The present invention relates to vertical electric connection of photoelectrochemical cells or DSSC (dye-sensitized solar cells).
More specifically, the invention relates to the structure of said vertical electric connections, integrated into photovoltaic modules of DSSC cells, and a process for the realisation thereof.
DSSC cells are photovoltaic cells made of a multilayered structure supported by a substrate or, more often, delimited by two substrates. Typically, said substrates are made of transparent materials (preferably glass, but also PET or PEN) and are coated, on the side facing towards the interior of the multilayered structure, by a transparent electrically conductive coating (generally a transparent conductive oxide, preferably a fluorine-doped tin oxide or an alloy of tin oxide and indium oxide, respectively FTO and ITO).
Between the two substrates one or more photoelectrochemical cells are arranged, electrically connected to one another in series and/or in parallel, each cell being made of a photo-electrode (the anode), arranged on the conductive coating of one of the two substrates; a counter-electrode (the cathode), arranged on the conductive coating of the other substrate; and an elecrolyte interpoed betweeen said photo-electrode and said counter-electrode. In particular, the photo-electrode is generally made up of a high band gap porous semi-conductive material, such as for example titanium oxide or zinc oxide, supporting the active material, made of a dye which is able to transfer electrons as a consequence of the absorption of a photon. The counter-electrode is generally made of platinum, whereas the electrolytic solution is generally based on iodine (I2) and litium iodide (LiI).
Photoelectrochemical cells of this kind are disclosed for example in U.S. Pat. No. 4,927,721; the materials that can be used in this kind of cells are disclosed for example in U.S. Pat. No. 5,350,644.
Because of their nature, the conductive coatings of the structures have high resistance. Moreover, single cells of this kind are not able to generate the level of tension required in most possible applications to which a photoelectrochemical cell can be dedicated.
To overcome these drawbacks it is therefore necessary to connect a plurality of photoelectrochemical cells in series, with the aim of generating higher differences of tension by minimizing the whole current, i.e. minimizing power losses due to the resistance of the conductive coatings.
Practically, a photo-electrochemical module is obtained over the same substrate, i.e. a plurality of side by side photoelectrochemical cells are made, connected in series by means of a connection integrated on the same substrate, made during the making of the module.
Connections in series integrated on the substrate can be made according to different schemes, known as Z connection, W connection and external connection).
Z type connections are made of a series of vertical contacts connecting to one another electrically insulated areas of the conductive coatings of both substrates, according to a configuration that will be explained in better detail in the description below.
W type connections are obtained with no need of contacts, but the configuration of the derived photoelectrochemical module tends to have internal power imbalances, because half of the cells within a module having this configuration is illuminated on the part of the counter electrode. Additionally, on the same substrate photo-electrode and counter-electrode alternate: titanium dioxide and platinum therefore, are deposited and sintered at the same time. This implies that it is impossibile to optimize singularly the sintering process of the two materials, normally having different optimal coking time and temperature (about 420° C. and 15 minutes for the platinum precursor (usually a solution and paste containing hexachloroplatinic acid); about 500° C. and 30 minutes for titanium dioxide).
As far as the external connection is concerned, on the contrary, the long path the electrons must pass through to exit from the sides of the module, where the connection of single cells occurs, limits the length of the cells (to avoid the addition of further losses due to resistances) and greatly influence the module fill factor, a characteristic parameter describing the ratio between the maximum power produced by the device and the product of the open circuit voltage for the current loop, and decreasing proportionally with the increasing of the resistance due to the connections between cells and the resistance of loss due to the long run of electrons.
With reference to
In particular,
Each cell is laterally limited by an incapsulant 16, the function of which is that of keeping the liquid electrolyte within the cell.
The connection in series between the two cells is obtained by jeans of the connecting element 17.
The connection path achieved through the vertical contact can be represented by three resistances: a first resistance constituted by the resistance of contact between the coating 11 arranged on the first substrate and the connecting element 17, a second resistance constituted by the resistance of the material of the connecting element 17 itself and a third resistance constituted by the resistance of contact between the connecting element 17 and the coating 11 arranged on the substrate 10 opposed to the first.
