KR101534756B1 - Thin film type solar cell, method of fabricating the same and method of increasing efficiency of a thin film type solar cell - Google Patents

Abstract

A thin film solar cell includes an active layer partially including a textured region; A film layer disposed on the active layer; And a lens array disposed on the film layer and including at least one lens arranged to focus incident light on the textured area. In addition, the method of fabricating a thin film solar cell includes forming a partially textured region in an active layer; And locating a light focusing layer on the active layer comprising the textured region, the light focusing layer comprising a lens array and a film layer, the lens array comprising at least one lens arranged to focus incident light on the textured region . Also, a method of increasing efficiency of a solar cell includes focusing an incident light by a lens array including at least one lens; Introducing the focused incident light into a textured region formed in an active layer of a thin film solar cell; And converting the incident light incident on the textured region into electrical energy by the active layer.

Description

TECHNICAL FIELD [0001] The present invention relates to a thin film type solar cell, a thin film type solar cell manufacturing method, and a method of increasing efficiency of a thin film type solar cell,

Embodiments relate to a technique for increasing the efficiency of a thin film solar cell by reducing surface recombination of electron-hole pairs while increasing light absorption in an active layer in a thin film solar cell.

A solar cell is a core element of a solar power generation system that converts solar light energy directly into electric energy. The active layer (absorption layer) of a solar cell that absorbs incident solar light is composed of a p-n junction semiconductor diode. In the active layer, electron-hole pairs are generated by the photons absorbed from the sunlight, and electrons move to the n layer and holes move to the p layer due to the generated electric field. Thus, a photovoltaic power is generated between the p-n junctions to produce electrical energy.

Solar cells are classified into various types according to the material of the active layer. Currently, solar cells made of bulk crystalline silicon are the most used. However, since the cost of the active layer material accounts for the highest proportion of the production cost of the photovoltaic power generation system, research and development of a thin film type silicon solar cell is actively carried out to reduce the amount of silicon contained in the active layer.

Thin-film silicon solar cells can reduce the amount of active layer material used compared to bulk silicon solar cells, which can lower the manufacturing cost. However, since the active layer becomes thinner, it can not sufficiently absorb the incident sunlight in the active layer . In order to overcome this disadvantage, an anti-reflection coating which minimizes light reflection on the incident surface and a light trapping technique which sufficiently lengthens the optical path in the active layer are used so as to sufficiently absorb the incident light in the active layer.

Among the optical trapping techniques, a texturing technique for increasing the light path by causing the incident light to be refracted in different directions on the uneven surface by forming a periodic uneven structure by using the wet etching process according to the crystal direction of crystalline silicon, which is an active material, Is widely used. The texturing technique is advantageous in that the desired concavo-convex structure can be obtained by a simple process. However, since the pn junction plane of the active layer is widened due to the uneven structure, compared with the crystalline silicon thin film solar cell having the planar active layer, The surface recombination of the electron-hole pairs is increased sharply. As a result, the flow of current due to electrons or holes is inhibited, so that the efficiency of the solar cell is not increased as the amount of light absorbed in the active layer is increased.

Korea Patent Publication No. 2011-0008873

According to an aspect of the present invention, there is provided a thin film solar cell that uses a light trapping technique to increase the light absorption amount in the active layer and reduces the recombination of electrons and holes on the surface of the active layer, .

The thin film solar cell according to one embodiment includes a partially textured active layer; A film layer formed on the active layer; And a lens array formed on the film layer; . ≪ / RTI >

A method of fabricating a thin film solar cell according to an embodiment includes: texturing a part of an active layer of a thin film solar cell; And attaching a light focusing layer comprising a lens array and a film layer over the portion of the textured active layer.

A method of increasing the efficiency of a thin film solar cell according to an embodiment includes focusing an incident light; Absorbing the focused incident light into a textured active layer of a thin film solar cell; And converting the energy of light absorbed in the active layer into electrical energy.

