Manufacturing method of a flexible photovoltaic device

Abstract: A flexible photovoltaic device comprises a first transparent, insulating, and flexible resin layer (2); a transparent electrode formed on the first resin layer (3); a flexible resin type locking member (3a) formed having satisfactory adherence along the inner periphery of the transparent electrode (3); a semiconductor (4) layer formed to cover the transparent electrode (3) and the locking member (3a) for photoelectric conversion; a back electrode (5) formed on the semiconductor layer (4); and a second insulating and flexible resin layer (14) formed on the back electrode (5).

Description: The present invention relates to a manufacturing method of a flexible photovoltaic device. A flexible photovoltaic device and the manufacturing method thereof is described in Japanese Patent Laying-Open No. 1-105581, for example. Referring to Fig. 1, a first resin layer 2 of polyimide resin with superior heat resistance is formed on a supporting substrate 1 such as glass, The first resin layer 2 is transparent and insulating, as well as flexible. A transparent electrode 3, a thin film semiconductor layer 4 for photoelectric conversion, and a back metal electrode 5 are layered in sequence on the first resin layer 2. Semiconductor layer 4 comprises p-i-n junction, p-n junction or the like parallel to the film face. A second resin layer 14 such as ethylene vinyl acetate copolymer (EVA) sheet is layered on back electrode 5. The second resin layer 14 is insulating and flexible. Referring to Fig. 2, the photovoltaic device formed on the supporting substrate 1 is immersed in water 16 in a container 15 to be separated from the supporting substrate 1. This results in a flexible photovoltaic device shown in Fig. 3. In the flexible photovoltaic device formed in the aforementioned manner, the second resin layer 14 is provided to protect the back metal electrode 5 from water 16. The second resin layer 14 is formed so as to have a shrinking force substantially equal to that of the first resin layer 2, to prevent the flexible photovoltaic device from curling after being separated from the supporting substrate 1. In the flexible photovoltaic device obtained in such a manner, the layers having a weak bond with each other in the multilayered structure, i.e. the transparent electrode 3 and the semiconductor layer 4, are apt to be separated from each other from the edge of the photovoltaic device, due to mechanical stress such as bending or torsion exerted on the device. If the transparent electrode 3 and the semiconductor layer 4 are locally separated, the photoelectric conversion efficiency will be reduced significantly. It is preferred that the first resin layer 2 has low adhesion to substrate 1 when the flexible photovoltaic device is separated from the supporting substrate 1. However, the first resin layer 2 must have sufficient adhesion to substrate 1 until the second resin layer 14 is formed. It generally takes a long time of two to three days for water 16 to permeate into the interface of the supporting substrate 1 and the first resin layer 2 to cause natural separation therebetween. If an additional external force is applied to separate the photovoltaic device from the supporting substrate 1 in a short period, high stress will be generated in the region A surrounded by a broken line in Fig. 2, whereby the transparent electrode 3 and the semiconductor layer 4 are separated from each other locally to degrade the photoelectric conversion efficiency significantly. Furthermore, because the first resin layer 2 of polyimide resin and the second resin layer 14 of EVA sheet have moisture permeability, local separation may be seen in the semiconductor layer 4 of the layered structure if the photovoltaic device is held in an environment of high humidity for a long time. Patent abstracts of Japan, Vol. 12, No. 348 (E-659) [3195], September 19, 1988 and JP-A-6 310 7073 discloses a method of manufacturing a flexible photovoltaic device, wherein the photovoltaic device is provided on a retaining substrate and separated from the substrate by diping in heated water such that the water penetrates from the boundary surface between the lower layer of the device and the retaining substrate. It is therefore an object of the invention to provide a method of manufacturing a flexible photovoltaic device in relatively short time. A further object of the invention is to provide a method of manufacturing a flexible photovoltaic device having moisture resistance. These objects are achieved by a method of