Engineering FRET-based carbon dots enables simple and ultrahighly solar-conversive luminescent solar concentrators

Carbon dots (CDs) have been attracting a great deal of attention as an emitter embedded into the waveguide layer to fabricate the luminescent solar concentrators (LSCs). Instead of the single-CDs-based LSCs, a strategy of tandem LSCs was adopted that was designed as a multi-layer structure to diffuse CDs with different emission wavelengths into each layer, thereby promoting the utilization of solar energy. However, the conversion for solar energy still remains significant challenges due to the numerous existing problems. Herein, we successfully synthesized two types of CDs with different fluorescent properties to jointly fabricate LSCs with the single waveguide layer. Benefiting from a variety of surface functional groups, both CDs have suitable Stokes shift and fluorescence quantum yields (FLQYs) are up to 75% for B-CDs and 85% for G-CDs. Especially, the extremely large overlap between the emission spectrum of B-CDs and absorption spectrum of G-CDs provides direct evidence for the occurrence of the Fӧrster resonance energy transfer (FRET) between the two types of CDs, which is confirmed through multiple spectral variations with increasing weights of the CDs in the as-fabricated LSCs. However, because of the concentration effect which occurred with more CDs added, the LSCs achieve the optimal values of 2.85% for ηopt and 2.14% for PCE at a loading of B-CDs = 30 mg and G-CDs = 1mg, which is also along with a solar conversion loss as low as 1.8% (calculation based on the PCE values), far lower than those of the tandem CDs-based LSCs reported recently. Our results demonstrate a simplified method for fabricating the single-waveguide layer LSCs using FRET-based CDs materials, enabling their use as a highly efficient photovoltaic technology for BIPV application.