NiO thin films synthesized by sol-gel: Potentiality for the realization of antireflection layer for silicon based solar cell applications

In this work we present a study on the effect of nickel oxide (NiO) thin films deposited by sol-gel technique on the optical reflectivity of silicon substrates with and without a thin porous layer. Up to six layers of NiO have been deposited at the same optimized experimental conditions. The as-deposited films were pre-heated at 300 °C for 10 min and then annealed in ambient atmosphere at 600 °C for 1 h The reflectivity spectra were measured by using a UV-vis spectrophotometer. The reflectivity of the untreated silicon is about 45% within 300-1200 nm spectral range. It was found that the reflectivity decreases after the deposition of the NiO thin layers. The minimum value of the reflectivity (about 15%) is obtained after the deposition of two layers of NiO. For a higher number of NiO layers, the reflectivity increases but remains still lower than that of the untreated silicon. Then, after the optimization on the number of layers, NiO thin films are treated at various temperatures after being deposited at the same experimental conditions. The Surface morphology of the NiO films was investigated by atomic force microscopy (AFM). The surface morphology of the NiO thin films has a pyramidal nano-textured surface and changes by varying the number of layers. The porous silicon thin films were elaborated using the chemical vapor etching technique. It was found that the total reflectivity decreases by increasing the etching time. The optimal result corresponding to a reflectivity of 12% was obtained by combination of NiO and PS to form NiO/PS structure.