The solar cell according to one aspect of the present invention can form a partially textured region only on the roughened layer so that the front surface of the active layer is exposed to sunlight within the active layer more than the optical trapping performance of the textured conventional solar cell The surface area of the active layer is reduced while absorbing, and the effect of surface recombination is greatly reduced, thereby providing a highly efficient solar cell that does not impede the current flow.

In addition, according to the solar cell according to one aspect of the present invention, since the structure for focusing sunlight and entering the active layer can be manufactured by using a separate process from that of the active layer, and then attached to the active layer, It is expected to be lowered.

FIG. 1 is a schematic cross-sectional view of a thin-film solar cell according to an embodiment of the present invention and a path through which sunlight is absorbed.
Figure 2 is a schematic diagram of a partially textured active layer according to an embodiment of the present invention.
FIG. 3 is a result of simulating a path of sunlight incident on a solar cell including a semi-spherical lens array, in which a part of the active layer is textured, using a ray-tracing technique.
4 is a result of simulating a path of sunlight incident on a solar cell including a portion of the active layer textured and including an aspheric lens array using a ray tracing technique.
FIG. 5 is a result of simulating the path of sunlight incident on a solar cell having a textured active layer on the front side using a ray tracing technique.
FIG. 6 shows a result of simulating the path of sunlight incident on a solar cell having a planar active layer using a ray tracing technique.
7 is a graph of the light absorptivity according to the wavelength in the active layer according to the structure of the solar cells in which the bottom surface of the active layer is flat.
8 is a graph of the light absorptance according to the wavelength in the active layer of the solar cells having the Lambertian structure on the bottom surface of the active layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a thin-film solar cell according to an embodiment and a path through which sunlight is absorbed.

Referring to FIG. 1, a thin film solar cell according to an exemplary embodiment includes an active layer 14 partially textured, a film layer 13 formed on the active layer 14, and a lens (not shown) Array 12 as shown in FIG. In the thin film solar cell according to the present embodiment, the active layer 14 is only partially textured. That is, some areas of the active layer 14 are textured areas 15, while other areas of the active layer 14, excluding the areas 15, are not textured.

Referring to FIG. 1, how light is absorbed by an active layer of a solar cell according to an embodiment will be described. The incident light 11 is incident on the lens array 12, is refracted and diffracted due to a refractive index difference between air and the material forming the lens, and is then incident on the film layer 13 located below the lens array 12. At this time, the incident light can be refracted and focused again due to the difference in refractive index of the material forming the lens array 12 and the film layer 13. The focused light is configured to be incident on the textured portion 15 of the active layer 14 by the structure of the film layer 13 and the lens array 12.

In this specification, texturing is intended to refer to patterning the surface of the active layer 14 in the form of a three-dimensional structure. Reflection occurs in the active layer when the sunlight is incident on the textured region of the active layer 14, so that the optical path in the active layer becomes longer as compared with the case where the incident light is incident on the non-textured region, The light absorption by the active layer 14 is increased. However, when texturing the entire surface of the active layer 14, the electron-hole recombination at the surface increases as the surface area of the active layer 14 increases. Therefore, the flow of current by electrons or holes is inhibited, and the efficiency of the solar cell is prevented from being increased as much as the light absorption in the active layer 14 is increased.

On the other hand, in the thin film solar cell according to the embodiments, the surface area of the active layer 14 is reduced by texturing only a part of the active layer 14 as compared with the conventional solar cell in which the front surface of the active layer is textured, And the incident light can be converged by the lens array 12 and the film layer 13 to be incident on the textured portion 15 so that the incident light can be incident on the active layer The optical trapping function can be maintained even if the entire surface of the active layer is not textured.

That is, according to an embodiment of the present invention, there is provided a method of manufacturing a thin film solar cell, comprising the steps of: focusing incident light; absorbing the focused incident light into a textured active layer of a thin film solar cell; A method of increasing the efficiency of a thin film solar cell including the step of converting a thin film solar cell into a thin film solar cell can be provided.

