X-ray spectroscopic analysis of the growth of CBD-CdS buffers on flexible Cu(In,Ga)Se2 thin-film solar cell structures

The chemical bath deposition (CBD) of CdS layers on Cu(In,Ga)Se₂ (“CIGSe”) absorbers on flexible polyimide substrates is examined using a combination of soft x-ray emission (XES) and photoelectron (XPS) spectroscopies. For this purpose, absorbers with with varying degrees of Cu-deficiency and NaF precursor thickness were studied. From the data, a detailed picture of the chemical surface composition (in particular the carbon and oxygen contamination) of the CBD-CdS layers can be drawn. The thickness and deposition rates were determined by monitoring the CdS-induced attenuation of the In 3d_5/2 XPS and In M_4,5 XES signals of the absorber, finding no significant impact of Na and/or Cu content of the CIGSe.