Synthesis of Iron Pyrite Film through Low Temperature Atmospheric Pressure Chemical Vapor Deposition
Pyrite phase of FeS2 has attracted substantial attention in the field of thin film solar technology because of its high optical absorption coefficient (~5 x 105 cm-1 at hν > 1.3eV) and the band gap of 0.95 eV. In this research, we have grown highly pure iron pyrite films using a low temperature atmospheric pressure chemical vapor deposition technique. The synthesis temperature is in the range of 375-400°C and Di-tert-butyl disulfide (TBDS) is used as the sulfur precursor. TBDS is a safe and low cost sulfur source unlike H2S, which is costly, highly toxic and requires extreme care in handling. The films obtained were uniform and free from common impurity phases such as troilite and marcasite. The FeS2 films grown earlier with CVD synthesis and sulfurized using H2S had pinholes and contained secondary phases like marcasite and troilite. The FeS2 pyrite phase was confirmed using various characterization techniques that included SEM, EDS, XRD and XPS.
Development of Low Cost and Earth Abundant Zinc Phosphide based Thin Film Solar Cells
Recent trend in thin film solar cells is to use earth abundant and non-toxic materials such as zinc and iron. Zinc phosphide (Zn3P2) has been explored as a choice for solar cell absorber and is currently reviving attention. Zinc phosphide based solar cell is synthesized from earth-abundant constituents. Our group has already synthesized the zinc phosphide films and nanowires which have been published earlier. Now, the experimental parameters have been further optimized in which the zinc phosphide film and nanowires are grown at a further low temperature of 300°C and are grown using zinc film instead of zinc foil giving us the flexibility of using various substrates. In this study, Trioctylphosphine (TOP) is used as a source of phosphorous which reacts with zinc and results in the growth of Zn3P2. The zinc phosphide phase has been successfully synthesized in both bulk thin film and nanowires form. The solar cells have been made using the zinc phosphide film as the p-type absorber. And, cadmium sulfide is being used as n-type hetero junction candidate in the initial experiments. We report efficiency ~ 0.1% using this zinc phosphide based thin film solar cell. The films have been characterized using SEM/EDS, XPS, XRD and PL.