Patent Publication Number: US-2023143531-A1

Title: Light concentrator based on quantum dot, and photovoltaic module including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based on and claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2021-0151081 filed on Nov. 5, 2021, and Korean Patent Application No. 10-2022-0115440 filed on Sep. 14, 2022, in the Korean Intellectual Property Office, the disclosures of which are herein incorporated by reference in their entireties. 
     BACKGROUND 
     Field 
     The disclosure relates to a light concentrator based on a quantum dot, and a photovoltaic module including the same. More specifically, the disclosure relates to a quantum dot-based light concentrator including a resin film layer with quantum dots dispersed and a glass layer or polymer layer in contact with upper and lower surfaces of the resin film layer, and capable of improving the power generation efficiency in a photovoltaic module by optimally adjusting the longest wavelength of the quantum dots, the average transmittance of the glass layer, the material of the polymer layer, and the cross-sectional aspect ratio (length/thickness) of the light concentrator. 
     Description of Related Art 
     Quantum dot is a nano-sized semiconductor structure particle that emits light when stimulated with energy such as light. 
     The principle of the quantum dot is as follows. When the dimension of a substance is reduced due to the small size of the substance, the electron state density and energy change, so the properties of the substance also appear differently depending on the dimension. For example, small nanoparticles with a size of several nanometers exhibit a quantum confinement effect that does not appear in general materials. 
     Strictly speaking, reducing the dimension refers to confining electrons in a region smaller than the de Broglie wave length. A zero-dimensional quantum dot is not a point with no area at all, but actually a particle whose three-dimensional size is smaller than the de Broglie wave length. In quantum mechanics, the length of the wave, that is, the de Broglie wave, accompanied by all particles with momentum varies depending on the material, and in the case of semiconductors, it is about 10 nm. A semiconductor quantum dot consists of about one million electrons, but in reality, the number of unbound free electrons is about 1 to 100 because electrons are tightly bound to the atomic nucleus of the material. Therefore, the free electrons in the quantum dot can be represented as waves, and the energy and the density of states are quantized. 
     Semiconductor nanoparticles of 10 nm or less, which are smaller than the De Broglie wave length, have a relatively increased band gap energy as the particle size decreases. Therefore, even with the same material, dozens of colors can be realized by slightly adjusting the particle size. For this reason, it has been reported that quantum dots have considerable application potential in various fields such as displays [Seth Coe-Sullivan, Wing-Keung Woo, Jonathan S. Steckel, Moungi Bawendi, Vladimir Bulovic, “Tuning the performance of hybrid organic/inorganic quantum dot light-emitting devices”, Organic Electronics, vol. 4, 123-130 (2003)], recording devices, sensors, nano-computers, biology, and medicine [X. Michalet, F. F. Pinaud, L. A. Bentolila, 1 J. M. Tsay, 1 S. Doose, 1. J. J. Li, 1 G Sundaresan, A. M. Wu, S. S. Gambhir, S. Weiss 1, “Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics”, SCIENCE VOL 307, 538-544 (2005)]. 
     Patent Document 1 (U.S. Patent Publication No. 2011/0171773 A1) relates to a method for making a planar concentrating solar cell assembly with silicon quantum dots, and discloses that a substrate disposed on both surfaces of a silicon quantum dot film is made of glass, plastic, or resin. 
     Patent Document 2 (Korean Patent Publication No. 2016-0061267) relates to an encapsulant employing non-cadmium quantum dots as a wavelength conversion material, and to a solar cell module and a light-emitting solar concentrator including the same, and discloses a polymer sheet containing the quantum dots. 
     Patent Document 3 (Korean Patent Publication No. 2021-0092521) relates to a sunlight concentrating device and a photovoltaic module including the same, and discloses a structure in which a low-refractive layer is disposed on both surfaces of a first quantum dot layer. 
     Meanwhile, the efficiency of a light concentrator based on quantum dots is affected by an appropriate dimension, medium (glass and polymer), and quantum dot photoluminescence characteristics. Specifically, the light concentrator should have an appropriate size (or dimension) to operate well in a realistic m 2  level, and when the transmittance of the medium is excellent, the light absorption by the quantum dots is facilitated and the high efficiency is guaranteed. Furthermore, the decrease in efficiency due to C—H stretching depending on the longest/shortest wavelength of the quantum dot [Bergren et. al., “High-performance CuInS 2 , Quantum dot laminated glass luminescent solar concentrators for windows”, ACS Nano, 3, 520 (2018)] is also a major consideration in the development of a high-efficiency light concentrator. 
