increased overall absorption through multiple bounces of light. In general, the Al cathode metal layer as a back reflector absorbs more than the Ag metal layer for visible light and infrared spectra, which are light confinement regions, so that the Ag metal layer is more advantageous from an optical point of view. Because of the work function, the Ag metal layer can be used as an anode layer in an inverted structure rather than as a cathode layer of a normal polymer structure. Furthermore, inverted structures have thick film optical spacers in front of the metal layer that enhances the electromagnetic field in the active layer. When using an Ag metal layer as a back reflector in the inverted polymer structure, for P _esc = 0.266 and 0, an increase in absorbance of 35.8% and 74.1%, respectively, is obtained.

FIG. 2D shows J _sc according to P _esc in small molecular PV for thickness CuPc (6.5nm) / C ₆₀ (20nm), CuPc (10nm) / C ₆₀ (31nm), CuPc (14nm) / C ₆₀ (38nm). It is a change. In FIG. 2B, FIG. 2C, and FIG. 2D, the position P _esc = 0.266 is indicated. However, it is assumed here that the diffusion lengths of CuPc and C ₆₀ are 10 nm and 20 nm, respectively.

Light confinement is more effective in small molecule compound PV structures. Because, a compromise is because (trade-off) relationship between the IQE (Internal Quantum Efficiency, internal quantum efficiency) and a light absorbent. By compensating the absorption with light confinement, the thickness can be reduced to obtain a larger IQE. For example, in the small molecule compound PV structure as shown in the table above, as shown in FIG. 2D, at P _esc = 0.96, CuPc and C ₆₀ optimum thickness 14 nm and 38 nm, J _sc at 6.8 mA / cm ² Increase to 12.8 mA / cm ² . Absorption recovers through light confinement, so that its thickness can be further reduced to have a higher IQE. _Esc P = 0, it was confirmed that the C ₆₀ from the CuPc and the optimal thickness 6.5nm and 20nm, increases to a J _sc 15.8 mA / cm ^2, which is greater than 5.2mA / cm ² in a plan view of the same cell thickness. Thus, in small molecule compound PV structures, the overall ideal absorption increase can be obtained up to 132%. In the same way, at P _esc = 0.266, at CuPc and C ₆₀ optimum thicknesses of 10 nm and 31 nm, J _sc increased to 10.2 mA / cm ² , which is 50% higher than in planar cells. In addition to IQE, the fill factor also depends on the thickness and can be increased by reducing the thickness with light confinement. Accordingly, power conversion efficiency (PCE) can be further increased through optimization of thickness.

<Optical component composition>

Herein, an optical component implementation method for effective light confinement will be described. In the above Polymer PV structure (normal structure / inverted structure), an Al / Ag metal layer as a back reflector was used. In the flat cell, and J is the normal structure _sc0 11.2mA / cm ^2, is in the inverted structure 10.3mA / cm ^2. The performance can be calculated using TMF, and the results are obtained by averaging 200 units of light in one period and averaging the unit structures with periodic boundary conditions.

<CPT array in simulation>

Compound Parabolic Trapper (CPT) can simply be arranged to implement sin (θ _a / 2) / n (n is the molding refractive index of CPT) for P _esc . Campbell et al. Proposed a theoretical approach to light confinement using CPC arrays in bulk cells, and Peumans et al. Applied two-dimensional CPC arrays to thin-film PVs. However, the proposed scheme by Peumans et al. Required not only a light tracking device but also could not be implemented. The present invention proposes a one-dimensional CPT array to remove the light tracking device as described above. The CPT is molded from glass, plastics, etc. and designed with an acceptance angle of ± 16.0 °. Hereinafter, the CPT is described as an example of a glass molding, but may be implemented as various plastics such as resin. Such moldings can be prepared by pouring a melt of the material for moldings, such as glass, plastics, into a metal mold and cooling it to a solid.

In such glass moldings the acceptable angle of incidence is in the range of ± 24.8 ° in air according to Snell's law which ensures to receive all incident light during the year. The height of the CPT and the thickness of the substrate are assumed to be 500 μm and 700 μm, respectively. The substrate may include a back reflector, a solar cell PV, and a space thereon except for an optical component CPT. The CPT is a parabolic mold consisting of bilateral curved surfaces having a parabolic long-axis cross section arranged one-dimensionally on such a substrate as shown in the right figure of FIG. a trapping mirror provided with an entrance (eg, rectangular shape). Here, each parabolic shape of the parabolic mold is inclined at an angle as needed according to the design, and the opening portion of the trapping mirror may be located at the focal point of the parabolic mold parabolic mold. . A metal coated metal mirror may be formed below the trapping mirror provided with the opening. Most incident light is incident on the parabolic shape at an angle greater than the critical angle (total reflection critical angle) for causing total internal reflection in the parabolic mold, so do not apply a metal mirror over the parabolic shape to avoid parasitic losses. It is preferable not to. This is because parasitic losses are greater than losses due to light escaping the parabolic shape.

