A Oxygen-free Diffusion Technology For Crystalline Silicon Solar Cells

Homojunction crystalline silicon solar cells account for a large share of the photovoltaic market.It is very important to further improve their efficiency.In the process,diffusion is the most core step,which is the decisive factor for the efficiency of the cells.In order to obtain a diffusion technology that is more suitable for the manufacture of the crystalline silicon solar cells than the most popular diffusion with liquid sources such as POCl3/BBr3,and to prevent oxygen atoms diffusion from the surface into the wafers in the diffusion process,we tried some novel methods.In the end,we set done a oxygen-free diffusion technology which is especially suitable for boron diffusion of n-type crystalline silicon solar cells.Oxygen-free diffusion source is the core of this technology,during wihich wafers are diffused at high temperatures with oxygen-free solid diffusion source in an oxygen-free atmosphere,and then oxidizedand gettering at lower temperatures.The main results of this research are as follows:1.Computer simulation analysis shows that the oxygen on the surface of the wafers has a strong ability to diffuse into wafers at high temperatures,especially at the boron diffusion temperature??1000??Its diffusion depth and concentration are far beyond those of boron.The experimental results are consistent with the theoretical analysis.In which,wafers deposited with heavily boron-doped ?-Si:H films were diffused in oxygen atmosphere and oxygen-free atmosphere respectively.XPS was used to test the distribution of oxygen concentration from the surface to the inside of wafers.2.Heavily boron-doped ?-Si:H films and heavily phosphorus-doped ?-Si:H films were used as diffusion sources,seperately.Boron-doped layers were gotten with the sheet resistance in the range of 40-400 ?/sq,the junction depth in the range of 0.4?m-1.2?m,and the surface doping concentration in the range of 1×10-9 cm^-3-1×10²⁰ cm^-3;For phosphorus-doped layers,the sheet resistance in the range of 10-200 Q/sq,the junction depth in the range of 0.3 ?m-1.4 ?m,and the surface doping concentration in the range of 1 × 10²⁰ cm^-3-4×10²⁰ cm^-3 could be accurately controlled.This technology was tried to prepare the p+layer on the back surface of the p-PERC cells.The cells showed good resistance to LID performance.The average LID efficiency attenuation of the cells is 2.97%better than traditional p-PERC cells?4.76%?.Although the average efficiency of the cells is only a low value of 16.62%compared to the traditional p-PERC cells?20.92%?.