According to the prior art, the connecting element can be made through different technologies:
In all these cases, the deposition occurs by making a “track” of material on the support coating, in a position on the side of the lines of interruption of the conductive coating, so that, coupling the supports to make the photoelectrochemical module, the lines of interruption are slightly staggered between one another, allowing the conductive elements constituting the vertical contact to connect the coating of the insulated regions of opposed substrates to each other.
In case of deposition of a conductive paste on both supports and subsequent sintering before encapsulation, shown at
In the case of deposition of the conductive paste on a single support and sintering the same before encapsulation, conduction is caused because of a simple mechanical contact and the resistance between the coating of the substrate on which no paste was deposited and the connecting element is not negligible.
The so made connections additionally have problems of electrical conduction due to the increasing of the temperature. This is due to the different thermal behaviour between the material constituting the connecting element and the material of incapsulant 16 keeping the liquid electrolyte 15 inside the respective cells.
Additionally, connections of this kind have non optimal values of conductivity (i.e. the metal pastes have smaller conductivity than bulk metal), beside the problem of the deterioration of their performance while increasing temperature.
Additionally, connections of this kind are extremely visible(generally they are 0,5 mm large or more), with consequent obvious problems of visual impact and shading in a possible application as glass window structure.
In the light of the above, it is evident the need for a vertical electric connection of photoeledtrochemical cells allowing for improving performances of the vertical contact and increasing the reliability of the connection in response of thermal mechanical stresses, and further increasing the transparence having the contact thickness reduced down to the order of 50 μm.
In this context it is proposed the solution according to the present invention, with the aim of providing vertical contacts which are resistant to thermal and mechanical stresses and highly transparent.
These and other results are achieved according to the present invention by proposing a vertical electric connection of photoelectrochemical cells made with conductive wires the dimension of which is in the order of tenth of micrometers (up to hundreds of micrometers). In practice, in order to realise the vertical connection, a solid conductive body is rolled directly in the module. The problem of this kind of connection is its extreme sensibility to thermal extensions of the incapsulant (generally a thermoplastic or silicon).
The proposed solution aims at improving the performance of the device in response to thermal stresses, in this way masking the use of micrometric wires as vertical electrical connecting element functionally possible from an electric point of view in addition to, evidently an aesthaetical point of view. A purpose of the present invention is therefore that of realising a vertical electric connection of photoelectrochemical cells allowing for overcoming the limits of the solutions according to the prior art and di achieving the previously described technical results.
Further aim of the invention is that said connecting element can be produced with substantially low costs.
Not last aim of the invention is that of obtaining a connecting element being substantially simple, safe and reliable.
It is therefore a first specific object of the present invention a vertical electric connection of photoelectrochemical cells, of the kind made of a multilayered structure delimited by two substrates that are coated, on the side facing towards the other substrate, by a conductive coating, and comprising a plurality of photoelectrochemical cells delimited by one or more structures of incapsulant material, said vertical electric connection comprising a conductive wire arranged between said two substrates, electrically connecting the conductive coating of the two substrates, said conductive wire being arranged between said two substrates according to a zigzag configuration, the bends of which alternately touch first the conductive coating of a first substrate, then the conductive coating of the other substrate.
Moreover, according to the invention said conductive wire arranged between said two substrates according to a zigzag configuration is surrounded by said encapsulation structures.
Still according to the invention, said encapsulation structures are made partly on a first substrate and partly on the other substrate and are geometrically complementary to each other.
Always according to the present invention, said conductive wire is made of a material having preferably a resistivity lower than 8·10−5 Ohm·cm, una Tensile Strength Yield higher than 10 MPa (more preferably higher than 500 MPa), a Tensile Strength Ultimate higher than 100 MPa (more preferably higher than 700 MPa).
