Ultrafast Laser-Annealing of Hydrogenated Amorphous Silicon in Tunnel Oxide Passivating Contacts for High-Efficiency N-Type Silicon Solar Cells

Abstract

The tunnel oxide passivated contact (TOPCon) concept has for the last few years been the brightest shining star in the field of emerging passivating contact techniques. It has shown great potential in industrial applications due to overwhelming advantages for high device efficiency and low cost. Here, we introduce a novel crystallization method using ultrafast laser-annealing by scanning a laser spot onto the surface of hydrogenated amorphous silicon (a-Si:H) film in TOPCon solar cells. By circumventing the high-temperature environment of the conventional annealing process, it is able to prevent a large number of dopant atoms from penetrating inside the crystalline silicon (c-Si) substrate during the diffusion process, reducing the Auger recombination. Moreover, we conduct extensive experiments to clarify the optimal conditions, including laser-annealing modes and process parameters. The hydrogenation experiments reveal that direct appropriation of the traditional hydrogenation method is not applicable. An additional “dehydrogenation” step proves to be necessary, which indicates that the differences in hydrogen content within the films due to the divergence between the principles of laser-annealing and high-temperature annealing are probably responsible for this. Consequently, the proof-of-concept devices using laser-annealing technology realize a champion efficiency of approaching 20%. To our knowledge, this is the first combination of this technology with TOPCon solar cells that has been announced to date, highlighting an alternative technical route with substantial potential to achieve high-efficiency c-Si solar cells.

Keywords: Tunnel oxide passivating contact, laser-annealing, crystallization, solar cell