METHOD FOR INCREASING THE EFFICIENCY OF PHOTOELECTRO-CHEMICAL CELLS, AND PHOTOELECTRO-CHEMICAL CELLS REALIZED ACCORDING TO SAID METHOD

Abstract: It is described a method for increasing the efficiency of elementary photoelectrochemical cells that comprise, in order, a first electrode (1), photoelectrochemical conversion means (2, 3, 4) and a second electrode (5), where one of the electrodes receives the incident radiation. Two or more elementary photoelectrochemical cells are assembled "back-to-back", and each pair of these elementary cells thus assembled has one of the electrodes in common. Photoelectrochemical cells realized according to the aforesaid method are also described.

Description: METHOD FOR INCREASING THE EFFICIENCY . OF PHOTOELECTROCHEMICAL CELLS, AND PHOTOELECTRO-CHEMICAL CELLS REALIZED ACCORDING TO SAID METHOD Scope of the invention The invention refers to a method for increasing the efficiency of elementary photoelectro-chemical cells (each of which comprises, in order, a first electrode, photoelectro-chemical conversion means and a second electrode), where two or more elementary photoelectro-chemical cells are assembled "back-to-back", and each pair of these elementary cells thus assembled has one of the electrodes in common. The invention refers also to photoelectro-chemical cells realized according to the aforesaid method. Prior art Photoelectro-chemical cells are circuit components, known and available on the market, which comprise photoelectro-chemical conversion means (consisting, for example, of a layer of a metal oxide, a layer of a colouring substance and an electrolyte) inserted between two electrodes, at least one of which, designed to receive the incident radiation, must be transparent or translucent for the incident radiation, at least on the range of frequencies that activate the photoelectro- chemical conversion means. Photoelectro-chemical cells will not be further described herein since they are well known to a person skilled in the art. The photoelectro-chemical cells of known type has the defect of a quite reduced efficiency, which decreases when the surface of the electrode receiving the incident radiation increases. This is a drawback that has so far limited their practical use. Subjects of the present invention are a method to realize photoelectro-chemical cells having an efficiency higher than that of known photoelectro-chemical cells having the same external surface receiving the incident radiation, and photoelectro-chemical cells realized according to said method. Summary of the invention The present invention refers to a method for increasing the efficiency of already known elementary photoelectro-chemical cells comprising, in order, a first electrode, photoelectro-chemical conversion means activated by the radiation incident on an electrode of the photoelectro-chemical cell, and a second electrode. According to this method, at least two elementary photoelectrochemical cells are assembled "back-to-back" and each pair of these elementary photoelectro-chemical cells thus assembled has one of the electrodes in common, which is different from the electrode receiving the incident radiation. The present invention refers also to photoelectro-chemical cells realized by assembling elementary photoelectro-chemical cells, each pair of elementary photoelectro-chemical cells thus assembled having a hemi-symmethcal structure with respect to the common electrode. List of figures The invention will now be better described with reference to an exemplary, non limiting embodiment illustrated in the enclosed figures, where - Figure 1 is a schematic representation of an elementary photoelectro-chemical cell C of known type; - Figure 2 shows a photoelectro-chemical cell realized by assembling, according to the invention, two elementary photoelectro-chemical cells C; - Figure 3 shows the photoelectro-chemical cell of Fig. 2, in which the two elementary photoelectro-chemical cells C are connected in parallel; - Figure 4 shows a photoelectro-chemical cell, which is dual of that shown in Fig. 2, realized by assembling, according to the invention, two elementary photoelectro-chemical cells C; - Figure 5 shows the photoelectro-chemical cell of Fig. 4, where the two elementary photoelectro-chemical cells C are connected in series; - Figure 6 shows a photoelectro-chemical cell realized by assembling, according to the invention, four elementary photoelectro-chemical cells C; - Figure 7 shows a photoelectro-chemical cell, dual of that shown in Fig. 6, realized by assembling, according to the invention, four elementary photoelectrochemical cells C. In the enclosed figures, the corresponding elements will be identified using the same numerical references. Detailed description Figure 1 is a schematic representation of an elementary photoelectro-chemical cell C of known type. In the figure are shown an electrode 1 receiving the incident radiation L, an additional electrode 5 and photoelectro-chemical conversion means, set between the two electrodes, which, in the present exemplary embodiment, comprise a layer 2 of a metal oxide applied on the electrode 1 , a layer 3 of a colouring substance applied on the layer 2 of metal oxide, and an electrolyte 4 set between the