KR20140075030A - Solar cell and method of manufacturing the same - Google Patents

Abstract

Provided in the present invention is a solar cell which absorbs not only visible rays, but also visible rays transformed from ultraviolet rays and can improve the efficiency by comprising different conductive types of first and second semiconductor layers; a first electrode and a second electrode formed to be contacted with the first and the second semiconductor layers respectively; and a transforming layer formed on the second semiconductor layer, and absorbing light of the wavelength having a first energy and transforming the light into a light of the wavelength having a second energy which is less than the first energy.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell,

The present invention relates to a solar cell, and more particularly, to a silicon solar cell capable of improving efficiency and a method of manufacturing the same.

A solar cell is a type of semiconductor device that converts solar energy directly into electrical energy. It has a junction structure of p-type semiconductor and n-type semiconductor, and its basic structure is the same as a diode.

The performance of such a solar cell largely depends on the efficiency of converting light energy into electric energy. Accordingly, researches for increasing the efficiency of solar cells have been conducted. As one of the methods, there is a method of maximizing absorption of light by texturing a portion where light is incident. Such texturing increases light absorption through light scattering.

However, it is difficult to further increase the amount of incident light by texturing. Accordingly, there is a demand for a method of increasing the amount of incident light and thereby improving efficiency.

The present invention provides a solar cell capable of improving efficiency and a method of manufacturing the same.

The present invention provides a solar cell capable of increasing the amount of visible light through energy down conversion and improving efficiency, and a method of manufacturing the solar cell.

The present invention relates to a solar cell capable of absorbing light of ultraviolet wavelength through energy down conversion using quantum dots to emit light of a visible light wavelength and absorbing it together with a visible light to thereby increase the amount of incident light, And a manufacturing method thereof.

A solar cell according to an aspect of the present invention includes first and second semiconductor layers of different conductivity types; First and second electrodes formed to contact the first and second semiconductor layers, respectively; And a conversion layer, formed on the second semiconductor layer, for converting light of a wavelength having a first energy into light having a second energy lower than the first energy.

The first semiconductor layer is formed by doping a semiconductor substrate with a first impurity of a first conductivity type, and at least one surface thereof may be textured.

The second semiconductor layer may be formed by doping a second impurity of a second conductivity type to a predetermined depth of the first semiconductor layer.

The first and second semiconductor layers may comprise crystalline silicon.

The conversion layer converts light in the ultraviolet region to emit light in the visible light region, and the first and second semiconductor layers absorb the visible light beam and the visible light converted from ultraviolet light by the conversion layer.

The conversion layer includes a core and a quantum dot including a shell surrounding the core. The quantum dot is formed of any one selected from CdSe, InP, InAs, CuInS ₂ , PbS, and PbTe, and is formed of any one of ZnS, ZnSe, and CdSe A shell is formed, wherein the core is formed of CdSe, and the shell may be formed of ZnS.

The conversion layer is adjusted in wavelength depending on the size of the core and the shell.

The core may be formed to a size of 0.1 nm to 10 nm, and the shell may be formed to a size of 8 nm to 20 nm. Further, as the core size increases, the converted wavelength increases, and as the core size decreases, the converted wavelength can be reduced.

The anti-reflection film may be formed on the second semiconductor layer, the conversion layer may be formed on the anti-reflection film, and the protection layer may be formed on the conversion layer.

An anti-reflection film may be formed on the second semiconductor layer to texture the anti-reflection film, and the conversion layer may be formed in the recess of the anti-reflection film.

The conversion layer may be formed on the second semiconductor layer, and an anti-reflection film may be formed to cover the conversion layer.

A method of manufacturing a solar cell according to another aspect of the present invention includes: forming a second semiconductor layer on one surface of a first semiconductor layer; Forming a first electrode on the other surface of the first semiconductor layer and forming a second electrode in a predetermined region on the second semiconductor layer; And forming a conversion layer on the second semiconductor layer that absorbs light having a first energy and converts the light to light having a second energy lower than the second energy.

The first and second semiconductor layers may be formed by forming a first semiconductor layer by doping a first impurity on a semiconductor substrate and then doping the first semiconductor layer with a second impurity to a predetermined depth to form the second semiconductor layer can do.

The semiconductor substrate may include a crystalline substrate and an amorphous substrate.

And texturing at least one side of the first semiconductor layer.

The method may further include forming an antireflection film between the second semiconductor layer and the conversion layer, and forming the antireflection film on the conversion layer.

