Patent Publication Number: US-2023163224-A1

Title: Solar cell and electronic device having the same

Description:
TECHNICAL FIELD 
     The present invention relates to a solar cell and an electronic device having the same and, more particularly, to a solar cell covered with a transparent plate through a predetermined gap and an electronic device having such a solar cell. 
     BACKGROUND ART 
     Solar-powered timepieces incorporating a solar cell have recently become widespread. The solar-powered timepiece is advantageous in that battery exchange and spring winding are not necessary. For example, a solar-powered watch disclosed in Patent Document 1 has a solar cell disposed below the dial thereof. 
     CITATION LIST 
     Patent Document 
     [Patent Document 1] JP 2011-013026A 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     When a solar cell to be used is thin and flexible, the solar cell may warp, so that even when a predetermined gap is provided between the solar cell and dial, they may partly contact each other. In this case, the solar cell and the dial adhere to each other at the contact portion to cause a ring-shaped appearance fault called a “tack mark”. Such a problem can occur not only in solar-powered watches but also in general solar cells covered with a transparent plate through a predetermined gap. 
     An object of the present invention is therefore to prevent, in a solar cell covered with a transparent plate through a predetermined gap and an electronic device having the same, the occurrence of the tack mark due to partial contact between the solar cell and the transparent plate. 
     Means for Solving the Problem 
     A solar cell according to the present invention is a solar cell covered with a transparent plate through a predetermined gap and includes a flexible power generating layer which photoelectrically converts light incident thereon through the transparent plate, a resin layer covering a light receiving surface of the power generating layer, and an adhesion preventing layer covering the surface of the resin layer and facing the transparent plate through a gap. The adhesion preventing layer is made of an inorganic material and has a surface roughness Sz of 1 nm or more and 500 nm or less. 
     According to the present invention, the outermost surface of the solar cell is constituted by the adhesion preventing layer, so that no tack mark occurs even when partial contact occurs between the solar cell and the transparent plate which face each other through a predetermined gap. As a result, it is possible to prevent deterioration in appearance due to the tack mark. 
     In the present invention, the adhesion preventing layer may have a surface hardness of 2H or more and a thickness of 10 nm or more and 1000 nm or less. This makes it possible to effectively prevent adhesion to the transparent plate. 
     In the present invention, the adhesion preventing layer may have a light transmittance of 70% or more. This makes it possible to suppress a reduction in the amount of power generation. 
     An electronic device according to the present invention is an electronic device including a solar cell and a transparent plate covering a solar cell through a predetermined gap. The solar cell includes a flexible power generating layer which photoelectrically converts light incident thereon through a transparent plate and a resin layer covering a light receiving surface of the power generating layer. At least one of the surface of the resin layer facing the transparent plate through the gap and the surface of the transparent plate facing the resin layer through the gap is covered with an adhesion preventing layer made of an inorganic material and having a surface roughness Sz of 1 nm or more and 500 nm or less. 
     According to the present invention, the outermost surface of the solar cell is constituted by the adhesion preventing layer, so that no tack mark occurs even when partial contact occurs between the solar cell and transparent plate which face each other through a predetermined gap. As a result, it is possible to prevent deterioration in appearance due to the tack mark. 
     In the present invention, the gap may be 1 mm or less. In this case, partial contact between the solar cell and the transparent plate is likely to occur; however, in this case, it is possible to prevent the occurrence of a tack mark. 
     In the present invention, the transparent plate may be a display panel of a timepiece. This makes it possible to maintain a good visual appearance of the display panel. 
     Advantageous Effects of the Invention 
     As described above, according to the present invention, it is possible to prevent, in a solar cell covered with a transparent plate through a predetermined gap and an electronic device having the same, occurrence of the tack mark due to partial contact between the solar cell and the transparent plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross-sectional view illustrating the configuration of an electronic device  1  according to a first embodiment of the present invention. 
         FIG.  2    is a schematic cross-sectional view for explaining the configuration of an electronic device  2  according to a second embodiment of the present invention. 
         FIG.  3    is a schematic cross-sectional view for explaining the configuration of an electronic device  3  according to a third embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG.  1    is a schematic cross-sectional view illustrating the configuration of an electronic device  1  according to a first embodiment of the present invention. 
     As illustrated in  FIG.  1   , the electronic device  1  according to the present embodiment includes a solar cell  10  and a transparent plate  20  covering the solar cell  10  through a gap G. Although there is no particular restriction on the type of the electronic device  1 , the electronic device  1  may be, for example, a solar-powered timepiece. In particular, when the electronic device  1  is a solar-powered watch, it is required to be miniaturized, and therefore, the gap G is set to be equal to or smaller than 1 mm. 
     The solar cell  10  includes a flexible power generating layer  11  made of silicon or the like, a resin layer  12  covering a light receiving surface lla of the power generating layer  11 , and an adhesion preventing layer  13  covering a surface  12   a  of the resin layer  12 . The total thickness of the solar cell  10  is equal to or less than 500 μm, preferably, equal to or less than 300 μm. The power generating layer  11  is a semiconductor device which photoelectrically converts light incident thereon through the transparent plate  20  and uses a film-like substrate made of resin such as polyimide, PET, or PEN. Thus, it is possible to process the power generating layer  11  into a complicated shape and to inexpensively and easily perform processing such as drilling. Power generated by the power generating layer  11  is supplied to a movement or electronic circuit (not illustrated). The resin layer  12  is, for example, a passivation film which protects the power generating layer  11  and has a thickness of 100 μm or less, preferably 30 μm or less. The resin layer  12  can be formed by printing a thermosetting resin. With this configuration, it is possible to form the resin layer  12  at a lower cost than when forming the resin layer  12  by sticking the film and to reduce the overall thickness. The thickness of the resin layer  12  is preferably 5 μm or more. This is because when the thickness of the resin layer  12  is less than 5 μm, a sufficient protective effect cannot be produced due to, for example, a reduction in moisture resistance, and this results in a reduction in reliability. 
