Complete Report - University of New South Wales

ARCPHOTOVOLTAICSCENTRE OFEXCELLENCE2010/11ANNUAL REPORTPL images of two multicrystallinesilicon wafers. (a) Centre wafer withlow dislocation density, (b) Centrewafer with high dislocation density,(c) bottom wafer with low lifetimeacross the entire wafer area, (d)corner wafer with low dislocationdensity [4.6.1.2].Figure 4.6.1.4Correlation of cell performancedata (normalised) with thedefect density obtained fromthe PL images on the as-cutwafers [4.6.1.1].Figure 4.6.1.5Very good quantitative agreementis observed between the twomeasurements in the central part,i.e. across the majority of the brick.This region is the section of the brickthat is supposed to be used for wafermanufacturing (the very low lifetimetop and bottom regions are supposedto be removed from the ingot).4.6.1.3 Raw wafer inspectionWafer quality in industrialmanufacturing of silicon solar cellsvaries substantially and can have astrong impact on the efficiency ofsolar cells, particularly in the caseof multicrystalline silicon. As-cutwafer inspection of incoming qualitycontrol (IQC) in solar cell productionis therefore indispensable in orderto maintain high efficiencies at highyield in production. To date IQC inproduction typically includes opticalinspection for cracks and large chips, thicknessand total thickness variation, surface morphology,resistivity measurements and in some casesμ-PCD lifetime scanning. A problem with thesetechniques is that the electrical cell performancedoes not correlate sufficiently strongly with thedata resulting from these measurements. One mainreason is surface recombination dominating totalrecombination (and thus effective lifetime) in as-cutwafers. Only wafers with very low bulk lifetime(