The conversion layer includes a core and a quantum dot including a shell surrounding the core.

Embodiments of the present invention are directed to energy down conversion in which quantum dots of a core / shell structure are formed on a semiconductor layer, quantum dots are used to absorb high energy in the ultraviolet region, and energy is dumped down to visible light. Thereby generating visible light. Therefore, the solar cell absorbs visible light rays converted from ultraviolet rays, in addition to visible light rays, as compared with the conventional solar rays absorbing only visible rays, thereby increasing incident light. In addition, efficiency can be improved by increasing incident light.

1 is a cross-sectional view of a solar cell according to an embodiment of the present invention;
2 is a partial enlarged photograph of a solar cell according to an embodiment of the present invention.
Figures 3 and 4 are cross-sectional views of a solar cell according to other embodiments of the present invention;
5 is a view showing energy according to the wavelength of sunlight;
6 is an energy band gap of a quantum dot of a core / shell structure according to the present invention.
7 is a photograph of the color and intensity of light emitted according to the structure of a quantum dot.
FIGS. 8 and 9 are graphs showing the luminous intensity and absorbance of the photoluminescence according to the structure of the quantum dots.
FIGS. 10 and 11 are photographs and sizes of morphology analyzed according to the structure of quantum dots. FIG.
FIGS. 12, 13 and 14 are graphs showing the measurement of the reflectivity after forming quantum dots of various structures at various concentrations. FIG.
FIGS. 15, 16 and 17 are graphs for measuring the external quantum efficiency according to the structure of the quantum dots.
18 and 19 are graphs showing photo-voltaic performance of a solar cell according to the structure of a quantum dot.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of other various forms of implementation, and that these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know completely.

FIG. 1 is a cross-sectional view of a solar cell according to an embodiment of the present invention, and FIG. 2 is a partial enlarged view of a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a solar cell according to an embodiment of the present invention includes a first semiconductor layer 110, a first electrode 120 formed on the rear surface of the first semiconductor layer 110, The antireflection film 140 formed on the second semiconductor layer 130, the conversion layer 150 formed on the antireflection film 140, and the second semiconductor layer 130 formed on the antireflection film 140 And a second electrode 160 connected to the second semiconductor layer 130 through a predetermined region of the conversion layer 150.

The first semiconductor layer 110 includes a semiconductor layer doped with a first impurity of a first conductivity type. Here, the first semiconductor layer 110 may be a semiconductor substrate, and may be formed by doping a first impurity of the first conductivity type in a semiconductor substrate. As the semiconductor substrate, a silicon substrate such as a single crystal silicon substrate or a polycrystalline silicon substrate can be used. That is, a silicon wafer can be used as the semiconductor substrate. Of course, a semiconductor substrate other than the silicon substrate may also be used. The first impurity may be a p-type impurity or an n-type impurity. The p-type impurity includes a Group III element such as boron (B), aluminum (Al) and gallium (Ga) P), arsenic (As), antimony (Sb), and the like. For example, the first semiconductor layer 110 may be doped with a Group III element such as boron or the like, and may be doped with a Group V element such as phosphorus. Meanwhile, in order to maximize the absorption of light, the first semiconductor layer 110 can be textured, thereby improving the efficiency of the solar cell. That is, the anti-reflection film 140 formed on the first semiconductor layer 110 by texturing the first semiconductor layer 110 is also textured. Therefore, incident light is not reflected because it is not reflected, and light absorption rate is increased through light scattering. At this time, the first semiconductor layer 110 is textured such that a pyramid or inverted pyramid structure is formed on the surface, or a porous or concave-convex structure is formed. In addition, the first semiconductor layer 110 may be formed by texturing not only the top surface but also the rear surface.

The first electrode 120 is formed on the rear surface of the first semiconductor layer 110. For example, the first electrode 120 is formed on the rear surface of the textured first semiconductor layer 110 so that the surface is planarized. For example, the first electrode 120 may be formed of a material having excellent conductivity, such as Ti, Cr, Au, Al, Ni, Ag, , Or an alloy thereof. In addition, the first electrode 120 may be formed as a single layer, or at least two or more layers may be laminated. In this embodiment, the first electrode 120 may be formed using aluminum.

