Abstract:
The invention is aimed to prevent that fall of characteristic of a solar battery and producing yield caused by particles of powder condition generating from working part at laser beam process in the method producing the solar battery by laser beam process. The constitution of the invention is characterized by comprising: a first step forming the lower electrode and the semiconductor layer on the insulating substrate by laminating; a second step forming a protective film on surface of the semiconductor; a third step forming an opening portion at the semiconductor layer, or the semiconductor layer and the lower electrode by laser beam process after the second step; and a fourth step removing the protective film.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a method for producing a solar battery having semiconductor film on insulating substrate, particularly to a method for producing an integrated solar battery produced using laser beam processing.  
           [0002]    In recent years, a thin film solar battery in which non-monocrystal silicon film is formed on an insulating substrate is getting attention. Here, the substance applied as non-monocrystal silicon is amorphous silicon, microcrystal silicon, thin film polycrystal silicon, and compound thereof. A thin film solar battery is characterized in that production cost is kept low and material used for production is little. By using plastic film substrate having flexibility as an insulation substrate, shape of the solar battery is set freely. It is one of important characteristics to make an integrated structure possible on the insulation substrate, where desired voltage is obtained by dividing an element to plural elements on single substrate and connecting the elements in series. It is possible to use a substrate having an insulating surface, for example a conductive substrate on which an insulating film is provided.  
           [0003]    Laser beam process is used widely for producing a solar battery of integrated structure. The laser beam process irradiates laser beam gathered on a certain area to a work piece, makes a hole by melting, evaporation, or scattering, performs melting, cutting off, and marking, and divides, thereby any shape can be processed by scanning laser beam. By this technique, separation of thin film can be performed with scribing width of equivalent width in high speed. The laser beam process is used even for means melting and connecting taking-out electrodes of the solar battery. Although the process is called bonding especially, the process is included in the laser beam process.  
           [0004]    There has been technique of photolithography hitherto as a method for shape-processing pattern for the purpose of electrode and semiconductor layer constituting solar battery. Patterning process of the solar battery using the photolithography applies a resist to allover face of the work piece, exposes through a mask, and after that, a resist mask is formed at developing process. Next, area except masked area with the resist is etched by etching process, after that, the resist is peeled off by alkali solvent, and cleaning and drying are performed, thereby the process is completed. The process has problems of complexity and many process steps, long processing time, and high production cost.  
           [0005]    The patterning process of the solar battery by laser beam process is simple and few in number of processes. It has a distinguishing characteristic that the processes are completed only by irradiating laser beam while scanning at a part desired to perform patterning.  
           [0006]    The laser beam process irradiates laser beam, melts a part of work instantly, and evaporates or scatters. At this time, material of the part of work melted at high temperature is cooled while scattering or after sticking at periphery, and becomes particles of powder condition. The particles of powder condition damage generating layer of the solar battery at manufacturing process after the laser beam process, thereby causes one of decline in characteristic.  
           [0007]    Here, producing process of the solar battery using laser beam process of the prior art will be described using FIGS. 2A to  2 E. First, a lower electrode  202  is formed on a substrate  201 , and on the lower electrode  202 , a semiconductor layer  203  being a generating of the solar battery is formed as shown in FIG. 2A. Next, to make an integrated structure of the solar battery on the same substrate, the lower electrode layer and the semiconductor layer are divided by laser beam process, and plural sections are made. Divided parts  204   a  and  204   b  by laser beam process are shown in FIG. 2B. At the laser beam process, the semiconductor layer and the lower electrode of the divided portions are melted and scattered by the laser beam. Particles  205   a ,  205   b , and  205   c  of powder condition generated at this time scatter and stick on the semiconductor layer  203  of periphery. The particles possibly get stuck in the semiconductor layer  203 .  
