Study of Mo selenisation process on different Mo substrates
- PDF / 263,859 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 178 Views
1165-M08-01
Study of Mo selenisation process on different Mo substrates L. Kaupmees1, M. Altosaar1, O. Volobujeva1, P. Barvinschi2 1 Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086, Tallinn, Estonia 2 West University of Timisoara, Faculty of Physics, Bvd. V.Parvan 4, 300223, Timisoara, Romania ABSTRACT In the present work we studied the influence of selenisation temperature, Se vapour pressure and duration of the process on the properties of MoSe2 layer formed on Mo-foil and on sputtered Mo layers on soda lime and Mo-on-ITO glasses. We found that MoSe2 layer thickness (dL) on Mo-foil depended linearly on selenisation time. The thickness of MoSe2 layer on Mo-foil (dL) depended on Se vapour pressure as a function dL ~ PSen , where n ≈ 0.5. The same dependence was also found for sputtered Mo layers in low Se vapour pressure region of 13 – 133 Pa. MoSe2 layer thickness depended on the origin of Mo layer which is related with the density of Mo layer: MoSe2 on Mo foil was thicker than on sputtered Mo. All the MoSe2 layers were full of cracks if Se vapour pressure was higher than 1333 Pa. All tested MoSe2 layers showed p-type conductivity. INTRODUCTION Mo is widely used as a back contact material in thin film solar cells. The main requirements for the back contact are low series resistance and ohmic behaviour in contact with the absorber layer. Matson et. al. [1] and Jaegermann et. al. [2] reported that Schottky barrier was formed. Several groups [2-5] have recognized a very thin MoSe2 layer between CuInGaSe2 absorber layer and Mo back contact layer that improved the back contact quality. MoSe2 grown perpendicularly to the surface of Mo (c-axis parallel to the Mo surface) contributes to the improvement of adhesion at the CIGS/Mo interface and the hetero-contact is found to be ohmic one (p-type MoSe2) [3,4]. Even ZnO:Al ohmic back contacts for CIGS solar cells have been achieved by using a thin Mo interlayer on the ZnO:Al together with additional NaF precursor, that catalysed the redox selenisation of the opaque Mo to transparent MoSe2 during the CuInGaSe2 evaporation process and transformed the rectifying ZnO:Al/CIGS interface into an ohmic contact [6]. MoSe2 formation process has been investigated in many previous works [5, 710]. Jäger-Waldau et. al. [7] have studied the composition and morphology of MoSe2 thin films. They found that the basal plane of the crystallites was oriented either perpendicular or nominally parallel to the Mo substrate surface depending on the used selenium partial pressure. Mallouky et. al. [8] claimed that the c-axis orientation depended strongly on the absorber thin film composition before annealing. They also found that stoichiometric MoSe2 thin films were obtained after appropriate annealing for any kind of Mo substrate and that thin films of MoSe2 crystallize in the hexagonal structure [9]. Abou-Ras et. al. [10], using dc-magnetron sputtered Mo layers on Si substrates and studying the reaction kinetics of the MoSe2 formation, found that the MoSe2 la
Data Loading...