The second semiconductor layer 130 is formed on the first semiconductor layer 110. The second semiconductor layer 130 includes a semiconductor layer doped with a second impurity of the second conductivity type. Here, the first impurity may be a p-type impurity or an n-type impurity. However, the first and second semiconductor layers 110 and 130 must have conductive characteristics opposite to each other in order to form a junction structure capable of inducing a photoelectric effect when incident light is absorbed. Therefore, if the first semiconductor layer 110 is a p-type semiconductor layer doped with a p-type impurity, the second semiconductor layer 130 should be an n-type semiconductor layer doped with an n-type impurity. Since the first semiconductor layer 110 of the embodiment of the present invention uses a silicon substrate, the second semiconductor layer 130 may be formed on the silicon substrate by doping an n-type impurity to a predetermined depth.

The antireflection film 140 is formed to lower the reflectivity of the light incident on the first and second semiconductor layers 110 and 130. The anti-reflection film 140 is a silicon nitride (SiNx) is a refractive index of 1.0 to 4.0, titanium oxide (TiO _2), aluminum oxide (Al ₂ O _3), niobium oxide (Nb ₂ O _5), magnesium oxide (MgO) It can be formed using silicon oxide (SiO ₂₎ or the like. That is, the antireflection film 140 may be formed of an oxide, a nitride or the like having a low refractive index. The anti-reflection film 140 may have a single-layer structure or a multi-layer structure. When the antireflection film 140 is formed into a multilayer structure, at least two layers having different refractive indexes may be laminated. At this time, at least two layers may be alternately formed repeatedly. The antireflection film 140 is formed on the textured first semiconductor layer 110 and thus textured. Since the antireflection film 140 is textured, incident light is not reflected and is not lost, and light absorption rate can be increased through light scattering.

The conversion layer 150 is formed on the antireflection film 140. That is, the conversion layer 150 is formed along the surface of the textured antireflection film 140. The conversion layer 150 includes a plurality of quantum dots 151 adsorbed on the antireflection film 140. The quantum dots 151 are formed in a core / shell structure, and a shell is formed to surround the core. The quantum dot 151 can be a shell of any one selected from any one the core is formed, ZnS, ZnSe, and CdSe selected from CdSe, InP, CuInS _2, PbS, and CdTe. Preferably, the quantum dots 151 may be formed of a core / shell structure using CdSe / ZnS. Meanwhile, CdSe / ZnS quantum dots can be synthesized by a hot injection method. First, a predetermined amount of a cadmium (Cd) raw material powder and a zinc (Zn) raw material powder are charged into a predetermined reactor maintained at room temperature. CdO may be used as the cadmium raw material, and zinc acetate may be used as the zinc raw material. In this way, the solvent is introduced into the reactor into which the cadmium raw material and the zinc raw material are introduced. Here, the solvent may be, for example, oleic acid and octadecene. Then, when the temperature of the reactor is raised, for example, at a temperature of about 120 DEG C, the raw powder starts to be dissolved in the solvent. When the temperature of the reactor is raised to about 150 ° C, cadmium (Cd) and zinc (Zn) ions are generated and dissolved in the acetate. When the reactor is maintained in a vacuum state, the acetate evaporates. For example, it is maintained for about 30 minutes to evaporate all of the acetate. Then, the temperature of the reactor is increased to, for example, about 310 ° C., TPO (trioctylphosohine) in which selenium (Se) and sulfur (S) are dissolved is rapidly injected into the reactor, and CdSe / ZnS quantum dots are formed when the temperature is maintained for a predetermined time. At this time, the size of the quantum dots can be adjusted according to the holding time after TPO injection and the molar ratio of materials to be mixed. The thus synthesized quantum dots 151 of the core / shell structure can be formed, for example, by mixing them with a dispersant such as chloroform at a predetermined ratio, forming them on the antireflection film 140 by spin coating or the like, and then drying them. The amount of the quantum dots 151 of the core / shell structure adsorbed on the antireflection film 140 varies depending on the molar ratio mixed in the dispersant, and the characteristics of the solar cell also vary. For example, FIG. 2 (a) is a photograph of a quantum dot of CdSe / ZnS structure adsorbed at a concentration of 0.3 wt%, and FIG. 2 (b) is a photograph of a quantum dot of a CdSe / ZnS structure adsorbed at a concentration of 1.0 wt% to be. As can be seen, the quantum dots of the core / shell structure are well adsorbed on the <111> textured surface and the amount adsorbed on the <111> textured surface increases as the concentration of core / shell quantum dots increases. The quantum dots 151 of the core / shell structure absorb light in the ultraviolet region and generate light in the visible region. In other words, the quantum dots 151 of the core / shell structure generate light in the visible light region by energy down conversion. The quantum dots 151 absorb the high energy of the ultraviolet region to reduce the energy and recombine the visible light And generates light of a line. By forming the quantum dots 151 of the core / shell structure in this way, visible light converted from ultraviolet light is absorbed in addition to visible light, thereby increasing incident light, thereby improving efficiency. On the other hand, the quantum dots 151 are formed in a size of nm. The core is formed in a size of 0.1 nm to 10 nm, for example, and the shell is formed in a larger size than the core to enclose the core. And may be formed in a size of 20 nm. Then, the color of light converted and generated according to the size of the core can be adjusted. For example, green light is generated when a CdSe core of 2.9 nm and a ZnS shell of 10.082 nm are used, and red light can be generated when 4.7 nm CdSe core and 8.989 nm ZnS shell are used. That is, as the size of the core becomes smaller, the energy band gap becomes larger and ultraviolet rays are converted into short-wavelength visible light. As the size of the core becomes larger, the energy band gap becomes smaller and ultraviolet rays can be converted into visible rays of longer wavelength. For example, when ultraviolet rays are changed to visible light of a first wavelength by using a core of a first size, ultraviolet light can be converted into visible light of a second wavelength longer than the first wavelength by using a core larger than the first size . Therefore, the core can be formed in a size larger than a size capable of converting ultraviolet rays into visible light, for example, 0.1 nm or larger. And, the shell can be formed to have a size larger than a certain size that can cover the core. On the other hand, the shape of the quantum dots 151 may have various shapes such as spheres, rods, wires, pyramids, and cubes, and is not particularly limited, but preferably has a spherical shape.