           [0008]    After the laser beam process, insulating layers  206   a  and  206   b  are formed. This is because contact of the lower electrode and an upper electrode is prevented when the conductive upper electrode is formed on the divided portion. The state using thermosetting resin as insulating layer and forming with screen printing method is shown in FIG. 2C. Insulating thermosetting resin  208  is applied on a screen printing plate  207 , a squeegee  209  is moved to direction  210  from right to left of the figure, and resin is printed at parts of the insulation layers  206   a  and  206   b . At the printing, the screen-printing plate  207  contacts the semiconductor layer  203  and particles of powder condition, and presses the particles of powder condition against the semiconductor layer. Even the particles of powder condition stuck on surface of the semiconductor layer are possibly taken in the semiconductor layer.  
           [0009]    In the printing process, when the screen-printing plate is separated from the semiconductor layer and further after the printing process, particles of powder condition possibly desorbs from surface of semiconductor layer or inside. Parts  212   a ,  212   b , and  212   c  where the particles of powder condition are desorbed exist at the semiconductor layer as shown in FIG. 2D.  
           [0010]    Although the upper electrodes  213   a ,  213   b , and  213   c  are formed as shown in FIG. 2E after the printing process and drying process, at this time, parts  215   b  and  215   c  where the upper electrode and the lower electrode contact are formed at parts  212   b  and  212   c  where the lower electrodes expose among the desorbed parts  212   a ,  212   b , and  212   c . Since the upper electrode and the lower electrode contact at unit cells  214   b  and  214   c , characteristic of the solar battery such as release voltage decreases. At a part  212   a  where the lower electrode is not exposed, a part  215   a  where the upper electrode and the lower electrode are close is formed. Although characteristic of the solar battery such as release voltage does not decrease directly by cause of the close part  215   a , damage caused by static electricity occurs easily at dealing as a product.  
           [0011]    Although method forming insulation layer using screen printing method is described in FIGS. 2A to  2 E, in the case forming insulation layer by another method or using another producing process of the solar battery, generation of the particles of powder condition can not be avoided as long as the laser beam process is performed. Although particles of powder condition generated at laser beam process stick at semiconductor layer and get in inside of the layer, the particles drop out by process forming the upper electrode, and the upper electrode contacts the lower electrode at forming the upper electrode.  
           [0012]    As one means to reduce foreign bodies of fine particles, there is a method adjusting condition of laser power, that is, feeding speed of a part of work in laser beam processing device. For example, means making laser power weak, that is, making feeding speed of the working portion fast may be used. However, particles of powder condition generated at laser beam process can reduce using the means, however, it is impossible to remove the entire particles. For example, although it is possible to make the sizes small or to reduce numbers of particles of powder condition  205   a ,  205   b , and  205   c  shown in FIG. 2B, it is impossible to remove the entire particles.  
           [0013]    As another means to reduce foreign bodies of fine particles, a method absorbing particles of power condition generated at process in laser beam processing device using absorbing mechanism. However, although material of a part processed by laser melts and scatters instantly, scattering speed is considerably high and temperature is high. Because of that, removing the particles of powder condition before adhesion to generating layer of the solar battery or removing the particles of powder condition stuck is not performed completely even by using strong absorbing mechanism.  
           [0014]    The invention is performed in view of the above-mentioned problem, an object of the invention is to prevent decrease of characteristic of the solar battery and production yield caused by particles of powder condition generating from a part of work at laser beam process.  
         SUMMARY OF THE INVENTION  
         [0015]    In order to solve the above-mentioned problem, the constitution of the invention is characterized by comprising: a first step forming the lower electrode and the semiconductor layer on the insulating substrate by laminating; a second step forming a protective film on surface of the semiconductor; a third step forming an opening portion at the semiconductor layer, or the semiconductor layer and the lower electrode by laser beam process after the second step; and a fourth step removing the protective film.  
           [0016]    Another constitution is characterized by comprising: a first step forming the lower electrode and the semiconductor layer on the insulating substrate by laminating; a second step forming a protective film providing an opening portion on surface of the semiconductor by screen-printing method; a third step forming an opening portion at the semiconductor layer, or the semiconductor layer and the lower electrode by laser beam process corresponding to the opening portion; and a fourth step removing the protective film.  
