Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2001-01-29
2003-09-02
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S033000, C438S026000, C438S022000
Reexamination Certificate
active
06613598
ABSTRACT:
This application claims priority of European Patent Application No. 98200940.9, filed on Mar. 26, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a method of making a photovoltaic (PV) cell at least comprising the following layers: a first electrode layer, a transparent wide band gap (and preferably high surface area) semiconductor layer provided with a (mono)layer of a photosensitising dye or pigment which in combination with the semiconductor layer has the ability to spatially separate photogenerated electrons from their positive countercharges, an electrolyte layer, a catalyst layer, and a second electrode layer, wherein at least one electrode layer is transparent. Given that, e.g., sunlight can thus be used to generate power, such photovoltaic cells form an interesting alternative source of energy, one much cleaner than fossil fuels or nuclear power.
2. Description of the Related Art
Methods for making the photovoltaic cells at hand are known in the art, for example from WO 91/16719. This international patent application describes (see, e.g., Example 34 in conjunction with FIG. 1) a photovoltaic cell comprising a light transmitting electrically conductive layer (commonly referred to as Transparent Conductive Oxide or TCO) as electrode layer deposited on a glass plate or transparent polymer sheet. On top of the TCO are deposited several TiO
2
layers which are dye-loaded. The last TiO
2
layer is covered with an electrolyte, a catalyst layer, and a counter- or back-electrode which can also be a TCO.
In order for at least one of the TCOs to have the desired properties (especially transparency) and texture, it should preferably be formed at a temperature of at least 400° C. Further, the semiconductor layer, which usually essentially consists of titanium dioxide, is preferably sintered at similar temperatures and in many embodiments, the catalyst layer is subjected to temperatures exceeding 350° C. Because of that, the transparent substrates which are suitable for applying these layers onto in forming photovoltaic cells of this type is restricted to, int. al., glass substrates or transparent polymer sheets having a high temperature resistance. These materials are either rigid or quite expensive.
For the PV cells at hand to become a serious and economically attractive alternative, they need to be provided in a suitable form (less rigid and bulky) and made by relatively low-cost processes, using relatively inexpensive raw materials. Hence, a process is required which allows the roll-to-roll manufacture of a photovoltaic cell as described in the first paragraph, while at the same time any desired transparent conductor material, deposition process, and sintering process can be used and without the use of expensive or rigid materials as transparent substrate being necessary. These requirements, and other desirable objectives, are met by the process of the invention.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to a method of making an organic photovoltaic cell wherein the first electrode layer and the semiconductor layer are deposited on a flexible temporary substrate that is removed later on and/or the second electrode layer and the catalyst layer are deposited on a flexible temporary substrate that is removed later on, wherein the electrode or electrodes that are deposited over a temporary substrate are transparent.
DETAILED DESCRIPTION OF THE INVENTION
These steps and their sequence essentially make it possible for the PV cells at hand to be produced roll-to-roll and in the form of a flexible foil, while for most embodiments at least part of the desired order of manufacture that is customary in the case of similar PV cells produced on glass substrates is still maintained. When following the process of the invention, the temporary substrate can be selected so as to allow any further process steps (like the high-temperature application of the first or second transparent conductor layer, the sintering of the semiconductor layer, and the formation of the catalyst layer) without any concerns about its (i.e. the substrate's) transparency or other properties needed (flexibility, durability, etc.) for the functioning of the eventual PV foil.
It is noted that Japanese Laid-open 1980-143706 describes the forming of a transparent electrically conductive (TCO) layer on the surface of a substrate, forming a polymer product (e.g., a film or a lens) on the conductive layer, and removing the substrate. Thus, the TCO layer and its method of deposition (in terms of temperature and duration) can be selected freely. This reference concerns a technical field differing from the one at hand (formed polymeric products instead of organic photovoltaic cells) and teaches that a transparent polymer should be applied to the TCO prior to instead of after the removal of the temporary substrate. Thus, the artisan would not combine this publication with WO91/16719 and, even if he were to do so, it would not result in the process according to the present idea.
Kishi et al., “Ultralight Flexible Amorphous Silicon Solar Cell and Its Application for an Airplane,”
Technical Digest of the International PVSEC
-5, Kyoto, Japan, 1990, pages 645-648, discloses a solar cell manufactured by depositing the respective layers on a transparent plastic film. A temporary substrate is neither mentioned nor implied. WO 97/15959 describes an electrochemical cell comprising a working electrode and a counter-electrode provided on flexible polymeric substrates. The working electrode comprises a semiconductor film which is deposited in the form of a paste, and then dried and sintered at a temperature below 200° C. The use of temporary substrates is not disclosed.
JP laid-open patent application 89-119072 describes a process for producing a PV cell comprising the steps of forming a heat resistant, flexible and electrically insulating transparent plastic layer on the surface of a temporary substrate, and sequentially depositing thereon a TCO, a semiconductor layer, a rear electrode, and a carrier. Then, the temporary substrate is removed. This process differs from the process of the invention in that in the process of the invention the TCO is coated onto the temporary substrate instead of onto a transparent plastic layer. This has the advantage that in the process according to the invention the transparent layer that is, optionally, applied to the TCO after removal of the temporary substrate does not have to be resistant to the conditions prevailing during the application of the TCO and the further layers.
The temporary substrate on the side of the first electrode layer is removed after the first electrode layer and the semiconductor have been applied. It is preferred that at least the dye and the electrolyte are also applied before the temporary substrate is removed.
Additional mechanical strength can be provided by laminating all the essential layers together before removal of the substrate or substrates. This is preferably done by spotbonding two separately prepared components (one at least comprising the first electrode layer, the semiconductor layer, and the dye, the other at least comprising the second electrode layer and the catalyst layer) together at the interface of the catalyst layer and the semiconductor layer. In that case, the electrolyte fills the space between the semiconductor layer and the catalyst layer.
It is further preferred to apply a carrier layer before removing the (last) temporary substrate, this in order to have the thin PV foil supported during as many process steps as possible and to ensure that the foil exhibits sufficient strength and bending stiffness (preferably adapted to the intended end product). After removal of the (last) temporary substrate, the exposed electrode is preferably provided with a carrier layer or a transparent layer, which further adds to the mechanical and barrier properties of the PV foil and/or the end product. Of course it is not the intention to provide both electrodes with a carrier layer. At least one of the electrodes sho
Middelman Erik
Salafsky Joshua Samuel
Schropp Rudolf Emmanuel Isidore
Akzo Nobel N.V.
Fennelly Richard P.
Rocchegiani Renzo N.
Smith Matthew
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