Abstract:
It is an object of the present invention to minimize an electrode in a solar cell to minimize the solar cell. The present invention provides a method for manufacturing a solar cell comprising the steps of forming a first electrode layer over a substrate, forming a photoelectric conversion layer over the first electrode layer, forming an organic layer over the photoelectric conversion layer, forming an opening reaching the first electrode layer in the photoelectric conversion layer, and forming a second electrode layer by filling the opening with a conductive paste, wherein the organic layer modifies the surface of the photoelectric conversion layer and a contact angle between the conductive paste and the photoelectric conversion becomes greater. According to the present invention, wettability of a photoelectric conversion layer can be decreased by forming an organic layer on a surface of the photoelectric conversion layer. Thereby an electrode layer and an insulating isolation layer can be thinned.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of a semiconductor device such as a solar cell and a manufacturing method thereof 
     2. Description of the Related Art 
     A solar cell has been spread not only to be used as a solar electric power generation system installed outdoors but also to be used as a power source of an electronic device with low power consumption such as a calculator, a radio, and a watch. In such a consumer use, when an appearance of an electronic device is as important as a function thereof as is the case for a wrist watch, for example, a mounting method of the solar cell is also devised. The solar cell is directly used as a dial of a watch, or is placed under a semitranslucent dial of the watch to make it unnoticeable. 
     A large part of a solar cell is composed of a substrate formed from glass, stainless, or an organic resin material or the like, and a photoelectric conversion layer formed by a thin film of an amorphous semiconductor, a microcrystalline semiconductor, or a chalcopalide-based (or II-VI group) compound semiconductor stacked over the substrate. Especially, a solar cell using an organic resin material for the substrate is thin and lightweight, and has an excellent shock resistance, so that it is not easily cracked even if it is dropped. Accordingly, it is suitable for the solar cell to be mounted to a portable product such as a card type calculator, or a wrist watch, and a remote-control device of an indoor electronic device such as a television (see Japanese Patent Application Laid-Open No. 2001-185745). 
     A solar cell which is used for various electric devices is needed to be reduced in size and weight as a reduction in size and weight of an electronic device. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solar cell in which an electrode layer and an insulating isolation layer are minimized by removing an excess portion to reduce a region which shields light, thereby a light receiving region can be enlarged. 
     In the present invention, an organic layer is formed on a surface of a photoelectric conversion layer such as an amorphous semiconductor layer to decrease wettability of the amorphous semiconductor layer. Thus, a contact angle between the amorphous semiconductor layer and an electrode or an insulating isolation layer becomes greater, thereby miniaturization of the electrode layer and the insulating isolation layer can be realized. In addition, since the contact angle between the amorphous semiconductor layer and the electrode or the insulating isolation layer becomes greater, a region which shields light can be reduced to enlarge a light receiving region. Further, an excess thickness of the electrode layer and the insulating isolation layer can be removed. 
     The present invention provides a method for manufacturing a solar cell comprising the steps of forming a first electrode layer over a substrate, forming a photoelectric conversion layer over the first electrode layer, forming an organic layer over the photoelectric conversion layer, forming an opening reaching the first electrode layer in the photoelectric conversion layer, and forming a second electrode layer by filling the opening with a conductive paste, in which a contact angle between the conductive paste and the photoelectric conversion layer becomes greater since the organic layer is provided. 
     The present invention provides a method for manufacturing a solar cell comprising the steps of forming a first electrode layer over a substrate, forming a photoelectric conversion layer over the first electrode layer, modifying a surface of the photoelectric conversion layer by treating the surface of the photoelectric conversion layer with an organic material, forming an opening reaching the first electrode layer in the photoelectric conversion layer; and forming a second electrode layer by filling the opening with a conductive paste, in which a contact angle between the conductive paste and the photoelectric conversion layer becomes greater by treating the photoelectric conversion layer with the organic material. 
     In the present invention, the substrate is formed from glass, stainless, or a polymeric material. 
     In the present invention, the polymeric material is a material selected from polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polybutylene naphthalate (PBN). 
     In the present invention, the organic layer contains a silane coupling compound. 