The second electrode 160 is formed to be in contact with the second semiconductor layer 130. That is, the second electrode 160 is formed in contact with the exposed second semiconductor layer 130 after the predetermined regions of the anti-reflection film 140 and the conversion layer 150 are removed. At this time, the second electrode 160 is partially formed to prevent the incident light from being reduced by the second electrode 160. The second electrode 160 may be formed of a material having excellent conductivity as in the case of the first electrode 120. Examples of the material include titanium (Ti), chromium (Cr), gold (Au), aluminum (Al) Ni, or Ag, or an alloy thereof. In addition, the second electrode 160 may be formed as a single layer, or at least two or more layers may be laminated. Here, the second electrode 170 may be formed of the same material as that of the first electrode 120, or may be formed of another material. In this embodiment, the second electrode 160 may be formed of silver (Ag).

3 and 4 are cross-sectional views of a solar cell according to another embodiment of the present invention. As shown in FIG. 3, a conversion layer 150 may be formed on the second semiconductor layer 130, and an anti-reflection layer 140 may be formed on the conversion layer 150. The antireflection film 140 may function as a protective film for protecting the conversion layer 150. Of course, a protective film may be separately formed. That is, the conversion layer 150 may be formed on the antireflection film 140, and a protective film may be formed on the conversion layer 150. In this case, the protective film may be formed of a transparent insulating material capable of transmitting light. 4, the conversion layer 150 may be formed only on the concave portion of the textured anti-reflection film 140 as shown in FIG. That is, the conversion layer 150 may be filled in the concave portion of the anti-reflection film 140 to flatten the surface, or may be formed thicker than the conversion film 150 and may be formed flat on the anti-reflection film 140.

As described above, the embodiments of the present invention provide a method of forming a core / shell structure conversion layer by energy down conversion, which absorbs high energy of the ultraviolet region using the conversion layer, Thereby generating visible light. Therefore, the semiconductor layer absorbs visible light converted from ultraviolet light in addition to visible light, thereby increasing the incident light, thereby improving the efficiency. Hereinafter, the efficiency of the solar cell is improved by the energy down conversion by the conversion layer of the core / shell structure.

FIG. 5 is a graph showing the energy according to the wavelength of sunlight, showing the spectrum of sunlight and the wavelength and energy (blue color) converted by the silicon solar cell. 6 is a diagram showing energy band gaps of quantum dots in a core / shell structure according to the present invention.