Since the lens array 12 serves as a focusing layer for focusing the incident light 11 toward the textured portion 15 of the active layer 14, the lens array 12 can be made of a material having properties that are strong against heat and excellent in translucency, For example, it may be a UV resin, which is generally used in the production of an optical film shape. In addition, the lens array 12 can be operated as a pressure-sensitive adhesive and a functional material, and can be formed into a large area by forming ultraviolet (UV) light while passing through a mold in the form of a roll. The lens forming the lens array 12 may be a microlens having a unit of micrometer (μm) or millimeter (mm) in diameter. The surface of the lens array 12 on which the sunlight is incident can be designed in various forms, for example, it can be an aspherical surface having a hemispherical or convex portion. When the incident light is focused on the textured portion 15 through the lens array 12, the optical path is totally reflected in the active layer by the texturing shape, so that the absorption of the incident light in the active layer is maximized.

The film layer 13 may serve as a spacer to adjust the focal length to focus the light from the lens array 12 to the textured portion 15 of the active layer 14. In addition, the film layer 13 may serve as an adhesive for the active layer 14 and the lens array 12. In general, when the focal length is designed to be short by constructing the film layer with a high refractive index material, the condensing ability is increased and the texturing area is narrowed. However, since the radius of curvature of the lens array 12 is increased, the margin of the manufacturing process is reduced, There is a disadvantage in that the acceptance angle due to a change in incident angle of light such as an altitude change is reduced. On the other hand, when the focal length is designed to be long, as the radius of curvature of the lens array 12 becomes small, the margin of the fabrication process increases and the allowable angle of incidence becomes large, but the texturing area must be wide. Therefore, it is required to optimize and design the material of the film layer 13 and the thickness of the film layer 13 in consideration of the texturing area, the margin of the manufacturing process, and the allowable angle of incidence of the lens array 12.

In one embodiment, the film layer 13 may also be used as a substrate when the lens array 12 is molded. Also, in one embodiment, the film layer 13 may be made of a dielectric. In addition, the film layer 13 may be made of a polymer material. For example, the film layer 13 may be a PET (Polyethyleneterephthalate) film.

The active layer 14 may be made of various materials used in an active layer of a general solar cell. For example, the active layer 14 may be a crystalline silicon thin film.

A solar cell according to an embodiment of the present invention includes a step of forming a partially textured region in an active layer and a step of positioning a light focusing layer including a lens array and a film layer on an active layer including the textured region Type solar cell fabrication method. For example, a film layer of the light focusing layer may be deposited over the textured active layer. It is expected that the production cost can be lowered by manufacturing the light focusing layer by a roll process different from the process of manufacturing the active layer.

The step of texturing a part of the active layer can be performed by various methods. For example, the shape of the textured portion and the portion of the textured portion can be adjusted by using a photolithography process using a photomask or the like, or a chemical wet etching process.

FIG. 2 is a schematic diagram illustrating a portion of the active layer of a solar cell textured in accordance with an embodiment of the present invention. FIG. As shown in FIG. 2, the texturing can be performed on a part of the active layer so that the concavo-convex structure has a pyramid shape (pyramid shape), and the concavo-convex structure can be any shape capable of totally reflecting the incident light in the active layer as well as the pyramid .

In order to quantitatively verify the efficiency of the solar cell according to the embodiments, the amount of light absorbed in the active layer was optically calculated for four solar cells having different structures.

3 is a result of simulating a path of sunlight incident on a solar cell including a semi-spherical lens array, in which a part of the active layer is textured, using a ray-tracing technique. Solar light (AM 1.5 GHz) having a wavelength of 300 nm to 1200 nm was transmitted through the solar cell as an incident beam, and the amount of light absorbed in the active layer set as crystalline silicon was quantitatively calculated. The diameter of the hemispherical lens was set to 100 μm, and the thickness of the film layer was set to 0.1 mm. The active layer is designed to be composed of 10 μm thick crystalline silicon and the concave and convex structure of active layer texturing is set to have a pyramid structure with a height of 5 μm from the bottom to the apex. Referring to FIG. 3, it can be seen that the sunlight absorbed in the active layer travels without total directionality while causing total reflection.

