Why NDSSC?

Although solar energy is a renewable source of energy, converting solar into electrical energy requires photovoltaic cells. Currently photovoltaic (PV) cells are silicon based. The manufacture of silicon-based PV cells requires chemically and energy intensive processing. Natural Dye Sensitized Solar Cells (NDSSC) are a type of solar cell that use plant matter in place of the silicon used in photovoltaic cells. NDSSCs mimic the light-capturing ability of plants, convert light energy into electrical energy, and can be manufactured using more sustainable methods than those used for silicon-based PV cells. While current conversion efficiencies of NDSSCs are lower that of silicon PV cells, NDSSCs can potentially serve as “cleaner” alternatives to PV cells for low power devices such as LEDs and phone chargers.

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How Does It Work?

The cell works by absorbing light (which is made of photons) through the dye into the underlying titanium dioxide, which has a complex nanoarchitecture that acts like a light sponge. These photons excite electrons in the dye, inducing an electron transfer as the electron leaves an electron hole behind on its journey to the electrode, made from titanium dioxide. Titanium dioxide (TiO2) is derived from minerals and is used as a nontoxic pigment, semiconductor, and refractive material. TiO2 is commonly found in paint, sunscreen, and food coloring. The electron is pulled in a current through an external load, doing work and producing electrical energy until it returns to the counter electrode, made out of graphite or platinum paste. The iodide electrolyte replenishes the electron hole and allows the system to continue, completing the circuit and maintaining a positive feedback loop. 

Different dyes absorb different wavelengths on the UV spectrum, but for my project I decided to work with anthocyanin rich pigments like raspberry juice. The dye must work with the oxide paste on a molecular, electrochemical level, so that the highest occupied molecular orbital (HOMO) of the dye and the lowest unoccupied molecular orbital (LUMO) have an appropriately sized band gap that electrons can pass through. Other oxide pastes, such as zinc oxide, can be used in the cells but will have different band gaps which will affect the efficiency of the cell. It is vital to find materials that have a good molecular match in order to achieve efficiencies between 5-12%. 

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Research on Existing Applications & Communities 

 

DSSC have already been integrated into facades of buildings, as stained-glass windows, and on the surfaces of furniture. Recent scientific research has produced screen-printed solar cells and dye-sensitized solar concrete, and innovators are working to push solar cells to the forefront of consumer culture. Scientists and artists alike have begun experimenting with DSSC as a medium for commercial and poetic values.

 

 

NDSSC Material Recommendations

Substrate: 2mm conductive glass from Solaronix (TCO22-15)

Having not had the chance to try Jerry Ellsworth’s DIY conductive glass tutorial, I recommend purchasing conductive glass substrates from Solaronix. Although the Arbor Scientific glass worked fine, the size is significantly smaller in surface area. Solaronix’s 5x5cm substrates worked well, shipped quickly, and were moderately priced when bought in bulk compared to others. Either of the 3mm, 2mm, or 1.6mm thick substrates will do, although if you intend to create closed cell configurations and seal using an easy-melt plastic gasket I recommend the thinner models. Overall, I would choose to work with the 2mm substrates again as they are thick enough not to chip corners easily like the 1.6mm substrates (chipped corners are awkward when trying to stagger the edges of cells when designing an array), but lighter in terms of weight compared to the 3mm. Transmission spectrum and resistance vary between models. I would not recommend ordering substrates pre-coated with TiO2 or platisol since they increase the price significantly and have often arrived with damaged coatings that are much more difficult to repair. 

 

Dye Material: Frozen organic raspberries (product of Chile) from Trader Joe’s

These raspberries worked well and were extremely affordable. I did not try other dye sources outside of the synthetic dyes, so I am not experienced enough to really give any other sort of recommendation. I would highly recommend you sieve or filter the many seeds out before immersing electrodes in dye to prevent areas where seeds blocks the electrode’s surface from staining. 

 

Electrolyte: Iodide electrolyte provided by Arbor Scientific’s NDSSC kit 

Please exercise caution and use gloves when working with the electrolyte. 

 

Titanium Dioxide: Titanium Dioxide paste provided by Arbor Scientific’s NDSSC kit

I also ordered Titanium Dioxide paste for spin-coating from Solaronix but preferred working with the thicker paste from Arbor Scientific after my attempts at DIY spin coating failed. 

 

Counter Electrode: Graphite from a pencil or Platisol platinum paste from Solaronix

Either product worked, the platisol paste is more expensive and requires more steps in synthesis but apparently works better to produce higher levels of current; however I cannot yet confirm this and do intend to examine if the platisol paste is worth the extended synthesis effort and higher cost. If using platisol paste, you MUST also have hydrogen peroxide available to test the activity of the paste.

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Materials for Synthesis

1. 95% Ethanol 

2. Pasteur Pipette (at least 2 recommended, glass preferred but plastic is fine)

3. Deionized (DI) Water (not required but recommended)

4. Microscope Slides (used for spreading TiO2)

5. Scotch Magic Tape (used for creating clean edges of TiO2)

6. Small Binder Clips (used to hold cell together if in open configuration)

7. Easy-Melt Gaskets (I used Meltonix purchased from Solaronix, seeking alternatives)

8. Laboratory Tape (used to label and ID individual cells, also helps in keeping track of conductive side of glass)

9. Alligator Clips (used to hook up cells to multimeter or to each other as an array)

10. Cookie Spatula (helpful for removing cells from the hot plate without scratching them)

11.  Mortar & Pestle (a blender can be used, but a pestle is still recommended)

12.  100mL container or beaker (used to rinse cells after dying, can also be used with a wire mesh at the opening to filter out seeds)

13.  Wire mesh (used for filtering raspberry seeds out)

14.  Tupperware or closed, flat container (used for storing dye and staining cells)

15.  Hot plate or stove top 

16.  Roll of aluminum foil 

17.  Hydrogen Peroxide if using platisol paste instead of graphite 

 

Materials for Testing and Evaluating NDSSC

     15. Multimeter (should be able to measure connectivity, resistance, DCA and DCV)

     16. Spectrophotometer (I used the Red Tide model from Ocean Optics)

     17. LED bulb (40 watts) (others have used an overhead projector. The sun can also be used but conditions must be well documented if comparison or analysis is intended