Low-efficiency solar cells for educational purposes can be simply made in school or home environments using wet-chemistry techniques and readily available chemicals of generally low toxicity. Instructions are given for making solar cells based on the heterojunctions Cu/Cu 2 O, Cu 2 O/ZnO and Cu 2 S/ZnO, together with a modified Grätzel cell.
An alcoholic extract of the spice turmeric can be used to create a light-sensitive dye that can be used to stain paper. On exposure to sunlight, the dyed paper can be used to capture photographic images of flat objects or reproduce existing images through the preferential degradation of the dye in light-exposed areas over a time period of a few hours. The images can be developed and preserved by spraying the exposed paper with a dilute solution of borax, which forms coloured organo-boron complexes that limit further degradation of the dye and enhance the colour of the image. Similar photochemical reactions that lead to the degradation of the turmeric dye can also be used for reducing the organic pollution load in wastewater produced by many industrial processes and in dye-sensitized solar cells for producing electricity.
Photoelectrochemical cells using dye-sensitized ZnO with a Cu 2+ /Fe 2+ /Fe 3+ electrolyte can be easily made at home or in a school classroom with household chemicals and other readily available materials. The cells, which are made with wire housed within plastic drinking straws, have open-circuit voltages of 0.5-0.7 V and short-circuit currents of about 0.5-2.5 mA cm −2 .Step-by-step instructions are provided on how to construct the photoelectrochemical cells, as are suggestions about how to use the cells to explore some concepts associated with utilizing solar energy.
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