WO2013050373A1

WO2013050373A1 - Dye-sensitised solar cell module, component for a dye sensitised solar cell module and method of manufacturing the same

Info

Publication number: WO2013050373A1
Application number: PCT/EP2012/069472
Authority: WO
Inventors: Guang-Kai JENG; Greg John JACKSON; Gerard Bree; Mazhar Bari
Original assignee: Solarprint Ltd
Current assignee: Solarprint Ltd
Priority date: 2011-10-03
Filing date: 2012-10-02
Publication date: 2013-04-11
Anticipated expiration: 2014-04-03
Also published as: TW201324815A; GB201117112D0

Abstract

A dye-sensitised solar cell module comprises a first substrate, a second substrate and an electrical interconnect. The first substrate has for each of a plurality of dye-sensitised solar cells a first conductive region. The second substrate has for each of a plurality of dye- sensitised solar cells a second conductive region. The second substrate opposes the first substrate such that for each of said plurality of dye-sensitised solar cells said first conductive region at least partly overlaps only the second conductive region of that dye-sensitised solar cell. The electrical interconnect is between the first substrate and the second substrate. The electrical interconnect electrically connects the first conductive region of one of said plurality of dye-sensitised solar cells to the second conductive region of an adjacent dye- sensitised solar cell.

Description

DYE-SENSITISED SOLAR CELL MODULE, COMPONENT FOR A DYE-SENSITISED SOLAR CELL MODULE AND METHOD OF MANUFACTURING THE SAME

This invention relates to a dye-sensitised solar cell module, a component for a dye-sensitised solar cell module, a method of manufacturing a dye-sensitised solar cell module and a method of manufacturing a component for a dye-sensitised solar cell module.

In particular the invention covers device designs and structures for various applications of a dye sensitized solar cell (DSSC). There are four types of structure included in this invention. The first structure is a DSSC module consisting of series-connected cells operating optimally under high light intensity. The second structure is a DSSC module with series-connected cells operating optimally under low light intensity. The third structure is a DSSC module with parallel connected cells operating optimally under high light intensity. The fourth structure is a DSSC module with parallel connected cells operating optimally under low light intensity.

The principle of DSSC operation has been widely published and is accepted to be as drawn in Figure 1 . The key description of DSSC is given from published material below (Hagfeldt et al, Chem. Rev. 2010, 1 10, 6595-6663).

At the heart of the device is a mesoporous oxide layer composed of a network of metal oxide (for example Ti0₂) nano particles that have been sintered together to establish electronic conduction across the photoelectrode, also called the working electrode (WE). Typically, the film thickness is 10-15μηι and the nano particle size 10-30nm in diameter. The porosity is 50-60%. The mesoporous layer is deposited on a transparent conducting oxide (TCO) on a glass or other substrate. The most commonly used substrate is glass coated with fluorine-doped tin-oxide (FTO). Attached to the surface of the mesoporous oxide layer is a monolayer of the charge- transfer dye sensitizer. Photo-excitation of the dye sensitizer results in the injection of electrons into the conduction band of the oxide, and leaves the dye in its oxidized state. The dye is restored to its ground state by electron transfer from an electrolyte, which is typically an organic solvent containing the iodide/tri-iodide redox system. The regeneration of the sensitizer dye by iodide is therefore by intercepting the recapture of the conduction band electron. The I^3" ions formed by oxidation of Γ diffuse a short distance (<50 μηι) through the electrolyte to the cathode, also referred to as the counter electrode (CE). The CE is coated with a thin layer of platinum catalyst, where the regenerative cycle is completed by electron transfer to reduce I^3" to . The circuit is completed via the load applied externally between the CE and WE.

The potential generated under illumination corresponds to the difference between the Fermi level of the electron in the mesoporous layer and the redox potential of the electrolyte.

Therefore the open circuit voltage (V_oc) of a typical DSSC is a function of the metal oxide semiconductor Fermi level in its WE and the chemical potential of the electrolyte which contains the redox system of iodine and tri-iodide, as well as the concentration of the electrolyte. The maximum possible ν_∞ of DSSC containing Ti0₂ WE and an iodide/tri-iodide redox system in its electrolyte is approximately 0.9V. An exploded view of a typical DSSC device structure is depicted in Figure 2. The WE can be formed by printing the nano-porous metal oxide paste, for example Ti0₂, on FTO coated transparent conductive glass substrate. Doctor blade printing or screen printing are among the most common printing techniques. After Ti0₂ is printed, dried and sintered at approximately 500°C, the WE is then soaked in a dye bath which contains the dye sensitizer. Ruthenium based dye is commonly used. The CE is formed by depositing a thin layer of platinum as catalyst on FTO coated glass, by using vacuum sputtering, electro-plating , electro-less plating, or printing followed by sintering at approximately 450°C. The electrodes are then assembled and a fluid-tight barrier around the cells is formed using a sealant between the two electrode plates. UV curable sealant or thermoplastic films are commonly used as the sealing material. A controlled cell gap, which is the distance between the two electrodes, can be established by choosing a correct forming process of the sealing material. After the cell is assembled and sealed, electrolyte is then introduced into each cell void through a pre-drilled hole on the counter electrode glass substrate. After filling, the holes are then sealed.

