B-Site Doping in Metal Halide Perovskite Nanocrystals
Colloidal nanocrystals of lead halide perovskites exhibit interesting structural, optical and optoelectronic properties, some of which are very different compared to their bulk counterparts. In the last four years, we have been working on cesium lead halide perovskite nanocrystals and Pb-free metal halides such as thallium halide, cesium antimony halide, and cesium bismuth halide nanocrystals. While I will talk about a few aspects of material design and photophysical properties Pb-halide and Pb-free halide nanocrystals, the major emphasis will be on our recent results on Mn and Yb doped into the B-site (Pb-site) of metal halide perovskite nanocrystals.
We have developed a post-synthesis doping method where Mn and Yb are doped into pre-formed colloidal CsPbX3 (X = Cl, Br, I) nanocrystals. The dopants Mn and Yb emits in the red and near-infrared regions, with huge (~1 eV) Stoke's shift compared to the absorption (of host) spectrum. We have got similar downconversion luminescence by doping Mn and Yb into Pb-free Cs2AgInCl6 double perovskites as well. This down-conversion luminescence can convert the UV-blue solar light to red-NIR light. Note that the photoconversion efficiencies of UV-blue light is significantly lower compared to that of red-NIR light for Si and CIGS solar cells. Therefore, a coating of our doped nanocrystals on top of traditional solar cells has the potential to improve solar cell efficiency.