layer 3 of colouring substance and the electrode 5. Without departing from the scope of the invention, it is possible to use other photoelectro-chemical conversion means functionally equivalent to those indicated herein, which are not described because they are in any case known to a person skilled in the art. The electrodes 1 and 5 may be realized with the same electrically conductive material, or with different electrically conductive materials. In any case, at least the electrode receiving the incident radiation L (in Fig. 1 , the electrode 1 ) must be transparent or translucent for said radiation, which must reach the photoelectrochemical conversion means of the photoelectro-chemical cell with a sufficiently high energy to activate them. Figure 2 shows a photoelectro-chemical cell realized by assembling "back-to- back", according to the invention, two elementary photoelectro-chemical cells C and by replacing the two electrodes 5 of the two elementary cells C thus assembled with a single electrode 5, which is common to both of the elementary cells C and is transparent or translucent for the incident radiation L at least for the range of frequencies by which the photoelectro-chemical conversion means set "downstream" of the common electrode 5 are activated. The common electrode 5 is obviously different from that (in Fig. 2, the electrode 1 ) receiving the incident radiation L. As may be readily noted from Fig. 2, the photoelectro-chemical cell thus obtained presents a hemi-symmetrical structure with respect to the central electrode 5, which is common to the two elementary photoelectro-chemical cells C, and comprises, in order, a first electrode 1 to which is applied a layer 2 of a first metal oxide, a layer 3 of a first colouring substance applied to the layer 2 of the first metal oxide, a first electrolyte 4, the electrode 5 set between the first electrolyte and a second electrolyte, a layer 3 of a second colouring substance (either the same as or different from the first colouring substance), applied on a layer 2 of a second metal oxide (either the same as or different from the first metal oxide), which in turn is applied on a second electrode 1. Preferably, but not necessarily, the second electrode 1 (which is set at the end of the photoelectro-chemical cell opposite to the first electrode 1 receiving the incident radiation L) is realized with an opaque and reflecting material (at least for the entire range of frequencies belonging to the incident radiation L), or its external surface is coated with a layer of said opaque and reflecting material. The fraction of the incident radiation L which reaches the second electrode 1 is reflected black and further activates the photoelectro-chemical conversion means, thus increasing the efficiency of the photoelectro-chemical cell realized according to the invention. The photoelectro-chemical conversion means set between the first electrode 1 and the common electrode 5 may be the same as those set between the common electrode 5 and the second electrode 1 (i.e., suitable to be activated by incident radiations L belonging to the same range of frequencies), or (preferably but not necessarily) different (i.e., suitable to be activated by incident radiations L belonging to a different frequency range) to increase the width of the absorption window of a photoelectro-chemical cell realized according to the invention and, consequently, its efficiency. Another method for increasing the efficiency of a photoelectro-chemical cell according to the invention is to increase the voltage, respectively the current, supplied by said photoelectro-chemical cell by connecting in parallel, respectively in series, the elementary photoelectro-chemical cells C belonging to the aforesaid photoelectro-chemical cell realized according to the invention. Figure 3 shows the photoelectro-chemical cell of Fig. 2, in which the two elementary photoelectro-chemical cells C are connected in parallel. However, without departing from the scope of the invention, it is possible to connect them in series, as illustrated in Fig. 5 for the elementary photoelectro-chemical cells C belonging to the photoelectro-chemical cell of Fig. 4, which is dual of that shown in Fig. 2. Again without departing from the scope of the invention, it is possible to connect in parallel the elementary photoelectro-chemical cells C belonging to the photoelectro-chemical cell of Fig. 4. In Figs. 3 and 5, LO is the external load on which the electric circuit supplied by the photoelectro-chemical cell realized according to the invention shown in these figures is closed. Figure 4 shows a photoelectro-chemical cell, which is dual of that shown in Fig. 2, realized by assembling, according to the invention, two elementary photoelectrochemical cells C and by setting the electrode 1 in common. The photoelectrochemical cell thus obtained comprises, in order, a first electrode 5, a first electrolyte 4, a layer 3 of a first colouring substance applied on a layer 2 of a first metal oxide, which is in turn applied on one side of the common electrode 1 , a layer 2 of a second metal oxide (the same as, or different from, the first metal oxide), applied on the other side of the common electrode 1 , a layer 3 