Electrons can thus be regenerated via the sensitizer from the electrolyte iodide/tri-iodide redox system and supplied to the WE from the CE repeatedly. The device generates electrical power from light without suffering any permanent chemical transformation. To the external load, a DSSC behaves very similarly to other types of photovoltaics, giving a typical l-V curve shown as in Figure 3.

However DSSC photovoltaic has many unique characteristics. The output potential changes little across a very wide range of light intensity. Even at low light down to 200 lux, the ν_∞ remains as high as 0.5V, and remains at 0.45V even at 50 lux. Therefore proper design of DSSC cells and modules can enable an electronic device to charge and function properly under very dim light.

A series connection in a DSSC module made using common metal running across the cell gap will be destroyed by corrosion in a very short period of time. To circumvent this issue, a number of structures have been designed and some are disclosed in the following prior arts.

In one of the prior arts, (Fujikura patent US 2010/0078060 A1 ), a carbon material, working as the conductive bridge, is printed on the working electrode of a cell, which is connected to the counter electrode of the adjacent cell through an extension part which is also made of a carbon material. The said extension part links between two opposite electrodes of two separate cells in a vertical direction. Isolation of the cells is required at the FTO layer; this can be implemented by e.g., laser scribing. With this connection, a DSSC module of cells connected in series can be constructed. The advantage of the art is that carbon is robust to chemical corrosion and should survive well in the DSSC internal environment over its service life. Nevertheless, despite its corrosion resistance, carbon is not a good choice for DSSC interconnection. First, its electrical resistance is still considered high for many interconnect configurations. Second, since carbon is black in color it will absorb most of the spectrum of light within the cell, which will reduce the internal light scattering effect , a proven beneficial optical property within the DSSC related to cell efficiency.

It can be extremely difficult to process the second conducting member and the connecting member between the first conductor and the second conductor in patent US 2010/0078060 A1. Connecting the conducting member to the first conductor of the next cell only through a delicate piece of conducting member, to form a series interconnect, is extremely difficult. The gap between the photoelectrode and the second conducting member is very small, which is in the order of 50μηι or less. The width of the cell is in the order of 5-10 mm, which is 100-200 times larger. Supporting the second conducting member through the connecting piece from only one side in a cantilever fashion without shorting each other is very difficult and unreliable. Once the second conducting member is leaned toward the photoconductor, the cell will be short circuited and will not function. The reliability issue serious.

In another prior art, (US 2005/0236037 A1 ) a concept of DSSC module with the internal cells lying in alternating polarity is proposed. Each of the cells has the opposite polarity to the cell next to it. A series connected module can then be made in such an arrangement and it seems to be a good concept. Practically, there are some difficulties or disadvantages to make modules in such arrangement. First, the configuration requires that WE and CE materials are formed in alternating strips or other cell shape on both of the substrates. This requires the printing (or other deposition technique) and sintering of WE and CE materials on both sides. It is a double work compared to the regular type of cells. Second, to process WE and CE on the same substrate poses a high risk of cross-contamination inside the device. It is likely that local vaporization of CE material (such as Pt) during processing will cause contamination spoiling of the Ti0₂ on the WE, and vice versa from the WE to the CE.

Another prior art also deals with the same issues in a different way. A thick silver wall is printed to connect vertically between the cathode of one cell and the anode of the next cell, and also ensuring cells are isolated at the FTO layer on each electrode. In this disclosure, a similar concept to the first prior art is used; the silver wall is inserted to replace the carbon interconnect. Since it is expected that silver will be corroded by electrolyte, a compartment must be constructed for protection. This is made by creating a vertical wall made of glass frit, printed and sintered, either side of the silver wall. The glass frit walls act as a barrier to separate the silver from the electrolyte. A few drawbacks exist with this structure. First the inter-cell compartment takes up a significant space, which reduces the DSSC active area for light absorption and therefore limits the overall efficiency. Second, since the compartment creates a void, any tiny defect in the glass frit wall can cause the electrolyte to flood the silver, both damaging the interconnect and reducing the quantity of electrolyte in the cell. It is desirable therefore to provide a dye-sensitised solar cell module that is optimised to function at various light levels and for various purposes.

According to the invention, there is provided a dye-sensitised solar cell module comprising: a first substrate having for each of a plurality of dye-sensitised solar cells a first conductive region; a second substrate having for each of a plurality of dye-sensitised solar cells a second conductive region, wherein the second substrate opposes the first substrate such that for each of said plurality of dye-sensitised solar cells said first conductive region at least partly overlaps only the second conductive region of that dye-sensitised solar cell; and an electrical

interconnect that is between the first substrate and the second substrate and electrically connects the first conductive region of one of said plurality of dye-sensitised solar cells to the second conductive region of an adjacent dye-sensitised solar cell.

