Calcium-doped ZnO multifunctional films for enhanced antireflection and surface passivation in silicon-based photovoltaics

Enhancing silicon surface nanostructures remains crucial for improving the efficiency of silicon-based solar cells. In this paper, calcium-doped zinc oxide (Ca:ZnO) thin films with Ca concentrations of 0, 1, 3, and 5 at% were coated on silicon substrates and explored as multifunctional layers combining antireflection and passivation effects. Detailed structural, morphological, and optical characterizations demonstrated that calcium incorporation induces pronounced modifications in the crystallinity, surface morphology, and optical band structure of ZnO films. Reflectance analyses revealed a reduction in optical reflectivity from approximately 34% for bare silicon to 11% for the 5 at% Ca-doped ZnO coating, confirming the effectiveness of the doped films in minimizing surface optical losses. Furthermore, photoconductance lifetime measurements revealed an enhancement in surface passivation, with the effective minority carrier lifetime increasing from 2 μs for the uncoated silicon substrate to 65 μs for the sample coated with 5 at% Ca-doped ZnO. The combined improvement in optical management and electronic passivation highlights the dual functionality of Ca-doped ZnO coatings for crystalline silicon photovoltaics. Overall, fine-tuning the calcium content emerges as a crucial strategy to simultaneously reduce carrier recombination and minimize optical losses, thereby enhancing the antireflection and surface passivation characteristics of silicon substrates.