Full potential of radial junction Si thin film solar cells with advanced junction materials and design

Combining advanced materials and junction design in nanowire-based thin film solar cells requires a different thinking of the optimization strategy, which is critical to fulfill the potential of nano-structured photovoltaics. Based on a comprehensive knowledge of the junction materials involved in the multilayer stack, we demonstrate here, in both experimental and theoretical manners, the potential of hydrogenated amorphous Si (a-Si:H) thin film solar cells in a radial junction (RJ) configuration. Resting upon a solid experimental basis, we also assess a more advanced tandem RJ structure with radially stacking a-Si:H/nanocrystalline Si (nc-Si:H) PIN junctions, and show that a balanced photo-current generation with a short circuit current density of J_sc=14.2mA/cm² can be achieved in a tandem RJ cell, while reducing the expensive nc-Si:H absorber thickness from 1-3 μ m (in planar tandem cells) to only 120nm. These results provide a clearly charted route towards a high performance Si thin film photovoltaics.