However, parabolic glass (or plastics, etc.) moldings may be manufactured in a filled form, and in some cases, parabolic glass (or plastics, etc.) moldings may be manufactured in a hollow form, and each parabolic product may be manufactured. It is possible to improve the provision of light by using a metal mirror coated with metal on the curved surfaces. For example, the molding of the hollow form may be coated with metal before and after forming the molding, and the molding of the filled form may be coated with metal before the molding.

In order to minimize the change in the angle of incidence on the cross section of the glass mold, the CPT one-dimensional arrays (each molding) are aligned east-to-west in the major axis direction, so that the CPT is a daily angle as shown in FIG. Regardless of the daily angle variation, all lights with an annual angle variation of ± 23.5 ° are acceptable. With respect to the above acceptable acceptance angle and zero daily angle variation, absorption improvements of approximately 30% (in the inverted structure) and 10% (in the normal structure) can be obtained. Larger daily angle variations can widen the acceptable angle of acceptance throughout the year, but reduce the degree of absorption improvement, meaning that it works better at noon than morning or evening. This is because scattering in a parabolic mold and a large daily angle variation are combined to increase the propagation angle of the light as described in FIG. 2B. In fact, solar energy per unit area is very small in the morning or evening, so it's a good idea to improve absorption at noon in real environments. At noon, the degree of absorption is lower than theoretically expected for the same permissible angle of acceptance, less than 37.7% in inverted structure PV, and usually less than 17.4% in structure PV. The reason is summarized in the following four ways.

(1) Absorption at a trapping mirror: Although A _ref is assumed to be theoretically zero in [Equation 3], this cannot be ignored in an actual structure.

(2) Large light propagation angle in space: The light propagation angle distribution becomes larger after light passes through the opening of the CPT's trapping mirror by reflection, unlike in bulk cells, FIG. 2B Too large a propagation gradient of light may degrade the absorption in the active layer of PV.

(3) direct reflection: In general, light is difficult to trap when passing directly through the entrance of the trapping mirror and out through the opening reflected from the bottom (top of the PV). I can get out. This can be seen from the fact that the absorption improvement near the normal angle appears smaller at the larger angle as shown in Fig. 3A. This means that power conversion efficiency (power production efficiency) is higher in summer and winter.

FIG. 3 shows the normalized change in J _sc for angles varying from 0 °, 30 ° and 60 ° per day in inverted and conventional structured polymer PV, as shown in the figure on the right. In order to trap light throughout the year, the CPT must be aligned in the east-west direction on the y axis. The z-axis represents the sun's position at noon at the vernal equinox.

(4) Incident loss on the CPT: incident light near the entrance of the parabolic mold and its entrance (trapping mirror) when the angle of incidence is near the boundary of the acceptable angle of incidence The angle of the liver may be smaller than the critical angle (total reflection critical angle that allows it to enter the entrance without escape), so that incident light can escape and escape out of the CPT rather than being reflected toward its entrance. It does not occur because the permissible acceptance angle is greater than ± 23.5 °, but at about noon it occurs because the permissible acceptance angle is near the ± 23.5 ° boundary. The parabolic mold can be solved by asymmetrically constructing the CPTs with different inclination angles (different focal points), which means that when light passes through the entrance, This asymmetric CPT (ACPT) offers advantages for practical applications such as building integrated photovoltaic (BIPV) systems, which align the entire system in the solar altitude direction. Absorption can be improved by further reducing the acceptable acceptance angle of the CPT, which is better than in a planar cell at almost all year-round total acceptable angle, regardless of the change in daily angle. Because of its good performance, it may be implemented with an annual light tracking apparatus throughout the year in a CPT with a limited smaller acceptance angle.

Although the above-described one-dimensional arrangement of the moldings of the CPT has been described, the present invention is not limited thereto, and the second periodic one-dimensional arrangement of the parabolic mold consisting of parabolic molds having a parabolic cross section vertically above the one-dimensional array is performed. Or a second periodic one-dimensional array of parabolic molds having a parabolic bilateral curved cross section at the end of the long axis in the one-dimensional array of moldings, thereby forming a two-dimensional CPT structure. It may be. Accordingly, it is possible to improve n / sin (θ _a / 2), which is the concentration of light in a one-dimensional array, to n ² / sin ² (θ _a / 2) without the daily light tracking apparatus. The probability of escape can be reduced to further improve absorbance.

