Characterization and diagnosis of silicon wafers, ingots, and solar cells

This chapter describes the electronic characterization of silicon ingots, wafers, and devices. The focus is on measurements of the effective minority carrier lifetime and their interpretation to extract relevant information about recombination losses in the bulk of the silicon wafer, at the highly doped regions, and at the interfaces between the wafer and passivating or conductive layers deposited onto it. A direct measurement of the open-circuit voltage under variable illumination gives the Suns-V_oc characteristics, which provide most of the parameters needed to model solar cells at the device level, including the total recombination (saturation) current, ideality factor, shunt resistance, and an upper bound on fill factor. The integration of the Suns-V_oc technique with final device testing at standard conditions leads to a reliable method to determine the series resistance of the solar cell at the maximum power point. The chapter outlines the application of these techniques to process monitoring and control, illustrating the correlation between the effective lifetime measured at various stages of fabrication and device performance.