As shown in FIG. 5, a conventional solar cell absorbs light having a wavelength of less than 1100 nm of a visible light ray from solar light that emits infrared rays, visible light, and ultraviolet rays to generate a photo current. The conventional solar cell absorbs visible light and converts it into a photocurrent. However, since the photovoltaic cell can not absorb ultraviolet rays, it can not convert to a photocurrent. However, the solar cell according to the present invention absorbs ultraviolet rays of a wavelength of 400 nm or less by applying quantum dots of a core / shell structure, and reduces the energy of ultraviolet rays and recombines to generate visible light. This will be described in more detail as follows. The nano-sized core surrounds the quantum dot of the core / shell structure according to the present invention, and the energy band gap Eg of the shell is larger than the energy band gap Eg of the core as shown in Fig. 6 . Therefore, quantization is performed outside the conduction energy band and the valance energy band of the core, and the electron quantum states of E1, E2, and E3 and the hole quantum states of H1, H2, and H3 are produced. In addition, the high energy band gap Eg of the shell serves as an energy barrier of the quantized electrons and holes of the core. When the quantum dots of the core / shell structure absorb ultraviolet rays, electrons at the H3 quantum level of the valence band of the core shift to the conduction band E3 quantum state as shown in FIG. 6 Electrons and holes are formed. The electron and hole pairs move to the lower quantum levels of electrons and holes, respectively. The electrons and holes in the E2 and H2 quantum states are recombined to emit visible light. In addition, when ultraviolet light having a lower energy is absorbed, the electrons at the H2 quantum level of the valence band of the core are transited to the E2 quantum level of the high conduction band, and electrons and holes . The electron and hole pairs move to the lower quantum levels of electrons and holes, respectively. The electrons and holes in the quantum states of E1 and H1 are recombined to emit visible light. At this time, the wavelength of the emitted visible light depends on the energy band gap Eg of the core, and the energy band gap Eg of the core depends on the size of the core and the energy band gap Eg of the shell. The light emitted from the quantum dots of the core / shell structure is absorbed by the surface of the layer textured with < 111 > to increase the photocurrent in the silicon solar cell. That is, the quantum dots of the core / shell structure absorb ultraviolet rays, convert energy to emit visible light, absorb visible light emitted from the quantum dots of the core / shell structure to the surface of the semiconductor layer, circuit current can be increased to improve the power conversion efficiency of the solar cell.

In order to prove this, the quantum dots of various concentrations of core / shell structure were adsorbed on the surface of the textured layer by spin coating method and surface reflectance, light emission intensity, , Photo luminescence, external quantum efficiency, and photovoltaic performance were measured.

FIG. 7 shows the results of measuring the color and intensity of light emitted according to the structure of the quantum dots. As a comparison example, the quantum dots of CdSe / ZnS structures having different sizes as CdSe quantum dots and embodiments of the present invention were compared. The CdSe quantum dot consists of only 4.7 nm core, and the CdSe / ZnS quantum dot consists of 2.89 nm CdSe core and 10.092 nm ZnS shell, and 4.91 nm CdSe core and 8.969 nm ZnS shell. That is, Example 1 of the present invention is composed of 2.89 nm CdSe core and 10.092 nm ZnS shell, and Example 2 of the present invention is composed of 4.91 nm CdSe core and 8.969 nm ZnS shell.

7 (a) is a result of measuring the wavelength of light emitted from each quantum dot when the quantum dots are dissolved in solvent and then irradiated with light of different wavelengths. That is, visible light and ultraviolet rays of wavelengths of 254 nm and 365 nm were irradiated, respectively. As shown in the figure, the CdSe quantum dot emits light with a wavelength of 578 nm, the CdSe / ZnS quantum dot emits light with a wavelength of 562 nm, and the CdSe / ZnS quantum dots according to Embodiment 2 emits light with a wavelength of 603 nm As shown in FIG. As shown in the figure, CdSe quantum dots emit red light when irradiated with visible light and emit red light with slightly different color depending on wavelength when ultraviolet light is irradiated. Further, in the case of the CdSe / ZnS quantum dots of Example 1, green light is emitted when visible light and ultraviolet light are irradiated. In the case of the CdSe / ZnS quantum dots of Example 2, red light is emitted when visible light is emitted, and red light is emitted with slightly different colors depending on the wavelength when ultraviolet light is emitted. It can be seen from this that the quantum dots absorb visible light and then emit visible light through energy down conversion.

