Nº 254
Farbstoffsolarzellen.
From DIY to Solar Chic

Even with current peak test results of 13 percent, dye-sensitized solar cells (DSCs) do not come close to the efficiency of silicon solar cells, which can convert over 20 percent of solar energy into electricity. But DSCs have other merits.

The first advantage concerns their manufacture: because they use dyes to absorb light (in a similar way to chlorophyll in leaves) they are so simple and cheap to make that in theory, anyone can produce them using readily available materials. They can even be edible, like the photoElectric Digestopians created by the artist Bartaku (see form 247). Moreover, their manufacture requires little energy and no toxic or rare materials. DSCs are thus more environmentally friendly and have a broader range of applications. The second advantage lies in their outstanding design potential. This results from their huge colour spectrum, their transparency, and their compatibility with screen printing and other printing techniques, even on flexible materials or filaments (as shown in form 244 by the textile DSCs from the material research institute TITK Rudolstadt). Unlike silicon solar cells, they do not have to be concealed, but can even be used as design elements in buildings and products. Today, high-quality DSCs with this potential are extremely costly, often made by hand in small production runs. But they also have the advantage of not needing to compete with Asianmade silicon solar cells, catering instead to what Toby Meyer of Solaronix calls the “solar chic” market.


KleinProduct designer Marjan van Aubel exploits and showcases the design potential of DSCs for her Current Table, a simple, aesthetically convincing table with integrated solar cells that can power mobile phones or small lamps. In her previous Energy Collection, van Aubel already explored functional and visual integration of DSCs into everyday items. What, she asked herself, if every object were capable of converting solar energy into electricity? In the resulting joint project with Solaronix, she developed a collection of coloured drinking glasses that use the special ability of DSCs to generate power indoors. Trailblazing and fascinating as the project may be, van Aubel found that the surface of these small objects is not large enough to generate sufficient power for the planned everyday purposes. Hence the idea of the dye solar table. The Current Table has eight DSCs integrated in the top. Working with Solaronix, van Aubel developed a unique cell design that departs from the most efficient strip structure without compromising on functionality, representing a symbiosis of form and function. For van Aubel, it was important to show and design all of the cell’s layers and materials: the orange photoactive dye and the yellow electrolyte become decorative elements. The cells are screen-printed, which achieves the aim of integrating the cells and their energy-generating function into objects in an aesthetically pleasing way so that people choose to use them not on principle alone but also on account of the way they look. Unsurprisingly, van Aubel sees designers as key figures in the successful development and marketing of DSCs.
The degree to which integrated solar cells are capable of changing the way devices are run and used is shown by the LivePaper e-reader recently launched as a pilot project by the Finnish company Leia Media. Their aim was to develop an e-reader that is as easy to use as reading a newspaper: no switching on, no charging – just turning pages. Leia Media achieved this with an e-paper display that only needs energy to switch to the next screen and a DSC made by G24 Power on the reverse. The e-reader is not only thinner and lighter than other tablets, thus more closely resembling paper, but it is also totally independent of chargers and power sockets.


