Integrated photovoltaic device

Abstract: An integrated photovoltaic device is disclosed, which comprises an integrated photovoltaic device which comprises a plurality of amorphous silicon based solar cells each comprising a transparent substrate (1) on the light-receiving face side that has a transparent electrode (21, 22, 23) on it and that has a metal electrode (40, 41, 42, 43) on the back side of said light-receiving face in such a manner that it faces said transparent electrode with an amorphous semiconductor layer (3) interposed, said plurality of solar cells being interconnected in a series or series-parallel fashion by means of said transparent electrode and said metal electrode, said metal electrode (40, 41, 42, 43) being formed of a metal film comprising, in superposition in order from the amorphous semiconductor layer side, the layers of aluminum (400), an additive metal for aluminum bronze (401) and copper (402).

Description: FIELD OF THE INVENTION This invention relates to photovoltaic devices for use in solar cells, photosensors and other applications. More specifically, this invention relates to an integrated photovoltaic device having a plurality of power generating zones on a thin film interconnected in a series or series-parallel fashion. BACKGROUND OF THE INVENTION Integrated photovoltaic devices, such as that disclosed in EP-A-0 275 166, have a basic structure in which a transparent electrode layer, an amorphous semiconductor layer and a metal electrode layer are superposed on a transparent insulating substrate, In particular, EP-A-0 275 166 concerns an integrated photovoltaic device which comprises a plurality of amorphous silicon solar cells, each comprising a transparent substrate, a transparent front electrode, an amorphous silicon layer and back contact formed of a lower layer of Al and an upper layer of Ni. The Ni film provides an improved seal to moisture over the aluminum film. An example of such integrated photovoltaic devices is described below with reference to the amorphous silicon (hereunder abbreviated as "a-Si") solar cell illustrated in Fig. 2. The a-Si solar cell system shown in Fig. 2 comprises a plurality of unit solar cells that are connected in a series or series-parallel fashion and each of which comprises a common transparent insulating substrate that has a transparent electrode layer, an amorphous semiconducting silicon layer and a metal electrode layer superposed thereon. The superposition of the metal electrode layers is conventionally achieved by vacuum evaporation techniques. According to the 17th IEEE Photovoltaic Specialists Conference 1984, Kissimmee, Florida 1-4 May 1984, pages 580-583, this technique can even be extended to the deposition of silver-free multilayer electrodes. The metal electrode layer is composed as the combination It was shown that a three-layer structure contact Al-Ni-Cu forms a satisfactory contact on Si solar cells. The metal electrode layer is composed as the combination of back electrodes and lead wire drawing terminals. Stated more specifically, the a-Si solar cell system comprises a single glass substrate 1 that has transparent electrodes 2 (21 - 23), a-Si film regions 3 and back electrodes 4 (41 - 43) superposed thereon to form a plurality of unit solar cells. The individual unit solar cells are interconnected via channels 50 - 52 such a way that the back electrode of a unit solar cell contacts the transparent electrode of an adjacent unit cell. Lead wires are drawn from terminals 40 and 43 in the form of a metal film. Lead wires can be drawn either by soldering them onto an adhesive-furnished electroconductive tape that is attached to the terminals 40 and 43 or by directly connecting them to the terminals with the aid of an electroconductive adhesive. These conventional methods of drawing lead wires have a common problem in that they reduce the production rate of finished solar cell systems. In the case of using adhesive-furnished conductive tape, attaching them to the terminals is a time-consuming operation and in the case of using a conductive adhesive, an extra step of drying the applied adhesive is necessary. SUMMARY OF THE INVENTION The present invention has been achieved under these circumstances and has as an object providing an integrated photovoltaic device that permits easy soldering of lead wires and that has high operating reliability. This object of the present invention can be attained by an integrated photovoltaic device which comprises a plurality of amorphous silicon based solar cells on a transparent substrate, each solar cell comprising on its light-receiving face a transparent electrode formed on said transparent substrate and a metal electrode on its back side facing said transparent electrode with said amorphous semiconductor interposed therebetween, said plurality of solar cells being interconnected in a series or series-parallel fashion by means of said transparent electrode and said metal electrode, said metal electrode being formed of a metal film comprising, in superposition in order from the amorphous semiconductor layer side, the layers of aluminum, an additive metal for aluminum bronze selected from iron and manganese, and copper, wherein the metal film is deposited on the amorphous silicon layer and the metal film has a thickness of about 0.2-0.8 µm. The use of the superposed layers of aluminum, an additive metal for aluminum bronze selected from iron and manganese, and copper as the material of the back electrode and the lead wire drawing output terminals insures reliable contact with amorphous silicon. At the same time, possible thermal deterioration of the aluminum-copper bond is prevented by the intermediate layer of an additive metal for aluminum bronze, say iron or manganese, and this not only helps improve the yield of photovoltaic devices produced but also permits lead wires to be soldered in an easy way. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the sequence of major steps for fabricating an integrated solar cell that is an example of the integrated photovoltaic device of the present invention; Fig. 2 is a diagram showing the structure of a prior art integrated solar cell. DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention is described hereinafter with reference to Figs. 1 and 3. Fig. 1(f) is a diagram showing the basic structure of an integrated solar cell incorporating the concept of the present invention, and Figs. 1(a) - 1(e) show the major steps of fabricating the solar cell. In Figs. 1(a) - 1(f), those components which are the same as those shown in Fig. 2 are identified by like numerals. The photovoltaic device of the present invention is characterized by forming a metallic back electrode not in the conventional single-layered structure of aluminum but in a three-layered structure composed of aluminum, an additive metal for aluminum bronze selected from iron and manganese, and copper. Stated more specifically, the integrated solar cell shown in Fig. 1(f) comprises a transparent insulating substrate 1 having a transparent electrode layer 2, an amorphous semiconductor layer 3 and a metal electrode layer 4 formed thereon in superposition. The metal electrode layer 4 has a laminated structure consisting, in order from the amorphous semiconductor layer side 3, of an aluminum layer 400, a layer of additive metal for aluminum bronze selected from iron and manganese 401, and a copper layer 402. The process of fabricating the integrated solar cell shown in Fig. 1(f) is described below more specifically. In the first step, a transparent electroconductive film made of ITO (indium tin oxide) or SnO 2 (tin oxide) is formed on the glass substrate 1 by thermal CVD, electron beam evaporation or sputtering as shown in Fig. 1(a). The deposited transparent conductive film is patterned with a YAG laser beam at 1.06 µm to form transparent electrodes 2 (21 - 23). In the next step, a-Si film 3 having a pin junction is formed in a thickness of about 0.3 - 0.8 µm by plasma-assisted CVD, as shown in Fig. 1(b). Further, as shown in Fig. 1(c), the a-Si film 3 is patterned with a YAG laser beam (1.06 µm) as applied from the glass substrate side, whereby cell interconnecting channels 50 - 52 are formed. Subsequently, in order to form a plurality of back electrodes 41 and 42 as well as output terminals 40 and 43 (also serving as back electrodes) on the a-Si film 3, a mask for back electrode formation 6 having windows of a predetermined shape is printed as shown in Fig. 1(d). By sputtering through the mask, a laminated metal film that is to serve as back electrodes 41 and 42 and as output terminals 40 and 43 is deposited by sputtering as shown in Fig. 1(e). This metal film is of a three-layered structure that consists, in order from the a-Si film side, of aluminum 400, additive metal for aluminum bronze selected from iron and manganese 401, and copper 402. The three-layered film has a thickness of about 0.2 - 0.8 µm. Thereafter, mask 6 is removed, whereby a plurality of back electrodes 41 and 42 of a predetermined shape as well as lead wire drawing terminals 40 and 43 are formed as shown in Fig. 1(f). The terminals 40 and 43 as well as back electrodes 41 and 42 are respectively connected to the transparent electrodes 21 - 23 via cell interconnecting channels 50 - 52, whereby the unit solar cells are connected in either a series or series-parallel fashion to construct an amorphous silicon based integrated solar cell system. The metal film formed on the back side of the system to provide a metal electrode has high thermal resistance since it has the layer of additive metal for aluminum bronze interposed between the layer of aluminum which provides good contact with to the a-Si film and the copper layer which can be easily soldered. If the aluminum layer were directly superposed on the copper layer, the thermally brittle aluminum-copper alloy at the interface of the two layers would be destroyed during soldering. As described above, the use of the superposed layers of aluminum, an additive metal for aluminum bronze selected from iron and manganese, and copper as the material of the back electrode in the present invention enables efficient production of integrated photovoltaic devices that permit easy soldering of lead wires and that operate with high reliability.

