Fabrication of Monolithic Dye-Sensitized Solar Cell Using Ionic Liquid Electrolyte
To improve the durability of dye-sensitized solar cells (DSCs), monolithic DSCs with ionic liquid electrolyte were studied. Deposited by screen printing, a carbon layer was successfully fabricated that did not crack or peel when annealing was employed beforehand. Optimized electrodes exhibited photovoltaic characteristics of 0.608 V open-circuit voltage, 6.90 cm −2 mA short-circuit current, and 0.491 fill factor, yielding 2.06% power conversion efficiency. The monolithic DSC using ionic liquid electrolyte was thermally durable and operated stably for 1000 h at 80°C.
Introduction
To meet the demand for renewable cost-effective energy sources, dye-sensitized solar cells (DSCs), which can be fabricated from low-cost materials (TiO2, dye, etc.) by nonvacuum printing, have attracted attention in academic and industrial research [1–4]. DSCs are normally fabricated by sandwiching TiO2 and Pt counter electrodes. F-doped tin oxide (FTO) glass substrates for these electrodes account for 80% of DSC-fabrication cost. Additionally, Pt used in the counter electrode is also expensive. Hence, to realize further cost reductions, the use of FTO glass and Pt should be minimized. Toward this end, monolithic DSCs have been fabricated on a single FTO glass substrate with a porous carbon counter electrode (Figure 1) [5–12]. A porous carbon layer and a porous ZrO2 layer are set on dyed porous TiO2 layer for the monolithic DSC. The porous ZrO2 layer has two functions: a function as transportation of electrolyte to dyed porous TiO2 layer and a function as spacing insulator to separate dyed TiO2 layer and carbon layer electrically. There are three roles in the porous carbon layer: (1) the catalyst to reduce I3 − to I − for the photocurrent flow; (2) the electrical current corrector to external circuits; (3) the transportation of electrolyte to dyed-porous TiO2 and porous ZrO2. By means of capillary force within nanoholes, monolithic porous electrodes prevent electrolyte leakage. Through the use of such porous electrodes, highly durable DSCs are expected.
In research on durable DSCs, industrial applications are now being emphasized. Volatility of the DSC electrolyte has been a major problem because the interface temperature of the cell rises considerably in sunlight. To address the problem of thermal instability, the electrolyte should be nonvolatile and solvent-free, which are notable properties of ionic liquids. Accordingly, ionic liquids have been investigated for use as the electrolyte in DSCs in order to enhance their durability [13–15].
In this paper, we report a screen-printing method for fabricating porous carbon electrodes that do not crack or peel off in monolithic DSCs. In particular, we focused on carbon-paste preparation. Finally, ionic liquid electrolyte was used to prepare thermally durable monolithic DSCs that operated stably for 1000 h at 80°C.
Experiments
The process for fabricating carbon paste is presented in Figure 2. Carbon powder and TiO2 powder (P25; Degussa, Germany) were ground in a mortar. The carbon powder was a mixture of Printex L (Degussa) and graphite (Aldrich, Germany) or a mixture of Printex L and active carbon (Degussa, Germany). The total weight of carbon powder was 6 g. Water (10 mL) and ethanol (20 mL) were added to the mortar containing the powder mixture, which was further ground. This mixture was transferred from the mortar to a beaker with an additional 100 mL portion of ethanol. Then, the mixture was agitated with a magnetic stir bar for 1 min and an ultrasonic homogenizer (Vibra Cell 72408 Bioblock Scientific, USA) for 2 min. α-Terpineol (20 g, Tokyo Chemical Industry Co., Ltd., Japan) was added to the carbon dispersion and agitated with a magnetic stir bar for 1 min and an ultrasonic homogenizer for 2 min. Ethyl cellulose solution in ethanol (10 wt%, 30 g) was added to the carbon solution and agitated with a magnetic stir bar for 1 min and an ultrasonic homogenizer for 2 min. The ethyl cellulose solution was prepared beforehand by adding equivalent amounts of two ethyl cellulose powders in ethanol (5 wt% of ethyl cellulose no. 46080 and 5 wt% of ethyl cellulose no. 86480, Tokyo Chemical Industries, Co., Ltd., Japan). Removal of water and ethanol by evaporation at 40°C and 125 m bar afforded the carbon paste.