     In the present invention, the conductive paste is any one of a conductive paste which contains silver (Ag), gold (Au), copper (Cu), or nickel (Ni), or a conductive carbon paste. 
     According to the present invention, miniaturization of an electrode layer and an insulating isolation layer can be realized. Accordingly, the number of cells per unit area can be increased to improve throughput. Further, since a contact angle between a photoelectric conversion layer and an electrode becomes greater, a region which shields light can be reduced to enlarge a light receiving region. The excess thickness of an electrode layer and an insulating isolation layer can be removed, and so reduction in size and weight of a solar cell can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are views showing a manufacturing step of a solar cell according to the present invention; 
         FIGS. 2A and 2B  are views showing a manufacturing step of a solar cell according to the present invention; 
         FIG. 3  is a view showing a manufacturing step of a solar cell according to the present invention; 
         FIGS. 4A to 4C  are views showing a manufacturing step of a solar cell according to the present invention; 
         FIG. 5  is a view showing a manufacturing step of a solar cell according to the present invention; 
         FIG. 6  is a top view of a solar cell according to the present invention; 
         FIG. 7  is an example of an electric device manufactured according to the present invention; 
         FIGS. 8A to 8C  are cross-sectional views of an example of an electric device manufactured according to the present invention; 
         FIG. 9  is an example of an electric device manufactured according to the present invention; 
         FIGS. 10A and 10B  are examples of an electric device manufactured according to the present invention; and 
         FIGS. 11A and 11B  are views showing a manufacturing step of a solar cell according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment Mode of the present invention will be described with reference to the accompanying drawings. However, it is to be easily understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the invention, they should be construed as being included therein. Note that identical portions or portions having the same function in all figures for explaining embodiment modes are denoted by the same reference numerals and detailed description thereof are omitted. 
     The embodiment mode of the present invention is described with reference to  FIGS. 1A and 1B ,  2 A and  2 B, and  3 . First, a transparent conductive film  102  is formed over a substrate  101 . In this embodiment mode, a flexible substrate is used as the substrate  101 . Specifically, a substrate formed from a polymeric material such as a film formed from polyethylene naphthalate (PEN) is used. In addition to a film formed from polyethylene naphthalate, a film formed from polyethylene terephthalate (PET), polybutylene naphthalate (PBN), or the like may be used. Alternatively, a glass substrate or a stainless substrate may be used. 
     In this embodiment mode, an indium tin oxide (ITO) film is used as the transparent conductive film  102 . In addition to an indium tin oxide (ITO) film, for example, a conductive film of an indium tin oxide containing Si, or a conductive film formed by using a target of an indium oxide containing 2 to 20 wt % of a zinc oxide may be used. 
     An amorphous semiconductor film  103  is formed over the transparent conductive film  102 . The amorphous semiconductor film  103  has a p-type amorphous semiconductor film  103   a , an amorphous semiconductor film  103   b  which does not contain an impurity element for imparting a conductive type, and an n-type amorphous semiconductor film  103   c.    
     In this embodiment mode, an amorphous semiconductor film containing boron (B) is formed by a plasma CVD method as the p-type amorphous semiconductor film  103   a . An intrinsic amorphous silicon film is formed by a plasma CVD method as the amorphous semiconductor film  103   b  which does not contain an impurity element for imparting a conductive type. An amorphous silicon film containing phosphorus (P) may be formed as the n-type amorphous semiconductor film  103   c , or the n-type amorphous semiconductor film  103   c  may be formed by forming an intrinsic amorphous silicon film and doping phosphorus thereto. 
     An organic layer  104  is formed after forming the amorphous semiconductor film  103  ( FIG. 1A ). A layer formed from an organic material which modifies the surface of the amorphous semiconductor film  103  such as a material having a fluorocarbon chain or a material having a silane coupling agent can be used as the organic layer  104 . A silane coupling agent is expressed by a chemical formula Rn-Si—X (4-n)  (n=1, 2, and 3). Here, R indicates a material having a relatively inactive group such as an alkyl group. X is formed by a hydrolysis group which can be bonded by condensation with a hydroxyl group or absorption water on a surface of the substrate such as halogen, a methoxy group, an ethoxy group or an acetoxy group. The surface of the amorphous semiconductor film  103  is modified to decrease wettability by forming the organic layer  104 , that is, treating the surface of the amorphous semiconductor film  103  with an organic material. 
