Design of μc-Si:H/a-Si:H coaxial tandem single-nanowire solar cells considering photocurrent matching

The single nanowire solar cells (SNSCs) with radial junctions are expected to show the superiority in efficient carrier collection benefited from the largely shortened junction length. Considering that the conversion efficiency of the existing SNSCs is still limited due to the low operation voltage, we design μc-Si:H(core)/a-Si:H(shell) radial tandem SNSCs, giving much attention to the intrinsic optical and electrical properties. The core and shell cells are carefully engineered in order to realize the photocurrent matching. It is found that under matching condition the radius of the entire cell (R) shows linear dependence on the radius of the core cell (r), i.e., R ~1.2r. Under an optimal design of the tandem cell, the open-circuit voltage (photoconversion efficiency) is increased by 160% (34% relative) compared to the equivalent-size μc-Si:H SNSCs.