Niobium-doped NiO as p-type nanostructured layer for transparent photovoltaics

Niobium-doped nickel oxide (NiO:Nb) thin films were investigated as p-type layer for all oxide transparent solar cells. The NiO:Nb films were grown by sputtering on room-temperature substrates in plasma containing 50% Ar and 50% O2 gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, exhibiting transmittance of less than 20%. Upon doping with Nb, the film remained p-type, the hole concentration increased from 4.3 x 1018 cm-3 to 1.2 x 1019 cm-3 but the optical properties remained almost the same with the undoped film. The changes in the properties of the films such as structural disorder, energy band-gap, Urbach states and resistivity were correlated with the incorporation of Nb in their structure. Improvement of the optical properties was achieved by thermal treatment at 300 degrees C. The visible transmittance increased to around 50% and the films showed a direct band-gap of 3.65-3.71 eV depending on the amount of Nb in the Ni-O structure. The optimum pNiO:Nb film was used to form a diode with a spin-coated, mesoporous on top of a compact, TiO2 film. The p-NiO: Nb/n-TiO2 heterojunction became transparent after thermal treatment, showing rectifying characteristics. The diode showed photovoltaic behavior upon illumination with ultraviolet light exhibiting short-circuit current density 1.5 & mu;A/cm2 and open-circuit voltage 200 mV. Transparent NiO:Nb films can be realized for all-oxide ultraviolet photovoltaics, tandem solar cells, solar-blind photodetectors and other optoelectronic devices.

Automated summary

Niobium-doped nickel oxide (NiO:Nb) thin films were investigated as p-type layer for all oxide transparent solar cells. The films were grown by sputtering on room-temperature substrates in a plasma containing 50% Ar and 50% O2 gases. The doping of Nb increased the hole concentration while maintaining similar optical properties as the undoped film. Thermal treatment improved the optical properties of the films. The transparent NiO:Nb films have potential applications in various optoelectronic devices.