Microcrystalline silicon (μc-Si:H) prepared by plasma-enhanced chemical vapor deposition (PECVD) has been investigated as material for absorber layers in solar cells. The deposition process has been adjusted to achieve high deposition rates and optimized solar cell performance. In particular, already moderate variations of the crystalline vs. amorphous volume fractions were found to effect the electronic material - and solar cell properties. Such variation is readily achieved by changing the process gas mixture of silane to hydrogen. Best cell performance was found for material near the transition to the amorphous growth regime. With this optimized material efficiencies of 7.5% for a 2 μm thick μc-Si:H single solar cell and 12% for an a-Si:H/μc-Si:H stacked solar cell have been achieved.