Energy efficient production: Diode laser annealing of thin film CZTS photovoltaic absorbers

Kesterite Cu 2 ZnSn (S x Se 1-x ) 4 (CZTSSe) solar cells, despite relatively slow progress in efficiency, remain one of the most promising options for PV absorber materials, having demonstrated efficiencies of 14.9% through a non-toxic, solution based eco-friendly approach, attractive for application prospects. These absorber materials necessitate a post-deposition high-temperature furnace annealing, which is essential for improving crystallinity and enhancing their electrical properties. A vital issue with thin films is the need to undergo an energy intensive, relatively slow annealing process involving batch processing in a furnace. To address the challenges with this process stage, this work demonstrates an alternative strategy that offers rapid, localised heating of kesterite thin film using a continuous wave (CW) 808 nm diode laser annealing. Control of the laser’s beam profile and careful selection of processing parameters, such as power and ambient conditions, enabled advanced control over the annealing process, enhancing the film’s crystallinity and grain size, confirmed using Raman and SEM analysis. This paper also presents an analysis of the energy requirements, demonstrating laser annealing to be of the order 25 times more energy efficient than furnace annealing. Further optimising this approach could enable industrial scale-up for low carbon production of photovoltaics.