FIG. 7 (b) shows spin-coating the quantum dots on the surface of the silicon nitride anti-reflective film textured with <111> at various concentrations and irradiating ultraviolet rays with a wavelength of 254 nm. In the case of CdSe quantum dots, it is difficult to find the concentration dependence of quantum dots when the emission intensity is below the detection limit. However, in the case of the CdSe / ZnS quantum dots of Example 1, the light emission intensity increases as the concentration of the quantum dots increases. However, in the case of the CdSe / ZnS quantum dots of Example 2, it is difficult to find the concentration dependency of the quantum dots when the light emission illuminance is below the detection limit.

As described above, it can be seen that the quantum dots of the core / shell structure absorb light in the ultraviolet region and then emit light in the visible light region by energy down conversion. In addition, it can be seen that visible light of different colors is emitted according to the size of the core, and it can be seen that the light emission illuminance increases as the concentration increases.

FIGS. 8 and 9 are graphs showing the intensity and absorbance of photo luminescence (PL) according to the structure of a quantum dot, respectively. 8 and 9 (a) show the PL intensity and absorbance according to the CdSe quantum dots concentration, and Figs. 8 and 9 (b) show the CdSe / ZnS quantum dots PL intensity and absorbance, and FIGS. 8 and 9 (c) show PL intensity and absorbance according to the concentration of CdSe / ZnS quantum dots emitting red light. 8 (b) and (c) are shown in comparison with a CdSe quantum dot having a concentration of 0.5 wt%.

PL measurement result As shown in FIG. 8, a light emission peak was detected at 575 nm for the CdSe quantum dot, a light emission peak was detected at 542 nm and 583 nm for the CdSe / ZnS quantum dot emitting green light, The emission peak of CdSe / ZnS quantum dots emitting light was detected at 607 nm. The CdSe / ZnS quantum dot emits green light at about 20,000 (arb, unit), the CdSe / ZnS quantum dot emits red light at about 3000, and the CdSe quantum dot at about 0.5% 600 respectively. Therefore, the CdSe / ZnS quantum dots emitting green light exhibit the highest PL intensity.

The absorbance shown in FIG. 9 was measured using a UV-vis instrument. CdSe quantum dots have absorption peaks at 559 nm, 483 nm and 266 nm. This is because there is a discontinuous quantum energy level above and below the conduction band and the valence band of CdSe and the absorption peaks are absorbed by this discontinuous quantum energy level exist. Also, it can be seen that the higher the concentration, the greater the degree of absorption. However, in the case of the quantum dots of the core / shell structure, such absorption peaks are not confirmed, and it can be confirmed that the wavelength range where the light is absorbed becomes wider as the concentration increases. Since this tendency is absorbed only by light having energy higher than the energy band gap of the core, the CdSe / ZnS quantum dot emitting green light has a smaller energy band gap due to the smaller size of the core (CdSe) ), That is, CdSe / ZnS quantum dots that start absorption in light having a wavelength of about 500 nm or less and emit red light start to absorb at a higher wavelength (low energy), that is, light having a wavelength of 600 nm or less .

Comparing the absorbance and PL intensity of each quantum dot, the CdSe quantum dot absorbs light having a wavelength of about 250 nm to 560 nm and emits light having a wavelength of 575 nm through energy down conversion. The CdSe / ZnS quantum dots, which emit green light, absorb light in the 250 nm to 500 nm wavelength range and emit light with wavelengths of 542 nm and 583 nm through energy down conversion. CdSe / ZnS quantum dots emitting red light absorb light with a wavelength of 250 nm to 600 nm and emit red light with a wavelength of 607 nm through energy down conversion.

10 and 11 are TEM and TEM images of the morphology according to the structure of the quantum dots. (B) is a photograph and a distribution diagram of a quantum dot of a CdSe / ZnS structure emitting green light, and (c) shows a CdSe / ZnS structure emitting red light &Lt; / RTI &gt;

As shown in FIG. 10, the CdSe quantum dot is about 4.7 nm in size and has an irregular shape. However, the CdSe / ZnS quantum dot emitting green light has a size of 10.098 nm, and the CdSe / ZnS quantum dot emitting red light has a size of 8.969 nm and an irregular shape. Also, as shown in FIG. 11, it can be seen that the size distribution of the CdSe / ZnS quantum dots emitting green light is uniform and the dispersion is better than that of the CdSe quantum dots after the synthesis according to the sizes of the quantum dots.

FIGS. 12, 13, and 14 are graphs showing the reflectance of a silicon nitride dry anti-reflective film textured with < 111 > texture by forming a quantum dot at various concentrations using a spin coating method. Here, FIGS. 12 to 14 (a) show the reflectance according to the wavelengths of the ultraviolet and visible light regions, and (b) show the reflectance according to the wavelengths of the ultraviolet region.

