Effect of annealing conditions on phosphorus inward diffusion from N+ Poly-Si layer in N-type TOPCon solar cells

This study focused on optimizing the high-temperature crystallization annealing process in the production of TOPCon solar cells to enhance power conversion efficiency. The annealing process is employed to transform amorphous silicon into polycrystalline silicon (Poly-Si). Furthermore, during this annealing process, phosphorus atoms can form Si–P bonds to achieve effective doping in the Poly-Si layer. The experimental results indicated that, under high-temperature conditions, phosphorus atoms in the Poly-Si layer near the crystalline silicon wafer surface crossed the tunneling layer and infiltrated into the silicon substrate. Intensive inward diffusion resulted in the accumulation of phosphorus close to the wafer surface. The loss of numerous phosphorus atoms in the Poly-Si layer and the accumulation of phosphorus in the wafer readily lead to the formation of an undesirable N−/N+ high-low junction, which is detrimental to carriers' output. However, the annealing condition affects the crystallinity of the Poly-Si layer, which is crucial to providing an excellent passivation effect. This study achieved the optimal annealing conditions for the current N-type TOPCon solar cell production process by adjusting the annealing temperature and crystallization time. Ensuring Poly-Si crystallization and minimizing phosphorus inward diffusion resulted in an approximate 0.1%abs. improvement in cells’ power conversion efficiency.