To fabricate monolithic electrodes, FTO glass plates (TEC-15, Nippon Sheet Glass Co., Ltd., Japan) were utilized. The FTO layer was divided into two parts by etching with Zn and HCl (see Figure 1). The etched FTO glass plates were washed with glass-cleaning detergent in an ultrasonic bath for 15 min. The substrates were then rinsed with water and ethanol. Subsequently, the surface of substrate was cleaned in a UV-O3 system for 18 min. Two types of TiO2 pastes—PST-30NRD and PST-400C (JGC-CCIC Co., Ltd., Japan)—were deposited by screen printing on one of the FTO layers (Figure 1) as a transparent nanocrystalline—TiO2 layer (10 μm thick) and a light-scattering layer (4 μm thick), respectively. The resulting TiO2 electrodes had a double-layered structure [16]. The substrate was sintered on a hotplate at 500°C for 2 h. When the substrate was cooled, ZrO2 paste was printed on the TiO2 layer to be 30 μm thick and to cover the porous TiO2 layer. The ZrO2 paste was dried on the hotplate at 125°C. The ZrO2 paste was prepared according to a published procedure [17] using ZrO2 nanoparticles (
= 40–50 nm; Fulka, USA). The substrate was heated on the hotplate at 200°C at 1 h. When the substrate cooled, carbon paste was printed on the ZrO2 layer to form a layer with thickness of 130 μm. At the same time, the carbon layer was connected to the other FTO layer and sintered at 400°C (Figure 1). The fabricated electrodes were immersed in dye solution (0.3 mM in acetonitrile and t-butyl alcohol; Z907 Ru-dye, Solaronix SA) and kept at room temperature for 12 h [18].
The dye-coated electrodes were rinsed with acetonitrile and combined with glass plates by heating a hot-melt glue film at 250°C for 1 min (150 μm thick; Bynel 4164, DuPont, USA). A drop of the electrolyte solution was placed into a hole drilled into the glass of the assembled cell and driven into the cell by vacuum backfilling. Finally, the hole was sealed using additional Bynel film and a glass cover slip (0.1 mm thick). The electrolyte was composed of 0.2 M I2, 0.5 M N-methylbenzimidazole, and 0.1 M guanidinium thiocyanate in PMII and EMIB(CN)4 (13 : 7 v/v), which has been used in highly durability DSCs [18, 19].
Photovoltaic measurements employed an AM 1.5 solar simulator. The power of the simulated light was calibrated to be 100 mW cm −2 by using a reference Si photodiode equipped with an IR-cutoff filter (BS-520, Bunkou-Keiki Co., Ltd., Japan) to limit mismatch in the region of 350–750 nm between the simulated light and AM1.5 to less than 2% [20, 21]. I-V curves were obtained by applying an external bias to the cell and measuring the generated photocurrent with a digital source meter (6240A, ADCMT, Japan). The thermal durability test was performed by keeping DSCs in oven at 80°C. The sheet resistances (four-point probe method), the X-day diffraction patterns, and the electrical impedance spectra were measured using Loresta-EP MCP-T360 (Mitsubishi Chemical Analytech Co., Ltd., Japan), MiniFlex II (Rigaku Co., Ltd., Japan), and SP-150 (Bio-Logic, France), respectively. The impedance spectra were analyzed using software (Z-view 2).
Results and Discussion
In past work, to prepare porous carbon counter electrodes for DSCs, colloidal amorphous TiO2 particles have been added as a binder for carbon particles [22]. In the present study, however, gas-synthesized TiO2 nanopowder (80% anatase/20% rutile, P25; Degussa) was added to carbon pastes instead of colloidal amorphous TiO2. When we used colloidal amorphous TiO2 nanoparticles to fabricate thicker porous carbon layers for monolithic DSCs, the annealed carbon layer easily cracked and peeled off the substrate, likely caused by crystallization and shrinkage of the amorphous TiO2 nanoparticles. On the other hand, the gas-synthesized TiO2 nanopowder gave a thicker (100 μm), more stable porous carbon layer that did not crack or peel, because the gas-synthesized TiO2 nanopowder does not undergo further crystallization and shrinkage.
