Improved photon absorption in dye-functionalized silicon nanocrystals synthesized via microwave-assisted hydrosilylation

Luminescence-guided and visibly transparent solar concentrators based on silicon quantum dots

In this work, we demonstrate a new tapered prism-shaped luminescent solar concentrator (LSC), which guides most of the luminescence toward one edge instead of four, for the solar window application. Only one Si photovoltaic (PV) strip attached to the light-emitting sidewall is needed to collect the luminescence, which further reduces PV material cost and avoids electrical mismatch. To achieve high visible transmission and mitigate reabsorption, colloidal silicon quantum dots (SiQDs) with ultraviolet-selective absorption and large Stokes shift are used as the fluorophores. With the SiQD concentration equal to 8 mg mL^-1, the SiQD-LSC as a solar window can attain a power conversion efficiency (PCE) equal to 0.27%, while ensuring high average visible transmission (AVT = 86%) and high color rendering index (CRI = 94 with AM1.5G as the incident spectrum). When adjusted to front-facing, the Si PV strip can harvest not only the direct sunlight but also the concentrated SiQD fluorescence guided from the LSC. As a result, the overall solar window PCE can be increased to 1.18%, and the PCE of the front-facing Si PV strip alone can be increased by 7% due to the luminescence guided from the SiQD-LSC.

Luminescent silicon nanocrystals appended with photoswitchable azobenzene units

Confinement of multiple azobenzene chromophores covalently linked at the surface of luminescent silicon nanocrystals preserves the photoswitching behavior and modulates the nanocrystal polarity. Concomitantly, the thermal Z→E isomerization is strongly accelerated and the nanocrystal luminescence is reduced by an energy transfer process resulting in photosensitized E→Z isomerization.

Enhancing Singlet Oxygen Generation in Conjugates of Silicon Nanocrystals and Organic Photosensitizers

Silicon nanocrystals (SiNCs) are regarded as a green and environmentally friendly material when compared with other semiconductor nanocrystals. Ultra-small SiNCs (with the size 4.6-5.2 nm) demonstrate strong UV absorption and photoluminescence in the near infrared (NIR) range with the high photoluminescence quantum yield (PLQY) up to 60%. In contrast to nanoporous silicon, ultra-small SiNCs do not possess an intrinsic ability to generate singlet oxygen (1O2). However, we demonstrate that SiNC-dye conjugates synthesized via microwave assistant hydrosilylation reaction produce 1O2 with moderate quantum yield (ΦΔ) up to 27% in cyclohexane. These interesting results were obtained via measurements of singlet oxygen phosphorescence at 1,270 nm. SiNCs play an important role in the production of singlet oxygen as SiNCs harvest UV and blue radiation and transfer absorbed energy to a triplet state of the attached dyes. It increases the population of the triplet states and leads to the enhancement of the singlet oxygen generation. Simultaneously, the SiNC-dye conjugates demonstrate NIR luminescence with the PLQY up to 22%. Thus, the luminescence behavior and photosensitizing properties of the SiNC-dye conjugates can attract interest as a new multifunctional platform in the field of bio-applications.