High efficiency thin film solar cells with intrinsic microcrystalline silicon prepared by hot wire CVD

Thin film microcrystalline silicon solar cells were prepared with intrinsic absorber layers by Hot Wire CVD at various silane concentrations and substrate temperatures. Independently from the substrate temperature, a maximum efficiency is observed close to the transition to amorphous growth, i.e. the best cells already show considerable amorphous volume fractions. A detailed analysis of the thickness dependence of the solar cell parameters in the dark and under illumination indicate a high electronic quality of the i-layer material. Solar cells with very high open circuit voltages V_oc up to 600mV in combination with fill factors above 70% and high short circuit current densities j_sc of 22mA/cm² were obtained, yielding efficiencies above 9%. The highest efficiency of 9.4% was achieved in solar cells of 1.4μm and 1.8μm thickness. These cells with high V_oc have considerable amorphous volume fractions in the i-layer, leading to a reduced absorption in the infrared wavelength region.