Degradation‐Free High‐Efficiency Fluoride‐Coating Solar Cells via Precision Interface Engineering

ABSTRACT Halogen compounds are widely used in many advanced photovoltaic technologies including silicon solar cells, perovskite solar cells, and perovskite/silicon tandem cells. They not only play a key role in passivating inter‐material contacts, but also act as an excellent anti‐reflective layer. Here we reveal that the halogen compound serves as a double‐edged sword for solar cells: on one hand, it maintains an inert surface with good anti‐reflectivity and enhances short‐circuit current density ( J SC ) by up to 0.46 mA/cm 2 , resulting in an enhanced power conversion efficiency ( E ff ) of silicon heterojunction (SHJ) solar cells to 25.37%; on the other hand, it significantly deteriorates the optoelectronic properties in subsequent damp‐heat (DH) tests. Extensive experimental analyses and first‐principles simulations demonstrate that the diffusion of fluoride ions and their subsequent reaction with water under DH conditions is key to such behaviors, producing corrosive substances and creating lattice defects in the microstructure of a‐Si:H/c‐Si(n). Importantly, we successfully reduce E ff degradation from >53 rel.% to 0 rel.% by incorporating a precisely engineered low‐cost dielectric thin layer to impede fluoride diffusion, leading to a degradation‐free high‐efficiency fluoride‐coated SHJ solar cell. This work provides vital insights for maintaining long‐term durability of SHJ and will facilitate wide adoption of high‐stability silicon solar cells and perovskite/silicon tandem devices.