     The wettability can be further decreased by using a fluorine-based silane coupling agent having a fluoroalkyl group as R (fluoroalkylsilane (FAS)) which is a typical example of a silane coupling agent. The R of FAS has a structure expressed by (CF 3 )(CF 2 ) x (CH 2 ) y  (x is an integer from 0 or more to 10 or less and y is an integer from 0 or more to 4 or less). When a plurality of R or X is bonded to Si, each of R and X may be the same or different. As a typical example of fluoroalkylsilane (also referred to as FAS hereinafter), such as heptadefluorotetrahydrodecyltriethoxysilane, heptadecafluorotetrahydrodecyltrichlorosilane, tridecafluorotetrahydrooctyltrichlorosilane, and trifluoropropyltrimethoxysilane can be given. 
     As a material for modifying the surface of the amorphous semiconductor film  103 , a silane coupling agent having an alkyl group as R instead of a fluorocarbon chain can be used. For example, octadecyltrimethoxysilane as organic silane can be used. 
     In the case where a layer formed from a material for modifying the surface of the amorphous semiconductor film  103  is formed on the surface of the amorphous semiconductor film  103  by an application method, a solvent in which the foregoing materials are dispersed such as a hydrocarbon solvent like n-pentane, n-hexane, n-heptane, n-octane, n-decane, dicyclopentane, benzene, toluene, xylene, durene, indene, tetrahydronaphthalene, decahydronaphthalene, or squalane; or tetrahydrofuran can be used. 
     The organic layer  104  modifies the surface of the amorphous semiconductor film  103 . When an electrode is formed from a conductive paste in a following step, a contact angle between the conductive paste and the surface of the amorphous semiconductor film  103  can be greater. Such a modification of the surface of the amorphous semiconductor film is considered to be caused by a reaction of a hydroxyl group in the amorphous semiconductor film and the organic layer. 
     Next, contact holes  106  and  107  are formed by laser scribing through the transparent conductive film  102 , the amorphous semiconductor film  103 , and the organic layer  104  ( FIG. 1B ). The contact holes  106  and  107  are formed to have widths of 50 μm to 300 μm. The contact holes  106  and  107  reach the transparent conductive film  102 , and bottom surfaces of the contact holes  106  and  107  may be the substrate  101  as shown in  FIG. 1B . 
     The contact hole  106  is filled with an insulating material to form an insulating layer  108  for insulating isolation ( FIG. 2A ). The insulating layer  108  is formed by an ink jet method, a screen printing method, or the like. When forming the insulating layer  108  by an ink jet method, a composition containing a photosensitive material is used. For example, a positive resist obtained by dissolving or dispersing a novolac resin and a naphthoquinone-diazide compound which is a photosensitive agent in a solvent; or a negative resist obtained by dissolving or dispersing a base resin, diphenylsilanediol, an acid generating agent, and the like in a solvent is used. As the solvent, esters such as butyl acetate or ethyl acetate, alcohols such as isopropyl alcohol or ethyl alcohol, and organic solvents such as methyl ethyl ketone or acetone, or the like are used. The concentration of the solvent is set appropriately according to a type or the like of a resist. 
     The contact hole  107  is filled with a conductive paste to form an electrode  109  by an ink jet method or a screen printing method ( FIG. 2B ). As the conductive paste, a conductive paste containing silver (Ag), gold (Au), copper (Cu), nickel (Ni), or the like or a conductive carbon paste can be used. In this embodiment mode, the electrode  109  is formed using a silver (Ag) paste. 
     Since the organic layer  104  is provided on a surface of the amorphous semiconductor layer  103 , a surface tension of the conductive paste to the organic layer  104  is increased. Therefore, the region where light is shielded by the conductive paste can be decreased. 
