Photovoltaic device and process for manufacturing the same

Abstract: The present invention discloses a process for manufacturing a photovoltaic device which comprises providing a plurality of spaced transparent electrode layer regions (21,22,23) on an insulating transparent substrate plate (1), forming an amorphous semiconductor layer (3) over the spaced transparent electrode layer regions, forming a patterned conductive printedeletrode layer (41,42,43) over the amorphous semiconductor layer to form a plurality of photovoltaic regions, and then irradiating the photovoltaic regions with a laser beam from the substrate plate side to heat and melt the transparent electrode, amorphous semiconductor, and conductive printed electrode in each photovoltaic region, thereby forming in each photovoltaic region a conductive path (51, 52) made of an alloy formed by the melting, thus electrically connecting the photovoltaic regions in series, and a photovoltaic device manufactured by the above process.

Description: The present invention relates to a photovoltaic device for use as a solar cell, photosensor, or the like, and more particularly, to a thin-film photovoltaic device having a plurality of photovoltaic regions connected in series, and also relates to a process for manufacturing the photovoltaic device. Film-form semiconductor conductive modules which have conventionally been utilized as solar cells, photosensors, etc. have a thin-film construction in which units each having a number of photovoltaic regions connected in series are arranged on the same plane in order that the modules capture as much light as possible in limited spaces and convert the light into electric energy. Fig. 3 is a plan view illustrating the construction of a conventional amorphous silicon (hereinafter referred to as a-Si) solar cell in which solar cell unit elements are connected in series on an insulating substrate plate, each solar cell unit element comprising a transparent electrode layer, an a-Si layer as an amorphous semiconductor layer, and a conductive printed electrode layer as a back electrode layer, superposed in this order. Illustratively stated, this a-Si solar cell comprises a single glass substrate plate 1 and, superposed thereon, a transparent electrode layer 2 (21-23), an a-Si layer 3 (31-33), and a conductive printed electrode layer 4 (41-43), thus forming a plurality of solar cell unit elements. These solar cell unit elements are connected in series by bringing the conductive printed electrode layer in an element into contact with the transparent electrode layer of an adjacent element. In manufacturing this kind of solar cell, a transparent conductive film, such as an ITO (indium tin oxide) or SnO₂ (tin oxide) film or the like, is first formed over a glass substrate plate 1 at a thickness of about 500 to 10,000 Å (10Å = 1nm) by electron beam vapor deposition, sputtering, or the thermal CVD process. A transparent electrode layer 2 is then formed by patterning the transparent conductive film by means of a laser beam, or by forming a patterned photoresist on the transparent conductive film by photolithography and subjecting the resulting transparent conductive film to etching. An a-Si layer 3 is then formed, for example, by depositing on the transparent electrode layer 2 a p-type a-Si layer at a thickness of about 200 Å, an undoped a-Si layer at 0.2-1 µm, and an n-type a-Si layer at about 500 Å, by the plasma discharge decomposition of silane gases. The p-type a-Si is obtained by doping boron and carbon, while the n-type a-Si is obtained by doping phosphorus. The thus-formed a-Si layer 3 is patterned, or divided, into regions 31, 32, and 33 by means of a laser beam. Subsequently, a patterned conductive back electrode layer 4 is formed by printing to prepare a solar cell. If, in the above process, a YAG laser beam used to pattern the transparent conductive film and having a wavelength of 1.06 µm is used for the patterning of the a-Si layer, the power of the laser beam should be heightened because of the low absorbance of the a-Si layer, and patterning of the a-Si layer with such a higher-power laser beam damages the transparent electrode layer at the regions 26 and 27 shown in Fig. 3 which are exposed to the laser beam. In order to avoid such a problem, a YAG laser beam with a wavelength of 0.53 µm, which is well absorbed by a-Si layers, has conventionally been used for the patterning of a-Si layers. Therefore, conventional patterning has been disadvantageous in that the laser necessarily has a complicated structure because it should be so constructed as to emit laser beams with different wavelengths respectively suited for transparent conductive films and a-Si layers, and that good reproducibility is not obtained because reflectance varies depending on the state of a-Si layer surfaces. From JP-A-62-89368 a method for manufacturing a solar cell device is known according to which first electrodes are provided on an insulating substrate by vapor depositing a light-transmitting conductive film of indium oxide, tin oxide or the like. An amorphous semiconductor layer is provided on the first electrodes by serially depositing P-type amorphous Su, I-type amorphous Si an N-type amorphous Si by means of plasma CVD forming a p-i-n junction. Therafter, second electrodes are provided by depositing Al, Ti or the like. YAG laser beams are applied through the amorphous Si layer to a region where the end of each first electrode overlaps with the end of the adjacent second electrode. The layers of the first electrode, the amorphous Si and the second electrode are welded together; thereby, the individual elements of the solar cell device are electrically connected in series. The conductive path formed in the welded area of the three layers provides for a good electrical connenction between the individual elements. However, solar cells of this structure suffer from corrosion especially in the area of the welded layers as reported in IEEE Conference Report (1987) "Corrosion of a-Si cells and modules", G.R. Mon et al. Due to corrosion the properties of the device a deteriorated. JP-A-161963 discloses the formation of conductive paths in solar cell devices by the use of laser irradiation to convert the amorphous structure of silicon to crystalline. In view of the above, it is an object of the present invention to provide a process for manufacturing a photovoltaic device and the photovoltaic device itself having high reliability and stable properties. The