     PRIOR ART LITERATURE 
     Patent Literature 
     Patent Document 1: U.S. Patent Publication No. 2011/0171773 A1 
     Patent Document 2: Korean Patent Publication No. 2016-0061267 
     Patent Document 3: Korean Patent Publication No. 2021-0092521 
     SUMMARY 
     The disclosure is intended to provide a light concentrator based on a quantum dot, and a photovoltaic module including the same, where the light concentrator based on a quantum dot comprises a resin film layer with quantum dots dispersed and a glass layer or polymer layer in contact with upper and lower surfaces of the resin film layer, and capable of improving the power generation efficiency in a photovoltaic module by optimally adjusting the longest wavelength of the quantum dots, the average transmittance of the glass layer, the material of the polymer layer, and the cross-sectional aspect ratio (length/thickness) of the light concentrator. 
     According to a first aspect of the disclosure, a light concentrator based on a quantum dot may include a resin film layer in which quantum dots are dispersed; an upper layer in contact with an upper surface of the resin film layer; and a lower layer in contact with a lower surface of the resin film layer, wherein each of the upper layer and the lower layer is selected from a glass layer or a polymer layer. 
     According to a second aspect of the disclosure, a light concentrator based on a quantum dot may include a polymer layer in which quantum dots are dispersed, wherein the polymer layer is provided in a form of slab. 
     In the light concentrator according to the first or second aspect, a longest wavelength of the quantum dot may be 650 nm to 900 nm. 
     In the light concentrator according to the first aspect, the glass layer may have an average transmittance of 91% to 95% at 400 nm to 1000 nm. 
     In the light concentrator according to the first or second aspect, the polymer layer may be selected from the group consisting of clear polyimide, fluorinated polymethyl methacrylate (fluorinated PMMA), and fluorinated polyimide. 
     In the light concentrator according to the first or second aspect, a cross-sectional aspect ratio (length/thickness) of the light concentrator may be 50 to 200. 
     According to the first aspect of the disclosure, a photovoltaic module may include a resin film layer in which quantum dots are dispersed; an upper layer in contact with an upper surface of the resin film layer; a lower layer in contact with a lower surface of the resin film layer; an adhesive provided on sides of the resin film layer, the upper layer, and the lower layer; and a photovoltaic cell attached to the adhesive, wherein each of the upper layer and the lower layer is selected from a glass layer or a polymer layer. 
     According to the second aspect of the disclosure, a photovoltaic module may include a polymer layer in which quantum dots are dispersed; an adhesive provided on sides of the polymer layer; and a photovoltaic cell attached to the adhesive, wherein the polymer layer is provided in a form of slab. 
     In the photovoltaic module according to the first or second aspect, a longest wavelength of the quantum dot may be 650 nm to 900 nm. 
     In the photovoltaic module according to the first aspect, the glass layer may have an average transmittance of 91% to 95% at 400 nm to 1000 nm. 
     In the photovoltaic module according to the first or second aspect, the polymer layer may be selected from the group consisting of clear polyimide, fluorinated polymethyl methacrylate (fluorinated PMMA), and fluorinated polyimide. 
     In the photovoltaic module according to the first or second aspect, a cross-sectional aspect ratio (length/thickness) of the light concentrator may be 50 to 200. 
     According to the disclosure, by optimally adjusting the longest wavelength of the quantum dots, the average transmittance of the glass layer, the material of the polymer layer, and the cross-sectional aspect ratio (length/thickness) of the light concentrator, it is possible to maximize the efficiency of the quantum dot-based light concentrator and increase the efficiency of the photovoltaic module including the light concentrator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows the structure of a quantum dot light concentrator based on laminated glass or laminated polymer according to a first aspect of the disclosure. 
         FIG.  2    shows the structure of a quantum dot light concentrator having a quantum dot dispersion polymer layer in the form of a slab according to a second aspect of the disclosure. 
         FIG.  3    is a graph showing the transmittance measured depending on materials of resin/polymer layers constituting a light concentrator according to the disclosure. 
         FIG.  4    is a graph showing the transmittance measured for various polymers including polymethyl methacrylate (PMMA). 
