Optical Study of Cuprous Oxide and Ferric Oxide Based Materials for Applications in Low Cost Solar Cells THI CUC THAN, 1 BAO THOA BUI, 1 BENJAMIN WEGMULLER, 2 MINH HIEU NGUYEN, 1 LAM HUONG HOANG NGOC, 1 VAN DIEP BUI, 1 QUOC HUNG NGUYEN, 1 CHI HIEU HOANG, 3 and THUAT NGUYEN-TRAN 1,4 1.—Nano and Energy Center, VNU University of Science, 334 Nguyen Trai, Thanh Xuan District, Hanoi, Vietnam. 2.—Polytech Lille, University Lille 1, Avenue Paul Langevin, 59655 Villeneuve d’Asq Cedex, France. 3.—Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan District, Hanoi, Vietnam. 4.—e-mail: thuatnt@vnu.edu.vn One of the interesting forms of cuprous oxide and ferric oxide based materials is CuFeO 2 which can be a delafossite-type compound and is a well known p- type semiconductor. This compound makes up an interesting family of mate- rials for technological applications. CuFeO 2 thin films recently gained re- newed interest for potential applications in solar cell devices especially as absorption layers. One of the interesting facts is that CuFeO 2 is made from cheap materials such as copper and iron. In this study, CuFeO 2 thin films are intentionally deposited on corning glass and silicon substrates by the radio- frequency and direct current sputtering method with complicated and well developed co-sputtering recipes. The deposition was performed at room tem- perature which leads to an amorphous phase with extremely low roughness and high density. The films also were annealed at 500°C in 5% H 2 in Ar for the passivation. A detailed optical study was performed on these thin films by spectroscopic ellipsometry and by ultra-violet visible near infrared spec- troscopy. Depending on sputtering conditions, the direct band gap was extrapolated to be from 1.96 eV to 2.2 eV and 2.92 eV to 2.96 eV and the indirect band gap is about 1.22 eV to 1.42 eV. A good electrical conduction is also observed which is suitable for solar cell applications. In future more study on the structural properties will be carried out in order to fully understand these materials. Key words: CuFeO 2 thin film, co-sputtering method, optical properties, solar cells INTRODUCTION Cuprous oxide (Cu 2 O) is known to be one of the oldest p-type binary oxide semiconductor materials and it is a promising candidate for applications in solar cells. The reasons why Cu 2 O is interesting in the solar cell research community are (i) non toxicity, (ii) good absorption in the range of visible and near infrared wavelength, (iii) Cu is an abundant material on earth and (iv) low fabrica- tion cost. 1 Due to the relatively low direct band gap, about 2.17 eV 2 Cu 2 O is a more favorable material in applications for solar cells than for transparent conductive oxide (TCO), but there have been few publications of solar cells based on Cu 2 O. Recently, the p-type Cu 2 O/n-type ZnO heterojunction solar cell with a power conversion efficiency (PCE) of about 3.8% was reported. 3 Other works were also performed with PCE less than 1%, 4 even though the expected PCE of Cu 2 O should be around 18%. 5 Another interesting aspect of Cu 2 O is its ability to combine with other oxides for making delafossite based p-type TCOs. There are quite various reports (Received October 10, 2015; accepted January 13, 2016) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-016-4353-4 Ó 2016 The Minerals, Metals & Materials Society