Development of Fabrication Process for Electroplated CZTS Absorber

Electroplating is a cost-effective method for deposition of copper-zinc-tin (CuZnSn) alloys which can be a precursor to fabricate CZTS absorbers for thin-film solar cells. Focus has been on development of simple and robust electroplating processes for deposition of both pure metals, copper (Cu), tin (Sn) and zinc (Zn), and alloys (CuZn, CuSn, SnZn and CuZnSn) on a molybdenum (Mo) substrate. The subsequent sulphurisation and annealing process is also discussed, and the resulting semiconductor material characterised by Raman spectroscopy. Of all the possible combinations of alloys and layers, direct deposition of brass alloy (CuZn) onto the molybdenum substrate, followed by electroplating of pure Sn, was found to be most feasible. It was also observed that tin electrodeposition in general suffers from instability of the electrolytes, resulting in large variation of the chemical composition tin alloys, as well as delamination problems. Only CuZn, deposited from an alkaline glycerol electrolyte, provided acceptable adhesion to the molybdenum substrates. Furthermore, a pure Sn electrolyte has been developed and optimized, based on pyrophosphate, which has a relatively neutral pH and good stability. Annealing experiments, with sulphur powder in combination with electroplated stacks of Sn/CuZn on a Mo substrate, show a clear CZTS phase formation.