     After the electrode  109  is formed, a conductive layer  110  which is electrically connected to the electrode  109  is formed ( FIG. 3 ). As a method for forming the conductive layer  110 , a sputtering method, a vapor deposition method, a plating method, a screen printing method, an ink jet method, or the like is used or a combination of those methods is used. When a sputtering method is used, an element selected from tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), or aluminum (Al), or an alloy material or a compound material containing the foregoing elements as a main component can be used as a material for the conductive layer  110 . When an ink jet method is used, a conductive paste containing a metal material such as silver (Ag), gold (Au), copper (Cu), nickel (Ni), or the like can be used. 
     Either the insulating layer  108  or the electrode  109  may be formed at first. 
     In  FIG. 3 , the insulating layer  108  and the electrode  109  can be formed so as not to overflow from the contact holes  106  and  107 , respectively, since the organic layer  104  is provided. 
     It is preferably that the insulating layer  108  and the electrode  109  are formed so as not to overflow from the contact holes  106  and  107 , respectively. As shown in  FIG. 11A , the insulating layer  108  and the electrode  109  may be slightly thinner than the contact holes  106  and  107 . Alternatively, as shown in  FIG. 11B , the insulating layer  108  and the electrode  109  may be slightly thicker than the contact holes  106  and  107 . 
     Accordingly, a solar cell according to the present invention can be manufactured. According to the present invention, a solar cell which has an enlarged light receiving region and a thinner thickness can be manufactured. Further, the number of a solar cell which can be manufactured per unit area of a substrate can be increased. 
     [Embodiment 1] 
     This embodiment is described with reference to  FIGS. 4A to 4C ,  5 , and  6 . In this embodiment, a method for manufacturing an integrated solar cell in which an organic resin material is used for a substrate and a plurality of unit cells is connected in series on one substrate is described. 
     In  FIG. 4A , a translucent organic resin material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES) is used for a substrate  501 . Of course, commercially available soda-lime glass, alkali-free glass, or a stainless substrate can also be used. 
     A sheet-like substrate of a suitable size may be used as the substrate  501 . When manufacturing a solar cell according to this embodiment by a roll-to-roll method, a rolled substrate may be used. In the case where a roll-to-roll method is applied, an organic resin film substrate having a thickness of 60 to 100 μm is preferably used. 
     The solar cell manufactured in this embodiment has such a structure in which light is received by a surface of a substrate opposite to a surface on which a photoelectric conversion layer is formed. First, a transparent electrode layer  502  is formed on the substrate  501 . The transparent electrode layer  502  is formed from an indium tin oxide alloy (ITO), a zinc oxide (ZnO), a tin oxide (SnO 2 ), an ITO-ZnO alloy, or the like to have a thickness of 40 to 200 nm (preferably, 50 to 100 nm). Since a continuously usable maximum temperature of the foregoing organic resin material is 200° C. or less, the transparent electrode layer  502  is formed by a sputtering method, a vacuum evaporation method, or the like, and the film formation is carried out while the substrate temperature is limited within the range from a room temperature to approximate 150° C. Detailed forming conditions may be determined appropriately by an operator to obtain a sheet resistance of 20 to 200 Ω/□ for the above film thickness. 
     In terms of decreasing the resistance of the transparent electrode layer  502 , an ITO film is suitable. However, if an ITO film is exposed to a plasma atmosphere containing hydrogen when forming a semiconductor layer thereon, a light transmitting property of the ITO film is deteriorated because of the reduction. In order to prevent this, it is appropriate that a SnO 2  film or a ZnO film is formed on the ITO film. The ZnO (ZnO:Ga) film containing gallium (Ga) of 1 to 10 wt % has a high transmittance and is suitable to be stacked over the ITO film. As an example of a combination, when the ITO film is formed to have a thickness of 50 to 60 nm and the ZnO:Ga film is formed thereon to have a thickness of 25 nm, it is possible to prevent a light transmitting property from being deteriorated, and an excellent light transmitting property can be obtained. In this stacked film, a sheet resistance of 120 to 150 Ω/□ can be obtained. 