On account of these properties, another Finnish project called SunEdu is currently exploring the possibility of using the LivePaper e-reader as a teaching aid in Tanzania, in areas with neither schools nor electricity. At present, the Leia Media e-readers cost roughly as much as normal tablets, but large production runs would likely bring a drastic reduction in price. Moreover, Leia Media is currently using standard cells from G24 Power, whereas in future a more convincing design solution will surely be possible.
The first prominent use of DSCs in architecture is in the facade of the SwissTech Convention Center that opened in April 2014 on the campus of the Swiss Federal Institute of Technology in Lausanne. Over a surface of 300sqm, the artists Daniel Schlaepfer and Catherine Bolle have made striking use of the various in red, green and orange shades of the solar cells. This project was also realized by Solaronix, the company founded by Toby Meyer, a former PhD student of Professor Michael Grätzel, the father of dye-sensitized solar cells. Unfortunately, the cells in question only achieve a conversion efficiency of 2–3 per cent, covering just a fraction of the building’s energy requirements. And at around 3000 euros per square metre, the price of the modules is so high that it is unlikely to be recouped. Both of these disadvantages are due to the modules still being made largely by hand. Today, then, solar energy generation alone is not enough to justify the use of such a solar facade.
Another approach to the facade-integrated DSCs is being taken by the research platform Bau Kunst Erfinden at Kassel University with the development of hi-tech, low-budget materials: in the DysCrete project, funded by the Zukunft Bau initiative, the artist Heike Klussmann and the architect Thorsten Klooster have joined forces with the department of building materials and building chemistry, and with industrial partners Fabrino and Lothar Beeck, to explore the upgrading of prefabricated concrete components into concrete DSCs. As they stress, their aim is to take timetested materials with their processing methods and material aesthetic and give them the added potential of DSCs in an innovative and cost-effective way, thus opening up new fields of application. First, they found that the production logic for prefabricated concrete parts is highly compatible with that for DSCs. While the typical layered structure of the cells was preserved, the individual layers were adapted and modified. The liquid electrolyte, for example, was replaced by a gel-like substance. The conducting concrete also developed by “Bau Kunst Erfinden” was used as an electrode. Initially, recycled reflective glass was used for the conductive outer layer, but tests with a coating of transparent conductive plastic are beginning to show positive results. The advantage of the plastic coating is that it preserves the material character of the concrete.
To obtain sufficient durability, Klussmann and Klooster are currently pursuing two concepts: either realizing all of the layers so that they have a long life cycle, or making certain layers replaceable. To prevent the solar cells from malfunctioning due to micro-cracks in the concrete, they are also in close contact with Henk Jonkers from Delft Technical University, who has developed a technique allowing small cracks to be filled with the help of bacteria (see form 249). With him, they are also planning a project to develop conductive, bioluminescent concrete surfaces. Like the facade at the SwissTech Convention Center, DysCrete has a conversion efficiency of around 2 percent – although so far only in the laboratory. Klussmann and Klooster are hoping to obtain a far more economical material, however. The system has the technological potential to be a low-cost energy source. Using recycled materials, initial prototypes have already achieved a price per square metre of less than 5 euros.


Fruit Dye Solar Cells


In order to achieve useful conversion efficiencies, the industrial production of DSCs uses synthetic dyes. In principle, natural dyes can also be used, as shown by the kit produced by Man Solar that allows even schoolchildren to make DSCs. The kit uses natural anthocyanin dyes from red fruits, natural dyes that have proved particularly efficient.
Even if fruit-dye solar cells do not achieve the efficiency of industrially produced DSCs, they do show that everyone can make solar cells cheaply to generate their own solar energy. This was also Andreas Mershin’s idea when he launched a biophotovoltaics project at the Massachusetts Institute of Technology. With the aim of universal access to electricity, he developed the concept of a DIY kit containing three simple basic substances and a set of instructions for turning plant waste containing suitable dyes (e.g. grass cuttings) and a piece of metal into a bio solar cell. The key to this development is a stabilizer made of peptides that prevent the grass cuttings from rotting, plus an immersion bath that gives any piece of metal a “nanoforest surface structure”. These two substances and the electrolyte are cheap, and they will be sold in a transparent plastic bag whose conductive coating allows it to serve as a transparent top electrode.
Further development of the idea and the individual components of the kit will be just as uncommercial as its manufacture: by means of crowdfunding, Mershin hopes to raise conversion efficiency to at least 1 or 2 percent so that a small roof surface could, for example, supply sufficient power for a small lamp.
Whether or not the idea is a success remains to be seen, but the project provides a fascinating illustration of the potential of dye-sensitized solar cells to use solar energy anywhere that the sun shines. For all the diversity of research methods and objectives, from DIY to solar chic, overall it is clear that dye-sensitized solar cells manage to combine efficiency, sustainability and aesthetics in a promising way.

Perovskite Solar Cells: The Sister of the Dye Solar Cell Opens Up a New Category


In the early 1990s, Michael Grätzel, professor at the Institute of Technology in Lausanne, laid the foundations for DSCs. Since then, he has received many awards for his research in this field. Recently he made another breakthrough, replacing the molecular dye with perovskite pigments in crystal form. Combining this with a solid electrolyte, he has been able to raise conversion efficiency to 15 per cent. The special aspect of this development is that pervoskites are unbeatably cheap and widely available. In addition, they can be applied in a layer 1,000 times thinner than the silicon layer in a standard solar cell. As a result, material costs are now near-negligible. Although perovskite solar cells are derived from DSCs, the silicon industry is also interested in the new technology and the possibility of producing tandem solar cells using silicon and perovskite.
Unfortunately, this new category of cells are neither coloured (ranging instead from brown to black) nor transparent. Moreover, they are less suited for use on flexible solar cells. Nonetheless, they could pave the way for a new generation of environmentally friendly, costefficient, affordable solar energy.
Since this breakthrough, a growing number of companies have been working on the further development of perovskite solar cells. Solaronix is planning to release another DIY kit, demonstrating the simplicity of producing of perovskite cells with cheap basic substances.


