Effect of the annealing temperature on the refractive index and extinction coefficient of aluminum-doped zinc oxide: a low-cost electron transport layer

Aluminum-doped zinc oxide (AZO) nanoparticles (NPs) are well-known for their cost-effectiveness, facile deposition, low sintering requirements, and excellent electron mobility, rendering them highly desirable as electron-transporting materials (ETMs) in third-generation photovoltaics. This investigation explores the influence of doping concentration and post-synthesis annealing on the optical properties of AZO. Structural and morphological characteristics were studied using powder X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM). The optical properties of the synthesized NPs were examined via UV–Visible spectroscopy and ellipsometry. The UV–Vis results revealed a red shift in the absorbance peak for samples with higher aluminum content, persisting even after annealing, primarily attributed to alterations in surface characteristics. Moreover, a slight increase in the refractive index (n) and extinction coefficient (k) was observed with escalating doping levels and annealing temperatures.