Solution-processed molybdenum oxide for hole-selective contacts on crystalline silicon solar cells

Sub-stoichiometric molybdenum oxide (MoO _x ) films are commonly deposited on crystalline silicon (c-Si) solar cells by thermal evaporation, a process that requires high vacuum and provides limited control of oxide stoichiometry and in consequence limited control of hole transport properties. Here, we report on a method of forming MoO _x films on crystalline silicon wafer surfaces by spin-coating hydrogen molybdenum bronze solutions. It is shown that a ∼2.8 nm thick interfacial SiO _x layer forms under the spin-coated MoO _x films and that the as-deposited MoO _x is amorphous and sub-stoichiometric (x = 2.73), with the concentration of oxygen vacancies in the MoO _x being able to be reduced by annealing in air. The as-deposited MoO _x films show comparable contact resistivity and passivation quality on c-Si wafers to thermally-evaporated MoO _x , demonstrating their potential to be an effective hole-selective contact layer for c-Si solar cells and an alternative for thermally-evaporated films.