Highly transparent ZnO bilayers by LP-MOCVD as front electrodes for thin-film micromorph silicon solar cells

ZnO bilayer films were deposited by a low-pressure metalorganic chemical vapor deposition technique in a single process step, by doping with boron only the nucleation stage of the growth. The resulting 2 μm thick layers are characterized by low free carrier absorption and electron mobilities over 40 cm2/Vs. They therefore combine high transparency in the infrared region and moderate sheet resistances of 30 Ω/sq. It is thought that the controlled introduction of boron in the early nucleation stage enables its diffusion through the layer, resulting in a very efficient reduction of the sheet resistance compared to samples deposited without doping, while preserving a strong light-scattering interface. These properties make ZnO bilayers ideal electrodes for the development of micromorph thin-film solar cells with enhanced photo-generated current.