Artificial Photosynthesis


Still far from ready for mass production, but closer to the natural model of photosynthesis than the DSCs, are photoelectrochemical cells (PECs). These function in essentially the same way as dye solar cells, but as well as converting solar energy into electricity, they also use the resulting power inside the cell itself to break water down into hydrogen and oxygen. Some developments go a step further, adding carbon dioxide to make hydrocarbons – in the same way that plants make sugar and other carbon compounds, performing, in effect, artificial photosynthesis. The production of fuels in the form of hydrogen, or even hydrocarbons like methanol, is advantageous, first, because fuel is in greater demand than electricity and, second, because fuels are easier to store.
Compared to dye solar cells, however, efficiency represents a growing obstacle for PECs. An unusual approach is being taken by Artur Braun and his team at the Swiss Federal Laboratories for Materials Science and Technology (Empa) in an attempt to increase efficiency without raising material costs or having to use rare soil: using cyanobacteria proteins to functionalize the photoactive material haematite, a ferrous mineral that is ecologically compatible, affordable and abundant. As Braun explains, cyanobacteria proteins act as a kind of absorbent light aerial to obtain significantly higher conversion efficiency in PECs. In addition, using genetic manipulation, the researchers have been able to make the cyanobacteria proteins grow molecular “wires” for improved transmission of the resulting electrical charges and energy. This principle has already been successfully replicated in the laboratory. Because extracting the proteins from cyanobacteria requires an additional step, attempts are now being made to use the whole bacterium, one that has such a molecular wire. One possible basis for this would involve Shewanella bacteria that grow wires of iron oxide naturally: genetic segments from this bacteria could be used to enhance the efficiency of PECs. Inspired by the bioreactor facade of the BIQ Algenhaus in Hamburg, Braun’s concept and objective is to integrate PECs directly into the windowpanes and facade elements of residential and office buildings, in the form of double glazing with a watery electrolyte filling the gap. The solar fuel generated in this way could be stored locally and used as required by means of fuel cells. As with dye solar cells, the advantage of photoelectrochemical cells is their versatility in terms of geometry. They do not even have to be flat, allowing, for example, cylindrical shapes or flexible substrates.


Recipe for Dye-sensitized solar cell


Ingredients (see the modular system of Man Solar):
  • at least eight glass plates with transparent conductive coating (TCO)
  • titanium dioxide solution
  • electrolytic solution
  • fresh fruits (blackberries, cherries, currant) or dried hibiscus flowers
  • tape
  • paper clips
  • hair-dryer
  • pencil
  • a small cup
  • a piece of aluminium foil
  • spirit burner
  • alligator clips
  • multimeter for measuring the electricity or an calculator

1.) negative electrode

  • clean and dry thoroughly four glas plates
  • mark the edges of the glass on the conductive rough side with tape
  • apply the solution of titanium dioxide all over on the marked area
  • dry it with a hair dryer and remove the tape
  • burn it in the flame of the spirit burner until the layer is brown and then changes to white again

2.) positive electrode

  • clean and dry thoroughly four glas plates
  • cover the conductive and rough side completely with a graphite pencil

3.) colourized by fruits

  • pour boiling water over the dried hibiscus flowers and let it steep 5 to 15 minutes
or: squash fresh raspberries, cherries, blackberries and currants
  • bathe the negative electrode in the fruit juice until the white TiO2 layer has colored red (about 5 minutes)
  • wash up the dye remaining
  • dry it with a hair dryer

4.) installation

  • give a drop of electrolyte solution on the graphite side of the plus electrode
  • place the minus electrode with the colored TiO2 layer on the electrolyte solution
  • secure them with a paper clips


5.) measurement

  • connect the solar cells in series
  • add the multimeter and measure the produced electricity
  • or add the calculator



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