Work function enhancement and interfacial diffusion behaviour of sputtered refractory Mo-W alloy thin films for back-contact engineering

Uncontrolled diffusion and interfacial degradation at refractory metal back contacts remain major bottlenecks to improving the reliability and efficiency of thin film solar cells (TFSCs). This study investigates the structural, electrical, and interfacial properties of Mo thin films, Mo-W0.25 capping layers (Mo-W0.25 CL), and W capping layers (W CL) deposited on Mo back contacts via direct-current magnetron sputtering. Comprehensive structural, morphological, topographical, vibrational, and electrical analyses were performed to elucidate how W incorporation influences microstructure and electronic behaviour. The Mo-W0.25 CL exhibited the smoothest surface (Ra = 3.8 nm) and the highest work function (4.80 eV), which is associated with enhanced surface uniformity and modified electronic structure compared to pure Mo and W CL thin films. Upon selenization at 580 degrees C, the Mo-W0.25Se2 interfacial layer displays localized selenide formation with limited selenium penetration, indicating enhanced resistance to selenium diffusion relative to the Mo and W counterparts. The selenized Mo-W0.25 CL also achieves the low resistivity (58.8 mu Omega cm) while maintaining high carrier concentration and mobility. Overall, the results demonstrate that controlled Mo-W alloying provides an effective strategy to tailor interfacial reactions and electronic properties of refractory back contacts in TFSCs, offering insights into the design of thermally stable metal/semiconductor interfaces for high-temperature electronic applications.