According to the invention, there is provided a component for a dye-sensitised solar cell module, the component comprising: a substrate having for each of a plurality of dye-sensitised solar cells a conductive region; and an electrical connector corresponding to each conductive region, wherein a part of the electrical connector is formed on the conductive region of the substrate and a part of the electrical connector is formed on the substrate outside of the conductive region. According to the invention, there is provided a method of manufacturing a component for a dye- sensitised solar cell module, the method comprising: providing a substrate having for each of a plurality of dye-sensitised solar cells a conductive region; and forming on the substrate an electrical connector corresponding to each conductive region such that a part of the electrical connector is formed on the conductive region of the substrate and a part of the electrical connector is formed on the substrate outside of the conductive region.

According to the invention, there is provided a method of manufacturing a dye-sensitised solar cell module, the method comprising: providing a first substrate having for each of a plurality of dye-sensitised solar cells a first conductive region; providing a second substrate having for each of a plurality of dye-sensitised solar cells a second conductive region; arranging the second substrate to oppose the first substrate such that for each of said plurality of dye-sensitised solar cells said first conductive region at least partly overlaps only the second conductive region of that dye-sensitised solar cell; and forming an electrical interconnect that is between the first substrate and the second substrate and electrically connects the first conductive region of one of said plurality of dye-sensitised solar cells to the second conductive region of an adjacent dye- sensitised solar cell.

The invention will now be described, by way of example only, with reference to the

accompanying drawings, in which:-

Figure 1 shows the working principle of a DSSC;

Figure 2 is an exploded view of a standard DSSC with the breakdown of its component layers; Figure 3 is a typical l-V curve of a single cell DSSC device. A typical cell delivers 0.7-0.75V open circuit voltage, with the output current proportional to the cell dimension;

Figure 4 shows the efficiency drop of a DSSC due to increasing series resistance under different light intensities; Figure 5 shows the electrical configuration of a series connected DSSC module in schematic. The output potential of the module is the product of the number of cells by the potential of the single cell, while the ideal output current is that of the single cell;

Figure 6 shows the series connected DSSC module optimized for high light intensity

applications. The top and side elevations are shown from cross section cut lines A-A and C-C respectively;

Figure 7 is magnified view of the circled part in Figure 6, showing one of the solder links between the silver pad of the cathode and anode of sequential cells;

Figure 8 is the anode-cathode pair of Figure 7 (solder link not shown in the figure) projected in isometric view;

Figure 9 is the series connected DSSC module optimized for low light intensity applications. The top and side elevations are shown from cross section cut lines A-A and C-C. The major difference from the design drawn in Figure 6 is the omission of the silver lines travelling vertically up the design; Figure 10 is magnified view of the circled part in Figure 9, showing one of the solder links between the silver pad of the cathode and anode of sequential cells;

Figure 1 1 is the anode-cathode pair of Figure 10 (solder link not shown in the figure) projected in isometric view;

Figure 12 shows the electrical configuration of a parallel connected DSSC module in schematic. The module output current is the product of the number of cells by the current of the single cell, while the ideal output potential is that of a single cell;

Figure 13 shows the parallel connected DSSC module optimized for high light intensity applications. The top and side elevations are shown from cross section cut lines A-A and C-C respectively; Figure 14 is the magnified view of the circled part in Figure 13;

Figure 15 shows the parallel connected DSSC module optimized for low light intensity applications. The top and side elevations are shown from cross section cut lines A-A and C-C respectively. The major difference from the design drawn in Figure 13 is the omission of the silver lines travelling vertically up the design; and Figure 16 is the magnified view of the circled part in Figure 15.

DSSC photovoltaic has many unique characteristics. The output potential changes little across a very wide range of light intensity. Even at low light down to 200 lux, the V_oc remains as high as 0.5V, and remains at 0.45V even at 50 lux. Therefore proper design of DSSC cells and modules can enable an electronic device to charge and function properly under very dim light.

Under AM1 .5g lighting conditions, a normal DSSC has an open circuit voltage of 0.7-0. 5V. AM1 .5g refers to a standardized illumination brightness and spectrum equivalent to "1 sun", which may be generated by a solar simulator containing xenon lamp. AM1.5g intensity is 1000 watt/m² or approximately 100,000 lux. Both AM1 .5g (watt/m²) and lux are familiar units used to express light intensity in two standard spectrums, and the scales will be used interchangeably in the following text for purpose of clarity and/or comparison. Other than AM1 .5g (assumed 100,000 lux), light intensities from 17000 lux down to 200 lux are created by using white LED for test purposes.