Finally, according to the invention, said conductive wire is preferably made of a material selected amongst: tungsten, aluminium alloys, inox steel alloys.
The present invention will be described in the following, for illustrative, non limitative purpose, according to some preferred embodiments, with reference in particular to the figures, of the enclosed drawings, wherein:
With reference to
In particular,
With reference to
Material which are particularly suitable for making the wire 31 are conductive materials (with a resistivity preferably lower than 6·10−6 Ohm·cm) having mechanical features making them suitable to resist the stresses to which they could be subjected as a consequence of the thermal dilatation of the incapsulant material or of the stress due to the process of sealing of the module. In particular, a suitable material should have characteristics of Tensile Strength Yield preferably upper than 10 MPa (and more preferably upper than 500 MPa) and characteristics of Tensile Strength Ultimate preferably upper than 100 MPa (and more preferably upper than 700 MPa).
Particularly suitable for producing the wire 31 made of a conductive material are: tungsten, aluminium alloys and inox steel alloys. Materials such as titanium, copper, gold, silver, aluminium and other metals and or alloys are also suitable.
Afterwards, as shown with reference to
From what was previously described, it is evident that the making of contacts is framed in the process of encapsulation of the module. The layout of the incapsulant is thus conceived and suitably designed, resulting to be necessarily different from the solutions according to the prior art.
With reference to the process of making the contact, the procedure provides for the application of complementary structures of incapsulant 21, 22 on the conductive coating 11 of both substrates 10. As already seen with reference to the description of
Subsequently, a conductive wire 31 is drawn from a coil on one of the two structures of incapsulant 21, 22. Then, the two substrates 10 are coupled together as a sandwich and the formed module is sealed by pressure and temperature. At this point, the wire 31 is cut by means of a device that, beside cutting, holds the end of the wire 31, keeping it ready for the subsequent application. This is made in parallel per each contact of the module.
The so realised structure is therefore completely enclosed in the incapsulant.
Making reference again to
As a practical example the production of DSSC modules is reported.
In particular, a module DSSC with cells arranged in series by means of Z-type vertical contacts was made with a wire of tungsten according to the embodiment of the present invention shown with reference to
In all cases, as incapsulant material a thermoplastic material (Dupont Surlyn 1702) was used having a thickness equal to 50 μm, whereas the used wires were made of tungsten, with a diameter equal to 50 μm, for the module made according to the present invention and tungsten, having a diameter equal to 50 μm, or made of gold, with a diameter equal to 50 μm, respectively for the two embodiments made, for comparative purposes, with a structure of incapsulant made according to the prior art.
In details, the steps of the process of making vertical contacts according to the present invention were the followings:
With reference to
With reference to
In this example it was chosen to realise a module giving preference to the aesthaetical impact with the criterium of uniformity rather than performance. Consequently, it is licit to expect performance can be surely improved, for example through the optimization of the cell geometry and the number of meanders of the connection. Nevertheless, modules realised according to the present invention reach anyway an efficiency of 3% on the active area (2.6% of the total area).
The electric performance of a prototype with a connection made with wires arranged as meanders according to the present invention is shown with reference to
As already said, the module made according to the present invention was further compared with two different modules respectively made with a wire of tungsten and with a gold wire and with a structure of incapsulant made in both cases according to the prior art, to put under evidence the thermal characteristic introduced by the proposed structure with respect to a standard encapsulation technique.
It is believed that the proposed ondulatory structure is much stronger, since the thermal expansion of the incapsulant helps the connection between conductive wire and conductive coating, which does not happen in the traditional structure.
In particular,
The present invention has been described for illustrative, non limitative purpose, according to its preferred embodiments, but it must be understood that variations and/or modifications can be made by the skilled in the art without escaping the relative scope of protection, as defined by the enclosed claims.
Number | Date | Country | Kind |
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RM2011A000040 | Jan 2011 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IT12/00030 | 1/31/2012 | WO | 00 | 10/10/2013 |