Paper SS-TuP14
Dependence on an O₂ Gas Flow Rate of NiO Thin Films Prepared by Reactive Magnetron Sputtering

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

As one solution to the power shortage and global warming, a renewable energy such as solar cells is desired. Silicon-based solar cells having over 30% in the theoretical efficiency are the present mainstream, however the single crystal-silicon has a problem on the manufacturing cost. Further more the high purity silicon that is the main raw material for solar cells is insufficient worldwide, and so a new solar cell without silicon that is replaced silicon-based solar cells has been required. Practical application of oxide-based thin film solar cells is expected in reduction of energy costs or environmental loads.

Generally a typical oxide-based thin film solar cell is a wet dye-sensitized solar cell composed of an electrolyte, an electrode of titanium oxide and a sensitizing dye. Recently a solid-state dye-sensitized solar cell which uses metal oxides instead of an electrolyte has been studied.

In our previous study on TiO₂/Cu₂O solid-state dye-sensitized solar cells, the problem was Cu diffusion from underlayer Cu₂O. The diffusion of Cu induced collapse of p-n junction. In this study, we used NiO as a next p-type oxide semiconductor instead of Cu₂O. The NiO thin film is used as the transparent oxide semiconductor. Most of the transparent oxide semiconductors are an n-type semiconductor, while NiO is a p-type semiconductor. The NiO thin films prepared by changing an oxygen gas flow rate were evaluated by crystallinity, optical properties, semiconductor properties, surface morphology in comparison with Cu₂O thin films.

NiO thin films were fabricated by reactive magnetron sputtering. As substrates, the glass (Corning#1737) and ITO-film coated glass were ultrasonically cleaned. The NiO thin film was deposited on those substrates using pure metallic nickel (99.99%) as a sputtering target material in an oxygen gas atmosphere. The flow rate of an argon gas for sputtering was 20 sccm. The flow rate of an oxygen gas was changed at 2.0 sccm, 2.7 sccm, 3.2 sccm, 3.7 sccm and 4.4 sccm. A thickness of the NiO thin films was kept at about 200 nm.

The NiO thin films were successfully fabricated by reactive magnetron sputtering. The XRD pattern of the NiO thin film showed the stronger peak at the (012) crystal plane of NiO, when the flow rate of an oxygen gas was lower. The resistivity of NiO thin films showed a higher value than that of Cu₂O thin film and the mobility of NiO thin films showed a lower value than Cu₂O.