Structural and optical studies of molybdenum oxides thin films obtained by thermal evaporation and atomic layer deposition methods for photovoltaic application

MoO_X (X < 3) has shown its promising potential as an efficient hole-selective passivating contact in crystalline Si solar cells. The device performance highly depends on the film properties of MoO_X film, which is significantly affected by different synthesis methods. In this work, Si solar cells with c-Si(p)/MoO_X rear contacts were demonstrated, where the MoO_X films were realized by thermal evaporation (TE), atomic layer deposition (ALD), and UV-assisted ALD (UV-ALD) methods. A pronounced efficiency drop was disclosed with the order of TE, ALD, and UV-ALD MoO_X. Subsequently, the contact propertieis, crystallinity, chemical states, roughness, density, and refractive indices of MoO_X films were systematically characterized by a series of microscopic and spectroscopic analyses. It is found that the TE film is composed of nanocrystals, while ALD methods yield amorphous feature with a smaller density and refractive indices. A mild UV illumination (3.5 mW/cm²) slightly reduces the film roughness, while a stronger (35 mW/cm²) one increases the film density, roughness, and growth rate significantly.