Numerical simulation and structural optimization of the diffusion furnace for crystal silicon solar cells

The diffusion furnace is an important device for crystalline silicon solar cell production. Given the rapid evolution of solar cell technology, large-scale, high-efficiency and mass-produced diffusion furnaces are required by the market. This puts forward higher requirements for the diffusion furnaces. In this study, a large-scale 3D model is established and validated by measured data in practical diffusion furnace. Its internal temperature, velocity and gas concentration fields are analyzed. The silicon wafer temperatures are found to be high at the top but low at the bottom. The temperature uniformity at both ends of silicon wafer groups is poor. To solve these problems, three structural optimization methods, namely the inlet pipe optimization, adding uniform-flow plates and the quartz boat optimization, are proposed and analyzed. The average mass fraction in the diffusion furnace is improved by 6.311% using the two-tube forked intake pipe. The uniform flow plates with evenly distributed pores on the lower half effectively improve the gas concentration uniformity on silicon wafer surfaces. The optimized quartz boat can improve the temperature uniformity of silicon wafers, though its deformation slightly increases by 0.338%. The silicon wafer temperature differences after quartz boat optimization are 13.77-50.27% smaller than those before optimization, which are conducive to reducing the thermal stress, the risk of thermal damage and the failure during manufacture and utilization of silicon wafers. Results in this study give guidelines for design and utilization of crystal silicon solar cell diffusion furnaces, some of which have been successfully used in Trina Solar Energy Co., China.