To optimize the conductivity of the porous carbon layer, the ratio of amorphous nanocarbon (Printex L) to graphite or the ratio of amorphous nanocarbon (Printex L) to active carbon was varied. A carbon layer of 13-14 μm in thickness was fabricated on the glass plate by the doctor blade method. The sheet resistance was measured by four-point probe method (Figure 3). The sheet resistance of amorphous nanocarbon (Printex L) layer was increased by adding the active carbon. In contrast, the sheet resistance of amorphous nanocarbon (Printex L) layer was decreased by adding the graphite, reaching a minimum of 90 Ω/□ at 40% amorphous nanocarbon in graphite (2.4 g amorphous nanocarbon (Printex L) and 3 g graphite). For the experiments below, carbon paste with this mixing ratio was used.
Introduction: How to Build Use a Dye-Sensitized Solar Cell (DSSC) a Discussion on Energy Efficiency
Harnessing renewable energy sources is crucial for supporting the energy demands of modern society. The IEA calculated that global energy usage increased by 10% from 1990 to 2008, and the number is expected to rise in the coming decades. At the same time, our currently predominant sources of energy pose serious threats to the environment and human health. The burning of fossil fuels—natural gas, coal, and oil—releases harmful greenhouse gases into the atmosphere, contributes to ocean acidification, and creates pollution with both economic and social costs.
Solar power is a particularly promising solution to the world’s energy needs. The Earth annually absorbs nearly 4 million exajoules of solar energy, and it would require less than an hour of this total energy to power mankind for an entire year. There are many technologies to capture and convert the sun’s energy. My research team has been experimenting with DSSCs: dye-sensitized solar cells. They differ from traditional photovoltaic (PV) cells that currently dominate the solar cell market, and DSSCs have their own advantages and disadvantages. The tradeoffs will be discussed later in this guide. (View the ground-breaking Smestad and Grätzel paper Demonstrating Electron Transfer Nanotechnology: A Natural Dye-Sensitized Nano-Crystalline Energy Converter to learn more about the technology).
I will be explaining how dye-sensitized solar cells are assembled, and how they can power an electronic gadget-in this case, a calculator.
Step 1: Gather Your Materials
Here are the necessary materials for this project:. Fluoride-doped tin dioxide conductive glass (≥2 plates) source of organic dye (ex: raspberries). Titanium Dioxide Paste. Acetic Acid. Water. Glass Stirring Rod. Scotch Tape. Graphite Pencil. Liquid Electrolyte Solution. Binder Clips. Wires. A Solar-powered Calculator (You will be removing the stock PV solar cell and replace it with your assembled DSSC). Soldering Equipment. A Multimeter or Vernier Lab Quest (with Voltage Current Probe(s)). Tungsten Halogen Lamp. Testing Apparatus
Step 2: Prepare the DSSC Electrodes
For every solar cell you assemble, you will need an anode and a cathode. The anode will contain the dye and titanium dioxide molecules. Photons will excite the dye molecules’ electrons, and the electrons will jump from the dye molecule to the titanium dioxide to the glass anode through diffusion. The electrons will subsequently travel through a circuit that connects the two electrodes and return to the cell through the glass cathode. To complete the circuit, an interstitial electrolyte solution facilitates the flow of electrons back to the anode’s organic dye molecules.
So, to assemble your anode, you must: 1) Prepare a titanium dioxide solution
Slowly add 20mL of an acetic acid solution (0.1675 mL CH3COOH per 99.8225 mL water) to 12g of titanium dioxide powder. Slowly adding the acid, in addition to vigorously mixing the solution, will ensure a uniform paste. It is recommended that you use a mortar and pestle for this step. (Figures 4 5)
2) Anneal titanium dioxide to your first glass plate
Cover each of the FTO glass plate’s four edges with a 2mm-thick piece of scotch tape (on the conductive side, as determined by a multimeter). This will create an ultra-thin bowl that will be filled with the titanium dioxide solution. Apply three drops of the TiO2 solution to your electrode, and spread evenly and gently with a glass stirring rod. (Figures 3 6)
Anneal the glass plate with an oven (or other heat source) at 450C for 30 minutes. (Figure 7)
3) Soak the annealed electrode in your dye solution
Create a solution that contains dye molecules. This is done most easily with the juice from frozen raspberries (which can easily be purchased in the frozen foods section of a supermarket). The organic dye solution can be purified through filtration methods (Note, however, my research team used very basic methods. We pulverized frozen raspberries into a juice with a mortar and pestle. Afterwards, we squeezed this solution through a cheesecloth, and this process removed the largest pieces of pulp.) Regardless, soak the annealed electrode in your dye solution for ten minutes. (You should notice by then end of this period that the color of your glass plate has changed as dye molecules covalently bonded to the TiO2. This is the process known as sensitization. You should also be aware that other dye solutions might require soaking for different lengths of time) Gently rinse off the glass plate with water once and ethanol twice so that remaining pulp and sugars are removed. (Figures 8, 9, and 10)
As for your cathode: 1) Cover one side of the glass surface with a carbon film (using the graphite pencil).
