Thermal stability of sputtered Mo/polyimide films and formation of MoSe2 and MoS2 layers for application in flexible Cu(In,Ga)(Se,S)2 based solar cells

Molybdenum (Mo) films with a thickness of about 800 nm were room temperature sputtered onto flexible polymeric substrates. Upilex® films were chosen as substrates on the basis of their high thermal endurance and reduced coefficient of thermal expansion. Thermal stability of Mo films has been proved by heat treatment of the Mo/Upilex® structures at a temperature comparable to that used in the preparation of the Cu(In,Ga)(Se,S)₂ absorber layer. A combination of high optical reflectance (maximum values of 75-80%), low electrical resistivity (about 30 μΩ cm) and a smooth surface free of cracks for heated films highlights their good thermal stability. The formation of MoSe₂ and MoS₂ layers, after selenization/sulfurization of the Mo/Upilex® structures, has been further investigated in view of their application as back contact layers in flexible CIGS based solar cells.