Figure 4 is a chart of DSSC cell conversion efficiency (performance) vs. series resistance across the cell under various lighting conditions, with the plots normalized to a typical low series resistance of 10Ω. The equation below explains the relationship between power and current flow through a DSSC (or indeed any electrical circuit) when it encounters series resistance:

Where P; represents power loss; / represents the current, which is the photocurrent generated through the conversion of light; and R is the series resistance. Therefore, following equation 1 , power (and therefore efficiency) loss is proportional to the series resistance and also proportional to the square of the photo-current. Photocurrent and series resistance are the two major factors affecting efficiency loss; though other types of current and resistance can exist in the DSSC circuit they are considered insignificant in comparison and not discussed any further here.

The photocurrent in a DSSC is proportional to light intensity. According to Eq. 1 , the device will encounter a high efficiency loss for a given series resistance in high light condition; therefore low series resistance is desirable to mitigate this loss. The higher the light intensity, the more the series resistance should be reduced to get optimal operation. Conversely, efficiency loss even for large series resistances under low light conditions becomes insignificant, and therefore low series resistance is not critical. Figure 4 shows that a cell with the series resistance below 50Ω experiences less than 5% performance drop loss up to 5000 lux light conditions. Whereas, the same cell encounters over 50% power loss when exposed to AM1.5g. Using this theoretical basis, cells and modules can be designed with different structures for different end applications, allowing reduction in the complexity of manufacturing costs giving possible economic and ecological benefits.

Series connected DSSC modules

Power from DSSC can be used for the charging of electronic devices, and is especially useful for wireless and portable equipment, for example mobile phones. For such applications, the DSSC module is preferably be in lightweight and small in size, as well as capable of providing the sufficient electrical power and voltage to meet the device requirements. Like most photovoltaics, a single-cell DSSC have a limited output potential, as stated previously 0.7-0.75V at AM1.5g, which is too low to drive most commercial electronic products. A mobile phone, for example, requires 3-5 volts to charge its battery. One solution is to use a DC-DC step-up converter (e.g., Linear Technology's LTC3108) to boost the potential output. However, this sacrifices output current and a significant portion of power is typically lost in conversion efficiency. An alternative solution is, of course, to use series-connected cells directly for voltage multiplication, the configuration of which for DSSC is shown in Figure 5. This is routinely implemented in conventional photovoltaic semiconductor modules. A semiconductor cell is made of a single piece of solid-state substrate, which has its cathode and anode reside on the opposite sides of the same substrate. In that case it is simple to link the topside of one cell to the underside of the next cell using such as a wire bond to make a series module. The situation in a DSSC is different. The CE and WE are built on two different substrates, and critically there is a liquid electrolyte in the cell-gap between the two electrodes. Furthermore that electrolyte is often corrosive to many groups of metals.

The present invention aims to address these issues with a simple design, resulting in higher reliability for the DSSC module over its service life.

As described herein, the present invention uses an approach that is different from the approach disclosed in US 2010/0078060 A1 . For example, in an embodiment, silver lines are printed and sintered onto one of the electrodes (e.g. the working electrode). These silver lines may be protected by printing glass frits or UV sealant on top of them followed by a sintering or curing process. The silver line is completely protected by the overcoat (glass frits or UV sealant) within the cell. The interconnections of the silver lines only happen outside the sealed part of the cells by extending the silver lines out of the sealant. Note the printed sealant to protect the silver lines is different from the sealant to seal the cells. With this design, the difficulties and challenges of delicate interconnections as well as the risk of cell failures can be avoided. Embodiment 1 , Series Connected DSSC Module for High Light Conditions

This structure is a configuration for a series connected DSSC module in high light conditions. Each substrate comprises a plurality of conductive regions, which may be formed of Fto, for example. FTO of 7-15 Ω/sq sheet resistance was used in our DSSC. FTO, the transparent conductive material on which the functional materials are printed (e.g., mesoporous Ti0₂ photo- electrode on WE, or Pt on CE), provides transparency to light and reasonable good electrical conductance between function electrodes and interconnects, is carefully scribed to isolate cells on the printed functional electrodes (WE or CE) and the Ti0₂ or Pt layers deposited within the a defined pattern. Electrical isolation is especially important between series connected cells because each of these cells may have a slightly different potential. FTO used anywhere in this invention can be replaced by other types of transparent conductive films such as ITO, AZO,

CNT or graphene-doped films or any transparent conductive films which are compatible with the device chemistry.

At least one electrical charge carrier is disposed (e.g. printed) on the substrate (e.g. FTO coated glass surface) along each cell for both WE and CE. The at least one electrical charge carrier may comprise flat, silver lines. They are dried and sintered and then protected by a protector, for example by printing glass frit paste, or alternatively, a UV curable sealant, over to completely cover them without creating any voids. Glass frit paste is dried and sintered in a high temperature oven between 400 and 550°C. If used instead, UV-curable sealant can be cured by cross linking using a UV lamp at room temperature with a power density of 50-1000 mW/cm². Silver has the lowest known resistance of all metals. It provides lower resistance than all other metals for a given cross section. When a single printed silver line is properly sintered, the series resistance can be as low as 0.01 Ω / cm, and, if necessary, it can be further reduced by increasing the line width, the line heights or by increasing the number of lines. Glass frit or UV- curable sealant protect the silver against electrolyte corrosion. For high light conditions, these lines are printed to create a low series-resistance path for charge carrying as an alternative to the FTO layer. A single line or dual line silver of 0.2-0.4mm wide and 10-15 microns in height is sufficient for most applications. It should be noticed that printed glass frit or UV curable sealant protection has a benefit over wall protection as described in one of the prior arts. The protected layer is printed directly and sealed in conformal contour the silver line surface and is mechanically integrated to the substrate. It has a strong resistance and robustness and therefore provides a very good protection against external impact. Our test results prove it survives in electrolyte over 1000 hours at 80°C in 85% relative humidity without any resistance increase.