         FIG.  5    is a graph showing the absorption coefficient [cm −1 ] of resin/polymer made of polymethyl methacrylate (PMMA) and fluorinated PMMA. 
         FIG.  6    is a graph showing the photoluminescence spectrum of quantum dots constituting a light concentrator according to the disclosure. 
         FIG.  7    is a diagram showing the efficiency of a light concentrator measured through a Monte-Carlo simulator using length (mm) and thickness (mm) as variables for the square-sized light concentrator based on quantum dot 1 according to the disclosure. 
         FIG.  8    is a graph showing the transmittance depending on normal glass, low iron glass, and quartz glass. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. The following description is intended to enable those skilled in the art to which the disclosure pertains to easily practice the disclosure, and is not intended to limit the technical subject matter and scope of the disclosure. 
     In the disclosure, the term ‘quantum dot’ refers to a nano-sized semiconductor structure particle that emit light when stimulated with energy such as light. 
     In the disclosure, the term ‘transmission’ refers to a phenomenon that incident light is not absorbed by resin/polymer in which quantum dots are dispersed, and the term ‘transmittance’ refers to the ratio of light not absorbed by resin/polymer compared to incident light. 
     In the disclosure, the term ‘longest wavelength’ refers to a limit wavelength at which incident light is minimally absorbed by resin/polymer and maximally absorbed by quantum dots dispersed in the resin/polymer. For example, the ‘longest wavelength of the quantum dot’ may be the upper limit wavelength of the full width at half maximum (FWHM) in the photoluminescence spectrum of the quantum dot. The ‘FWHM’ (hereinafter also referred to as ‘spectral FWHM’) may be a difference between the upper limit wavelength and the lower limit wavelength at which energy in the photoluminescence spectrum of the quantum dot is ½ of the maximum relative radiant energy. 
     In the disclosure, the term ‘slab’ indicates that a quantum dot dispersion polymer constituting the light concentrator based on the quantum dot according to the second aspect is formed of ‘one lump in a flat shape’ rather than ‘multiple layers’. 
       FIG.  1    shows the structure of a quantum dot light concentrator  100  based on laminated glass or laminated polymer and the structure of a photovoltaic module  200  including the light concentrator according to a first aspect of the disclosure. 
     Specifically, the quantum dot light concentrator  100  based on laminated glass or laminated polymer according to the first aspect of the disclosure includes a resin film layer  110  in which quantum dots (QD) are dispersed, an upper layer  120  in contact with an upper surface of the resin film layer  110 , and a lower layer  130  in contact with a lower surface of the resin film layer  110 . The upper layer  120  may be formed of a glass layer or a polymer layer, and the lower layer  130  may also be formed of a glass layer or a polymer layer. 
     In addition, the glass layer is preferably a low iron glass, a quartz glass, or a high transmittance glass equivalent thereto. The high transmittance glass preferably refers to a glass having an average transmittance of 94% at 400 to 700 nm, and more preferably a glass having an average transmittance of 94.5% at 400 to 700 nm. In addition, the polymer layer is also preferably formed of a material having high transmittance, such as clear polyimide, fluorinated polymethyl methacrylate, or fluorinated polyimide, and more preferably formed of fluorinated polymethyl methacrylate. 
     Meanwhile, the photovoltaic module  200  according to the first aspect of the disclosure includes the quantum dot light concentrator  100  composed of the resin film layer  110 , the upper layer  120 , and the lower layer  130 , and further includes an adhesive  140  provided on sides of the quantum dot light concentrator  100 , and a photovoltaic cell  150  attached to the adhesive  140 . 
       FIG.  2    shows the structure of a quantum dot light concentrator  100 A having a quantum dot dispersion polymer layer in the form of a slab and the structure of a photovoltaic module  200 A including the light concentrator according to a second aspect of the disclosure. 
     Specifically, the quantum dot light concentrator  100 A according to the second aspect of the disclosure is composed of only a quantum dot dispersion polymer  110 A in the form of a slab, unlike the quantum dot based light concentrator  100  according to the first aspect in which multiple layers are formed by laminated glass or laminated polymer positioned above and below the resin film layer  110 A in which quantum dots (QD) are dispersed. 
     The quantum dot dispersion polymer  110 A is preferably formed of a material having high transmittance, such as clear polyimide, fluorinated polymethyl methacrylate, or fluorinated polyimide, and more preferably formed of fluorinated polymethyl methacrylate. 
