Characterization of CdS sputtering deposition on low temperature pulsed electron deposition Cu(In,Ga)Se-2 solar cells

The present paper reports the investigation of sputtered CdS as a buffer layer in Cu(In,Ga)Se-2 (CIGS) solar cells, for a dry-low temperature all in-line production technology method. The CdS film is deposited using radio-frequency magnetron sputtering in argon atmosphere. Compared to the well-known CdS grown by chemical bath deposition, the sputtering technology is feasible for the serial manufacturing process. The morphology and optical transmittance of CdS thin films are studied, as well as the CdS/CIGS interface and the solar cell characteristic. We observe that CdS layer deposited on glass is uniform and continuous with optical transmittance above 90% in the wavelengths range corresponding to the energy gap of the absorber. Current density-voltage (J-V) curve shows an overall efficiency of 6% affected by inhomogeneity at the CIGS/CdS interface. Sputtering deposition is not able to create a homogeneous layer on the absorber irregularities due its growth process. Moreover, Auger depth profile shows oxygen contamination at the interface, due to absorber surface oxidation. Within this work, the main crucial aspects of a new solar cell production technology, as well as related solutions, are reported.