     A non-monocrystalline semiconductor film formed by using a plasma CVD method is used as a photoelectric conversion layer  503  over the transparent electrode layer  502 . Typically, the photoelectric conversion layer  503  is formed of a hydrogenated amorphous silicon (a-Si:H) film formed using SiH 4  gas as a raw material. Besides, a hydrogenated amorphous silicon germanium (a-SiGe:H) film, a hydrogenated amorphous silicon-carbon (a-SiC:H) film, a hydrogenated microcrystalline silicon (μc-Si:H) film, or the like are used for the photoelectric conversion layer  503 . The photoelectric conversion layer  503  is formed of a pin junction, and then p-type and n-type layers with valence electron control may be formed by using a-Si:H or μc-Si:H added with an impurity element such as boron or phosphorus. Especially, μc-Si:H is suitable for the purpose of lowering light absorption loss or making excellent ohmic contact with the transparent electrode layer or a rear electrode layer. 
     In this embodiment, the photoelectric conversion layer  503  is formed by stacking a p-type semiconductor layer  503   a , an i-type semiconductor layer  503   b , and an n-type semiconductor layer  503   c  sequentially over the transparent electrode layer  502 . These layers are formed respectively to have thicknesses of 10 to 20 nm, 200 to 1000 nm, and 20 to 60 nm. When a pin junction is formed of such a non-monocrystalline silicon material, an open circuit voltage of approximate 0.4 to 1 V can be obtained. If this pin junction is assumed to be one unit and a plurality of such units are stacked to form a stack type structure, the open circuit voltage can also be raised. 
     An organic layer  504  is formed over the photoelectric conversion layer  503  to modify the surface of the photoelectric conversion layer  503 . The organic layer  504  is formed like the organic layer  104  which is formed in the embodiment mode. 
     As shown in  FIG. 4B , in order to form a plurality of unit cells on one substrate, openings M 1  to M n  and C 1  to C n  are formed by a laser processing method (laser scribing) through the organic layer  504 , the photoelectric conversion layer  503 , and the transparent electrode layer  502 . The openings C 1  to C n  are openings for insulating isolation and are provided to form the unit cells. The openings M 1  to M n  are openings for forming connection between the transparent electrode layer and the rear electrode layer. However the kind of a laser used for the laser processing method is not limited, an Nd-YAG laser, an excimer laser, or the like may be used. In any case, by performing a laser process to the lamination of the transparent electrode layer  502  and the photoelectric conversion layer  503 , it is possible to prevent the transparent electrode layer from peeling off the substrate when the laser processing is carried out. 
     In this way, the transparent electrode layer  502  is divided into T 1  to T n , and the photoelectric conversion layer  503  is divided into K 1  to K n . Then, as shown in  FIG. 4C , the openings M 1  to M n  are filled with a conductive paste by an ink jet method, a screen printing method, or the like to form connecting electrode layers E 1  to E n . 
     As the conductive paste, a conductive paste containing silver (Ag), gold (Au), copper (Cu), nickel (Ni), or the like or a conductive carbon paste can be used. In this embodiment, the connecting electrode layers E 1  to E n  are formed using a silver (Ag) paste. 
     Since the organic layer  504  is provided on the surface of the photoelectric conversion layer  503 , a surface tension of the conductive paste is increased. Therefore, the conductive paste is prevented from overflowing from the openings M 1  to M n  when forming the connecting electrode layers E 1  to E n  and the region which shields light can be decreased to enlarge a light receiving region. 
     The openings C 1  to C n  are filled with insulating resin layers Z 1  to Z n  to insulate and isolate an element. The insulating resin layers Z 1  to Z n  are formed by an ink jet method, a screen printing method, or the like. 
     In the case where the insulating resin layers Z 1  to Z n  are formed by an ink jet method, the insulating resin layers Z 1  to Z n  can be formed to have thinner widths because of the organic layer  504  on the surface of the photoelectric conversion layer  503 , as in the case of the connecting electrode layers E 1  to E n . 
     In the case of forming the insulating resin layers Z 1  to Z n  by an ink jet method, a composition containing a photosensitive material may be used as a material of the insulating resin layer. For example, a positive resist obtained by dissolving or dispersing a novolac resin and a naphthoquinone-diazide compound which is a photosensitive agent in a solvent; or a negative resist obtained by dissolving or dispersing a base resin, diphenylsilanediol, an acid generating agent, and the like in a solvent is used. As the solvent, an organic solvent like esters such as butyl acetate or ethyl acetate, alcohols such as isopropyl alcohol or ethyl alcohol, organic solvents such as methyl ethyl ketone, or acetone is used. The concentration of the solvent is set appropriately according to a type or the like of a resist. 