           [0017]    Although the protective film is formed of thermosetting resin, it is desirable to form the protective film with thermosetting polyester system resin. The protective film can be removed without complex process by peeling an adhesive tape and the protective film at the same time after the adhesive tape is bonded to the protective film.  
           [0018]    By providing the protective film at laser beam process, particles of powder condition generating from a part of work is prevented to stick directly at the semiconductor layer so that the semiconductor is prevented to damage. By removing the protective film after laser beam process, particles of powder condition gets in the inside of the semiconductor layer and drops out by the forming process of the upper electrode even at screen-printing process so that shortage of the lower electrode at forming the upper electrode is prevented. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIGS. 1A to  1 E are views describing process producing a solar battery using protective film at laser beam process;  
         [0020]    [0020]FIGS. 2A to  2 E are views describing process producing a solar battery using laser beam processing method of the related art;  
         [0021]    [0021]FIGS. 3A to  3 D are graphs showing transmissivity and reflectance as influence to monocrystal silicon film by protective film;  
         [0022]    [0022]FIGS. 4A and 4B are graphs showing output characteristic of solar battery as influence to monocrystal silicon film by protective film;  
         [0023]    [0023]FIGS. 5A and 5B are graphs showing spectral characteristic as influence to monocrystal silicon film by protective film;  
         [0024]    [0024]FIGS. 6A to  6 E are views describing process producing a solar battery using protective film; and  
         [0025]    [0025]FIGS. 7A and 7B are histograms showing comparison of production characteristic by existence of protective film.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    A mode for carrying out the invention will be described referring FIGS. 1A to  1 E. First, a lower electrode  102  and a semiconductor layer  103  are formed on a substrate  101  as shown in FIG. 1A. Next, protective films  106   a ,  106   b , and  106   c  are formed except places  107   a  and  107   b  where laser beam process is performed as shown in FIG. 1B. For the protective films, thermosetting resin, for example, is printed using screen-printing method so as to form by thermosetting.  
         [0027]    After forming the protective film, laser beam process is performed to divide the semiconductor layer  103  and the lower electrode  102  as shown in FIG. 1C. Divided portions  104   a  and  104   b  of the semiconductor layer and the lower electrode are formed by laser beam process. At laser beam process, particles of powder condition  105   a ,  105   b , and  105   c  melted from the semiconductor layer  103  and the lower electrode  102  by laser beam scatter and stick on protective films  106   a ,  106   b , and  106   c.    
         [0028]    After the laser beam process, the protective films  106   a ,  106   b , and  106   c  are removed as shown in FIG. 1D. Although melting by organic solvent is general in removing method of resin, it is difficult to melt only the protective film selectively at producing process when another resin is already formed on surface of substrate. On the other hand, when thermosetting resin having elasticity easy in exfoliation is used for the protective film, only protective film can be removed easily without crush by method that adhesive tape is put on surface of the substrate and is peeled off, that is, peeling method. Such the peeling method without using solvent can omit washing process, and can reduce process. Because the protective film and particles of powder condition stuck on the protective film are removed at the same time, particles of powder condition on the semiconductor layer  103  become nothing at all.  
         [0029]    After removing the protective films, divided portions of the semiconductor layer and the lower electrode are filled with insulators  108   a  and  108   b  as shown in FIG. 1E. The insulators are formed of thermosetting insulating resin, for example, using screen-printing method. Further upper electrodes  113   a ,  113   b , and  113   c  are formed to become a laminated structure. For example, the upper electrode  113   a  of a unit cell  114   a  connects to the lower electrode  102   b  of a unit cell  114   b , and each unit cell is connected in series. The upper electrodes are formed of conductive resin, for example, using screen-printing method. At the same time, an ejecting electrode  116  of the lower electrode side and an ejecting electrode  117  of the upper electrode side are formed. When process forming the protective films is used, contact of the semiconductor and the lower electrode is not generated at forming the upper electrode because the semiconductor does not have parts where particles of powder condition are omitted. Characteristic of the solar battery does not fall, and yield of product improves.  