The electrodes are then ready for assembly. The module is assembled by laminating the two electrodes together with a proper sealing and curing process, establishing a number of isolated cell voids. This can be carried out using hot-melt thermoplastic sealant (e.g., Surlyn^® provided by DuPont) or a UV curable sealant. The electrolyte is then introduced into each cell through a pre-drilled hole. The primary purpose of the seal is to confine the electrolyte within each cell, isolating it from the external environment for the length of the module's service life.

To achieve a series interconnects inside the DSSC module, a three dimensional connection circuit may be implemented, involving connection between two electrodes in two different planes (i.e in the 'z' direction to the 'x-y' plane of the electrode plates). The anode of one cell on one plane may be connected to the cathode of another cell which is located on another plane. This connection is duplicated for all adjacent anode-cathode pairs so that a multiplication of the cell potential to achieve the desired module potential can be obtained. An electrical connector, for example a silver lead from the anode extends itself to and aligns vertically with a lead from the cathode of the next cell, and vice versa. Two metal leads can then be joined together in vertical direction by an electrical conductor by, for example, a junction method such as soldering. The schematic drawing in Figure 6 shows the top view and two side views seeing from cross section cut in lines A-A and line C-C of this interconnection. The circled part on the upper left is magnified in Figure 7 for clarity, which shows the solder links between one of the cathodes and the anode next to it. For further clarity, the silver lead pair (without solder) is further projected in a three-dimensional view in Figure 8.

To create the solder junction, solder paste can be printed or dispensed and dried on the silver pad before assembly. Alternatively, solder balls, bumps or preforms can be picked and placed between the printed silver leads. The solder is then caused to reflow by heating the module at a moderate temperature. Depending the composition of solder, reflow temperature can range between 100°C and 270°C. A lower temperature solder is preferred to reduce the risk of damage to the cell. Alternatively, to avoid direct heating, the solder reflow can be achieved by IR lamp, LED or laser or inductive heating methods, optionally assisted by ultrasonic treatment. The same junction method between cathode-anode pairs is duplicated on every cathode-anode pair. Junction made by solder reflow is only one of the methods to achieve this electrical interconnect. An alternative junction method can be made by printing a thick silver pad on each side and subsequently bringing them into intimate contact in the lamination process during assembly, or alternatively by a mechanical clamping technique. In addition to silver, any of a large group of conductive materials such as copper, nickel, tin or carbon can be used for this interconnect pad. The pad can be made by any method from (and not limited to) screen- printing, electroplating or electro-less plating, sputtering or evaporation shadowed by a mask or followed by lithograph and patterning.

Embodiment 2, Series Connected DSSC Module for Low Light Intensity

Printing the silver lines along each cell and their protection layers should be practiced only when necessary. The process of printing the silver lines and its sintering followed by glass frit paste printing and sintering, or by UV sealant printing and curing is not only tedious but also time consuming, costly and labor intensive. The risk of a diminished yield is another general issue caused by complicated processing. Therefore, we simplify the process for series connected module dedicated to lower light application.

This is accomplished by subtracting the at least one electrical charge carrier parts on the cell section in embodiment 1. Since we have shown that the higher series resistance of the FTO layer is acceptable as a charge path under low light conditions, it is acceptable to remove this component. With the subtraction of the silver lines, the protective layer, (glass frit or UV curable resin) and many drying, sintering and curing processes are completely removed from the previous embodiment. The silver extensions (leads) and interconnect pad are the only printed metal parts at both ends of the cells. These are required to assure low contact resistance to the FTO and good interconnection between cells. The schematic drawing in Figure 9 shows the top view and two side views seeing from cross section cut in lines A-A and line C-C of this interconnection. The circled part on the upper left is magnified in Figure 10 for clarity, which shows the solder links between one of the cathodes and the anode next to it. For further clarity, the silver pair (without solder) is further projected in a three-dimensional view in Figure 1 1 . This interconnection can be further simplified wherein even the printing of the silver leads is not required. By directly printing solder paste, or placing the solid phase solder preform between the FTO layers, then initiating reflow by direct heat, or alternatively locally heated by IR LED or laser, or by inductive heating and optionally assisted by ultrasonic methods, the interconnection can be established.