This process is rather self-explanatory. Just make sure that you are applying a complete coating of graphite to the plate. This may take time depending on your pencil. (Figure 11)
2) Optional: Anneal the cathode in an oven at 450C for a few minutes.
3) Gently rinse the cathode with ethanol.
Step 3: Assemble Your Solar Cell
Awesome! With an anode and a cathode, you’ve almost finished constructing the DSSC.
To assemble this DSSC, place the carbon-coated side of your cathode on top of the dye-coated side of your anode. Do not allow your glass plates to overlap completely, offset the electrodes so that they fully line up horizontally but extend beyond each other’s vertical ends. The offset will allow alligator wires to clip into each of the electrodes, thus allowing you to assemble a circuit. Secure your offset glass plates with binder clips on the two horizontal sides that line up completely. (Figure 13)
To insert the electrolyte solution between the two electrodes, apply the electrolyte liquid along an offset edge in between the two glass plates. Then, open and close the binder clips in an alternating fashion (one binder clip at a time, not both). This will cause the electrolyte solution to be sucked up into the cell and be distributed evenly among the graphite coating and TiO2/anthocyanin complex. (Figure 12)
Step 4: Test Your Solar Cell
Connect your assembled DSSC to a multimeter via alligator clips and wires. After the assembled circuit is complete, place your cell under an indoor light source-or along a windowsill. (Warning: Placing your solar cell directly under the sun without the proper protection will cause severe degradation. Do initial testing under light sources that do not emit UV radiation). Record the maximum voltage and current produced by your solar cell. Multiply these two figures to obtain the power output.
Power is simply the voltage potential multiplied by the current. So, for example, if my DSSC produced 0.400 Volts and 250 microamps (0.000250A), the power output would be 0.1 milliwatt (0.0001 watt).
Step 5: Modify Your Calculator
The utility of an assembled solar cell is found through powering electronic devices, with energy that has either been produced in real-time or previously stored. I will demonstrate how I powered a calculator with the cells that I produced. However, with some customization, you could power a cornucopia of electronic devices. Charging (rechargeable) batteries could be extremely useful. If you wish to follow along my guide, try powering a calculator for now.
It is preferable to find a calculator that is already solar-powered, for it will have the existing circuitry that will allow it to be easily powered with your DSSC. Remove the external casing with the necessary tools so that you may have access to the internal circuitry. Solder off the wires that connect the calculator’s built in solar cell to the circuit board and solder in two new wires that will connect to your DSSC.
(If needed, view this useful tutorial for information on soldering)
Before connecting the two new wires to the DSSC, connect the calculator to a variable power supply. Determine the minimum voltage and current needed to power the calculator, and ensure that these demands can be satisfied by your solar cells. If not, consider producing more solar cells. Connecting multiple DSSCs in series would boost the voltage, while connect them in parallel will boost the current. If these methods still prove insufficient, you could charge batteries or capacitors with your DSSC(s), and then power your calculator with the stored energy.
View the circuit I created to power a calculator here: http://youtu.be/g1KwfynkDIU
Step 6: Discussion on Energy: Efficiency
As an emerging technology, dye-sensitized solar cells perform poorly when compared to either traditional solar cells or fossil fuel energy sources. Although the sun is a plentiful source of energy, many factors limit DSSCs’ efficiency of converting sunlight into electrical energy. (View the article Advancing beyond current generation dye-sensitized solar cells for more information about DSSC‘s limitations and potential avenues for improvement).
While fossil fuels have many drawbacks, their advantages include energy density and low cost (without considering externalities). To best demonstrate the advantages and disadvantages of alternative energies, it is best to examine this issue through the lens of powering the calculator from earlier in this guide.