         [0030]    Embodiments  
         [0031]    Embodiment 1  
         [0032]    In the embodiment, existence of influence to output characteristic of the solar battery by forming and peeling the protective film is shown. First, a translucent lower electrode and a non-monocrystal silicon layer are formed on a translucent substrate, and at a part on the non-monocrystal silicon layer, protective films protecting the non-monocrystal silicon layer from particles of powder condition generating at laser beam process are formed. For the protective films, thermosetting resin of polyester system (STRIP MASK #228-T made by Asahi chemical laboratory, Inc.) is used. After forming the protective films, the protective films are peeled by an adhesive tape after designated time.  
         [0033]    After the process peeling the protective films, a part not forming the protective films and a part forming and peeling the protective films exist, then, transmissivity and reflectance are measured at each part. Transmissivity at the part not forming the protective films is shown in FIG. 3A, transmissivity at the part forming and peeling the protective films is shown in FIG. 3B, reflectance at the part not forming the protective films is shown in FIG. 3C, and reflectance at the part forming and peeling the protective films is shown in FIG. 3D. In transmissivity and reflectance, there is not difference between the part not forming the protective films and the part forming and peeling the protective films.  
         [0034]    After the process peeling the protective films, an upper electrode is formed at each f the part not forming the protective films and the part forming and peeling the protective films to form the solar battery. After that, output characteristic of each solar battery is measured to compare the characteristic. Output characteristic (I-V characteristic) of each solar battery is shown in FIGS. 4A and 4B, and spectral characteristic of each solar battery is shown in FIGS. 5A and 5B. Even in output characteristic and spectral characteristic of each solar battery, there is not difference between the part not forming the protective films and the part forming and peeling the protective films.  
         [0035]    By the experimentation, it is known that forming and peeling the protective films on the non-monocrystal silicon layer does not influence output characteristic of the solar battery produced using the non-polycrystal silicon layer. The similar effect can be obtained even at another process producing the solar battery.  
         [0036]    Embodiment 2  
         [0037]    In the embodiment, a non-monocrystal silicon solar battery of a laminated structure is produced on an elastic substrate, and comparison of yield of final product is shown. Producing processes are shown in FIGS. 6A to  6 E. First, ITO (Indium tin oxide) and GZO (Gallium addition zinc oxide) are filmed as translucent conductive material on translucent PEN (Polyethylene naphthalate) film substrate by spattering method to form a lower electrode. Thickness of the ITO layer and the GZO are set to 50 to 60 nm and 20 to 30 nm respectively. Non-monocrystal silicon layers of each of conductive types of p, i, and n are coated to form a generating layer of the solar battery. Thickness of the non-monocrystal silicon layers is set to 300 to 800 nm, in the embodiment, 600 nm.  
         [0038]    Next, the non-monocrystal silicon film and the lower electrode layer are divided in order to form the laminating structure on the same substrate, and one unit of the solar battery is produced. The one unit of the solar unit means a part having one stage of pin junction. Although there is a case including conductive ejecting electrode in the pin junction, in the embodiment, the one unit of the solar battery is called unit cell. Protective films are formed in order to protect the generating layer of the solar battery from particles of powder condition.  
         [0039]    A state forming protective films  601   a ,  601   b ,  601   c , and  601   d  on the generating layer are formed is shown in FIG. 6A. In FIG. 6A, periphery of the protective films shows the lower electrode portion and the generating layer portion. Thermosetting resin easy in peeling is used for the protective films to form using screen-printing method. In the embodiment, STRIP MASK #228-T made by Asahi chemical laboratory, Inc. is used for the thermosetting resin.  