     Meanwhile, the photovoltaic module  200 A according to the second aspect of the disclosure includes the quantum dot light concentrator  100 A composed of the quantum dot dispersion polymer  110 A in the form of a slab, and further includes the adhesive  140  (see  FIG.  1   ) provided on sides of the quantum dot light concentrator  100 A, and the photovoltaic cell  150  attached to the adhesive  140 . 
     For reference, the adhesive  140  is made of a material having a refractive index similar to that of the glass layer or the polymer layer constituting the quantum dot light concentrator  100  or  100 A in order to reduce Fresnel reflection. This allows the quantum dot light concentrator  100  or  100 A according to the disclosure and the photovoltaic module  200  or  200 A including the same to maintain high efficiency. Therefore, the adhesive  140  is preferably formed of a material having high transmittance, such as clear polyimide, fluorinated polymethyl methacrylate, or fluorinated polyimide, and more preferably formed of fluorinated polymethyl methacrylate. 
       FIG.  3    is a graph of the transmittance measured using different materials for resin/polymer layers, that is, the resin film layer  110  and the polymer layers of the upper and lower layers  120  and  130  in the light concentrator  100  of  FIG.  1    and the polymer layer  110 A in the light concentrator  100 A of  FIG.  2   . 
     Specifically, an experiment was conducted with resin/polymer including a material A of isobornylacrylate (IBOA), a material B in which the IBOA and dipentaerythritol hexaacrylate (DPHA) are mixed in a weight ratio of 3:1, and a material C in which photoinitiator Oxe-02 is added to the material B in a weight ratio of 3%. For each of the material A, the material B, and the material C,  FIG.  3    shows the transmittance according to the wavelength of the corresponding resin/polymer. 
       FIG.  4    is a graph showing the transmittance measured for various polymers including polymethyl methacrylate (PMMA). 
     Specifically, it can be seen that the transmittance of PMMA, which is known to have high transmittance, is also slightly reduced near a wavelength region of 850 nm. This suggests that there is a need for a more improved material with no change in transmittance even near that wavelength region. 
       FIG.  5    is a graph showing the absorption coefficient [cm −1 ] of resin/polymer made of polymethyl methacrylate (PMMA) and fluorinated PMMA. 
     Specifically, when the resin/polymer is made of PMMA, it can be seen that it has an absorption coefficient between about 10 −3  and 10 0  over the entire wavelength region between 500 nm and 1500 nm, and it can be seen that as the wavelength increases, the absorption coefficient increases along with an inconsistent range of fluctuations. On the other hand, when the resin/polymer is made of fluorinated PMMA, it can be seen that it has a lower absorption coefficient than that of PMMA over the entire wavelength region between 500 nm and 1500 nm, and it can be seen that unlike the case of PMMA, the absorption coefficient decreases uniformly as the wavelength increases. In particular, it can be seen that in the vicinity of 850 nm, the absorption coefficient of fluorinated PMMA is about 10 −4  (cm −1 ), which is a low about 1000 times that of PMMA having an absorption coefficient of about 10 −1  (cm −1 ). 
       FIG.  6    is a graph showing the photoluminescence spectrum of quantum dots constituting a light concentrator according to the disclosure. 
     Specifically, it can be seen that quantum dot 1, quantum dot 2, and quantum dot 3 have a peak emission wavelength between 650 nm and 700 nm, between 700 nm and 750 nm, and 720 nm and 770 nm, respectively, and also have a full width at half maximum (FWHM) of about 150 nm, 170 nm, and 240 nm, respectively. 
       FIG.  7    is a diagram showing the efficiency of a light concentrator measured through a Monte-Carlo simulator using length (mm) and thickness (mm) as variables for the square-sized light concentrator based on quantum dot 1 according to the disclosure. In the disclosure, “the efficiency of a light concentrator” may refer to “the intensity of light emitted from the sides of the light concentrator with respect to the intensity of light incident on the light concentrator (light incident on the upper surface of the light concentrator)”. 
     Specifically, it can be seen that the efficiency (η opt ) of the light concentrator increases as the thickness of the light concentrator increases, whereas the efficiency decrease as the length increases. In other words, it can be seen that the efficiency of the light concentrator is inversely proportional to a cross-sectional aspect ratio (length/thickness) of the light concentrator. 
       FIG.  8    is a graph showing the transmittance depending on normal glass, low iron glass, and quartz glass. 
     Specifically, over the entire wavelength region between 400 nm and 1000 nm, it can be seen that normal glass has a transmittance of approximately 87 to 92%, whereas low iron glass and quartz glass have a transmittance of approximately 92 to 95%. 
