Emitter quantum efficiency from contactless photoconductance measurements

As the silicon photovoltaic manufacturing industry continues to mature and expand, there is a demand for new process control and monitoring techniques for production. The spectral response of a solar cell, the short-circuit current per unit incident illumination power as a function of wavelength, is a powerful device characterization tool in research and development. A similar technique, the spectral response of the steady-state photoconductance, is described here. The main advantages of the method are that it is fast, contactless, and can be used immediately after junction formation before metallization. The focus of this paper is on its application to evaluate the carrier collection efficiency of the emitter region. This is demonstrated with modelling results and measurements of silicon solar cell precursors having different emitters with widely varying levels of surface and bulk recombination losses. The results show that it is possible to discern the shortwavelength carrier collection efficiency of the emitter region by comparing the photoconductance response to violet (/spl lambda/=410 nm) and longer wavelength illumination.