Molybdenum incorporated Cu1.69ZnSnS4 kesterite photovoltaic devices with bilayer microstructure and tunable optical-electronic properties

•Mo incorporated CZTS with no secondary phases deposited by magnetron co-sputtering.•Formation of bilayer CZTS absorber with different grain microstructure and porosity.•Mo enhances P-type conductivity and absorbance of CZTS for wavelengths <600 nm.•Voc deficit, Jsc, and FF improved for CZTS/CdS devices with optimized Mo content.•PCE of optimized Mo incorporated CZTS solar cell increased to 5.49% from 1.63%