Gadolinium Fluoride As a High-Thickness-Tolerant Electron-Selective Contact Material for Solar Cells

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 (rho(c)) Ohmic contact with lightly doped n-type c-Si (n-Si). Besides, the low rho(c) 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.