To power this calculator with our DSSCs, we connected three cells (each approximately 3 cm^2 in surface area) in series to the calculator. Our circuit produced 1.04V and 630 microamps, i.e. 0.6552 milliwatts of power. The cells had been placed on a windowsill, receiving a moderate amount of sunlight during the early afternoon of a New England winter day. According to the aforementioned Grätzel paper, one could expect 600-800 W/m^2 (0.54-0.72 W/ 9 cm^2) from sunlight to be reaching the solar cells. To find the amount of energy produced by the calculator’s original solar cell, I also connected the PV cell to a multimeter while it rested on the same windowsill. However, the PV cell and DSSCs were measured on different days with different amounts of available sunlight, so this is not a perfect comparison. Nevertheless, it is reasonable to expect only small variations between two winter afternoons in New England that were less than one week apart. The PV cell produced 9.2 milliwatts of power (2.8 milliamps and 3.27 volts). This is 14X the performance of the 3 DSSCs, and 21X the performance of the DSS cells per unit of area. (15.20661157 W/m^2 for the PV vs 0.728 W/m^2 for the DSSCs).
To find the amount of a conventional energy source needed to power this calculator, I know that a kilogram of coal (typically the most energy dense fossil fuel) will approximately produce 7.4 megajoules of electricity. Therefore, one would need 2.9210^(-7) kilograms (i.e. 0.292 milligrams) of coal to power this calculator for every hour used.
These numbers show the inherent difficulties with converting solar energy into electricity. I set out to calculate an efficiency measurement for the DSSCs that were produced, in addition to the photovoltaic (PV) solar cell that originally powered the calculator. Both cells were tested inside a cardboard box apparatus where a single light source (45W 120V tungsten halogen lamp) shone on the solar cells at an equal distance from above. There were no other light sources that entered this apparatus, and the inside was spray painted black to minimize light reflection from the cardboard.
One of the DSSCs produced 5.5 microwatts of power, or 0.01897 Watts/m^2 when tested inside the box. This power output per unit area was significantly lower than the original calculator cell’s 1.49 Watts/m^2 (2.99V 301 microamps / 6.05 cm^2). Considering that the DSSCs had 1.27% the efficiency of a cheap, mass-market calculator’s solar cell, the capabilities of basic anthocyanin-based DSSC technology left much to be desired. The original Grätzel paper mentioned that one could expect efficiencies between 0.5% and 1% for DSSCs constructed in their experimental procedures. This creates confusion as to why the PV outperformed the DSSC 78X per unit of area. Based on current technologies, it would be impossible for an inexpensive calculator’s PV cell to create electricity with an efficiency between 39% and 78%. This discrepancy could be the result of a tungsten halogen lamp emitting rays of light different than those of the sun. The DSSCs did in fact perform more comparably when tested along the windowsill. It is also possible that our research team did not create cells of the same quality and efficiency as those who wrote the original Grätzel paper.
There are some other important considerations to these comparisons of energy sources. First of all, dye-sensitized solar cells have issues of stability that would most likely prevent them from operating for twenty-plus years (the typical lifespan of a PV cell). My team has noticed significant performance degradation to our cell mere weeks after assembly; however, we have not taken many of the possible precautions in extending the cell’s lifetime. (Read about one research team’s efforts with enhancing the outdoor stability of their DSSCs) Nevertheless, this limitation highlights one problem with current renewable energy production. There are some technologies that have the opportunity to reasonably compete with coal and other carbon-based energy sources, but many technologies have serious financial and technological roadblocks that prevent mainstream adoption. Based on my research team’s experiments, photovoltaic solar cells currently hold much more potential than dye-sensitized ones at powering the world’s future energy needs.
Info
A solar cell or photovoltaic cell is a device that converts solar energy into electricty by the photovoltaic effect. Solar cells have many applications: individual cells are used for powering small devices such as electronic calculators; photovoltaic arrays generate a form of renewable electricity, particularly useful in situations where electrical power from the grid is unavailable such as in remote area power systems, Earth-orbiting satellites and space probes. A traditional solid-state solar cell is made from two doped crystals (P-N junction), like silicon solar cell. Fig.1 A solar cell made from a monocrystalline silicon wafer Fig.2 Polycrystaline PV cells laminated to backing material in a PV module
Dye-sensitized solar cells (DSSC)
Dye-sensitized solar cells (DSSC) based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system. These cells were invented by Michael Grätzel and Brian O’Regan and are also known as Grätzel cells Dye-sensitized solar cell (DSSC) provides us a technically and economically viable alternative way for traditional p-n junction silicon solar cells. Although they use a number of advanced materials (like TiO2 nanoparticles). these are inexpensive compared to the silicon needed for normal cells because they require no expensive manufacturing steps. TiO2, for instance, is already widely used as a paint bas. The record of liquid-electrolyte based DSSC can reach a conversion efficiency of 11%.
