Efficient solar energy conversion with electrochemically conditioned CuInS2 thin film absorber layers

The replacement of a toxic KCN etch step used for the preparation of efficient thin film solar cells with CuInS2 by a mixed photoelectrochemical and electrochemical anodic conditioning procedure is reported. Processing in V2+/V3+ – 4.4 M HCl redox electrolyte with specific potential ramps results in photoelectrochemical solar cells (PECS) superior to KCN etched cells after combination with an additional procedure employing anodic potential pulses. Solar-to-electrical conversion efficiencies of PECS yield η = 2.4% for KCN etched samples and of 3.3% for the new two-step treatment. X-ray photoelectron spectroscopy (XPS) and solar cell analysis show removal of Cu–S phases and formation of ordered defect compounds (OVCs) on CuInS2. After electrochemical treatment the surface is less Cu-depleted than after KCN etching attributed to a non-sulfide monovalent Cu compound.