Systematic inspection on the interplay between MoNa-induced sodium and the formation of MoSe2 intermediate layer in CIGSe/Mo heterostructures

Abstract

The critical impact of sodium-doped molybdenum (MoNa) in shaping the MoSe₂ interfacial layer, influencing the electrical properties of CIGSe/Mo heterostructures, and achieving optimal MoSe₂ formation conditions, leading to improved hetero-contact quality. Notably, samples with a 600-nm-thick MoNa layer demonstrate the highest resistivity (73 μΩcm) and sheet resistance (0.45 Ω/square), highlighting the substantial impact of MoNa layer thickness on electrical conductivity. Controlled sodium diffusion through MoNa layers is essential for achieving desirable electrical characteristics, influencing Na diffusion rates, grain sizes, and overall morphology, as elucidated by EDX and FESEM analyses. Additionally, XRD results provide insights into the spontaneous peeling-off phenomenon, with the sample featuring a ~ 600-nm MoNa layer displaying the strongest diffraction peak and the largest crystal size, indicative of enhanced Mo to MoSe₂ conversion facilitated by sodium presence. Raman spectra further confirm the presence of MoSe₂, with its thickness correlating with MoNa layer thickness. The observed increase in resistance and decrease in conductivity with rising MoSe₂ layer thickness underscore the critical importance of optimal MoSe₂ formation for transitioning from Schottky to ohmic contact in CIGSe/Mo heterostructures. Ultimately, significant factors to the advancement of CIGSe thin-film solar cell production are discussed, providing nuanced insights into the interplay of MoNa and MoSe₂, elucidating their collective impact on the electrical characteristics of CIGSe/Mo heterostructures.

Keywords: CIGSe; Energy; MoNa; MoSe2; Molybdenum; Sodium; Solar cells; Sputtering.