Mechanisms of enhanced optical absorption for ultrathin silicon solar microcells with an integrated nanostructured...

This paper investigates mechanisms of enhanced light absorption exhibited by ultrathin Si solar microcells integrated with a periodically nanostructured, semitransparent metallic reflector. This backside reflector comprises periodic nanoscale relief features formed by soft-imprint lithography with a thin (~35 nm) coating of Au. The work shows that microcells placed in direct contact above the nanostructured reflector's surface creates Fabry-Pérot cavities, which traps impinging light inside the Si slab via the excitation of cavity modes. Experimental measurements show that the short-circuit current and efficiency values for devices incorporating this thin, semitransparent backside reflector outperform similar Si microcells integrated with a planar thick (~300 nm) opaque mirror by ~10-15% because of enhanced absorption. Computational modeling that is supported by experimental measurements reveal that the dominant methods of enhancement stem from a complex interplay between backside diffraction/scattering and Fabry-Pérot resonances. These same data demonstrate that plasmonic interactions contribute minimally to the optical enhancements seen.