As shown in FIG. 12, when the CdSe quantum dots are coated, the surface reflectance of the CdSe quantum dots increases in comparison with the case where the surface reflectance does not form a quantum dot in the ultraviolet region (200 nm to 450 nm) . In particular, the CdSe quantum dot concentration of about 1 wt% decreases from about 25% to about 17.5%. As shown in FIG. 13, when the CdSe / ZnS quantum dot emitting green light is coated, the surface reflectance decreases from about 25% to 15% when the quantum dot concentration in the ultraviolet region increases. Also, as shown in FIG. 14, when the CdSe / ZnS quantum dots emitting red light are coated, the surface reflectance decreases from about 25% to 15% when the quantum dot concentration increases in the ultraviolet region. These results indicate that the quantum dots absorb light in the ultraviolet region. However, CdSe / ZnS quantum dots emitting CdSe / ZnS quantum dots, and CdSe / ZnS quantum dots emitting red light in the region other than ultraviolet light (450 nm to 1100 nm) increase in surface reflectivity when the quantum dots concentration increases. However, this efficiency is further increased because ultraviolet light is converted into energy downconverted and converted into visible light compared with light absorbed by the solar cell.

15, 16, and 17 are results of measurement of external quantum efficiency (EQE) according to the structure of a quantum dot using IPCE equipment. Here, FIGS. 15 to 17 (a) show the external quantum efficiency according to the wavelengths in the ultraviolet and visible light regions, and (b) show the external quantum efficiency according to the wavelengths of the ultraviolet region.

As shown in FIG. 15, it can be seen that the EQE data is hardly changed in the case of the CdSe quantum dot. This indicates that although the quantum dots absorbed light and the reflectivity decreased, the amount of emitted light was not sufficient and there was no change in the EQE data. However, as shown in FIGS. 16 and 17, the efficiency of the CdSe / ZnS quantum dots emitting green light and red light increases between 300 nm and 500 nm, unlike the CdSe quantum dots. The conversion efficiency of the silicon solar cell was not good at a wavelength of 300 nm to 500 nm, but it was confirmed that the efficiency of the silicon solar cell was increased by converting light of this wavelength to light of 500 nm or more. On the other hand, in the range of 500 nm to 1100 nm, the conversion efficiency decreases as the concentration increases due to the reduction of the reflectivity. However, this efficiency is further increased because ultraviolet light is converted into energy downconverted and converted into visible light compared with light absorbed by the solar cell.

 FIGS. 18 and 19 are graphs showing the photo-voltaic performance of a solar cell having quantum dots formed on the surface of the silicon nitride anti-reflective film textured with < 111 >. FIG. 18 shows the short circuit current density (Jsc) of the solar cell according to the concentration of the quantum dot, and FIG. 19 shows the efficiency of the solar cell according to the concentration of the quantum dot. Figs. 18 and 19 (a), (b) and (c) show short-circuit current densities and efficiencies of CdSe / ZnS quantum dots emitting CdSe / ZnS quantum dots emitting green light and CdSe / .

As shown in Figs. 18 (a) and 19 (a), the short circuit current density Jsc and the power conversion efficiency PCE of the solar cell having CdSe quantum dots are not increased compared to a reference where no quantum dots are formed I did.

However, in the case of a solar cell having a quantum dot of a CdSe / ZnS structure emitting green light, as shown in Fig. 18 (b), the shortcircuit current density Jsc is about 0.2 wt% And it decreases slightly as the concentration of the quantum dots increases after about 0.5 wt%. However, at a concentration of about 0.2 wt%, the short circuit current density is increased by about 2.2 mA / cm 2 compared with the reference, which is improved by about 6.34%. As shown in FIG. 19 (b), the CdSe / ZnS quantum dot emitting green light has an increase of about 0.91% and a 6.5% increase compared to the reference when the concentration increases to 0.2 wt% have. However, when the concentration of the CdSe / ZnS quantum dot emitting green light exceeds 0.3 wt%, the PCE decreases. This increase in PCE up to a concentration of 0.3 wt% is due to the absorption of ultraviolet light and absorption of visible light emitted through energy down conversion. When the concentration of the quantum dot is above 0.3 wt%, the reflectance in visible light, The PCE is decreased.