of a second colouring substance (the same as, or different from, the first colouring substance), applied on the layer 2 of the second metal oxide, and a second electrolyte 4 set between the layer 3 of the second colouring substance and a second electrode 5. The considerations set forth previously with reference to the cell of Fig. 2 apply to the cell of Fig. 4, with modifications, if any, which are obvious for any person skilled in the art. Without departing from the scope of the invention, it is possible to extend the structure shown in Fig. 2 or Fig. 4 to photoelectro-chemical ceils realized by assembling, according to the invention, three or more elementary photoelectrochemical cells C. Figures 6 and 7 show photoelectro-chemical cells which are mutually dual, realized by assembling, according to the invention, four elementary photoelectro-chemical cells C. In the photoelectro-chemical cell of Figure 6, the first and the second elementary photoelectro-chemical cells C, respectively the third and the fourth elementary photoelectro-chemical cells C have electrode 1 in common, whilst the second and the third elementary photoelectro-chemical cells C have electrode 5 in common. In the photoelectro-chemical cell of Fig. 7, the first and the second elementary photoelectro-chemical cells C, respectively the third and the fourth elementary photoelectro-chemical cells C, have electrode 5 in common, whereas the second and the third elementary photoelectro-chemical cells C have electrode 1 in common. The above considerations made with reference to the photoelectro-chemical cell of Fig. 2 apply to the photoelectro-chemical cells of Figs. 6 and 7, with modifications, if any, that are obvious for a person skilled in the art. Preferably, but not necessarily, at least one of the photoelectro-chemical conversion means present in the photoelectro-chemical cells of Figs. 6 and 7 is activated by the incident radiation L belonging to a frequency range different from that (or those) that activates (or activate) the other photoelectro-chemical conversion means, respectively each of the other photoelectro-chemical conversion means. The three or more elementary photoelectro-chemical cells C belonging to photoelectro-chemical cells realized according to the invention may be connected in series, in parallel, or by means of series-parallel connections. Without departing from the scope of the invention, it is possible for a skilled person to make to the method for increasing the efficiency of photoelectro-chemical cells and to the photoelectro-chemical cells realized by using this method, as described herein, all the modifications and improvements suggested by the normal experience and by the natural evolution of techniques.

Claims: CLAIMS 1 1. Method for increasing the efficiency of elementary photoelectro-chemical cells 2 (C) comprising, in order, a first electrode (1 ), photoelectro-chemical conversion 3 means, activated by the radiation (L) incident on the said photoelectro-chemical 4 cell, and a second electrode (5), one of the said electrodes (1 , 5) receiving said 5 incident radiation (L), characterized in that at least two of the said elementary 6 photoelectro-chemical cells (C) are assembled, "back-to-back", one of said 7 electrodes (1 , 5) being common to each pair of said elementary photoelectro- 8 chemical cells (C), said common electrode being different from said electrode (1 , 9 5) receiving said incident radiation (L). l 2. Method according to Claim 1 , characterized in that the said electrode set at "> the end of the said photoelectro-chemical cell opposite to the said electrode 3 receiving said incident radiation (L) is realized with an opaque and reflecting 4 material. 1 3. Method according to Claim 1 , characterized in that the external surface of said 2 electrode set at the end of said photoelectro-chemical cell opposite to the said 3 electrode receiving said incident radiation (L) is coated with a layer of an opaque 4 and reflecting material. 1 4. Method according to Claim 1 , characterized in that each of said electrodes (1 , 2 5) common to each pair of said elementary photoelectro-chemical cells (C) is 3 transparent or translucent at least for the range of frequencies by which said 4 photoelectro-chemical conversion means set "downstream" of said common 5 electrode (1 , 5) are activated. 1 5. Method according to Claim 1 , characterized in that one pair of said elementary 2 photoelectro-chemical cells (C) is assembled "back-to-back", and in that said first 3 electrode (1 ) constitutes the said common electrode. 1 6. Method according to Claim 1 , characterized in that one pair of said elementary 2 photoelectro-chemical cells (C) is assembled "back-to-back", and in that said 3 second electrode (5) constitutes the said common electrode. 1 7. Method according to Claim 1 , characterized in that at least three elementary 2 photoelectro-chemical cells (C) are assembled "back-to-back", and in that said first electrode (1 ), respectively said second electrode (5), constitute in order the said common electrodes. 8. Method according to Claim 1 , characterized in that at least three elementary photoelectro-chemical cells (C) are assembled "back-to-back", and in that said second electrode (5), respectively said first electrode (1 ), constitute in order the said common electrodes. 