Claims: An integrated photovoltaic device which comprises a plurality of amorphous silicon based solar cells on a transparent substrate (I), each solar cell comprising on its light-receiving face a transparent electrode (21-23) formed on said transparent substrate and a metal electrode (41-43) on its back side facing said transparent electrode with said amorphous semiconductor (3) interposed therebetween, said plurality of solar cells being interconnected in a series or series-parallel fashion by means of said transparent electrode and said metal electrode, said metal electrode being formed of a metal film comprising, in superposition in order from the amorphous semiconductor layer side, the layers of aluminum (400), an additive metal for aluminum bronze (401) selected from iron and manganese, and copper (402), wherein the metal film is deposited on the amorphous silicon layer and the metal film has a thickness of about 0.2-0.8 µm.

Inventors: SICHANUGRIST PORPONTH, TANAKA NORMITSU, SICHANUGRIST, PORPONTH, TANAKA, NORMITSU, Sichanugrist, Porponth, c/o Showa Shell Sekiyu KK., Tanaka, Normitsu, c/o Showa Shell Sekiyu K. K.
Applicants: SHOWA SHELL SEKIYU, SHOWA SHELL SEKIYU KABUSHIKI KAISHA
Application year: 1991
Main classification: H01L31
IPC codes: H01L31, H01L27