Exploring laser annealing as an alternative approach to improve CZTS thin film quality for photovoltaic cells

With the ever-growing global demand for renewable energy sources, Cu₂ZnSnS₄ (CZTS) thin films can complement the existing Silicon-based photovoltaic (PV) cell market. However, low carrier mobility and lifetime, non-uniformity, and defects in the film structure have reduced the widespread application of CZTS. Post-process annealing is a critical step in improving cell quality. Nevertheless, conventional furnace annealing methods have failed to enable this technology's commercialisation, and the heating of the complete PV cell limits the selection of available substrates. This research explored alternative approaches using diode laser annealing for CZTS films deposited on flexible Mo foils in different gas atmospheres. SEM and XRD spectroscopy techniques were used to analyse the laser-annealed samples. Processing parameters were established by which grain enlargement was observable with the pure CZTS phase retained. The results demonstrated that laser annealing has the potential to transform nanocrystalline as deposited films into a crystal structure with more intense and sharper diffraction peaks of kesterite structure. The key findings build confidence in laser annealing as an alternative method to enhance the crystallinity, surface morphology, chemical composition of CZTS thin films for nextgeneration PV cells. Laser annealing can potentially reduce the reliance on vacuum furnace heating of PV cells and enable annealing on more thermally sensitive substrates.