Micromorph tandem solar cells have been realized growing the intrinsic layers of both amorphous silicon top cell and microcrystalline silicon bottom cell by VHF-PECVD at 100 MHz at low substrate temperature (150 degrees C). The influence of the microcrystalline p-layer on the bottom cell have been studied by growing single microcrystalline devices. For the bottom absorber material two different regimes have been explored by setting the plasma power at 20 W and 33 W. The effect of the structural composition of the microcrystalline absorber layer on the electrical parameters of the device has been investigated. A wider amorphous to crystalline transition region has been found at 33 W, while larger V-OC and FF values have been obtained at 20 W. The highest efficiency (11.1%) has been obtained at 20 W. (c) 2007 Elsevier B.V All rights reserved.