On-going price reductions with wafer-based cells is making silicon technology increasing difficult to dislodge. With market leaders expected to be manufacturing modules above 16% efficiency at $0.36/Watt by 2017, even the cost per unit area ($60-$70/m2) will be difficult for thin-film technologies to significantly undercut. This may make dislodgement likely only by appreciably higher energy conversion efficiency approaches. A silicon waferbased cell able to capitalize on on-going cost reductions within the mainstream industry but with an appreciably higher than present efficiency might therefore provide the ultimate PV solution. With average selling prices of 156 mm quasi-square monocrystalline Si wafers recently approaching $1 (per wafer), wafers now provide clean, low cost templates for overgrowth of thin, wider bandgap high performance cells, nearly doubling silicon’s ultimate efficiency potential. The range of Si-based tandem approaches are reviewed together with recent results and ultimate prospects.