Sub-stochiometric MoO_x by radio-frequency magnetron sputtering as hole-selective passivating contacts for silicon heterojunction solar cells

The silicon heterojunction (SHJ) solar cell has long been considered as one of the most promising candidates for the next-generation PV market. Transition metal oxides (TMOs) show good carrier selectivity when combined with c-Si solar cells. This has led to the rapid demonstration of the remarkable potential of TMOs (especially MoO_x) with high work function to replace the p-type a-Si:H emitting layer. MoO_x can induce a strong inversion layer on the interface of n-type c-Si, which is beneficial to the extraction and conduction of holes. In this paper, the radio-frequency (RF) magnetron sputtering is used to deposit MoO_x films. The optical, electrical and structural properties of MoO_x films are measured and analyzed, with focus on the inherent compositions and work function. Then the MoO_x films are applied into SHJ solar cells. When the MoO_x works as a buffer layer between ITO/p-a-Si:H interface in the reference SHJ solar cell, a conversion efficiency of 19.1% can be obtained. When the MoO_x is used as a hole transport layer (HTL), the device indicates a desirable conversion efficiency of 17.5%. To the best of our knowledge, this current efficiency is the highest one for the MoO_x film as HTL by RF sputtering.