Improvement of CZTSSe film quality and superstrate solar cell performance through optimized post-deposition annealing.

Improving the performance of kesterite solar cells requires high-quality, defect-free CZTS(Se) films with a reduced number of secondary phases and impurities. Post-annealing of the CZTS films at high temperatures in a sulfur or selenium atmosphere is commonly used to improve the quality of the absorbing material. However, annealing at high-temperatures can promote material decomposition, mainly due to the loss of volatile elements such as tin or sulfur. In this work, we investigate how the additional step of sulfurization at reduced temperatures affects the quality and performance of CZTSSe based solar cells. A comprehensive structural analysis using conventional and high resolution XRD as well as Raman spectroscopy revealed that the highest CZTSSe material quality with the lowest structural disorder and defect densities was obtained from the CZTS films pre-sulfurized at 420 °C. Furthermore, we demonstrate the possibility of using Sb2Se3 as a buffer layer in the superstrate configuration of CZTSSe solar cells, which is possible alternative to replace commonly employed toxic CdS as a buffer layer. We show that the additional low-temperature selenization process and the successful use of Sb2Se3 as a buffer layer could improve the performance of CZTSSe-based solar cells by up to 3.48%, with an average efficiency of 3.1%.

Magnetic graphene oxide based nano-composites for removal of radionuclides and metals from contaminated solutions.

Magnetic graphene oxide based composites of the nano-particle size of <10 nm were synthesized, characterized and used in sorption experiments. The adsorption of Cs(I), Co(II), Ni(II), Cu(II) and Pb(II) to nano-composites was studied in a wide range of initial concentrations and analyzed by Langmuir and Freundlich models. In addition, the effects of pH and coexisting ions on the adsorption of Cs to Prussian blue based composites were investigated. The maximum adsorption capacities of studied elements varied from 29 to 641 mg g-1. The obtained Langmuir and Freundlich constants indicated the dominating physisorption mechanism and favorable adsorption conditions.

Final decontamination of the filtrates obtained after interaction of two ligand-containing Cu2+ and Zn2+ electroplating solutions.

A cheap and simple way to decontaminate two ligand-containing rinsing waters of metal finishing has been previously suggested. Both the copper diphosphate-containing rinsing wastewater and acidic zinc ammonium-containing rinsing wastewater may be decontaminated by mixing them which results in precipitation of solid solutions of copper-zinc-potassium-ammonium diphosphates. This way of decontamination requires no expensive reagents since only a small amount of H2SO4, is needed for pH adjustment. 80-99.5 % of environmentally dangerous substances, viz. zinc, copper and diphosphate, are removed from the mixture. However, Cu2+ and Zn2+ amounts in filtrates significantly exceed the discharge consent level (DCL). Besides, high concentrations of undesirable diphosphate and ammonium ions, which cause the eutrophication of natural water reservoirs, are present in the filtrates. There are relatively small concentrations of heavy metals: Cu2+ (approximately 0.4 mM dm-3) and Zn2+ (approximately 1 mM dm-3), and relatively large quantities of ligands: P2O7(4-) (approximately 20 mM dm-3) and NH4+/NH3 (approximately 500 mM dm-3) in these filtrates. Our investigation has shown, that decontamination may be easily achieved in industry by using cheap materials or industrial by-products: lime, MgO, phosphogypsum, extractive phosphoric acid and spent steel etching solution. Using lime, Cu2+ and Zn2+ ions may be removed below their DCL. After that, diphosphate ion concentration may be reduced approximately 1000 fold by addition of spent steel etching solution or continuous mixing with phosphogypsum. The amount of NH4+/NH3 may be reduced 20 to 30 fold, the concentration of soluble phosphates -- 5 to 40 fold and both c Cu2+ and c Zn2+ -- lower than their DCL by precipitating barely soluble fine crystalline MgNH4PO46H2O (struvite).