Influence of thickness on physical and optoelectronic properties of DC sputtered bilayer molybdenum thin films for CIGS solar cell

Abstract

For rear ohmic contact of CIGS solar cell, bilayer Mo thin film on 2 sq- inch glass substrate was deposited using DC sputtering technique. Thickness of bilayer Mo thin film was 300 nm, 500 nm, 1000 nm, and substrate temperature were maintained constant at 215 °C and room temperature. From XRD, FESEM, optical and electrical analysis it was found that Mo bilayer with low thickness (300 nm) have low optical reflectivity 35% and high sheet resistance 2.03 Ω/□ compared to Mo bilayer having high thickness (500 nm and 1000 nm) i.e. about 72% and 0.52 Ω/□. XRD analysis reveals that 300 nm have low crystallite size 6.62 nm while Mo 1000 nm have 12.24 nm. Micro-structure of Mo 500 has closed dense pack dendric structure while 300 nm has columnar growth uneven in size with small circular grains. Slight wide columns appeared for 1000 nm due to interdiffusion of Mo adatoms deposited at pressure 1 mTorr onto 10 mTorr forming homogenous structure.