Optical and photoelectrochemical properties of transparent NiO quantum dots

Intrinsic p-type NiO quantum dots were applied to study the thickness-dependent optical properties and photoelectrochemical performances. The reactive sputtering method was applied to grow quality NiO quantum dots (size of 5-7 nm) at a room-temperature for large-scale production. By controlling the NiO film thickness, the optical and photoelectrochemical features can be modulated, which are for the blue shift of band gap value (from 3.6 eV to 3.9 eV, Burstein-Moss shift), enhanced optical absorption, electrical conductivity, and a shift of flat band potential. A thin NiO film (50 nm) exhibited the same amount of photocurrent that of the 200 nm-thick NiO film. This strongly suggests the intensive light absorption property of the NiO film to illuminate of possibility of thin film uses. The transparent optical property and degenerate nature of NiO quantum dots will be a great interest to integrate them with low bandgap materials for the advantage of high light absorption and heterojunction for the water-splitting and hydrogen production.