     In the case of forming the insulating resin layers Z 1  to Z n  by a screen printing method, the insulating resin layers Z 1  to Z n  are formed according to the following steps. A phenoxy resin, cyclohexane, isophorone, high resistance carbon black, aerosil, a dispersing agent, an antifoaming agent, and a leveling agent are prepared as insulating resin materials for forming the insulating resin layers Z 1  to Z n . 
     First, among the foregoing raw materials, the phenoxy resin is completely dissolved in a mixture solvent of cyclohexanone and isophorone, and is dispersed for 48 hours by a ball mill made of zirconia with carbon black, aerosol, and the dispersing agent. Next, the antifoaming agent and the leveling agent are added and are further mixed for two hours. Then, a thermal crosslinking reactive resin such as an n-butylated melamine resin and a hardening accelerator is added thereto. 
     These are further mixed and dispersed to obtain an insulating resin composition for a passivation film. 
     An insulating film is formed by a screen printing method using the obtained insulating resin composition ink. After applying the insulating resin composition ink, thermal hardening is conducted in an oven for 20 minutes at 160° C. to obtain the insulating resin layers Z 1  to Z n . 
     Although the connecting electrode layers E 1  to E n  are formed first in this embodiment, either the connecting electrode layers E 1  to E n  or the insulating resin layers Z 1  to Z n  may be formed at first. 
     Next, the rear electrode layers D 1  to D n+1  are formed as shown in  FIG. 5 . The rear electrode layers D 1  to D n+1  may be formed by a sputtering method, a vapor deposition method, a plating method, a screen printing method, an ink jet method, or the like. 
     In the case where a sputtering method is used, an element selected from tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), or aluminum (Al), or an alloy material or a compound material containing the foregoing elements as a main component can be used as a material for the rear electrode layers D 1  to D n+1 . In the case where an ink jet method is used, a conductive paste containing a metal material such as silver (Ag), gold (Au), copper (Cu), or nickel (Ni) can be used as a material for the rear electrode layers D 1  to D n+1 . 
     A method for forming the rear electrode layers D 1  to D n+1  by a screen printing method is described hereinafter. A graphite powder, a high conductive black, an oleic acid (dispersing agent), and isophorone (solvent) are prepared as a conductive ink to be used. 
     These materials are put into a ball mill to be crushed for 24 hours to obtain finer particles. Then, 20 wt % of y-butyrolactone lacquer of a saturated polyester resin is added thereto. 
     Then, the antifoaming agent and the leveling agent are added thereto. 
     Further, a paste obtained after dispersing and mixing by the ball mill is further dispersed by a three-roll mill to obtain a conductive carbon paste. 
     This paste is added with ethyl acetoacetate block body (solid content 80 wt %, NCO content 10 wt %) Coronate 2513 which is obtained by blocking isocyanate of hexamethylenediisocyanate-based polyisocyanate of aliphatic polyfunctional isocyanate by ethyl acetoacetate and by diluting it with a solvent of cellosolve acetate and xylene at a rate of 1 to 1, and mixed sufficiently by a disper, to be defoamed sufficiently. Thus, a conductive carbon paste is obtained. 
     Then, the obtained conductive carbon paste is printed into a predetermined pattern by a screen printing method, and after being leveled and dried, the paste is firmly hardened at 150° C. for 30 minutes to form the rear electrode layers D 1  to D n+1  as shown in  FIG. 5 . 
     The respective rear electrode layers D 1  to D n+1  are formed so as to be connected with the transparent electrode layers T 1  to T n  at the openings M 1  to M n . The openings M 1  to M n  are filled with the connecting electrode layers E 1  to E n . The rear electrode layers D 1  to D n+1  are electrically connected to the transparent electrode layers T 1  to T n , respectively, through the connecting electrode layers E 1  to E n . 
