Diode laser induced crystallization of CZTS thin films deposited on flexible molybdenum foils

Abstract

Copper zinc tin sulfide (CZTS) thin films have the potential to be an absorber material in photovoltaic (PV) cells due to their optimal bandgap and high absorption coefficient. Despite their potential, issues such as low carrier mobility, short lifetime, and structural defects limit their application. Post-deposition annealing, which involves heating the films in a controlled atmosphere is usually required to improve film structure. Traditional annealing is a slow, energy-demanding process and incompatible with certain substrates, including temperature-sensitive polymeric materials and metallic foils. This work demonstrates a diode laser (808 nm) treatment as a rapid alternative to induce crystallization in CZTS films, potentially eliminating the need for traditional furnace annealing, thereby offering potential advantages in both time and energy consumption. The results show that diode laser treatment can promote crystallization of CZTS thin films, as confirmed by Raman studies. Photoluminescence (PL) spectroscopy revealed that the wider bandgap (∼1.78 eV) of the as-deposited material nanocrystalline material is reduced to around 1.4 eV upon laser annealing and the PL emission intensity showed significant enhancement, which are ascribed to improvement in both the crystal size and quality. Such improvements promise to have the potential to address some of the remaining challenges in using CZTS as an absorber material in next-generation PV cells.