Simple comparison of P-N junction solar cell and DSSC
In P-N junction solar cell semiconductor achieves task of light absorption and charge carrier separation and transportation. While in DSSC these functions are separated. the bulk of the semiconductor is used solely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte (or organic hole transport materials). By combining a sensitizer as a light- absorbing material (a broad absorption Band) with a wide-bandgap semiconductor films of mesoporous or nanocrystalline morphology permits harvesting a large fraction of sunlight.
Fig.3 DSSC Demonstration Fig.4 A prototype of a stainless steel supported flexible DSSC.
DSSC Structure
The basic structure of the Dye-sensitized solar cell is that in the case of the original Grätzel design: the cell has three primary parts. Glass sheet with transparent conducting oxide coating (ITO or FTO) as anode on top of it; and semiconductor oxide (normally mesoscopic TiO2which forms into a highly porous structure with an extremely high surface area. ) film deposits on the conductive side of the glass sheet which is then immersed in a mixture of a photosensitive ruthenium-polypyridine dye (also called molecular sensitizers[5]) and a solvent. After soaking the film in the dye solution, a thin layer of the dye is left covalently bonded to the surface of the TiO2. A separate backing is made with a thin layer of the iodide electrolyte spread over a conductive sheet, typically platinum metal.The front and back parts are then joined and sealed together to prevent the electrolyte from leaking.
Fig.5 Schematic of the construction of Grätzel cell.
Basic working principle
We elaborate the the mechanism of DSSC using Dye-sensitized solid-state heterojunction solar cell as an example which we will FOCUS on. In Dye-sensitized solid-state heterojunction solar cell, a monolayer of dye is attached to the surface of a mesoscopic film of TiO2 (wide-bandgap oxide) and serves to harvest solar light dye absorbs light and then injects electrons into the conduction Band of semiconductor oxide (the nearby TiO2 particles) upon excitation, then the electrons transport through its nanoparticle network by diffusion to the current collector (anode),subsequently pass through the external circuit, perform electrical work, processed to the counter electrode (cathode)at the mean while, the dye also injects holes to the hole conductors and transport to the counter electrode, and with the outside circuit which the finishes loop. And there is no chemical change under solar exposure. The Only difference for original Grätze cell compared with Dye-sensitized solid-state heterojunction solar cell is that the former uses electrolyte and the latter uses as hole conducting medium.
Fig.6 Schematic illustraion of the working principle of original Grätze cell Fig.7 Schematic illustraion of the working principle of Dye-sensitized solid-state heterojunction solar cell
Inorganic electron conductor
The semiconductor oxide materials (with wide-Band gap) TiO2 (anatase) serves to harvest the solar light, which only absorbs a small fraction of the solar photons (those in the UV).[5] However when we combine the this wide-Band gap semiconductor of mesoporous or nanocrystalline morphology with the sensitizers(Dye) of broad absorption Band, this interpenetrating network junction can harvest a large fraction of the sunlight. There are other alternative semiconductor oxides such as ZnO, SnO2, Nb2O5 which are not as good as TiO2 under current investigations. In DSSC, the inorganic films are made of a network of wide-Band-gap oxide nanocrystallites, producing a junction with large contact area. The surface amplification for a film composed of 15~20 nm sized particles is about 100 times the area it occupied for each micron of thickness. A roughness factor, real surface/projected area, of at least 1000 to ensure efficient light harvesting.
