Ru-substitution effect on the FeSe2 thin films properties

• Published in: Journal of alloys and compounds 2021-08, Vol.871, p.159490, Article 159490
• Main Authors: Ouertani, Beya, Boughzala, Habib, Theys, Bertrand, Ezzaouia, Hatem
• Format: Article
• Language: English
• Subjects: Absorptivity; Alloying; Annealing; Aqueous solutions; Electrical; Electrical properties; Ferric chloride; FeSe2; Glass substrates; Hall effect; Iron oxides; Optical; Optical measurement; Optical properties; Photovoltaic; Ruthenium; Ruthenium trichloride; Selenium; Spray pyrolysis; Thin films; Tubes; XRD
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159490

•Ruthenium percentages and the annealing temperatures are the variables having effects on the synthesis of the Ru-alloyed FeSe2 layers as well as on their properties improvement.•Different molar ratios [RuCl3.3H2O][FeCl3.6H2O] = 0.01, 0.0156, 0.10, and 0.25 were used.•The obtained amorphous Ru-alloyed iron oxide were annealed under selenium atmosphere at different annealing temperature (400 °C, 450 °C, 500 °C, and 550 °C).•Simple and low cost method was used: spray pyrolysis.•Optical band gap energy of Ru-alloyed FeSe2 pyrite has been improved to 1,5 eV.•The obtained Fe(1−x)RuxSe2 layers can be used as multispectral photovoltaic cells. [Display omitted] In the aim of improving the FeSe2 thin films properties (structural, optical, and electrical), the ruthenium was incorporated into their composition by the spray pyrolysis technique. Indeed, an aqueous solution of FeCl3.6H2O (0.03 M) was sprayed on pre-heated glass substrates (at 350 °C) for 4 min, on which immediately, another aqueous solution of RuCl3.3H2O with different molar ratios such as [RuCl3.3H2O][FeCl3.6H2O] = 0.01, 0.0156, 0.10, and 0.25, was sprayed for 1 min. The as obtained amorphous films are heated under selenium atmosphere (~10−4 Pa) in sealed tubes at different temperatures (400 °C, 450 °C, 500 °C, and 550 °C) for 3 h into RTP oven and submitted to X-ray diffraction analysis. Iron oxide phases are identified for 400 °C and 450 °C. At 500 °C and 550 °C the PXRD patterns present the FeSe2 phase. For the samples alloyed with the molar ratios of 0.01 and 0.0156 and annealed under selenium atmosphere at 550 °C, the optical measurements showed a high absorption coefficient (α > 4 × 104 cm−1 for wave lengths lower than 800 nanometer) and an amelioration of the corresponding direct band gap value from 1.03 eV (for 0% of ruthenium) to, respectively, 1.50 eV and 1.64 eV, desired values for photovoltaic application. Electrical properties are determined using the Hall Effect measurements. All the obtained Ru-alloyed films showed N-type conductivity. The bulk concentration reached a value about 1020 cm−3 and the sheet concentration reached a value about 1015 cm−2. For the different percentages of ruthenium and at the different annealing temperatures, the conductivity of the as obtained films is the range of 0.057278–89.699 Ω−1 cm−1. The resistivity varies from 0.011148 (Ω cm) to 17.459 (Ω cm). The measured values of the mobility vary from 0.076098 (cm2/(V s)) to 11.71 (cm2/(V s)). The noted improvement