CuIn1−xAlxSe2 solar cells fabricated on the flexible substrates by co-sputtering and modified selenization

CuIn_1-xAl_xSe₂ (CIAS) thin films were grown on the flexible stainless steel substrates, by dc co-sputtering from the elemental cathodes. CuInAl alloyed precursor films were selenized both by noble gas assisted Se vapor transport and vacuum evaporation of Se. X-ray diffraction, scanning electron microscopy and UV-visible absorption spectroscopy were used to characterize the selenized films. The composition (x=Al/Al+In) with 0≤x≤0.65 was varied by substituting Al with indium in CuInSe₂. Lattice parameters, average crystallite sizes and compact density of the films compared to CuInSe₂, decreased and (112) peak shifted to higher Bragg´s angle, with Al incorporation. Cells were fabricated with the device structure SS/Mo/CIAS/CdS/iZno-AZO/Al. Best cell showed the efficiency of 6.8%, with x=0.13, E_g=1.17 eV, fill factor 45.04, short circuit current density J_sc 30 mA/cm².