The European project 20plμs is developing Si wafer solar cells with efficiencies above 20% on wafers less than 100 μm thick. Three principal solar cell process routes are investigated. The three approaches are distinguished by the doping type and maximum process temperature: p-type monocrystalline Cz-Si and multicrystalline Si solar cells subjected to high temperature processes are called pht, and n-type Cz-Si cells fabricated with low and high temperature processes are called nlt and nht, respectively. Already at the project’s midterm, a particular pht solar cell process was transferred to pilot line production. Key issues such as wafering, surface passivation, light trapping, metallisation and life cycle analysis were tackled to determine which process should be transferred. To date, by integrating the processes investigated within the project into full solar cells, efficiencies up to 18.7% (pht), 19.0% (nht) and 20.8% (nlt, 4 cm2) have been achieved on 100 μm thick large area Si wafers
