Investigation of microstructural and optical properties of (K,Ba)(Ni,Nb)O_3-δ thin films fabricated by pulsed laser deposition

Perovskite-type ferroelectrics are increasingly being studied for applications in solar-energy conversion because of their efficient ferroelectric polarization-driven carrier separation and above-bandgap generated photovoltages. (K,Ba)(Ni,Nb)O_3-δ ferroelectric films, a highly promising and low-cost absorber layer material for solar cells, have been fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates for the first time, using a modified pulsed laser deposition method. Well-crystallized near-stoichiometric (K,Ba)(Ni,Nb)O_3-δ film was obtained by adjusting the target-substrate distance to 50 mm and setting the substrate at an oblique angle of ∼11° from the plume axis. Microstructural characterizations show the as-grown film exhibits a single-phase perovskite structure with a dense and uniform surface. The optical absorption spectrum of (K,Ba)(Ni,Nb)O_3-δ has two main peaks, i.e., a significant peak at the intermediate energy adjacent to a much larger peak at higher photon energy, which indicates intraband multiple electronic transition. The present results could be crucial for potential solar-energy device applications.