A Novel Ultra-Low Work Function TbFx for High Efficiency Dopant-Free Silicon Solar Cells

The ability of carrier selective contact is mainly determined by the surface passivation and work function for dopant-free materials applied in crystalline silicon (c-Si) solar cells, which have received considerable attention in recent years. In this contribution, a novel electron-selective material, lanthanide terbium trifluoride (TbF_x), with an ultra-low work function of 2.4 eV characteristic, is presented, allowing a low contact resistivity (ρ_c) of ≈3 mΩ cm². Additionally, the insertion of ultrathin passivated SiO_x layer deposited by PECVD between TbF_x and n-Si resulted in ρ_c only increase slightly. SiO_x/TbF_x stack eliminated fermi pinning between aluminum and n-type c-Si (n-Si), which further enhanced the electron selectivity of TbF_x on full-area contacts to n-Si. Last, SiO_x/TbF_x/Al electron-selective contacts significantly improves the open circuit voltage (V_oc) for silicon solar cells, but rarely impacts the short circuit current (J_sc) and fill factor (FF), thus champion efficiency cell achieved approaching 22% power conversion efficiency (PCE). This study indicates a great potential for using lanthanide fluorides as electron-selective material in photovoltaic devices.