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

Abstract

MoOX (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 MoOX film, which is significantly affected by different synthesis methods. In this work, Si solar cells with c-Si(p)/MoOX rear contacts were demonstrated, where the MoOX 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 MoOX. Subsequently, the contact propertieis, crystallinity, chemical states, roughness, density, and refractive indices of MoOX 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.