Copper zinc tin sulfite CZT(S,Se) for solar cell applications

Over the last years, the need for renewable energy has grown day by day. Solar energy is one of the most important assets of renewable energy. The earth has proved itself as a non-infinite energy source. Climate change and global warming are warning the humanity for sustainable solutions. Renewable energy is one of those solutions that needs an urgent attention. Solar energy is one of the early corners of this subject. But the technology has to change as soon as possible. Silicon solar cells have been dominating the solar energy market since the day one. Their reliable performance makes silicon solar cells a viable asset but the availability of the raw materials is a matter of concern. They are physically fragile and heavy form makes it ungainly technology. Thin film solar cell technologies are the biggest rival on the subject to silicon, they have important advantages like being lightweight, flexible, cheap and easily manufactured. However, they cannot achieve the same performance as silicon solar cells yet. CZTS is a quaternary absorber layer material for solar cell technologies. It has several advantages like consisting of earth abundant, cheap, and non-toxic materials. Also one of the most important competitive edges for CZTS is that its structure is quite similar with CIGS and CIS. They have high-efficiency numbers to compete with silicon cells. However, they have two disadvantages. One of them is having toxic materials inside and the other one is that they are getting more expensive day by day (their cost is increasing over the last years). The screening technologies are using the same raw materials (elements) with them so the market price for those elements are getting more expensive. That makes element prices higher and higher every second. So, CZTS already has a place on market for itself. The advantages mentioned before makes CZTS attractive for scientists. In this study, CZTS ink was produced by hot injection method. Metal precursors were used in the reaction. Precursors can be listed as; Copper (II) acetylacetonate, Zinc acetylacetonate hydrate and tin (IV) bis(acetylacetonate) dibromide as cation precursors and elemental sulfur as a sulfur source were used. Oleylamine was used to dissolve the precursors and also as a surfactant for the reaction. The reaction occurred in a closed chamber under an inert atmosphere. Reactants were washed from oleylamine after the reaction. The product has been kept dispersed in toluene. Cadmium Sulfide layer was coated on samples by chemical bath deposition technique. Cadmium acetate and thiourea were used as source materials. Zinc oxide powder was produced by using zinc acetate and potassium hydroxide. The final product was kept in methanol solution to be used later as an n-type layer. Spray coating technique was utilized to coat samples with CZTS and ZnO. The molybdenum coated glass was used as the substrate. CZTS layer was coated first, followed by annealing of the film at 330 oC for an hour. After the annealing step, spin coating was utilized to coat CZTS one more time. This step is applied to reduce the roughness of the film. Annealing was then applied one more time on samples after the spin coating. CdS layer was coated onto the CZTS layer via chemical bath deposition as mentioned above. Finally, ZnO layer is deposited via spray coating. Molybdenum is used as an electrode and for the counter electrode aluminum was thermally evaporated onto the samples. Masks were used to protect the samples to be coated fully. Mo / CZTS / CdS / ZnO / Al configuration was obtained. Samples were characterized at each step to see if the films were what they are expected. Diodic plots were identified by current-voltage characterization. The final formation was showing the effects of the solar cell, producing current. To sum up, quaternary CZTS compound was produced and made into a film form successfully. Coating a CdS layer on top of the CZTS layer was achieved. ZnO particles were produced and used as an n-type layer. Solar cell layers were prepared in that order, and then it's tested against light until a working solar cell was achieved. In the study, CZTS solar cell production conditions were optimized.