The Tuning of Broad-band Absorption in the Visible Range from Plasmonic CZTS-Ag Multilayer Thin Film for Solar Cell Application

The absorption co-efficient of CZTS in the entire visible range can be enhanced by inducing the localized surface plasmon resonance by means of introducing Ag nanoparticles. CZTS-Ag multilayer thin films were fabricated by successive sputtering of CZTS and Ag. The concentration of Ag nanoparticles embedded in CZTS matrix was varied by increasing the number of Ag layer. The crystal structure and surface properties of the as-prepared multilayers were modified by annealing at 500 degrees C under vacuum condition. The formation of single phase kesterite structure of CZTS has been studied by XRD and micro Raman spectroscopy. A broad band absorption is followed by band edge absorption is achieved with 3 layers of Ag sandwiched between 4 layers of CZTS films. The direct band gap for CZTS film is calculated to be 1.45 eV whereas it is blue shifted on multilayers due to the combined effect of surface plasmon resonance and excitonic transition attributed to hybrid nature of Ag and CZTS phases respectively. The observed increase in absorption in the entire visible region could probably be helpful for increasing the trapping of incident photons in CZTS based thin film solar cells.