Compared to embodiment 1 , this structure simplifies the manufacturing steps and reduces material usage. Also, since a metal line is completely opaque and completely blocks all the light, and glass frit and UV curable sealant are also partially opaque and block a large part of the light, therefore, when metal lines are required on the working electrode, a significant amount of incoming light will be blocked. By removing them, extra space is created on the electrode plane, allowing the proportion of active to inactive area for light absorption to be increased on the DSSC module. The overall module efficiency can thereby be increased. Additionally, subtraction of the metal lines can not only reduce the number of processing steps but also reduces the risk of corrosion defects, improving the production yield rate.

This design is especially useful for very dim to medium light conditions, for example indoor light harvesting for wireless sensor applications. The available light intensity to drive a simple indoor sensor can be as low as 50 lux. Under such conditions, a single cell of a DSSC module, cell dimensions 60 mm x 10 mm, will produce typically 0.45V V_oc and 0.055 mA short circuit current. By removing the silver line within the cell, the series resistance, which is essentially equivalent to the series resistance of the FTO coated glass, is around 50Ω. At this low light environment, voltage drop due to series resistance is only 0.055mA * 50Ω, which is approximately 2.75 mV. At 0.45V, this results in only 0.6% loss. When the light intensity increases to 1000 lux, V_oc increases to 0.56 V and the short circuit current increases to 0.11 mA. In this condition, the voltage drop due to series resistance is around 5.5 mV; from the output voltage of 0.56V, this is still under 1.0%. With this verified data, we conclude that cells without the silver lines can be used from very dim light (i.e. 50 lux) to medium light condition, i.e. 25 % of the standard AM1.5G intensity, which is roughly 25000 lux. Still, less than 20% power drop compared to the embodiment 1 structure is expected in this intermediate light intensity. This power loss is compensated for by the increased absorption area created by the removal of the opaque and translucent areas of metal lines and their protective layers. Often the performance benefit due to additional absorption area is higher than the disadvantage of the series resistance power drop.

The remainder of the constructional features of the series-connected cell for low light conditions may independently be identical to that in embodiment 1.

Parallel Connected DSSC Modules As described above, small, series-connected DSSC modules find good application in charging portable devices and wireless sensors. However, not all applications require a high output voltage from a small single module. Where space is not a critical issue, internal series interconnection is not required. Instead, series connections for potential multiplication can be made between modules rather than cells. Applications such as (and not limited to) BIPV or solar roofs for automobiles fall into this category. A parallel module of electrical configuration shown in Figure 12 is preferred to a series-connected module as it reduces the complexity of manufacturing, maximizing yield and allowing room to maximize module efficiency. The following two structures described are parallel-connected module designs for the above mentioned applications.

Embodiment 3: Parallel connected module for high light conditions

A parallel connected DSSC module for high light intensity applications is described in this embodiment. As with embodiment 1 , after the Ti0₂ and Pt layers are deposited within the scribed FTO, flat, silver lines are printed onto the FTO coated glass substrate for both WE and CE. They are dried and sintered and then protected by printing glass frit paste, or alternatively, a UV curable sealant, over to completely cover them without creating any voids. Glass frit paste is dried and sintered in a high temperature oven between 400 and 550°C. If used instead, UV- curable sealant can be cured by cross linking using a UV lamp at room temperature with a power density of 50-1000 mW/cm². The electrodes are then ready for assembly. As with embodiment 1 and 2, the module is assembled by laminating two electrodes together using a proper sealing and curing process., with thermoplastic sealant (e.g., Surlyn ^® provided by DuPont) or a UV curable sealant. Figure 13 shows the top view and two side views of this embodiment. One is the cross section viewed from line A-A; the other is from line C-C. The circled part on upper left corner is magnified as shown in Figure 14, where silver leads on each anode and cathode pair as well as the substrate spacing are indicated.

As in embodiment 1 , the silver lines are present to reduce the cell series resistance by providing an alternative, low resistance path to the FTO. Glass frit or UV-curable sealant protects the silver against electrolyte corrosion. For high light conditions, a single line or dual line silver of 0.2-0.4mm wide and 10-15 microns in height is sufficient for most applications. It is also important to note that for parallel cells DSSC, the number of cells on the module is not critical, because the multiplication of voltage is not required. Therefore, within a fixed area, the number of cells and the geometry of each cell can be tailored to maximize the total power output and therefore increase the overall module efficiency. This can be realized by simultaneously reducing the number of the cells and by increasing the cell width to the limits allowed by the production process. By doing so, the proportion of active to inactive area can be increased as the number of spaces between the cells is reduced.

