Employing a uc‐Si:H(P ⁺ )/MoO _x Bilayer Hole Transport Layer for Enhanced Performance in Silicon Heterojunction Solar Cells

In silicon heterojunction (SHJ) solar cells, thinning the hydrogenated microcrystalline silicon hole layer (uc‐Si:H(p + )) reduces its parasitic absorption and increases the short‐circuit current density ( J sc ), but deteriorates passivation, significantly lowering the open‐circuit voltage ( V oc ) and fill factor (FF), thus limiting efficiency. This work proposes and validates an ultrathin nanocrystalline silicon/molybdenum oxide (uc‐Si:H(p + )/MoO x ) bilayer hole transport structure that effectively resolves this tradeoff. The ultrathin uc‐Si:H(p + ) layer within the bilayer minimizes sputtering damage from MoO x deposition and provides a degree of carrier selectivity. The MoO x layer enhances cell passivation by blocking indium diffusion from the transparent conductive oxides (TCO) into the uc‐Si:H(i) layer and passivating dangling bonds at the uc‐Si:H(p + ) surface, thereby boosting V oc . Furthermore, due to its high work function, large conduction band offset, and small valence band offset, MoO x reduces carrier recombination and improves hole extraction and transport, consequently increasing J sc and FF. The champion cell achieved a V oc of 0.72 V, J sc of 40.10 mA/cm 2 , FF of 78.42%, and power conversion efficiency (PCE) of 22.72%, surpassing the performance of the initial cell with an unthinned uc‐Si:H(p + ) layer ( V oc 0.72 V, J sc 38.89 mA/cm 2 , FF 78.10%, PCE 21.82%).