9. Method according to any one of the claims from 5 to 8, characterized in that said at least two elementary photoelectro-chemical cells (C) are connected in series. 10. Method according to any one of the claims from 5 to 8, characterized in that said at least two elementary photoelectro-chemical cells (C) are connected in parallel. 11. Method according to Claim 9 or Claim 10, characterized in that the said at least three elementary photoelectro-chemical cells (C) are connected by means of series-parallel connections. 12. Method according to Claim 1 , characterized in that said elementary photoelectro-chemical cells (C) comprising photoelectro-chemical conversion means activated by incident radiations (L) belonging to the same range of frequencies are assembled "back-to-back". 13. Method according to Claim 1 , characterized in that said elementary photoelectro-chemical cells (C) comprising photoelectro-chemical conversion means activated by incident radiations (L) belonging to different ranges of frequencies are assembled "back-to-back". 14. Photoelectro-chemical cell realized by assembling "back-to-back" elementary photoelectro-chemical cells (C) comprising, in order, a first electrode (1 ), photoelectro-chemical conversion means activated by the radiation (L) incident on the said photoelectro-chemical cell, and a second electrode (5), one of the said electrodes (1 , 5) receiving said incident radiation (L), characterized in that each pair of said elementary photoelectro-chemical cells (C) thus assembled presents a hemi-symmet cal structure with respect to a central electrode (1 , 5), common to said elementary photoelectro-chemical cells (C) belonging to said pair of elementary photoelectro-chemical cells (C), said common electrode being different from said electrode (1 , 5) receiving said incident radiation (L). 15. Photoelectro-chemical cell according to Claim 14, characterized in that said electrode set at the end of said photoelectro-chemical cell opposite to said electrode receiving said incident radiation (L) is realized with an opaque and reflecting material. 16. Photoelectro-chemical cell according to Claim 14, characterized in that the external surface of said electrode set at the end of said photoelectro-chemical cell opposite to the said electrode receiving said incident radiation (L) is coated with a layer of an opaque and reflecting material. 17. Photoelectro-chemical cell according to Claim 14, characterized in that each of said electrodes (1 , 5) common to each pair of said elementary photoelectro- chemical cells (C) is transparent or translucent at least for the range of frequencies by which said photoelectro-chemical conversion means set "downstream" of said common electrode (1 , 5) are activated. 18. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises a pair of said elementary photoelectro-chemical cells (C), and in that it presents a hemi-symmetrical structure with respect to said first electrode (1 ), which constitutes said common electrode. 19. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises a pair of said elementary photoelectro-chemical cells (C), and in that it presents a hemi-symmetrical structure with respect to said second electrode (5), which constitutes said common electrode. 20. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises at least three elementary photoelectro-chemical cells (C) assembled "back-to-back", and in that said first electrode (1 ), respectively said second electrode (5), constitute in order said common electrodes. 21. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises at least three elementary photoelectro-chemical cells (C) assembled "back-to-back", and in that said second electrode (5), respectively said first electrode (1 ), constitute in order said common electrodes. 22. Photoelectro-chemical cell according to any one of the claims from 18 to 21 , characterized in that said at least two elementary photoelectro-chemical cells (C) assembled "back-to-back" are connected in series. 23. Photoelectro-chemical cell according to any one of the claims from 18 to 21 , charactehzed in that said at least two elementary photoelectro-chemical cells (C) assembled "back-to-back" are connected in parallel. 24. Photoelectro-chemical cell according to Claim 22 or Claim 23 characterized in that said at least three elementary photoelectro-chemical cells (C) assembled "back-to-back" are connected by means of series-parallel connections. 25. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises elementary photoelectro-chemical cells (C) comprising photoelectro- chemical conversion means which are activated by incident radiations (L) belonging to the same range of frequencies. 26. Photoelectro-chemical cell according to Claim 14, characterized in that it comprises elementary photoelectro-chemical cells (C) comprising photoelectro- chemical conversion means activated by incident radiation (L) belonging to different ranges of frequencies.

Inventors: SINICCO IVAN, SINICCO, IVAN
Applicants: ELIODORO S A, SINICCO IVAN, ELIODORO S.A., SINICCO, IVAN
Application year: 1997
Main classification: H01G9
IPC codes: H01G9, H01M6, H01M14