     More specifically, used in the disclosure are low iron glass and quartz glass. Normally used glass contains SiO 2  of 65 to 75%, CaO of 5 to 15%, Na 2 CO 3  of 10 to 20%, etc. with respect to the total weight of the composition. Meanwhile, “low iron glass” may refer to “glass in which the ratio of the total weight of FeO, Fe 2 O 3 , and Fe 3 O 4  to the total weight of the glass is 0.01% or less”. Also, the quartz glass used in the disclosure is a glass made of pure silicon dioxide (SiO 2 ) only. 
     EMBODIMENTS 
     Hereinafter, embodiments of the disclosure will be described in detail. The following embodiments are, however, only exemplary to help the understanding of the disclosure, and the disclosure is not limited to the following embodiments. 
     &lt;Experimental Example 1&gt; Experiment on Transmittance of Quantum Dot Dispersion Resin/Polymer 
     In order to specify the photoluminescence characteristics of the quantum dots used in the quantum dot light concentrator according to the disclosure, the transmittance of the resin/polymer constituting the quantum dot light concentrator was preliminarily evaluated through the following materials and sizes. 
     Prior to the experiment on transmittance, as described above, the resin/polymer was prepared with each of a material A of isobornylacrylate (IBOA), a material B in which the IBOA and dipentaerythritol hexaacrylate (DPHA) are mixed in a weight ratio of 3:1, and a material C in which photoinitiator Oxe-02 is added to the material B in a weight ratio of 3%. In this case, all the resins/polymers were prepared in the same size of 10 cm (length)×10 cm (length)×1 cm (thickness), and the experiment was carried out. 
     With reference to  FIG.  3   , all the resins/polymers made of the materials A, B, and C have a rapidly increased transmittance around a wavelength of about 400 nm, and then have an almost constant transmittance of about 90% from a wavelength of about 500 nm or more. However, it was observed that all the resins/polymers made of the materials A, B, and C have a slightly decreased transmittance in the vicinity of a wavelength region of approximately 850 nm. This was confirmed because all the materials A, B, and C of the resin/polymer are organic materials including C—H bonds, and the absorption wavelength of the C—H bonds is in the 850 nm region. 
     This means that the longest wavelength of quantum dots should be less than 850 nm. Also, this suggests that in order to provide the quantum dot-based light concentrator and the photovoltaic module including the same according to the disclosure, the quantum dot dispersion resin/polymer having excellent transmittance should be provided. 
     &lt;Comparative Example 1&gt; Comparison of Transmittance Between PMMA and Fluorinated PMMA 
     With reference to  FIG.  4   , when the resin/polymer is made of polymethyl methacrylate (PMMA), it can be seen that the transmittance is slightly reduced in the vicinity of a wavelength of 850 nm as in case of polystyrene or polycarbonate. 
     Based on the comparative example 1 and  FIG.  4   , the resin/polymer constituting the quantum dot light concentrator was prepared in the same size as in the experimental example 1, but was made of each of polymethyl methacrylate (PMMA) and fluorinated PMMA. Then, additional experiments were performed. The experimental results are shown in  FIG.  5   , and in this case, the lower the absorption coefficient [cm −1 ], the higher the transmittance. 
     With reference to  FIG.  5   , it can be seen that the resin/polymer has a lower absorption coefficient over the entire wavelength region between 500 nm and 1500 nm when the resin/polymer is made of fluorinated PMMA than made of PMMA. In particular, it can be seen that in the vicinity of 850 nm, the absorption coefficient of fluorinated PMMA is about 10 −4  (cm −1 ), which is a low about 1000 times that of PMMA having an absorption coefficient of about 10 4  (cm −1 ). 
     Therefore, as the results of the above experiments, it is preferable that the “resin film layer  110 ” and the “polymer layers of the upper and lower layers  120  and  130 ” constituting the quantum dot-based light concentrator according to the first aspect and the “polymer layer  110 A” according to the second aspect are made of fluorinated PMMA. 
     &lt;Experimental Example 2&gt; Efficiency Evaluation of Quantum Dots and Quantum Dot-Based Light Concentrator 
     Prior to evaluating the efficiency of the light concentrator according to the disclosure, the photoluminescence characteristics of the quantum dots constituting the light concentrator were preliminarily evaluated.  FIG.  6    is a graph showing the photoluminescence characteristics of quantum dot 1, quantum dot 2, and quantum dot 3, and the photoluminescence characteristics are shown as specific values (unit: nm) of a peak wavelength and spectral full width at half maximum (spectral FWHM) in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Peak wavelength 
                 Spectral FWHM 
               