As a result of fabricating a parabolic mold as described above, light scattering may occur due to poor illumination. In order to reduce the light loss, the light trapping device 100 without a trapping mirror is possible, and at this time, the PCE has increased from 6.25% without the trapping device to 7.15%.

4 is a change in normalized J _sc according to an annual incident angle change using 1D MLA (Micro Lenses Array, Micro Lens Array) (another example of the present invention) in an inverted structure and a conventional structure polymer PV. In FIG. 4 it is assumed that the annual incidence angle changes in the xz plane and the daily angle variation is zero. In addition, h and d represent the size of the entrance of the trapping mirror (eg, the ratio of the width to the period) and the daily angle change.

<MLA (Micro Lens Array) Structure>

4, instead of the one-dimensional CPT arrangement as shown in FIG. 3, the light concentrator integrated light confinement device 100 of the present invention may be embodied in an MLA to have a highly limited allowable angle of acceptance. A trapping mirror having an entrance is provided under the MLA at the focal length portion of the lens (e.g., glass or plastic with a convex upside surface having a semi-circular cross section in the form of a semi-circle). Here too, the MLA can simply be arranged to implement sin (θ _a / 2) / n (where n is the refractive index of the lens of the MLA) for P _esc .

In the one-dimensional MLA structure, the graph of FIG. 4 is designed to approximate a cylindrical period with a microlens array period of 400 μm and a curved surface of each lens having a radius of 342.1 μm. The theoretical focal length of the _lens can be calculated by f = radius × (n _lens −1) / n _lens (n _lens is the refractive index of the lens), which is about 1000 μm when made of glass. In reality, however, the focal length can be shortened, unlike the cylindrical approximation, so that the focal length, that is, the lens thickness, is set to 940 m.

As shown in FIG. 4, it was confirmed that the performance varies depending on the size of the entrance of the trapping mirror (eg, the ratio h of the opening width to the period). In the inverted structure, at noon, the maximum absorbances were 49% and 42% at h = 0.10 and 0.15, respectively, and the values decreased to approximately 19% and 17% in the normal structure under the same conditions. There is a trade-off between the degree of absorption and the acceptance angle, as in the CPT arrangement. For larger daily angle variations, the focal length was reduced, for example, at the angle change 60 °, the light was not guided towards the entrance. This is because the annual light plane (xz plane) is affected by the daily light plane (yz plane). This phenomenon does not appear in optical systems using only reflection, such as CPC / CPT.

Here, the one-dimensional array of MLAs has been described, but the present invention is not limited thereto, and the second two-dimensional array of MLAs may be further provided at the end of the long axis direction of the MLA of the one-dimensional array so that the two-dimensional MLA structure is formed. You may. Accordingly, it can be improved to be larger than the condensing magnification in the one-dimensional array without the daily light tracking apparatus, and thus the probability of light escape can be reduced to further improve absorbance.

As described above, according to the light concentrator integrated light trapping apparatus (FIGS. 1, 3, and 4) according to the exemplary embodiment of the present invention, the CPT (Compound Parabolic Trapper) (or MLA) array is not a planar one-dimensional linear array of light. Can be collected at a small entrance and locked out of the bottom (sometimes effective without a confinement mirror), improving the power conversion efficiency of thin-film solar cells. The linear condensation eliminates or minimizes the need for a separate light tracking device. Reducing the CPT / MLA condensation magnification can increase the permissible incident angle, which allows about 3.8 times condensation when the permissible incident angle is ± 23.5 ° in a one-dimensional array, which allows all changes in solar altitude throughout the year, Placing the one-dimensional concentrator array east-west allows the light confinement effect to be achieved without light tracking.

Further, in the present invention, the light concentrator integrated light trapping apparatus 100 may include an annual light tracking apparatus for tracking the altitude of the sun during the year, so that the annual light tracking apparatus is the sun. By controlling the entire system to move along the direction (which is tilted to the solar altitude at each time), it reduces the acceptance angle range, i.e., the allowable incident angle to less than 47 °, further increasing the confinement effect. It may be. The daily light tracking apparatus is unnecessary, and since only an annual light tracking apparatus can be operated, it is possible to operate much more economically than the conventional method. That is, although an annual light tracking apparatus may be used at an allowable incident angle of 47 ° or more, performance may be further improved through the year-round light tracking device at 47 ° or less. As such, the present invention operates without a daily light tracking apparatus, and when the components of the light concentrator integrated light confinement apparatus 100 are manufactured to receive light with an allowable angle of incidence of less than 47 °, through the year-round light tracking apparatus. It can improve performance.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Compound Parabolic Trapper (CPT)
Photovoltaic Cells (PV)
MLA (Micro Lens Array)
Asymmetric CPT (ACPT)
Building integrated photovoltaic (BIPV)

