The application of dopant-free carrier-selective contacts has great advantages in simplifying the fabrication process and has potential to achieve higher power conversion efficiency (PCE) for crystalline silicon (c-Si) solar cells over traditional highly doped ones. In this paper, we demonstrate a material, GdF3, which shows a low work function and forms a low contact resistivity (ρc) Ohmic contact with lightly doped n-type c-Si (n-Si). Besides, the low ρc can be easily repeated and show good stability in an ambient atmosphere within a wide thickness variation (1.4–5.6 nm) for the GdF3/Al stack. Furthermore, the diffusion of Al into the GdF3 layer is observed from the interface image and elemental distribution, which explain its high thickness tolerance. The dopant-free GdF3/Al electron-selective contact is applied to n-Si solar cells with partial rear contact architectures, achieving a champion PCE of 20.71%, demonstrating its great potential for mass production of optical–electrical devices.

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 (TbFx), with an ultra‐low work function of 2.4 eV characteristic, is presented, allowing a low contact resistivity (ρc) of ≈3 mΩ cm2. Additionally, the insertion of ultrathin passivated SiOx layer deposited by PECVD between TbFx and n‐Si resulted in ρc only increase slightly. SiOx/TbFx stack eliminated fermi pinning between aluminum and n‐type c‐Si (n‐Si), which further enhanced the electron selectivity of TbFx on full‐area contacts to n‐Si. Last, SiOx/TbFx/Al electron‐selective contacts significantly improves the open circuit voltage (Voc) for silicon solar cells, but rarely impacts the short circuit current (Jsc) 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.

Commercialized passivated emitter rear cell (PERC) silicon solar cells feature direct contact of metal with silicon, which leads to severe recombination loss and low open circuit voltage (V). To overcome the loss, the authors demonstrate a highly stable and thickness-tolerant dopant-free electron-selective contact consisting of a strontium fluoride/aluminium (SrF/Al) stack. The inserting SrF layer can mitigate the Fermi-level pinning effect between the silicon substrate and the Al electrode. Besides, a relatively low Ohmic contact resistivity of 2 mΩ·cm on lightly doped n-type c-Si can be achieved when using 4 nm of SrF. Moreover, the formed contact within 9 nm SrF is stable for over 5000 hours in the air without encapsulation. Solar cells with this novel dopant-free electron-selective contact reach a power conversion efficiency (PCE) of 21.56%. The promising results and its stable nature, indicate its potential to act as efficient electron-selective contact for various optoelectronic devices.