Electrochemical Studies of One-Step Electrodeposition of Cu-Sn-Zn Layers from Aqueous Electrolytes for Photovoltaic Applications

Copper, tin and zinc have been co-electrodeposited on Mo-coated glass substrates from an aqueous acid sulfate solution at room temperature with the aim of preparing kesterite absorber layers for solar devices. The solution contains copper, tin and zinc sulfate, potassium sulfate and sodium citrate at pH = 4.75. The effect of two complexing agents (sodium citrate and tartaric acid) is characterized by solution chemistry analysis, by voltammetry using a rotating disk electrode and an electrochemical quartz crystal microbalance. A deposition process is developed to co-deposit the three metals with the appropriate composition (copper poor and zinc rich). Deposition kinetics has been investigated. The composition can be tuned by mass transport control and by deposition potential. Composition, morphology and structure are characterized by Inductively Coupled Plasma analysis, Energy Dispersive X-ray Spectrometry coupled to Field Emission Scanning Electron Microscopy and X-ray Diffraction. The co-deposited layers are porous due to dendritic growth. After annealing at 530°C during 15 min in a selenium atmosphere, a 5.8% solar cell efficiency has been obtained.