Ultra-stable carbon quantum dot nanofluids as excellent spectral beam splitters in PV/T applications

Nanofluids have potential application as spectral beam splitters (SBSs) in photovoltaic/thermal (PV/T) systems due to their tunable spectral absorption properties, while current nanofluid SBSs have some disadvantages, which limit their large-scale application in practice. In this work, carbon quantum dot (CQD) nanofluids have been proven to be excellent SBSs in PV/T systems. CQD-nanofluid filters can be synthesized by a simple microwave heating method and show ultra-stability for a long period. Meanwhile, the optical property of CQD nanofluids was fine-tuned by changing the heating time and PEG concentration. The absorption of nanofluids can be enhanced in the whole spectrum by increasing heating time, and the absorption of nanofluids to specific wavelengths can be regulated by adjusting the PEG concentration. The nanofluid filter with 50% PEG concentration and 20 min heating time shows the best performance with a merit function (MF) value of 1.904 when the worth factor ( w ) is 3, which outperforms the reported nanofluid filters in the literature. This work paves the way for the application of ultra-stable CQD nanofluids as SBSs for large-scale utilization in solar energy power generation stations.