Low Oxygen Content MoOx and SiOx Tunnel Layer Based Heterocontacts for Efficient and Stable Crystalline Silicon Solar Cells Approaching 22% Efficiency

Abstract In crystalline silicon ( c‐ Si) solar cells, the hole transport layer (HTL) made of high oxygen content MoO x ( x > 2.85, H‐MoO x ) evaporating from molybdenum trioxide is not ideal due to low optical bandgap and interface reaction effects. This limits the power conversion efficiency (PCE) and stability of c ‐Si solar cells. To improve this, low oxygen content MoO x ( x < 2.85, L‐MoO x ) with a wide bandgap of 3.87 eV, deposited using molybdenum dioxide (MoO 2 ), is explored and implemented. The c ‐Si/SiO x (FGA, forming gas annealing)/L‐MoO x heterojunction has a low contact resistivity of ≈15.06 mΩ cm 2 , which is almost one order of magnitude lower than that of c‐Si/SiO x (FGA)/H‐MoO x heterojunction. Using L‐MoO x as the HTL, a c ‐Si solar cell based on the SiO x passivation layer shows a fill factor of 84.38% and PCE of 21.75%, representing the highest efficiency for MoO x ‐based p ‐type c ‐Si solar cells. Scanning transmission electron microscopy results show that the L‐MoO x HTL effectively enhances the stability of c ‐Si solar cells when exposed to air by reducing Ag and Si element diffusion into MoO x . This successful preparation of efficient and stable MoO x HTL films, while preserving their field‐effect passivation ability, provides valuable insights into the development of high‐performance HTL.