Photovoltaic characteristics of screen-printed monocrystalline silicon solar cells (SPSSCs) with molybdenum oxide (MoO x ) as hole-selective layers (HSLs) were demonstrated. A H2/Ar plasma pretreatment (PPT) was incorporated into a MoO x /p-Si(100) interface, which shows the expected quality in terms of passivation. Moreover, the charge trapping characteristics of the MoO x /p-Si(100) interface were presented. The PPT parameters, including power, treated time, flow ratio of H2/Ar, and temperature, were investigated. The experimental results indicate that the Si-H bond with a relatively high intensity was demonstrated for the H2/Ar PPT. The achievement of a conversion efficiency (CE) improvement of more than 1.2% absolute from 18.3% to 19.5% for SPSSCs with H2/Ar PPT was explored. The promoted mechanism was attributed to the reduction of the interface trap density caused by the large number of Si-H bonds at the silicon substrate and MoO x interface.