Claims (17)

In the light concentrator integrated light trapping device for transmitting light to the solar cell (PV),
An optical component having components of a periodic one-dimensional array,
The optical system includes a periodic one-dimensional array of parabolic molds having bilateral curved surfaces having parabolic cross sections as the components,
The optical system is installed on a predetermined space on the solar cell PV, and condenser-integrated light confinement, characterized in that to trap the incident light in the space to improve the power conversion efficiency in the solar cell PV. Device. The method of claim 1,
And the molding is aligned such that its long axis is in an east-to-west direction. The method of claim 1,
The molded article is a light concentrator integrated light confinement device, characterized in that it comprises glass or plastics. The method of claim 1,
An opening is provided at a lower portion of each of the paraboloids of the molding on the solar cell PV side, and a trapping mirror having a metal coating on the lower portion to trap light incident through the opening in the space. Concentrator integrated light confinement device further comprising a. The method of claim 1,
The molding is a light concentrator integrated light confinement device, characterized in that produced in the form filled. The method of claim 5,
Light concentrator integrated light confinement device, characterized in that the parabolic both sides of the molding is formed in the form of a metal coating. The method of claim 1,
The molding is hollow inside, and the light concentrator integrated light confinement device, characterized in that the parabolic-shaped both sides of the molding is made of a metal coating. The method of claim 1,
The molded article having a parabolic cross section is a light concentrator integrated light confinement device, characterized in that the curved surface of both sides is made asymmetrical with a curved surface of different inclination angle. The method of claim 1,
A molding further comprising a periodic second one-dimensional array of parabolic molds having a parabolic bilateral curved surface vertically over the one-dimensional array, or having a bilateral curved surface having a parabolic cross section at the long axis direction of the molding. and a second periodic one-dimensional array of parabolic molds. In the light concentrator integrated light trapping device for transmitting light to the solar cell (PV),
An optical component having components of a periodic one-dimensional array,
The optical system includes, as the components, a micro lens array (MLA) in a periodic one-dimensional array,
The optical system is installed on a predetermined space on the solar cell PV, and condenser-integrated light confinement, characterized in that to trap the incident light in the space to improve the power conversion efficiency in the solar cell PV. Device. The method of claim 10,
And a trapping mirror having a predetermined width at a focal length of each lens of the MLA, the trapping mirror for confining light incident through the opening to the space. The method of claim 10,
And an MLA of a second one-dimensional array further at the end of the long axis direction of the MLA of the one-dimensional array. 11. The method according to claim 1 or 10,
The solar cell (PV) is usually a structure or inverted structure, the active layer is a thin film type containing crystalline silicon (c-Si), organic material or dye-sensitized polymer material, amorphous silicon (a-Si), CdTe, or CIGS, A light concentrator integrated light confinement device comprising a bulk cell type containing crystalline silicon (c-Si). 11. The method according to claim 1 or 10,
The condensing magnification is n / sin (θ _a / 2) between the solar cell PV and the optical component, where θ _a is the allowable angle of light acceptance and n is the refractive index of the optical system. A light concentrator integrated light trapping apparatus, characterized in that the. 11. The method according to claim 1 or 10,
It further includes an annual light tracking apparatus for tracking the altitude of the sun year round, operates without a daily light tracking apparatus,
The condenser integrated light confinement device according to the control of the light tracking device during the year, wherein the entire system of the condenser integrated light confinement device moves toward the sun. 16. The method of claim 15,
And the components of the light concentrator integrated light confinement device are manufactured to receive light with an allowable incident angle of 47 ° or less. In the manufacturing method of the light concentrator integrated light trapping device for transmitting light to the solar cell (PV),
An optical component having components of a periodic one-dimensional array is manufactured, and a molten material of the material for the molding is poured into a metal mold and cooled to a solid state, thereby forming both curved surfaces having parabolic cross sections as the components. Fabricating the optical system including a periodic one-dimensional array of parabolic molds; And
And installing the manufactured optical system on a predetermined space on the solar cell PV,
The optical system is a method for manufacturing a light concentrator integrated light confinement device, characterized in that for trapping the incident light in the space to improve the power conversion efficiency in the solar cell (PV).

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