Finally, by printing a horizontal silver strip across the common electrode leads from each cell, a module of optimized output can be produced. Embodiment 4: Parallel interconnected module for low light condition

A design for a parallel connected DSSC module for low light intensity applications is disclosed in this embodiment. Since we have shown that the higher series resistance of the FTO layer is acceptable as a charge path under low light conditions, it is acceptable to remove this component. With the subtraction of the silver lines, the protective layer, (glass frit or UV curable resin) and many drying, sintering and curing processes are completely removed from the previous embodiment. The silver extensions (leads) and interconnect pad are the only printed metal parts at both ends of the cells. These are required to assure low contact resistance to the FTO and good interconnection between cells. The schematic drawing in Figure 15 shows the top view and two side views seeing from cross section cut in lines A-A and line C-C of this interconnection. The circled part on upper left corner is magnified as shown in Figure 16, where silver leads on each anode and cathode pair as well as the substrate spacing are indicated.

Compared to embodiment 3, this structure simplifies the manufacturing steps and reduces material usage. Also, since a metal line is completely opaque and completely blocks all the light, and glass frit and UV curable sealant are also partially opaque and block a large part of the light, therefore, when metal lines are required on the working electrode, a significant amount of incoming light will be blocked. By removing them, extra space is created on the electrode plane, allowing the proportion of active to inactive area for light absorption to be increased on the DSSC module. The overall module efficiency can thereby be increased. Additionally, subtraction of the metal lines can not only reduce the number of processing steps but also reduces the risk of corrosion defects, improving the production yield rate. With the silver lines removed, this parallel-module is useful from very dim light (i.e. 50 lux) to medium light condition, i.e. 25 % of the standard AM1.5G intensity, which is roughly 25000 lux. Still, less than 20% power drop compared to the embodiment 3 structure is expected in this intermediate light intensity. This power loss is compensated for by the increased absorption area created by the removal of the opaque and translucent areas of metal lines and their protective layers. Often the performance benefit due to additional absorption area is higher than the disadvantage of the series resistance power drop.

As with embodiment 3, the number of cells on the module is not critical, because the multiplication of voltage is not required. Therefore, within a fixed area, the number of cells and the geometry of each cell can be tailored to maximize the total power output and therefore increase the overall module efficiency. This can be realized by simultaneously reducing the number of the cells and by increasing the cell width to the limits allowed by the production process. By doing so, the proportion of active to inactive area can be increased as the number of spaces between the cells is reduced. Finally, by printing a horizontal silver strip across the common electrodes on each cell, a module of optimized output can be produced.

Claims

1. A dye-sensitised solar cell module comprising:

a first substrate having for each of a plurality of dye-sensitised solar cells a first conductive region;

a second substrate having for each of a plurality of dye-sensitised solar cells a second conductive region, wherein the second substrate opposes the first substrate such that for each of said plurality of dye-sensitised solar cells said first conductive region at least partly overlaps only the second conductive region of that dye-sensitised solar cell; and

an electrical interconnect that is between the first substrate and the second substrate and electrically connects the first conductive region of one of said plurality of dye-sensitised solar cells to the second conductive region of an adjacent dye-sensitised solar cell.

2. The dye-sensitised solar cell module of claim 1 , comprising a plurality of said electrical interconnect such that at least three of said plurality of dye-sensitised solar cells are connected in series.

3. The dye-sensitised solar cell module of any of claims 1 to 2, wherein each dye- sensitised solar cell comprises an electrolyte between the two substrates, wherein the electrical interconnect is isolated from the electrolyte.

4. The dye-sensitised solar cell module of any preceding claim, further comprising a

sealing member that isolates each dye-sensitised solar cell from any neighbouring dye- sensitised solar cell, wherein at least a part of the electrical interconnect is isolated by the sealing member from the electrolyte of each of the two dye-sensitised solar cells that it directly electrically connects.

5. The dye-sensitised solar cell module of any preceding claim, wherein the electrical interconnect is formed from a material that has an electrical resistivity of less than about 1 x 10^"6 Ω-m at 20 °C, and optionally less than about 5 x 10^"7 Ω-m at 20 °C.

6. The dye-sensitised solar cell module of any preceding claim, wherein the electrical interconnect is integral to the dye-sensitised solar cell module.

7. The dye-sensitised solar cell module of any preceding claim, wherein each dye- sensitised solar cell is elongate and the electrical interconnect is disposed outside of an elongate end of the dye-sensitised solar cells.

8. The dye-sensitised solar cell module of any preceding claim, wherein the first conductive region and the second conductive region are formed from a transparent conducting film.

9. The dye-sensitised solar cell module of any preceding claim, comprising:

a working electrode printed on the first conductive region; and

a counter electrode printed on the second conductive region.

10. A component for a dye-sensitised solar cell module, the component comprising:

a substrate having for each of a plurality of dye-sensitised solar cells a conductive region; and

an electrical connector corresponding to each conductive region, wherein a part of the electrical connector is formed on the conductive region of the substrate and a part of the electrical connector is formed on the substrate outside of the conductive region.

1 1 . The component of claim 10, further comprising at least one electrical charge carrier for each conductive region, wherein the electrical charge carrier is formed wholly on the conductive region of the substrate and extends along substantially the whole length of the conductive region.

12. The component of claim 10 or 1 1 , wherein the at least one electrical charge carrier in total cover less than about 20% of the conductive region, and optionally less than about 10% of the conductive region.

