Influence of microcrystalline silicon bottom cell on micromorph tandem solar cell performance

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 °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 VOC and FF values have been obtained at 20 W. The highest efficiency (11.1%) has been obtained at 20 W.