Interface Contact Optimization via Phosphomolybdic Acid Enables 24.9% Efficiency in MoO_X-Based Silicon Solar Cells

The development of cost-effective carrier-selective passivating contacts is critical for enhancing the commercial feasibility of silicon compound solar cells. Molybdenum oxide (MoO_X) has garnered considerable interest as a promising hole transport layer (HTLs). A key advantage of MoO_X is high work function, in addition to the low-cost processability. However, in silicon photovoltaics, MoO_X-based p-type contacts face fundamental limitations at hydrogenated amorphous silicon (i-a-Si:H)/MoO_X interface, where oxygen vacancy defects lower work function, as well as, weak van der Waals-dominated interactions impair charge carry transport. To address these challenges, we introduced an ultrathin phosphomolybdic acid (PMA) interlayer at the i-a-Si:H/MoO_X interface. PMA passivated oxygen vacancy defects, resulting in a notable improvement in open-circuit voltage from 713 to 730 mV, and 0.11 eV work function elevation via dipole formation; meanwhile, PMA strengthened the interfacial bonding energy, reducing saturation current density and contact resistance by 63% and 24%, respectively, contributing to a fill factor enhancement from 83.7% to 84.9%. In the end, we demonstrated a record efficiency of 24.9% for MoO_X-based silicon solar cells, which provides valuable insights for developing high-performance MoO_X HTL devices for dopant-free p-type contact technologies.