4 is a result of simulating a path of sunlight incident on a solar cell including a portion of the active layer textured and including an aspheric lens array using a ray tracing technique. The setting of the incident light, the film layer, and the active layer is the same as that in Fig. 3, and the aspheric lens has a configuration in which the conical portion of the cone in the cone forming the apex angle of 79.61 ^o (that is, ) Was replaced with a part of a sphere having a radius of 0.025 mm. Referring to FIG. 4, it can be seen that the solar light absorbed in the active layer is totally reflected without any directionality as shown in FIG.

Design factors such as the shape and arrangement of the lens array of the solar cell, the thickness of the film layer, the texturing shape and size of the active layer can be optimized using the optical design techniques used in FIGS. 3 and 4. FIG. The hemispherical lens array and the aspherical lens array are only one embodiment, and the shape of the lens is not limited thereto.

In order to compare with the solar cell according to the embodiments of the present invention, the path of the solar light incident on the solar cell having the active layer having the textured front surface and the planar active layer according to the present invention, And FIG. 6. 5 and 6, the setting of the thickness of the incident light and the active layer is the same as that of FIG. 3, and the texturing request structure of the active layer of FIG. 5 is also the same as that of FIG. The sunlight absorbed by the front surface textured active layer is refracted and totally deflected when incident on the active layer, while the solar cell having the planar active layer absorbs incident sunlight as it is and absorbs into the active layer of FIGS. 3 to 5 Which is shorter than that of the sunlight.

FIG. 7 is a graph showing the light absorptance according to wavelengths in an active layer of a solar cell having a bottom plane in which the bottom surface is flat so that scattering does not occur on the bottom surface of the active layer, using the ray tracing technique. 7, a part of the active layer is textured and the solar absorptance 71 of the solar cell including the aspheric lens array and the film layer is the highest, and a part of the active layer is textured and includes a hemispherical lens array and a film layer The light absorptance 72 of the solar cell is also higher than that of the conventional solar cell 73 having the active layer textured on the front surface and the solar cell 74 having the planar active layer.

Table 1 below shows the results of calculating the amount of light absorbed by the active layer of each solar cell shown in Fig. 7, and the 'absolute value' is the absolute absorbed light amount obtained by integrating the graph of the light absorption rate of Fig. 7 with respect to the wavelength. 'Relative value' represents the relative amount of absorbed light when the absolute absorption amount of the active layer in the active layer of the solar cell having the active layer in which both the top and bottom surfaces are plane is set to 100 .

Structure of solar cell Absolute value Relative value Solar cell with planar active layer 43.45 100.00 A solar cell having a textured front active layer 64.36 148.12 A portion of the active layer is textured and a solar cell comprising a hemispherical lens array and a film layer 69.71 160.44 A portion of the active layer is textured and a photovoltaic cell comprising an aspheric lens array and a film layer 72.55 166.97

Referring to Table 1, while a solar cell having a front-side textured active layer absorbs about 1.48 times as much light as a solar cell having a planar active layer, a portion of the active layer is textured, and a hemispherical or aspheric lens array and film Lt; RTI ID = 0.0 > 1.6 < / RTI > or 1.67 times. That is, a solar cell in which a part of the active layer is textured and includes a lens array and a film layer has a much higher absorption light amount than a solar cell having a planar active layer, and has a higher absorption than a solar cell having a front- And has a light amount. In other words, a solar cell having a partially textured active layer, a lens array, and a film layer has a surface area smaller than that of a textured solar cell of the active layer, thereby reducing the surface recombination and further increasing the light absorption amount in the active layer , It is expected to have improved efficiency compared to conventional solar cells.

According to an embodiment of the present invention, the bottom surface of the active layer may have a Lambertian structure in order to maximize light scattering in the active layer to prevent reflection. In the present specification, the Lamborcan cyan structure refers to a structure that has been surface-treated so that the brightness of an object at a specific surface has an isotropic Raman reflectance regardless of the angle at which the observation car observes. Since the lambda cyan structure is well known in the technical field of the present invention, detailed illustration and description are omitted. FIG. 8 is a graph showing a light absorptance according to wavelengths in an active layer of a solar cell having the structure of FIGS. 3 to 6, in which the bottom surface of the active layer is set as a lamellar cyan scattering body. 7, a portion of the active layer is textured and a solar cell comprising an aspheric (81) or hemispherical (82) lens array and a film layer is formed on the planar active layer 84 or the active layer 83, Which is higher than that of the solar cell.

