Cu(In,Al)Se2 thin films by one-step electrodeposition for photovoltaics

• Growth of CuInAlSe2 thin films through one-step electrodeposition is demonstrated.
• Binary phases that appeared in the as-deposited films are removed by vacuum annealing.
• An optimum In/Al ratio improved the band gap without significant structural change.
• For higher (In + Al) values, the conductivity changed from p to n-type.
• Grain size up to 1.1 μm is obtained.

Chalcopyrite Cu(In,Al)Se2 (CIAS) thin films are grown on stainless steel substrate through one-step electrodeposition at room temperature. Indium is partially replaced with aluminum to increase the band gap of CuInSe2 without creating significant change in the original structure. The deposition potential is optimized at − 0.8 V (vs. SCE) and annealing of the films is performed in vacuum to remove binary phases present in the as-deposited films. In/Al ratio is varied from 1/9 to 8/2, to find the suitability for solar cell fabrication. For In/Al ratio of less than 8/2, CuAlSe2 phase is formed in the film in addition to the CIAS phase. Depth profile X-ray photoelectron spectroscopy analysis of the CIAS sample prepared with In/Al ratio of 8/2 in the precursor solution confirmed the existence of single phase CIAS throughout the film. This film showed p-type conductivity while the rest of the samples with In/Al ratio less than 8/2 showed n-type conductivity. The band gap of the film varied from 1.06 to 1.45 eV, with variation in deposition potential. Structural, optical, morphological, compositional and electrical characterizations are carried out to establish the suitability of this film for solar cell fabrication.