Rocking disc electro-deposition of CuIn alloys, selenisation and pinhole effect minimisation in CISe solar absorber layers

The co-electrodeposition of copper and indium from a pH 3 tartrate bath onto 4.8 cm × 2.5 cm Mo and MoSe2 substrates is studied and conditions are optimised for CuIn alloy films. Selenisation at ca. 500 ◦C for 30 min in selenium vapour gives CuInSe2 (or CISe). Mapping using the photo-electrochemical reduction of Eu(NO3)3 is used to asses the relative photoactivity as a function of position and surface treatment. Etching of detrimental CuxSe phases is investigated with 5% and 0.5% (w/w) aqueous KCN. The slower 0.5% (w/w) KCN etch allows better process control, and re-annealing at 500 ◦C for 30 min followed by further etching significantly improved the photo-activity. However, over the large area local pinhole recombination effects are substantial. An alternative low temperature film optimisation method is proposed based on (i) KCN over-etch, (ii) hypochlorite (5%, w/w) pinhole removal (Mo etch), and (iii) a final KCN etch to give good and more uniform activity.