A light-trapping structure was fabricated on crystalline Si wafers. In this method, a Ge/Si(001) self-assembled dot structure was etched using KOH and a commercial alkaline solution including nanomask particles. Many nanoscale islands were formed by adding the nanomask particles. The enhancement of light absorption was successfully confirmed in samples with nanostructures after etching. Since the etching margin of a nanostructure was less than 2 µm, the nanostructure could be applied to an ultrathin Si substrate. To investigate the effect of surface passivation on the nanostructure, the nanostructure was passivated using hydrogenated amorphous Si thin films by plasma-enhanced chemical vapor deposition. By quasi-steady-state photoconductance measurement, the suitable implied open-circuit voltage and implied fill factor for heterojunction solar cells were obtained. From calculations based on these parameters, solar cells with nanostructures at a substrate thickness of 100 µm are expected to have a conversion efficiency of 23.21%.

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