Fabrication and characterization of wide band-gap CuGaSe2 thin films for tandem structure

The effects of CuGaSe2 (CGS) absorber layers with various film thicknesses have been investigated by using scanning electron microscopy (SEM) and photoluminescence (PL). SEM measurements show that the thickness of the CGS absorber layers grown on Mo-coated soda-lime glass substrate increases with an increase in Ga flux. Moreover, a trend in the grain size and surface roughness can be observed. Single broad peaks centered around 1.64 eV are observed in the PL spectra of the CGS samples. From the excitation power-dependent PL measurement, the single broad peaks are associated with the donor–acceptor pair transition from CGS absorber layers. In addition, we demonstrate that different film thicknesses of CGS absorber layer result in different defect concentration by temperature-dependent PL measurement.