above object is solved by a process of manufacturing a photovoltaic device according to claim 1. In a preferred embodiment of the above process, conductive printed electrode layers are formed of a paste containing a resin binder and Ni particles as a filler. In another preferred embodiment of the above process, the spaced transparent electrode layers are formed by patterning a transparent conductive film formed on the substrate plate, said patterning being performed by means of a laser beam having the same wavelength as that of the laser beam used for forming the conductive paths. In another preferred embodiment of the above process, the wavelength of the laser beam is 1.06 µm. The above object is moreover solved by a photovoltaic device according to claim 5. According to the present invention, the photovoltaic device is manufactured such that the conductive path connecting the transparent electrode layer with the conductive printed electrode layer can be formed without being affected by the surface state and thickness of the amorphous semiconductor layer. A preferred embodiment of the invention will be described in the following where reference will be made to the drawings of which Fig. 1(a) to (d) are schematic views illustrating the steps of the process for manufacturing a photovoltaic device according to the present invention; Fig. 2 is an enlarged sectional view of a conductive path area of the structure of Fig. 1 (d); and Fig. 3 is a plan view illustrating the construction of a conventional solar cell. Upon irradiation with a laser beam from the substrate plate side, not only the transparent electrode layer and a-Si layer in each photovoltaic region but the conductive printed electrode layer in an adjacent photovoltaic region are heated and, as a result, the irradiated portion of the transparent electrode layer and conductive printed back electrode layer are melted to form an alloy, which provide a conductive path. Thus, the transparent electrode layer in each photovoltaic region is internally connected by the conductive path with the conductive printed electrode layer in the adjacent photovoltaic region, thereby giving a solar cell. Due to the irradiation with laser beam by the above method, conductive paths can be formed without being affected by the surface state and thickness of the a-Si layer. Further, since the conductive printed electrode layer has a sufficient thickness, the conductive paths can be formed so as not to extend through the conductive printed electrode layer by controlling the power of the laser beam. Hence, photovoltaic devices can be produced with good reproducibility. Furthermore, the wavelength of the laser beam used in the process of the invention can be limited to 1.06 µm, which is suited for the patterning of the transparent electrode layer, the irradiating device can have a simple construction. Fig. 1 (a) to (d) illustrate the steps of a process for manufacturing an amorphous silicon solar cell as one embodiment of the photovoltaic device of this invention. In Figs. 1 and 3, like portions or parts are designated by like numerals or symbols. First, as shown in Fig. 1 (a), a transparent conductive film of SnO₂ which has been formed on a glass substrate plate 1 at a thickness of 800 Å by thermal CVD is patterned by means of a YAG laser beam with a wavelength of 1.06 µm to form a transparent electrode layer 2 (21-23). Subsequently, an a-Si layer 3 having a pin junction is formed by the plasma CVD process with a thickness of about 0.8 µm as shown in Fig. 1 (b). On the a-Si layer 3, a conductive printed electrode layer 4 (41-43) is formed by printing with a thickness of 10 to 30 µm as shown in Fig. 1 (c). The conductive printed electrode layer 4 has been formed such that a portion thereof overlaps an adjacent portion of the transparent electrode layer 2 through the a-Si layer 3. Connection between solar cell unit elements is established at this portion where a conductive printed electrode layer overlaps an adjacent transparent electrode layer. That is, when this portion of each photovoltaic region is irradiated with a laser beam with a wavelength of 1.06 µm from the glass substrate plate side, the irradiated portion of the transparent electrode layer 2 and a-Si layer 3 are heated and melted along with the irradiated portion of the conductive printed electrode layer 4 of the adjacent photovoltaic region to form an alloy 6, which provide conductive paths 5 (51 and 52) as shown in Fig. 2. The conductive paths 5 connect the conductive printed electrode layer regions 41 and 42 with the transparent electrode layer regions 22 and 23, respectively. Thus, an a-Si solar cell is fabricated in which solar cell unit elements are connected in series. As the material for the conductive printed electrode layer, use may be made of a paste which contains Ni particles as a filler and a resin as a binder and is able to be calcined at a relatively low temperature of 150 to 200°C. As the material for the transparent electrode layer, ITO, SnO₂, and ZnO can be used, for example. As the material for the amorphous semiconductor layer, a-Si and a-Ge can be used, for example. A solar cell as an application of the photovoltaic device of this invention has achieved a conversion efficiency of 7% or more at an incident light illuminance of 200 luxes. As described above, since according to the present invention, the irradiation with a laser beam for forming conductive paths for connecting the photovoltaic regions is effected through the insulating transparent substrate plate, the conductive paths can be formed without adversely affecting the conductive printed electrode layer even if the power of the laser beam is increased to some degree, and without being affected by a difference in the reflectance of the a-Si layer due to a change in the surface state and thickness of the layer. Therefore, photovoltaic devices can be fabricated with good reproducibility. Furthermore, since the conductive paths connecting solar cell unit elements are made of an alloy formed by irradiation from the substrate plate side and can be prevented from being exposed, the photovoltaic device can have improved reliability and show stable and high-efficiency output properties. Moreover, since a laser beam having the wavelength suited for the patterning of the transparent electrode film can be used for the formation of the conductive paths, the irradiating device can be of a simpler structure, so that the production cost can be reduced.