     Finally, in order to form a sealing resin layer  505  by a printing method, an epoxy resin, γ-butyrolactone, isophorone, an antifoaming agent, and a leveling agent are prepared as a raw material of a sealing resin. 
     First, among the foregoing raw materials, the epoxy resin is completely dissolved in a mixture solvent of γ-butyrolactone/isophorone, and is dispersed by a ball mill made of zirconia. Next, the antifoaming agent and the leveling agent are further added thereto. The solvent is further mixed, and a butylated melamine resin is added as a thermal crosslinking reactive component. 
     These are further mixed and dispersed to obtain an ink composition having a transparent and insulating property for a surface protecting and sealing film. 
     The sealing resin layer  505  is formed by a screen printing method using the obtained ink composition and is thermally hardened at 150° C. for 30 minutes. In the sealing resin layer  505 , opening portions are formed so as to reach the rear electrode layers D 1  and D n+1 . The sealing resin layer  505  is connected to an external circuit substrate through the opening portions. 
     As described above, a unit cell having the transparent electrode layers T 1  to T n , the photoelectric conversion layers K 1  to K n , the connecting electrode layers E 1  to E n , and the rear electrode layers D 1  to D n+1  are formed over the substrate  501 . And a solar cell of the n series-connected unit cells can be formed by connecting the adjacent rear electrode layers D 1  to D n+1  to the transparent electrode layers T 1  to T n  through the openings M 1  to M n . The rear electrode layer D 1  becomes a lead-out electrode of the transparent electrode layer T 1  in the unit cell U 1  whereas the rear electrode layer D n+1  becomes a lead-out electrode of the transparent electrode layer T n  in the unit cell U 1 . 
       FIG. 6  is a top view showing a positional relationship between the openings C 1  to C n , and M 1  to M n , the connecting electrode layers E 1  to E n , the insulating resin layers Z 1  to Z n , and the rear electrode layers D 1  to D n+1  in  FIG. 5 . As shown in  FIG. 6 , the unit cells U 1  to U n  are series-connected to form a solar cell. 
     [Embodiment 2] 
     In this embodiment, examples of various electrical devices having a solar cell manufactured according to the present invention are described with reference to  FIGS. 7 ,  8 A to  8 C, and  9 . 
       FIG. 7  is a top view of a solar cell according to this embodiment seen from a rear electrode side.  FIG. 7  shows an example of a wrist watch in which a solar cell placed at the lower side (portion in which a movement of a wrist watch is installed) of a semitranslucent dial. A substrate  601  is an organic resin film having a thickness of 70 μm. Although any of the organic resin materials referred in Embodiment 1 can be applied, a PEN substrate is typically used for the substrate  601 . The shape of the substrate  601  is not limited to a circle. An insertion port  607  of a pointer shaft is provided at the center. 
     In the solar cell, a transparent electrode layer, a photoelectric conversion layer, a rear electrode layer, and a sealing resin layer are stacked over the substrate  601  sequentially. These are formed in the same manner as Embodiment 1. Although four unit cells are concentrically arranged on the substrate  601 , the structure of series connection of the solar cell is basically the same as the embodiment 1. 
     In  FIG. 7 , unit cells YU 1  to YU 4  are defined by an opening YC 0  formed in transparent electrode layers YT 1  to YT 4  and photoelectric conversion layers YK 1  to YK 4 , and by openings YC 1  to YC 4  in the inside of the opening YC 0 . The openings YC 0  to YC 4  are filled with insulating resin layers YZ 0  to YZ 4 . 
     Connecting electrode layers YE 1  to YE 4  are formed by an ink jet method using a metal paste such as a silver (Ag) paste in the photoelectric conversion layers and the transparent electrode layers. Rear electrode layers YD 1  to YD 4  are connected respectively to the transparent electrode layers YT 2  to YT 4  of the adjacent unit cells by the connecting electrode layers YE 1  to YE 4  formed in the openings YM 2  to YM 4 . A sealing resin layer  604  is formed on the entire surface of the rear electrode layers except for connection portions  605  and  606  which are connected to a circuit substrate of the wrist watch. An output electrode YD 0  of the transparent electrode is formed at the connection portion  605  which is connected to the circuit substrate and, the output electrode YD 0  is connected to the transparent electrode layer through an opening YM 1 . As shown in the drawing, the output electrode YD 0  is formed to be isolated from the rear electrode layer YD 1 . The rear electrode layer YD 4 , which is the other connection portion  606  serves also as an output electrode. 
