Exploring Dependence of Rapid Thermal Annealed Ag/ITO Bilayer Films Properties on the Systematic Ag Layer Thickness Increment for Bifacial CZTS Solar Cell Application

Abstract

This study investigated the impact of Ag layer thickness on the properties of rapid thermal annealed Ag/ITO bilayer films, aimed at addressing conductivity loss in ITO substrates used as a back contact for optoelectronic applications, such as bifacial CZTS solar cells. Ag layers of varying thickness (10 nm, 20 nm, 30 nm, and 40 nm) were sputter-deposited onto a commercially acquired ITO-coated glass substrate and rapidly thermally annealed. The samples’ characterization was performed using AFM, XRD, four-point probe, Hall Effect measurements, and UV-VIS-NIR spectrophotometry. Results indicated that thinner Ag layers exhibited relatively stable surfaces with uniformly distributed grains, smaller roughness, and higher electrical conductivity due to increased carrier mobility and concentration. The XRD analysis showed a preferential delafossite AgInO₂ structure for thinner Ag layers. Optical measurements revealed that the sample with thinner Ag layers had lower solar transmittance and bandgap narrowing, while thicker layers showed bandgap broadening. The samples had bandgaps within reported ITO bandgaps (3.38 to 4.15 eV). Ag/ITO films with thinner layers achieved a high average transmittance of 76%, lower sheet resistance of and enhanced micro-strain and crystallite size properties. These results suggest that thinner Ag/ITO bilayer films hold potential for use in optoelectronic applications, particularly as back contacts in bifacial CZTS solar cells.