Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2001-11-19
2003-04-01
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S256000, C136S291000, C136S252000, C429S111000, C257S043000, C257S040000, C257S431000
Reexamination Certificate
active
06541697
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photovoltaically self-charging storage system having a layer structure in which a first material, which forms a first redox system, a second material, which forms a second redox system, and a photosensitive material are arranged in or between a first and a second electrically conductive layer. This system is a multi-layer system which stores electric energy electrochemically when illumuniated and can release electric energy at a later time to operate an electrical consumer.
BACKGROUND OF THE INVENTION
For the mentioned application of operating an electrical consumer, the state of the art presently provides photovoltaic systems which release the required energy directly to the consumer. If the energy is not needed until later, these systems require an additional battery for storage.
Furthermore, DE 29 24 079 discloses an arrangement in which a p-n junction is employed in conjunction with a solid electrolyte to generate a charge and to store it. Such type systems, however, have the disadvantage that they are relatively complicated in structure and the selection of material is greatly limited.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a photovoltaic self-charging storage system which is of simple construction and permits storing the energy provided for the operation of an electrical consumer photovoltaically.
This object is solved with the photovoltaic self-charging storage system of the valid claim
1
. Advantageous embodiments and further developments of this system are the subject matter of the subclaims.
A key element of the present invention is that the photovoltaically self-charging storage system has a layer structure, in which a first material, which forms a first redox system A
ox
/A
red
, a second material, which forms a second redox system B
ox
/B
red
, and a photosensitive material are arranged in or between a first and a second electrically conductive layer, with at least one of the electrically conductive layers being transparent for visible light. The first and the second material are each in electrical contact with one of the electrically conductive layers. Furthermore, the first material, the second material and the photosensitive material are selected and arranged in the layer structure in such a manner that, due to the effect of light, the photosensitive material releases electrons to the first redox system and picks them up again from the second redox system, thereby inducing a redox reaction A
ox
+B
red
→A
red
+B
ox
(direct reaction), which can be reversed (back reaction) if light ceases, and with the back reaction being substantially slower than the direct reaction. Someone skilled in the art is familiar with combinations of materials suited for this purpose. The thickness of the layer over which the first and/or second material extends is configured in such a manner that a charge storage in the layer structure yielded by the direct reaction and in its capacity sufficient for operating an electrical consumer is made possible.
The invented storage system combines, in an advantageous manner, in a layer structure, a photovoltaic element with an electrochemical storage. A photosensitive material, preferably a coloring matter and two redox pairs A
ox
, A
red
and B
ox
, B
red
are combined in a suited manner and arranged between two electrically conductive layers. One of the materials can, of course, also itself form the electrically conductive layer respectively be embedded in the electrically conductive layer. Charging the storage system occurs by means of the reaction A
ox
+B
red
→A
red
+B
ox
initiated by the photosensitive material (for example: coloring matter) under light. The coloring matter (F) is excited by the light and can release an electron e
−
directly or via a semiconductor to A
ox
, leading to a reduction of A
ox
. For charge compensation of the coloring matter, the latter picks up an electron from B
red
(directly or indirectly) and thereby oxidizes B
red
. These processes can be expressed by the following formulae:
F+photon→F*(excitation coloring matter) (1)
F*+A→F*(rapid injection of e
−
from coloring matter to A; oxidation of A) (2)
F
+
+B→F+B
+
(injection of e
31
from B to the coloring matter; reduction of B) (3)
The function principle of the storage system is that the photosensitive material injects under light energetically excited charge carriers directly or indirectly via another material (see, e.g. claim 4) into the redox pair A and leads to a redox reaction there. In the case of the electron injection, A is reduced. From redox pair B, the photosensitive material receives a charge carrier again. In the case of electron injection, B is oxidized.
Depending on the layer structure respectively the layer sequence (see, e.g. claims 6, 9 and 13), A
red
and B
ox
can, for example—in the case of electron injection by means of the photosensitive material—lie directly adjacent and form an electrochemical double layer or a counter ion to one of the components of a redox pair passes over to the other and in this way compensates the charge transfer by means of the photosensitive material. In the latter case, intermediate layers possibly present between the redox pairs have to be permeable for the counter ion.
Besides this direct reaction, in redox reactions, the back reaction constantly occurs simultaneously. However, it should be greatly checked by the selection of materials. For functioning of the invented system as a storage system, a slow back reaction rate is required in the region in which the direct reaction occurs. Someone skilled in the art knows numerous materials which possess these properties. For example, a combination of WO
3
or TiO
2
as the first redox system combined with inorganic ruthenium compounds as photosensitive material and with LiI in propylene carbonate as the second redox system demonstrates a very slow back reaction rate.
The back reaction is a prerequisite for the discharge of the system. A slow back reaction permits operation of only a consumer with very low current requirements. Suited external circuitry of the system combined with a suited layer structure, as will be described in more detail in the following, can result in spatial separation between the direct reaction and the back reaction. If a catalyst material is provided at the site of the back reaction for the back reaction in the layer structure, the back reaction can be substantially accelerated depending on the external circuitry and thus supply greater current strengths. Even tiny additives of platinum act as a catalyst on the back reaction of the just described redox systems.
Functioning of the invented storage system requires that the layer thickness, over which the first or the second redox system extends, is great enough to be able to store sufficient amount of charge for the operation of an electrical consumer. Preferably layer thicknesses of 0.01 to 1 mm or more are employed.
Thus, with the photovoltaic storage system according to claim 1, the light energy is photovoltaically converted and stored in a simple layer structure to operate an electrical consumer immediately with the energy or at some later time. Besides the simple structure, this system has the further great advantage over the state-of-the art systems that, an additional battery is no longer needed for charge storage.
Materials like those used for coloring-matter-sensitized solar cells , electrochromic systems and electrochromic coloring-matter-sensitized solar cells can be employed for the layer structure. These systems are optical components which reversibly alter their optical or electrical properties by means of illumination or external circuitry. Such an optical component is, for example, described in “Photoelectrochromic Window and Displays”, C. Bechinger et.al., Nature, Vol. 383, 17 October 1996, pp. 608 to 610. In this system, the layer structure is realized by two re
Georg Andreas
Hauch Anneke
Diamond Alan
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Kinberg Robert
Venable LLP.
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