Solution-based hafnium oxide thin films as potential antireflection coating for silicon solar cells

Hafnium oxide (HfO2) thin films were formed by spin coating deposition and annealed in ambient air. Following the molarity optimization of hafnium content in the solution, effect of spin coating and thermal processes on the antireflection properties were analyzed. Characterizations were carried out by spectrophotometer, X-ray diffraction, spectroscopic ellipsometer and scanning electron microscopy measurements. Post deposition annealing temperatures range from 500 to 1000 °C. Annealing led the crystallinity of the films above 500 °C and possess monoclinic phase. Average reflectivity of 11.32% was achieved with 71.36 nm HfO2 film after annealing at 700 °C. Ellipsometer measurements reveals refractive index of such a film as 1.934 at 600 nm. Average reflectance increases when annealing temperature is over 700 °C mainly due to the increase of refractive index which is recorded as 2.05 after annealing at 800 °C. Fresnel equations, transfer matrix method and PC1D simulations were carried out for reflectance spectra approximations. The experimental results and the theoretical data were relatively comparable. Spin coating HfO2 thin films are found promising as an antireflection layer for solar cells.