Preparation of n+ emitter on p-type silicon wafer using the spin-on doping method

There is a strong need for cost reduction in manufacturing crystalline silicon solar cells, and one of the approaches is to merge two steps of silicon wafer processing into one step without degrading the performance of solar cells. In this work, we intended to employ the spin-on doping (SOD) method for the purpose of dual tasks, phosphorus diffusion to form n⁺ emitters and antireflection coating (ARC) to reduce optical reflection. Different from the commercial SOD solutions based on SiO₂, we used tetraethylorthosilicate (TEOS) to prepare SOD solutions containing different concentrations of phosphorus acid as the phosphorus doping source. We first investigated the dependence of the sheet resistance of the n⁺ emitters on the concentration of phosphorus acid in the SOD solution as well as the thermal diffusion temperature and time. It was found that all these three factors can effectively influence the sheet resistance of the n⁺ emitters, suggesting a relatively easier optimization process for forming n⁺ emitters using the SOD method. The SOD thin films formed after the thermal diffusion process were found to be SiO₂ films. We then investigated the antireflection properties of the as-grown SOD thin films, and found that they can effectively reduce the optical reflection of silicon wafers.