Stable tandem luminescent solar concentrators based on CdSe/CdS quantum dots and carbon dots.

Luminescent solar concentrators (LSCs) serve as large-area sunlight collectors, which are suitable for applications in semi-transparent, low-cost photovoltaics. Colloidal quantum dots (QDs) are promising candidates as a new type of absorber/emitter in LSCs, due to their size-tunable wide absorption spectrum, narrow emission spectrum, high quantum yield and structure-engineered large Stokes shift. However, due to the lack of long-term photo-stability of QDs, it is still a challenge to prepare photostable LSCs. Compared with colloidal QDs, carbon dots (C-dots) exhibit excellent photo-stability, presenting a very promising solution to improve the long-term photo-stability of quantum dot based LSCs. Here, as a proof-of-concept, we report the enhancement of the photo-stability of LSCs based on CdSe/CdS QDs by using a tandem structure of LSCs. We fabricated a large-area (∼100 cm²) thin film and placed this thin film on the top of a luminescent solar concentrator (LSC) based on CdSe/CdS QDs. The as-fabricated semi-transparent tandem device exhibits an external optical efficiency of ∼1.4% under one sun illumination, which is a 16% enhancement in the efficiency over the LSC based on CdSe/CdS QDs. More importantly, the presence of C-dots largely enhances the photo-stability of the LSC device based on CdSe/CdS QDs under ultraviolet (UV) illumination. After 70 hour UV illumination, the QD-based LSC with a protective layer of C-dot thin film retains 75% of its initial integrated photoluminescence intensity, which is 1.8 times higher than that of the LSC without the C-dot layer. Our work indicates that C-dots can be used as an additional layer in LSCs to enhance both the efficiency and long-term photo-stability. [ABSTRACT FROM AUTHOR]