The following Table 2 shows the calculation of the amount of light absorbed by the active layer of each solar cell of FIG. 8, where 'Absolute Value' is the Absolute Absorbed Light Amount obtained by integrating the graph of FIG. 7 with respect to wavelength, And has the same meaning as in Table 1.

Structure of solar cell Absolute value Relative value Solar cell with planar active layer 54.66 125.80 A solar cell having a textured front active layer 73.96 170.22 A portion of the active layer is textured and a solar cell comprising a hemispherical lens array and a film layer 77.14 177.54 A portion of the active layer is textured and a photovoltaic cell comprising an aspheric lens array and a film layer 78.22 180.02

Referring to Tables 1 and 2, it can be seen that the amount of light absorbed in the active layer of the solar cells including the active layer having the bottom surface of the lamba cyan structure is increased in comparison with the solar cells having the active layer having the bottom plane as a whole . In addition, as in Table 1, when a part of the active layer is textured and the absorbed light amount of the solar cell including the hemispherical or aspherical lens array and the film layer is larger than the absorbed light amount of the solar cell having a planar or front- .

As confirmed from the simulation results, the solar cell including the lens array and the film layer for focusing the incident light into the textured and textured part of the active layer has a better light absorptivity in the active layer than the conventional solar cell , The surface area of the active layer is smaller than that of a solar cell having a textured active layer on the front surface thereof, so that the surface recombination is reduced and a solar cell having high efficiency can be provided.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments or constructions. .

11: incident light 12: lens array
13: Film layer 14: Active layer
15: Textured part

Claims (17)

An active layer partially including a textured area;
A film layer disposed on the active layer; And
A lens array positioned on the film layer and comprising at least one lens arranged to focus incident light on the textured area;
, ≪ / RTI &
Wherein the material of the film layer and the material of the lens array have different refractive indices,
Wherein the film layer refracts incident light focused by the lens array. The method according to claim 1,
Wherein the lens is made of UV resin. The method according to claim 1,
Wherein a surface of the active layer opposite to the film layer has a Lambertian structure. The method according to claim 1,
Wherein the lens is semi-spherical. The method according to claim 1,
Wherein the lens is an aspherical lens having a convex portion. The method according to claim 1,
Wherein the film layer is made of a dielectric material. The method according to claim 6,
Wherein the film layer is a PET film. Focusing the incident light by a lens array comprising at least one lens;
Introducing the focused incident light into a textured region formed in an active layer of a thin film solar cell; And
Converting incident light incident on the textured region into electrical energy by the active layer;
, ≪ / RTI &
The step of injecting the focused incident light into a textured region formed in an active layer of a thin film solar cell is performed by a film layer made of a material having a refractive index different from that of the material of the lens array, The method comprising the steps of: 9. The method of claim 8,
Wherein the lens is made of UV resin. 9. The method of claim 8,
Wherein the surface of the active layer opposite the textured region has a Lambertian structure. 9. The method of claim 8,
Wherein the lens is semi-spherical. 9. The method of claim 8,
Wherein the lens is an aspherical lens having a convex portion. 9. The method of claim 8,
Wherein the film layer is made of a dielectric material. 14. The method of claim 13,
Wherein the film layer is a PET film. Forming a partially textured region in the active layer; And
A lens array including at least one lens arranged to focus incident light on the textured area on an active layer including the textured area and a material having a refractive index different from that of the material forming the lens array, A light focusing layer including a film layer that refracts light focused by the light focusing layer;
Wherein the thin film solar cell comprises a plurality of thin film solar cells. 16. The method of claim 15,
Wherein positioning the light focusing layer comprises attaching the film layer coupled to the lens array to the active layer. 16. The method of claim 15,
Wherein the forming of the textured region uses a photolithographic process or a chemical wet etching process.

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