Study of process induced variation in the minority carrier lifetime of silicon during solar cells fabrication

摘要

A systematic study of the variation in the minority carrier effective lifetime in silicon associated with the different solar cell processing steps in a conventional industrial production line has been carried out using the microwave photoconductive decay (μ-PCD) technique. The solar grade silicon wafers used for this study presented bulk carrier lifetime of ～10 μs and resistivity 0.5-3 Ω cm. Alkali texturing, phosphorus diffusion using POCl_3, thermal oxide growth for surface passivation, plasma etching for edge isolation, and APCVD of TiO_2 for surface passivation and antireflection coating were the major steps taken into consideration. The results clearly showed that the lifetime increased as the fabrication process proceeds from the bare wafer with the exception of the step associated to plasma edge isolation. The effective lifetime of the bare wafer was 4.04 μs, which increased to 16.67 μs after the antireflection coating and surface passivation with TiO_2. The results of a systematic study of the effective minority carrier lifetime of silicon due to different surface passivation processes are also reported. The results obtained are useful for the design and implementation of proper measures for minority carrier lifetime enhancement during silicon solar cell fabrication at the industrial scale.