       FIG. 8A  shows a sectional view taken along a line A-A′ of the periphery of the connection portion  605  which is connected to the circuit substrate in  FIG. 7 . The transparent electrode layer, the photoelectric conversion layer, and the rear electrode layer are formed over the substrate  601 . The openings YC 0  and YM 1  are formed by a laser processing method through the transparent electrode layer and the photoelectric conversion layer, and the insulating layer YZ 0  is formed in the opening YC 0  to fill the opening. The output electrode YD 0  at the side of the transparent electrode layer side is connected to the transparent electrode layer YT 1  of the unit cell YU 1  through a connecting electrode layer YE 0  formed in the opening YM 1 . The sealing resin layer  604  is formed over the rear electrode layer YD 1  of the unit cell YU 1 . 
     Similarly,  FIG. 8B  shows a sectional view taken along a line B-B′ of the periphery of the connection portion  606  to an external circuit. The transparent electrode layer YT 4 , the photoelectric conversion layer YK 4 , and the rear electrode layer YD 4  are formed over the substrate  601 . The transparent electrode layer YT 4  is formed at the inside of the edge by the opening YC 0 . The insulating layer YZ 0  fills the opening. Although the sealing resin layer is formed over the rear electrode layer YD 4 , it is not formed over the connection portion  606 . 
       FIG. 8C  shows a sectional view taken along a line C-C′ of the periphery of the connection portion of the adjacent unit cells in  FIG. 7 . The transparent electrode layers YT 3  and YT 4  are formed over the substrate  601 , and are insulated and isolated from each other by the insulating layer YZ 3  formed in the opening YC 3 . Similarly, the photoelectric conversion layers YK 3  and YK 4  are also isolated. The rear electrode layer YD 3  is connected to the transparent electrode layer YT 4  through the connecting electrode layer YE 4  formed in the opening YM 4 , thereby the unit cells YU 3  and YU 4  are connected. 
     As described above, it is possible to form the solar cell in which the four unit cells YU 1  to YU 4  are connected in series. In solar cells installed in various electronic devices such as a calculator or a watch, there is an adopted method of direct connection using a coil spring or a plate spring, in addition to a connecting method using soldering or a thermosetting adhesive to connect a solar cell to a circuit in the electronic device.  FIG. 9  is a view for explaining an example of such a connection where connection between a photoelectric conversion device  702  and a circuit substrate  706  is made through a connection spring. The structure of the photoelectric conversion device  702  is simply shown in which a rear electrode  702   b , an insulating resin  702   c , and a sealing resin  702   d  are formed over a substrate  702   a . In addition, a stainless structural body  703 , a support body  701  and the like are also included. A connection spring  704  is in contact with the rear electrode at an opening portion of the sealing resin  702   d , and electrical connection is formed to a circuit substrate  706  through a terminal portion  705 . A connection structure of a contact by applying pressure using mechanical force like this does not give severe damage to a solar cell compared with a connection method such as soldering or heat sealing, and does not cause a yield to be lowered in a manufacturing process. 
       FIG. 10A  shows a wrist watch which has a solar cell manufactured by the foregoing method. The wrist watch includes a housing  801 , the solar cell  802  shown in  FIG. 7 , a dial  803  having a long hand and a short hand, and a cover  804 . 
       FIG. 10B  shows a calculator which has a solar cell manufactured according to the present invention. The calculator includes a housing  901 , a solar cell  902 , buttons  903 , and a display panel  904 . The solar cell shown in  FIGS. 5 and 6  in Embodiment 1 may be used as the solar cell  902 . 
     According to the present invention, by forming an electrode layer and an insulating isolation layer of a solar cell minutely, excess portion can be omitted, a region shielding light can be reduced, and thereby a light receiving region can be enlarged. Thus, reduction in size and weight of a solar cell and an electronic device having the solar cell can be realized.