               
                   
                   
               
             
            
               
                   
                 Quantum dot 1 
                 670 
                 150 
               
               
                   
                 Quantum dot 2 
                 720 
                 170 
               
               
                   
                 Quantum dot 3 
                 735 
                 240 
               
               
                   
                   
               
            
           
         
       
     
     Glossary 
     
         
         
           
             Peak wavelength: The wavelength at which light is emitted with the maximum intensity in the photoluminescence spectrum 
             Spectral FWHM: The interval between two wavelengths having an intensity of ½ of the emission peak appearing in the photoluminescence spectrum 
           
         
       
    
     As can be seen in Table 1, the peak wavelength of quantum dot 1 appearing in the photoluminescence spectrum is 670 nm, which is smaller than those of quantum dots 2 and 3, and also the spectral FWHM of quantum dot 1 is 150 nm, which is smaller than those of quantum dots 2 and 3. 
     Based on the above efficiency evaluation of quantum dots, a light concentrator of 10 cm (length)×10 cm (length)×1 cm (thickness) was prepared and the light efficiency of the light concentrator based on the quantum dots 1, 2, and 3 was measured. The results are shown in Table 2 below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Light concentrator 
                 Light concentrator 
                 Light concentrator 
               
               
                   
                 based on quantum 
                 based on quantum 
                 based on quantum 
               
               
                   
                 dot 1 
                 dot 2 
                 dot 3 
               
               
                   
               
             
            
               
                 Light 
                 41.1% 
                 26.6% 
                 21.3% 
               
               
                 efficiency 
               
               
                   
               
            
           
         
       
     
     With reference to Table 2, the light efficiencies of the light concentrators based on the quantum dots 2 and 3 were measured to be 26.6% and 21.3%, respectively, and the light efficiency of the light concentrator based on the quantum dot 1 was 41.1%, which is significantly higher than the light efficiencies of the light concentrators based on the quantum dots 2 and 3. In other words, it can be seen that the light efficiency of the light concentrator gradually decreases as the wavelength approaches 850 nm, and decreases significantly upon reaching 850 nm. This is confirmed, considering the photoluminescence characteristics of the quantum dots shown in Table 1, because the peak wavelength of the quantum dot 1 was measured at the farthest point from the 850 nm wavelength region corresponding to the absorption wavelength of the C—H bond among quantum dots, and the FWHM of the quantum dot 1 was the smallest. 
     Therefore, the experimental example 2 supports the experimental results of the experimental example 1 that the longest wavelength of the quantum dot is more advantageous as it is smaller than 850 nm. It is therefore desirable that the light concentrator according to the disclosure uses the quantum dot 1. 
     &lt;Experimental Example 3&gt; Measurement of Efficiency of Light Concentrator Depending on Various Sizes 
     In the experimental example 2, a light concentrator based on the quantum dot 1, which was evaluated to have the best efficiency, was prepared in a square shape, and the light efficiency was measured by using the length and thickness as variables. The results are shown in Table 3 below (unit: %). 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Size 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Length 
                 Thickness 
                 Length 
                 Thickness 
                 Length 
                 Thickness 
               
