Rapid thermal processing for printed Cu(In,Ga)(S,Se)2 solar cells: Comparison of precursor materials

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We investigate three different precursor types for selenisation using a rapid thermal process. Two of the precursor sample types are deposited via non-vacuum methods using particle based precursor inks, and the third precursor type investigated are films that are sputtered from a single ternary Cu–In–Ga target. The rapid thermal process is suitable for high throughput with a short optimum selenisation duration of 5min or less and employs elemental selenium vapour. In order to investigate the phase development in the film, the selenisation process was interrupted at different stages and the samples were monitored via X-ray diffraction and surface-sensitive Raman measurements. We find different growth mechanisms for the investigated precursor types with fast CuInSe2 formation for the highly reactive elemental Cu and In particles and a slower formation of polycrystalline Cu(In,Ga)Se2 for Cu(In,Ga)S2 particle based precursors without the formation of additional phases. For selenisation of the sputtered precursor layers, we find the formation of InSe and In2Se3 during the selenisation temperature ramp up. Using the rapid thermal selenisation process, conversion efficiencies of about 2.9% and 4.0% for the printed and 6.0% for the sputtered precursor layers could be demonstrated.