manufacturing a flexible photovoltaic device comprising the steps of forming a first transparent, insulating, and flexible resin layer on a supporting substrate; forming a transparent electrode, a semiconductor layer for photoelectric conversion, and a back plate in sequence on the first resin layer; forming a second insulating and flexible resin layer having shrinking force on the back electrode; separating the first resin layer from the supporting substrate by using the shrinking force of the second resin layer; forming a third transparent and flexible resin layer having shrinking force on the free surface of the first resin layer; whereby the bending moment in the photovoltaic device caused by the shrinking force of the second resin layer is cancelled by the bending moment caused by the shrinking force of the third resin layer. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. Figs. 1-3 are sectional views showing the manufacturing steps of a flexible photovoltaic device by prior art. Figs. 4-8 are sectional views showing the manufacturing steps of a flexible photovoltaic device in accordance with an embodiment of the present invention. The embodiment of the present invention will be described in reference to Figs. 4-8. Referring to Fig. 4, a first transparent, insulating and flexible resin layer 2 of organic polymer film is formed on the supporting substrate 1 constituted by glass, ceramic, metal, or the like. A transparent polyimide varnish, for example, is applied in uniform by a spin coater or a roll coater, and the temperature of the same is raised from 100°C to 300°C stepwise, to form the first resin layer 2. It is preferred that the first resin layer 2 has a thickness of not less than 5 µm from the standpoint of mechanical strength, and a thickness of not more than 100µm from the standpoint of transparency. A transparent electrode 3 constituted by tin oxide (SnO₂) or indium tin oxide (ITO) and the like is formed on the first resin layer 2 to a thickness of 200-500 nm (2000-5000Å). The transparent electrode 3 is covered by a semiconductor layer 4 for photoelectric conversion. The semiconductor layer 4 has a thickness of approximately 300-700 nm (3000-7000Å), comprising semiconductor junction such as p-i-n junction or p-n junction parallel to the film face. As the semiconductor layer 4, a layer comprising amorphous silicon (a-Si), amorphous silicon carbide (a-SiC), or amorphous silicon germanium (A-SiGe) and the like may be formed by plasma CVD method or photo-assisted CVD method. A metal back electrode 5 having a thickness of approximately 400nm (4000Å)-2µm is formed on the semiconductor layer 4. The back electrode 5 may comprise a single layer structure of aluminum (Aℓ), a double layer structure of Aℓ and titanium (Ti), a double layer structure of Aℓ and titanium silver alloy (TiAg), or other multilayer structures. Thus, a photoelectric conversion element is formed comprising the transparent electrode 3, the semiconductor layer 4, and the back electrode 5. Referring to Fig. 5, a second resin layer 14a having a high shrinking force is formed to a thickness of approximately 20µm-1mm on the back electrode 5. The shrinking force of the second resin layer 14a is greater than that of the first resin layer 2, so as to curl in a concave manner the side of the second resin layer of the photovoltaic device of multilayered structure. The second resin layer 14a can be formed by applying a thermosetting varnish of polyimide type or acryl type, for example, onto the back electrode 5 in uniform using a spinner, a roll coater, a spray or the like, followed by a rise in temperature to 100°C-200°C. The second resin layer 14a may alternatively be formed by layering a thermoplastic resin sheet such as EVA of approximately 20µm-100µm in thickness , and a moisture-proof film such as polyethylene telephthalate (PET) or fluorine-contained resin of approximately 20µm-1mm in thickness in sequence, whereby the double layer film is heated to a temperature of 100°C-150°C and a pressure of 0.1-10kg/cm² is applied thereto for thermal bonding. The second resin layer 14a formed in the above manner generates shrinking force when cooled down to room temperature from the raised temperature. Referring to Fig. 6, the photovoltaic device formed on the supporting substrate 1 is immersed in water to separate the first resin layer 2 from the supporting substrate 1. Because the shrinking force of the second resin layer 14a which is greater than that of the first resin layer 2 acts so as to curl the second resin layer side of the photovoltaic device