Tunable Hole-Selective Transport by Solution-Processed MoO3−x Via Doping for p-Type Crystalline Silicon Solar Cells

Molybdenum oxide (MoO 3− x , x < 3) has been successfully used as an efficient hole-selective contact material for crystalline silicon heterojunction solar cells. The carrier transport capability strongly depends on its work function, that is, oxygen vacancies; however, there are lack of effective methods to modulate the multiple oxidation states. Herein, the oxidation states of solution-processed MoO 3− x by doping Nb 5+ to improve its hole-selective contact performance with silicon are tuned. With the optimum doping concentration of 5%, both the reduced Mo 5+ and oxygen vacancies increase, resulting in a decrease in the contact resistivity between the MoO 3− x film and p -type silicon from 161.1 to 62.9 mΩ·cm 2 and an increase of the effective carrier lifetime from 165.4 to 391.0 μs simultaneously. Similarly, the doping of Ta 5+ or V 5+ in MoO 3− x improves the passivated contact performance with silicon, while the former increases the concentration of oxygen vacancies and the latter reduces it. The solar cell with the structure of Ag/MoO 3− x :Nb/ p -Si exhibits a conversion efficiency of 18.37%, which is the highest so far reported for the solution-processed MoO 3− x /silicon heterojunction. This work demonstrates a feasible strategy of tuning hole selectivity in MoO 3− x by doping for high-efficiency solar cells and other optoelectronic device applications.