Water-assisted grown ZnO transparent conductive oxide enables efficient thin-film solar cells

We report the development of a novel water-assisted growth ZnO (HZO) transparent conductive oxide (TCO) deposited by reactive d.c. magnetron sputtering in Ar/O 2 /H 2 O atmosphere. Controlled water dosing acts as a surface surfactant, promoting c-axis oriented columnar grains with enhanced crystallinity and superior carrier transport properties. The HZO films exhibit high optical transparency across the visible spectrum (E g = 3.28 eV) and low resistivity arising from degenerate conduction mechanisms. Electron mobility exceeds 30 cm 2 V -1 s -1 and the carrier concentration is on the order of 10 19 cm -3 , consistent with a Burstein-Moss blue-shift partially compensated by band-gap renormalization. Density Functional Theory (DFT) supports these findings, elucidating the electronic origin of the Fermi level shift and the interplay between band filling and defect. When integrated as a front contact in Sb 2 Se 3 -based solar cell, HZO matches or surpasses conventional ITO or aluminum doped ZnO contacts, improving short circuit current (J sc ) and reducing series resistance due to enhanced light scattering and charge transport. In short, rather than inserting an additional buffer layer, a single HZO layer can directly serve as the TCO, thereby eliminating the free-carrier absorption often seen in ITO as well as the In/Al contamination issues commonly associated with ITO- and AZO-based stacks. The combination of environmentally friendly elements, scalable low-cost manufacturing, and exceptional optoelectronic properties make HZO a promising next-generation TCO solution for sustainable energy technologies.