Near-Infrared Emitting Yb3+-doped CsPbX3 (X = Cl, Br) Perovskite Nanocrystals for Luminescent Solar Concentrators

Abstract

Yb3+-doped CsPbX3 (X = Cl, Br) perovskite nanocrystals (NCs) make for excellent luminophores to be used in Luminescent Solar Concentrators (LSCs) due to their low reabsorption and high photoluminescent quantum yield (PLQY). These properties can be attributed to an effect called quantum cutting where one high energy photon is split into two low energy photons. However, this effect is not fully understood just yet. In this thesis, a novel synthesis route to Yb3+-doped CsPbX3 perovskite NCs is presented. Doping is improved by adding more Yb3+ precursor and by performing the synthesis at a higher temperature. At too elevated temperatures the NCs induce scattering. No Yb3+ emission is observed until the samples are anion exchanged, both for bromide and chloride. This observation suggests that the anion exchange somehow activates the Yb3+ emission. Even CsPbBr3 NCs have been synthesized with a high amount of Yb3+ emission through this synthesis route. We suspect that the samples do not exhibit quantum cutting, but instead single Yb3+ emission. However, photon correlation measurements need to be carried out to prove whether the Yb3+ emission is quantum cutting. The NCs have been used to fabricate an LSC. The Yb3+ emission is no longer observed in these LSCs due to stability issues or absorption from the polymer. To investigate the potential of the synthesized NCs in LSC applications, simulations were performed using a software called LightTools. Among the several waveguide materials investigated, polycarbonate was found to be a poor waveguide material for the perovskite NCs and optical quartz glass had the best performance. The Yb3+-doped CsPbBr3 NCs are almost 80% more efficient than Yb3+-doped CsPbCl3 NCs in LSCs. Simulations on this model showed that the luminophore layer thickness has a huge influence on the light that is converted, and both the luminophore and the waveguide layer thicknesses have a big influence on the light lost through attenuation. LightTools proved to be a useful program to calculate the efficiency of LSCs.