On the other hand, in the case of a solar cell having CdSe / ZnS quantum dots emitting red light, as shown in Fig. 19 (b), the shortcircuit current density Jsc is rapidly increased to about 0.4 wt% And after 0.5 wt%, it decreases slightly as the concentration of the quantum dots increases. However, at a concentration of about 0.4 wt%, the short circuit current density is increased by about 1.9 mA / cm &lt; 2 &gt; Also, as shown in FIG. 19 (c), it can be seen that PCE increases by 0.54% compared to the reference by 3.8% when the concentration of quantum dots increases to 0.4 wt%. However, when the quantum dot concentration is increased at a quantum dot concentration of 0.5 wt% or more, it decreases slightly. Therefore, the PCE increase (0.91%) of the CdSe / ZnS quantum dot emitting green light is greater than that of the CdSe / ZnS quantum dot emitting red light PCE (0.54%).

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. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention.

110: first semiconductor layer 120: first electrode
130: second semiconductor layer 140: antireflection film
150: conversion layer 151: quantum dot of core / shell structure
160: Second electrode

Claims (23)

First and second semiconductor layers of different conductivity types;
First and second electrodes formed to contact the first and second semiconductor layers, respectively; And
And a conversion layer formed on the second semiconductor layer, for converting light of a wavelength having a first energy into light having a second energy lower than the first energy.
The solar cell according to claim 1, wherein the first semiconductor layer is formed by doping a semiconductor substrate with a first impurity of a first conductivity type.
The solar cell according to claim 2, wherein at least one surface of the first semiconductor layer is textured.
The solar cell according to claim 3, wherein the second semiconductor layer is formed by doping a second impurity of a second conductivity type to a depth of the first semiconductor layer. The solar cell according to claim 4, wherein the first and second semiconductor layers comprise crystalline silicon.
The solar cell according to claim 5, wherein the conversion layer converts light in an ultraviolet region by energy down conversion to emit light in a visible light region.
The solar cell according to claim 6, wherein the first and second semiconductor layers absorb visible light beams converted from ultraviolet rays by visible light rays and energy down conversion of the conversion layers.
The solar cell according to claim 6, wherein the conversion layer comprises a core and a quantum dot including a shell surrounding the core.
The solar cell according to claim 8, wherein the quantum dot is formed of a core selected from the group consisting of CdSe, InP, CuInS ₂ , PbS, and CdTe, and a shell is formed of any one selected from ZnS, ZnSe, and CdSe.
The solar cell according to claim 9, wherein the core is formed of CdSe, and the shell is formed of ZnS.
10. The solar cell according to claim 9, wherein the conversion layer is adjusted in wavelength to be converted according to a size of the core and the shell.
The solar cell according to claim 9, wherein the core is formed in a size of 0.1 nm to 6 nm, and the shell is formed in a size of 8 nm to 20 nm.
The solar cell according to claim 6, wherein an antireflection film is formed on the second semiconductor layer, and the conversion layer is formed on the antireflection film.
14. The solar cell of claim 13, further comprising a protective layer formed on the conversion layer.
The solar cell according to claim 6, wherein an antireflection film is formed on the second semiconductor layer, the antireflection film is textured, and the conversion layer is formed in the concave portion of the antireflection film.
The solar cell according to claim 6, wherein the conversion layer is formed on the second semiconductor layer, and an anti-reflection film is formed to cover the conversion layer.
Forming a second semiconductor layer on one surface of the first semiconductor layer;
Forming a first electrode on the other surface of the first semiconductor layer and forming a second electrode on a predetermined region of the second semiconductor layer; And
Forming a conversion layer on the second semiconductor layer by absorbing light having a first energy and converting the light into light having a second energy lower than the second energy.
The semiconductor device according to claim 17, wherein the first and second semiconductor layers
Wherein the first semiconductor layer is formed by doping a first impurity on a semiconductor substrate, and then the second semiconductor layer is formed by doping the first semiconductor layer with a second impurity to a predetermined depth.
The method of manufacturing a solar cell according to claim 18, wherein the semiconductor substrate comprises a crystalline silicon substrate.
19. The method of manufacturing a solar cell according to claim 18, further comprising texturing at least one surface of the first semiconductor layer.
20. The method of claim 19, further comprising forming an antireflection film between the second semiconductor layer and the conversion layer.
The method of manufacturing a solar cell according to claim 19, further comprising forming an antireflection film on the conversion layer.
19. The method of claim 18, wherein the conversion layer comprises a core and a quantum dot including a shell surrounding the core.

Images