Claims: A process of manufacturing a photovoltaic device comprising the steps of: providing a plurality of spaced transparent electrode layers (21,22,23...) on an insulating transparent substrate plate (1); forming an amorphous semiconductor layer (3) on the spaced transparent electrode layer (21,22,23...) and exposed portions of the insulating transparent substrate plate (1), said amorphous semiconductor layer having a pin junction; forming a plurality of patterned conductive printed electrode layers (41,42,43...) on the amorphous semiconductor layer (3) such that a portion of each one of said conductive printed electrode layers (41,42,43...) overlaps a portion of an adjacent one of said spaced transparent electrode layers (21,22,23...) thus defining device regions formed by the overlapping portions of said transparent and printed electrodes with the corresponding portion of the amorphous semiconductor layer in between; irradiating said device regions with a laser beam from the substrate plate side to heat and melt the portions of transparent electrodes, the amorphous semiconductor layer and printed electrodes comprised in said device regions, thereby forming a conductive path (51,52...), in each of said irradiated device regions which is made of an alloy formed by the melting and which does not extend through the conductive printed electrode layer (4), and which electrically connects the printed electrode layer with the adjacent transparent electrode layer, thus connecting the non-irradiated photovoltaic device regions in series. A process according to claim 1 wherein the conductive printed electrode layers (41,42,43) are formed of a paste containing a resin binder and Ni particles as a filler. A process according to claim 1 or 2, wherein the spaced transparent electrode layers are formed by patterning a transparent conductive film (2) formed on the substrate plate (1), said patterning being performed by means of a laser beam having the same wavelength as that of the laser beam used for forming the conductive paths (51,52). A process according to claim 1, 2 or 3, wherein the wavelength of the laser beam is 1.06 µm. Photovoltaic device comprising: an insulating transparent substrate plate (1); a plurality of spaced transparent electrode layers (21,22,23...) on the insulating transparent substrate plate (1); an amorphous semiconductor layer (3) formed on the spaced transparent electrode layers (21,22,23...) and exposed portions of the insulating transparent substrate plate (1), said amorphous semiconductor layer having a pin junction; a plurality of patterned conductive printed electrode layers (41,42,43...) formed on the the amorphous semiconductor region (3) such that each one of said conductive printed electrode layers (41,42,43) overlaps an adjacent one of said spaced transparent electrode layers (21,22,23...); conductive paths (51,52) connecting each one of said spaced transparent electrode layers (21,22,23...) with the corresponding adjacent one of said conductive printed electrode layers (41,42,43...), said conductive paths formed of an alloy obtained by melting portions of the transparent electrode layers, the amorphous semiconductor layer and the printed electrode layers, and said conductive paths not extending through the conductive printed electrode layer (4).

Inventors: NISHI HIROFUMI SHOWA SHELL SEK, SICHANUGRIST PORPONTH SHOWA SH, SUZUKI HIROHISA SHOWA SHELL SE, NISHI, HIROFUMI, SHOWA SHELL SEKIYU K.K., SICHANUGRIST, PORPONTH, SHOWA SHELL SEKIYU K.K., SUZUKI, HIROHISA, SHOWA SHELL SEKIYU K.K.
Applicants: SHOWA SHELL SEKIYU, SHOWA SHELL SEKIYU KABUSHIKI KAISHA
Application year: 1990
Main classification: H01L27
IPC codes: H01L27, H01L31