of the multilayered structure in a concave manner, the first resin layer 2 is separated from the substrate 1 in a relatively short time of 30 minutes to 10 hours. Referring to Fig. 7, the flexible photovoltaic device separated from the supporting substrate 1 has the second resin layer side curled in a concave manner due to the shrinking force of the second resin layer 14a. The second resin layer 14a generates a great shrinking force in proportion to the thickness thereof. Although it is possible to separate the photovoltaic device from the supporting substrate 1 in a shorter period if the shrinking force of the second resin layer 14a is great, the radius of curvature of the curl of the photovoltaic device after the separation will become smaller. The transparent electrode 3 and the semiconductor layer 4 are susceptible to local separation if the radius of curvature of the curl becomes too small. Therefore, it is preferred that the second resin layer 14a has a shrinking force which generates a radius of curvature of the curl of approximately 2cm-10cm. Referring to Fig. 8, a third transparent and flexible resin layer 2a having shrinking force is formed on the free surface of the first resin layer 2. A thermal setting varnish of polyimide type or acryl type, for example, is applied in uniform onto the free surface of the first resin layer 2 using a roll coater, a spray, or the like, and heated to a temperature of 100°C-200°C, to form the third resin layer 2a having a thickness of approximately 20µm-1mm. The third resin layer 2a may alternatively be formed by layering a thermoplastic resin sheet such as of EVA of approximately 20µm-100µm in thickness and a film superior in moisture-proofness such as of PET or fluorine-contained resin of approximately 20µm-1mm in thickness on the free surface of the first resin layer 2 in sequence, whereby the double layer film is heated to 100°C-150°C and a pressure of 0.1-10kg/cm² is applied thereto for thermal bonding. The bending moment caused by the shrinking force of the third resin layer 2a cancels the bending moment caused by the shrinking force of the second resin layer 14a, to straighten and flatten the curl of the flexible photovoltaic device. In the case the second resin layer 14a and the third resin layer 2a comprise a moisture-proof PET film or a fluorine-contained resin film, the undesired effect of moisture to the transparent electrode 3, the semiconductor layer 4, and the metal back electrode 5 is prevented to obtain a flexible photovoltaic device of high reliability.

Claims: A method of manufacturing a flexible photovoltaic device comprising the steps of: forming a first transparent, insulating, and flexible resin layer (2) on a supporting substrate (1), forming a transparent electrode (3), a semiconductor layer for photoelectric conversion (4) and a back electrode (5) on said first resin layer (2) in sequence, forming a second insulating and flexible resin layer (14a) having shrinking force on said back electrode (5), separating said first resin layer (2) from said supporting substrate (1) by using the shrinking force of said second resin layer (14a), and forming a third transparent and flexible resin layer (2a) having shrinking force on the free surface of said first resin layer (2), wherein the bending moment in said photovoltaic device caused by the shrinking force of said second resin layer (14a) is cancelled by the bending moment caused by the shrinking force of the third resin layer (2a). The method according to claim 1, wherein said first resin layer (2) is separated from said supporting substrate in water. The method according to claim 1, wherein each of said second (14a) and third resin layers (2a) is formed by applying a member selected from the group consisting of thermoseting varnish of polyimide type and acryl type, and heating. The method according to claim 1, wherein each of said second and third resin layers is formed by a double layer film comprising sheets of EVA and PET, and applying a predetermined pressure for thermal bonding. The method according to claim 1, wherein each of said second and third resin layers is formed by a double layer film comrising sheets of EVA and fluorine-contained type resin and applying a pretermined pressure for thermal bonding.

Inventors: INOUE HIROSHI, KISHI YASUO, KOUZUMA SHINICHI, MURATA KENJI, TANAKA HIROYUKI, INOUE, HIROSHI, KISHI, YASUO, KOUZUMA, SHINICHI, MURATA, KENJI, TANAKA, HIROYUKI
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO., LTD.
Application year: 1990
Main classification: H01L31
IPC codes: H01L31