     When the electronic device  1  according to the present embodiment is a solar-powered timepiece, the transparent plate  20  is a dial, a decorative plate, a liquid crystal panel, or the like and serves to display a current time and the like. As described above, the transparent plate  20  may not necessarily be completely transparent and only needs to have light transmittance high enough to allow light passing therethrough to reach the power generating layer  11 . The transparent plate  20  may be flexible or rigid. 
     The adhesion preventing layer  13  is made of an inorganic material such as silica, and its surface  13   a  faces a surface  20   a  of the transparent plate  20  through the gap G. The adhesion preventing layer  13  serves to prevent the occurrence of the tack mark caused by the contact of the flexible solar cell  10  with the transparent plate  20  and adhesion thereof to the transparent plate  20 . To achieve this, the surface  13   a  of the adhesion preventing layer  13  has a nano-level fine unevenness. Specifically, the surface  13   a  of the adhesion preventing layer  13  has a surface roughness Sz defined in ISO 25178 of 1 nm or more and 500 nm or less. As a result, even when the solar cell  10  contacts the surface  20   a  of the transparent plate  20 , no tack mark is caused due to the effect of the adhesion preventing layer  13 . 
     In order to prevent the occurrence of the tack mark more effectively, the adhesion preventing layer  13  preferably has a surface hardness (Vickers hardness) of 2H or more and a thickness of 10 nm or more and 1000 nm or less. Further, the adhesion preventing layer  13  preferably has a light transmittance of 70% or more so as to sufficiently ensure the amount of incident light to the power generating layer  11 . 
     Although a method of forming the adhesion preventing layer  13  is not particularly limited, there may be employed a method of fixing the adhesion preventing layer  13  to the surface  12   a  of the resin layer  12  by forming silica on the surface  12   a  of the resin layer  12  by a sol-gel method, followed by heating treatment at about 160°. Alternatively, a solvent containing fine silica powder may be applied to the surface  12   a  of the resin layer  12 , followed by heating treatment at about 160°, whereby the adhesion preventing layer  13  may be fixed on the surface  12   a  of the resin layer  12 . 
     As a method for preventing adhesion of the solar cell  10  and the transparent plate  20 , a method of adding an anti-blocking agent to the resin layer  12  may be considered. However, in this method, the resin layer  12  becomes white, and the amount of incident light to the power generating layer  11  is significantly reduced. On the other hand, in this embodiment, the anti-blocking agent is not added to the resin layer  12 , but the adhesion preventing layer  13  having a nano-level fine unevenness on the surface  12   a  of the resin layer  12  is provided, so that it is possible to suppress a reduction in power generation amount. Rather, since the outermost surface of the solar cell  10  has a moth-eye structure, reflected light on the outermost surface of the solar cell  10  is reduced, and the amount of incident light to the power generating layer  11  can be increased. Specifically, when the light transmittance of the resin layer  12  before forming the adhesion preventing layer  13  is about 93%, the light transmittance is improved to about 96% by providing the adhesion preventing layer  13  on the surface  12   a  of the resin layer  12 . 
     As described above, according to the present embodiment, in the electronic device  1  having a structure in which the flexible solar cell  10  and the transparent plate  20  face each other through the gap G, it is possible to prevent the occurrence of the tack mark even when the solar cell  10  and the transparent plate  20  partially come into contact with each other while suppressing a reduction in the power generation amount. 
       FIG.  2    is a schematic cross-sectional view for explaining the configuration of an electronic device  2  according to a second embodiment of the present invention. 
     The electronic device  2  illustrated in  FIG.  2    differs from the electronic device  1  according to the first embodiment in that the adhesion preventing layer  13  is provided on the surface  20   a  of the transparent plate  20 . Other configurations are the same as those of the electronic device  1  according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. 
     As exemplified by the present embodiment, it is not essential to provide the adhesion preventing layer  13  on the solar cell  10  side in the present invention, and the adhesion preventing layer  13  may be provided on the transparent plate  20  side. 
       FIG.  3    is a schematic cross-sectional view for explaining the configuration of an electronic device  3  according to a third embodiment of the present invention. 
     The electronic device  3  illustrated in  FIG.  3    differs from the electronic device  1  according to the first embodiment in that the adhesion preventing layer  13  is provided on both the surface  12   a  of the resin layer  12  and the surface  20   a  of the transparent plate  20 . Other configurations are basically the same as those of the electronic device  1  according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. 
     As exemplified by the present embodiment, the adhesion preventing layer  13  may be provided on both the solar cell  10  and the transparent plate  20  in the present invention. 
     While the preferred embodiment of the present invention has been described, the present invention is not limited to the above embodiment, and various modifications may be made within the scope of the present invention, and all such modifications are included in the present invention. 
     REFERENCE SIGNS LIST 
     
         
           1 - 3  electronic device 
           10  solar cell 
           11  power generating layer 
           11   a  light receiving surface 
           12  resin layer 
           12   a  surface of resin layer 
           13  adhesion preventing layer 
           13   a  surface of adhesion preventing layer 
           20  transparent plate 
           20   a  surface of transparent plate 
         G gap