Visible to near-infrared sensitization of silicon substrates via energy transfer from proximal nanocrystals: Further insights for hybrid photovoltaics

摘要

We provide a unified spectroscopic evidence of efficient energy transfer (ET) from optically excited colloidal nanocrystal quantum dots (NQDs) into Si substrates in a broad range of wavelengths: from visible (545 nm) to near-infrared (800 nm). Chemical grafting of nanocrystals on hydrogenated Si surfaces is achieved via amine-modified carboxy-alkyl chain linkers, thus ensuring complete surface passivation and accurate NQD positioning. Time-resolved photoluminescence (PL) has been measured for a set of CdSe/ZnS and CdSeTe/ZnS NQDs of various sizes and compositions grafted on Si and SiO _2 substrates. The measured acceleration of the PL decays on Si substrates is in good agreement with theoretical expectations based on the frequency-dependent dielectric properties of Si and NQD-Si separation distances. A comparative analysis reveals separate contributions to ET coming from the nonradiative (NRET) and radiative (RET) channels: NRET is a dominant mechanism for proximal NQDs in the middle of the visible range and becomes comparable with RET toward near-infrared wavelengths. The broad range over which the ET efficiency is estimated to be at the level of ～90% further supports the concept that hybrid nanocrystal/silicon thin-film photovoltaic devices could efficiently harvest solar energy across the entire spectrum of wavelengths.