         [0040]    After forming the protective films, the protective films are divided using laser beam process as shown in FIG. 6B. The method dividing with laser beam is called laser scribing. A divided portion  602   a  is divided to each unit cell, and a divided portion  602   b  is divided to the periphery portion and an external form of the solar battery. It is need to consider the following items for dimension design of space between the divided portion and the protective film. Actual width of made by laser beam process is about 0.1 mm. The width varies a little by kind of film processed, laser power, and processing speed. Margin of alignment shift at laser beam process is considered. Therefore, distance between protective films provided at both side of the divided portion by the laser beam process is need to set 0.2 mm or more at least. In the case forming the protective film using thermosetting resin by screen-printing method, design of a screen-printing plate considering the dimension is need. Since the object of the protective film is to prevent damage of the generating layer caused by particles of powder condition, it is desirable to cover the generating layer part as far as possible and to make space between the divided portion and the protective film by laser beam process as small as possible. In the embodiment, distance between protecting films provided at both sides of the divided portion by laser beam process is set to 0.5 mm.  
         [0041]    After the laser beam process, the protective films are peeled as shown in FIG. 6C. In the peeling process, a tape having stronger adhesion than adhesion of the protective films to the generating layer is put, and the tape and the protective films are peeled at the same time.  
         [0042]    The divided portions  602   a  and  602   b  are filled with insulating resin  603  as shown in FIG. 6D. The reason is as the following. That is, when the upper electrode of the unit cell is formed so as to get over the divided portion to connect to the lower electrode of adjacent unit cell, it is prevented to contact the lower electrode of the upper electrode itself so that output falls. Insulating resin is formed using thermosetting resin by screen-printing method.  
         [0043]    After forming the insulating resin, conductive upper electrodes  604   a ,  604   b ,  604   c , and  604   d  are formed as shown in FIG. 6E. The conductive upper electrode is formed using thermosetting resin containing silver or carbon by screen-printing method. The upper electrode are connected the lower electrodes of the unit cell adjacent to laser-bonding portions  605   b ,  605   c , and  605   d . For example, the upper electrode  604   a  of a unit cell  606   a  is connected to the lower electrode of adjacent unit cell  606   b  at the laser-bonding portion  605   b . A rejecting electrode  607   a  is connected to the lower electrode of the unit cell  606   a  by laser bonding, is ejected to upper side. After the laser bonding process, unit cells  606   a ,  606   b ,  606   c , and  606   d  are laminated in series, and a solar battery having an ejecting electrode  607   a  of the lower electrode side and an ejecting electrode  607   b  of the upper electrode side electrode is completed. By forming the protective films protecting the generating layer of the solar battery at laser beam process, damage of the generating layer by particles of powder condition can be prevented. The solar battery shows excellent characteristic, and production yield of characteristic improves.  
         [0044]    Histograms of Fill Factor (F.F) as product characteristic by existence of the protective film of resin are shown in FIGS. 7A and 7B. FIG. 7A shows in the case not having the protective film, and FIG. 7B shows the case having the protective film. Yield is defined as that F.F is larger than 0.65 at characteristic of the solar battery of low illuminance 200 lux. Although characteristic of the solar battery does not almost change as shown in Embodiment 1, it is shown that effect of the protective films appears largely in yield.  
         [0045]    There is the following characteristic when screen-printing on the protective film is possible and thermosetting resin easy in peeling is used. First, the resin has viscosity enabling to perform screen-printing process similarly as another thermosetting resin, and the desired shape can be obtained by pattern hole plate. Because drying (curing) temperature is low, it is hard to generate damage to another film and change in quality of material by temperature. Cure of the resin is performed by volatizing solvent component at low temperature baking of some degree. The cured resin is peeled with simple contact. For example, an adhesive tape is used. Since adhesion of the resin and face of the protective film is weak, damage does not appear at surface of the protective film so that peeling is possible. At this time, since resin has flexibility, resin itself is not crushed at peeling operation of the resin, and new fine particles are not increased. Like this, since thermosetting resin easy in peeling is possible to perform the similar screen-printing as usual printing process and is removed easily at peeling process, it is possible to use as mask material of various uses. The present invention can be applied to not only the solar battery but also other photovoltaic devices and semiconductor devices.  
         [0046]    As described above, particles of powder condition generated from working part can be removed easily at laser beam process by using the present invention in patterning process of the solar battery by laser beam process. In producing process after laser beam process, characteristic can be improved without damage of the generating layer of the solar battery. Further, in product, product yield of characteristic can be improved.