Hydrogenated microcrystalline silicon prepared at low temperatures by the glow discharge technique is examined here with respect to its role as a new thin-film photovoltaic absorber material. XRD and TEM characterizations reveal that microcrystalline silicon is a semiconductor with a very complex morphology. Microcrystalline p-i-n cells with open-circuit voltages of up to 560-580 mV could be prepared. `Micromorph' tandem solar cells show under outdoor conditions higher short-circuit currents due to the enhanced blue spectra of real sun light and therefore higher efficiencies than under AM1.5 solar simulator conditions. Furthermore, a weak air mass dependence of the short-circuit current density could be observed for such micromorph tandem solar cells. By applying the monolithic series connection based on laser patterning a first micromorph mini-module (total area of 23.6 cm2) with 9% cell conversion efficiency could be fabricated.