               
                   
                 50 mm 
                 1.4 mm 
                 100 mm 
                 1.4 mm 
                 100 mm 
                 10 mm 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Effi- 
                 36.2% 
                 32.1% 
                 41.1% 
               
               
                 ciency 
               
               
                   
               
            
           
         
       
     
     With reference to Table 3, when the light concentrator has a length of 50 mm and a thickness of 1.4 mm, the light efficiency is 36.2%. In addition, when the light concentrator was 100 mm long and 1.4 mm thick, the light efficiency was measured to be 32.1%. Therefore, it was confirmed that the efficiency of the light concentrator decreases as the length increases. On the other hand, when the light concentrator has a length of 100 mm and a thickness of 100 mm, the light efficiency was measured to be 41.1%. Therefore, it was confirmed that the efficiency of the light concentrator increases as the thickness increases. 
     Therefore, it can be seen that the efficiency of the light concentrator is inversely proportional to the cross-sectional aspect ratio (length/thickness) of the light concentrator, which is also consistent with the Monte-Carlo simulator results with the size as a variable shown in  FIG.  7   . However, because the weight per unit area of the light concentrator increases excessively if the cross-sectional aspect ratio of the light concentrator becomes too small, the lower limit as well as the upper limit of the cross-sectional aspect ratio of the light concentrator are set as follows. 
     The cross-sectional aspect ratio (length/thickness) of the light concentrator is preferably 50 to 200, more preferably 70 to 140, and particularly preferably 80 to 120. 
     Therefore, the thickness required for each area of the light concentrator is preferably area (cm 2 )/40,000 (cm) to area (cm 2 )/2,500 (cm), more preferably area (cm 2 )/20,000 (cm) to area (cm 2 )/5,000 (cm), and particularly preferably area (cm 2 )/15,000 (cm) to area (cm 2 )/8,000 (cm) (e.g., when thickness is expressed as area/10,000, the thickness is 1 cm in an area of 1 m 2 ). 
     &lt;Experimental Example 4&gt; Measurement of Light Efficiency of Light Concentrator Depending on Various Glasses 
     Light concentrators having a size of 100 mm in length and 10 mm in thickness were prepared by making contact with each of ‘commercially available normal glass’, ‘low iron glass in which the ratio of the total weight of FeO, Fe 2 O 3 , and Fe 3 O 4  to the total weight of the glass is 0.01% or less’, and ‘quartz glass containing 100% pure SiO 2 ’ on the upper and lower surfaces of the resin/polymer layer in which quantum dots 1 are dispersed. 
     With respect to the light concentrators prepared as above, light having a wavelength range of 400 nm to 700 nm was incident to measure the light efficiency, and the results are shown in Table 4 below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Normal glass 
                 Low iron glass 
                 Quartz glass 
               
               
                   
                   
               
             
            
               
                   
                 efficiency 
                 22.9% 
                 41.1% 
                 42.3% 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen in Table 4, the efficiency of the light concentrator using normal glass was measured to be 22.9%, and the efficiencies of the light concentrators using low iron glass and quartz glass was 41.1% and 42.3%, respectively, which are higher than the case of using normal glass. 
     Therefore, it can be seen that the glass layer constituting the light concentrator according to the first aspect of the disclosure is preferably selected from low iron glass, quartz glass, or high-transmittance glass equivalent thereto, and furthermore, preferably formed of glass having an average transmittance of 91% to 95% at 400 nm to 1000 nm, more preferably having an average transmittance of 92% to 95% at 400 nm to 1000 nm, and particularly preferably having an average transmittance of 94% to 95% at 400 nm to 1000 nm. 
     In the disclosure, “average transmittance at 400 nm to 1000 nm” may refer to “a value obtained by dividing the integral value of transmittance over a wavelength region from 400 nm to 1000 nm by 600 nm (i.e., 1000 nm minus 400 nm)”. 
     Meanwhile, embodiments of the disclosure and the accompanying drawings are only examples presented in order to easily describe the disclosure and facilitate comprehension of the disclosure, but are not intended to limit the scope of the disclosure. Therefore, the scope of the disclosure should be construed as including all changes or modifications derived from the technical contents of the disclosure in addition to the embodiments disclosed herein.