13. The component of any of claims 10 to 12, wherein the electrical connector and the at least one electrical charge carrier are parts of a unitary piece of conductive material.

14. The component of any of claims 1 1 to 13, further comprising a protector that covers substantially all of the at least one electrical charge carrier, wherein the protector is resistant to corrosion by an electrolyte of the dye-sensitised solar cell.

15. The component of any of claims 10 to 14, wherein the conductive region is formed from a transparent conducting film.

16. The component of any of claims 10 to 15, comprising a working electrode or a counter electrode printed on the conductive region.

17. The component of any of claims 10 to 16, wherein the electrical connectors are

electrically connected to each other.

18. A pair of components for a dye-sensitised solar cell module, the pair of components comprising:

a first component as claimed in any of claims 10 to 16; and

a second component as claimed in any of claims 10 to 16;

wherein the pair of components are arranged such that when the first component opposes the second component, each conductive region of the first component matches an opposing conductive region of the second component, and each electrical connector of the first component partly overlaps a paired electrical connector of the second component corresponding to an adjacent opposing conductive region.

19. A dye-sensitised solar cell module comprising:

two of said component as claimed in any of claims 10 to 17; or

the pair of components as claimed in claim 18.

20. The dye-sensitised solar cell module of claim 19, wherein the dye-sensitised solar cells are connected in parallel.

21 . A dye-sensitised solar cell module comprising the pair of components as claimed in claim 18, wherein the dye-sensitised solar cells are connected in series.

22. The dye-sensitised solar cell module of claim 21 , further comprising an electrical conductor that electrically connects said electrical connector to said paired electrical connector.

23. The dye-sensitised solar cell module of any of claims 19 to 22, wherein each dye- sensitised solar cell comprises an electrolyte between the two substrates, wherein the electrical connector is isolated from the electrolyte.

24. The dye-sensitised solar cell module of any of claims 19 to 23, further comprising a sealing member that isolates each dye-sensitised solar cell from any neighbouring dye- sensitised solar cell, wherein at least a part of the electrical connector is isolated by the sealing member from the electrolyte of each of the two dye-sensitised solar cells that it directly electrically connects.

25. The dye-sensitised solar cell module of any of claims 19 to 24, wherein the electrical connector is formed from a material that has an electrical resistivity of less than about 1 x 10^"6 Ω-m at 20 °C, and optionally less than about 5 x 10^"7 Ω-m at 20 °C.

26. The dye-sensitised solar cell module of any of claims 19 to 25, wherein the electrical connector is integral to the dye-sensitised solar cell module.

27. The dye-sensitised solar cell module of any of claims 19 to 26, wherein each dye- sensitised solar cell is elongate and the electrical connector is disposed outside of an elongate end of the dye-sensitised solar cells.

28. A method of manufacturing a component for a dye-sensitised solar cell module, the method comprising:

providing a substrate having for each of a plurality of dye-sensitised solar cells a conductive region; and

forming on the substrate an electrical connector corresponding to each conductive region such that a part of the electrical connector is formed on the conductive region of the substrate and a part of the electrical connector is formed on the substrate outside of the conductive region.

29. The method of claim 28, further comprising forming on the substrate at least one electrical charge carrier for each conductive region such that the electrical charge carrier is formed wholly on the conductive region of the substrate and extends along

substantially the whole length of the conductive region.

30. The method of claim 29, further comprising forming on the substrate a protector that covers substantially all of the at least one electrical charge carrier, wherein the protector is resistant to corrosion by an electrolyte of the dye-sensitised solar cell.

31 . A method of manufacturing a dye-sensitised solar cell module, the method comprising:

providing two of said component as claimed in any of claims 10 to 16; and arranging the two components such that they oppose each other and such that each conductive region of the first component matches an opposing conductive region of the second component, and each electrical connector of the first component partly overlaps a paired electrical connector of the second component corresponding to an adjacent opposing conductive region.

32. The method of claim 31 , further comprising electrically connecting said electrical

connector to said paired electrical connector.

33. The method of claim 32, wherein said electrical connector is connected to said paired electrical connector by:

providing a conductive material on said electrical connector before said arranging; and

heating the conductive material after said arranging so as to at least partially melt the conductive material, thereby forming the electrical connection.

34. A method of manufacturing a dye-sensitised solar cell module, the method comprising:

providing a first substrate having for each of a plurality of dye-sensitised solar cells a first conductive region;

providing a second substrate having for each of a plurality of dye-sensitised solar cells a second conductive region;

arranging the second substrate to oppose the first substrate such that for each of said plurality of dye-sensitised solar cells said first conductive region at least partly overlaps only the second conductive region of that dye-sensitised solar cell; and forming an electrical interconnect that is between the first substrate and the second substrate and electrically connects the first conductive region of one of said plurality of dye-sensitised solar cells to the second conductive region of an adjacent dye- sensitised solar cell.

35. The method of claim 34, wherein said forming comprises: