Improvements in the techniques for the growth of Si substrates, used for commercial solar cells, have yielded wafers that exhibit low average defect density × typically less than 105 cm−2. We have observed that low defect density leads to the formation of defect clusters. This defect configuration influences the device performance in a unique way × by primarily degrading the voltage-related parameters. We discuss the nature of the defect clusters and show that they constitute regions of high carrier recombination. Network modeling is used to show that, in a device, these regions act as shunts that dissipate power generated within the cell.