Development of a new family of hole transport semiconductor oxides for fully transparent optoelectronic devices

Abstract

Highly crystalline p-type NbxNi1-xO films have been prepared at various concentrations of Nb doping (x = 0–0.17) using a solution growth approach. The films exhibit cubic crystal structures with preferential orientation along the (200) plane. The Nb-doping of NiO films increases the lattice constant, lattice strain, and deformation energy density. The SEM images depict the increase in the grain size of NiO nanocrystals with increasing the Nb concentration. The EDS spectra inspect the stoichiometry of the prepared films. The AFM measurements revealed that the surface roughness increases from 0.4 nm to 2.1 nm with increasing Nb doping. The deposited films showed high optical transparency reaching 80 %. The optical bandgap energy decreases from 3.35 eV to 2.63 eV, and the Urbach tail energy decreases from 0.78 eV to 0.52 eV with the increase of Nb doping. The photoluminescence measurements reveal the suppression of the density of the Ni and O vacancies by 70 % due to the inclusion of Nb doping in the Ni sites. The electrical resistivity of the Nb-doped NiO films decreased by 200 times, the hole mobility increased by 12-fold, and the carrier density increased by 15-fold compared to un-doped NiO films. Owing to these outstanding properties, NbxNi1-xO films are a promising alternative to PEDOT: PSS for developing durable and efficient optoelectronic devices.