Fig.8 a) scanning electron micrograph of TiO2 film. b) orientation of exposed facets of the particles. and c) histogram showing the frequency of occurrence of a given particle size for a mesoscopic TiO2 film prepared at 230 o C, which has demonstrated optimal photovoltaic performance so far The film thickness is 5~20um, the TiO2 mass—1-4mg/cm2, the Porosity is 50~65% and the average particle diameter is 20nm. The prevailing structure of anatase– bipyramidal. pseudocubic, bricklike. The Most expose face (101) then (100) and (001). The formation of the (101) is favored by its low surface energy. The oxide particle are in the intrinsic insulating state (without doping). However, the injection of one single electron from the dye into the TiO2 particle which then switched from an insulating to a conducting state. The TiO2 film is deposited by screen printing from a colloidal suspension providing a reproducible and controlled porous high-surface area texture. Presently, hydrothermal route is used since it is ease to control particle size hence of the nanostructure and porosity.
Organic hole transport Materials
Spiro-MeOTAD in this work. The spiro center confers to the material in a high thermal stability in the glassy state without adversely affecting its electronic properties 120 °C of the glass-transistion temperature assures stability of the amorphous state under ambient conditions for years. Crystallization is undesiable, as it prevents the close contact between the hole transport materials with the oxide film.
Sensitizing dye itself does not provide a conducting functionality, but it distributed at an interface in the form of immobilized molecular species. 1×10-4 cm2/V s hole mobility.
Swiss scientists’ new see-through solar panels are sweet nectar for startups
As Europe’s transparent solar panel market swells, Swiss scientists have set a new efficiency record for the technology. This could lead the way to energy-generating Windows that power up our homes and devices.
Also known as Grätzel cells, dye-sensitised solar cells (DSCs) are a type of low-cost solar cell that use photosensitized dye to convert visible light into electricity.
Previous versions of DSCs have been reliant on direct sunlight, but a team of researchers at the École Polytechnique Fédérale de Lausanne (EPFL) have found a way to make transparent photosensitizers that can absorb light across the entire visible light spectrum, including both direct and ambient.
The researchers developed a way of improving the combination of two newly designed photosensitizer dye molecules. They did this by creating a technique in which a monolayer of a hydroxamic acid derivative is pre-adsorbed onto the surface of nanocrystalline mesoporous titanium dioxide.
Crystals, jets, and magnets — is this how to make cooling greener?
On top of the new photosensitizers being able to harvest light across the entire visible domain, the scientists have also increased the DSCs’ photovoltaic performance — which has been a weak point of the technology compared to traditional solar cells.
To put that in numbers, the enhanced DSCs’ efficiency reaches above 15% in direct sunlight and up to 30% in ambient light. For reference, commercial solar panels have an average efficiency between 15% to 22%.
In other words, if this technology can hit scale, we may soon see a transparent solar panel revolution in Europe.
How are DSCs already being used?
DSCs aren’t a new technology, but the advances from the École Polytechnique Fédérale de Lausanne could deliver a lifeline to sustainable buildings.
Dye-sensitised solar cells are not only transparent, but can also be fabricated in multiple colors and for low cost. In fact, some are already being used in skylights, greenhouses, as well as glass facades.
For example, think of the SwissTech Convention Center — a location that became the first public building to install the DSCs technology in 2012.
While in 2017, the Copenhagen International School also used the same technology to inaugurate its building with 12,000 colored solar panels, which meet over half of the school’s annual energy needs.
Why dye-sensitised solar cells could be a boon to European startups
The scientists at the EPFL have improved this technology’s ability to work in low light conditions, something that’s vital in cloudier, colder countries.
As the authors wrote, “Our findings pave the way for facile access to high performance DSCs and offer promising prospects for applications as power supply and battery replacement for low-power electronic devices that use ambient light as their energy source.”
For European startups, this could be a game changer. While there’s an obvious benefit for installing transparent solar cells on buildings to help meet nations’ net-zero climate goals, the technology’s applicability goes beyond energy-generating Windows and glass facades.
DSCs take up far less space than traditional panels, which opens up their use for a wide number of items, whether that’s portable electronic devices (such as earphones and ereaders) or connected sensors that are part of the Internet of Things.
When a scientific advance like this happens, it opens the door for bright minds to create something new and efficient. Let’s just hope Europe’s startups are ready to walk through.
You can find the full research here.
Story by Ioanna Lykiardopoulou
Ioanna is a writer at TNW. She covers the full spectrum of the European tech ecosystem, with a particular interest in startups, sustainabili (show all) Ioanna is a writer at TNW. She covers the full spectrum of the European tech ecosystem, with a particular interest in startups, sustainability, green tech, AI, and EU policy. With a background in the humanities, she has a soft spot for social impact-enabling technologies.
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