Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

The tunnel oxide passivated contact (TOPCon) concept has been the brightest star in the field of emerging passivating contact techniques for the last few years. It has shown great potential in industrial applications due to the overwhelming advantages of 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 film in TOPCon solar cells. By circumventing the high-temperature environment of the conventional annealing process, it can prevent a large number of dopant atoms from penetrating inside the crystalline silicon (c-Si) substrate, reducing the Auger recombination. Moreover, we can 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 necessary, indicating 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 19.91%,highlighting an alternative technical route with substantial potential to achieve high-efficiency crystalline silicon solar cells.