Determining the Bulk Lifetime of Unpassivated Multicrystalline Silicon Wafers

Abstract

The determination of the bulk lifetime of bare multicrystalline silicon wafers without the need of surface passivation is a desirable goal. The implementation of an in-line carrier lifetime analysis is only of benefit if the mea- surements can be done on bare unprocessed wafers and if the measured effective lifetime is clearly related to the bulk lifetime of the wafer. In this work we present a detailed experimental study demonstrating the relationship between the effective carrier lifetime of unpassivated wafers and their bulk carrier lifetime. Numerical modelling using the device si- mulation program PC1D is used to describe this relationship for different surface conditions taking into account the im- pact of a saw damage layers with poor electronic quality. Our results show that a prediction of the bulk lifetime from qua- si-steady state photo conductance (QSSPC) carrier lifetime measurements on bare wafers is possible. Based on these re- sults we suggest a simple procedure to implement the analysis for in-line inspection. Furthermore, we examine the rela- tion between the effective lifetime of the bare, unprocessed wafers and the energy conversion efficiencies of solar cells made from neighboring wafers and find a clear correlation independent of the wafer position in the multicrystalline block.