The 1000x efficiency headline is from Figure 4 of the source PDF: https://advances.sciencemag.org/content/advances/7/23/eabe42... Units are Amps per miliwatt on the Y axis and electron volts on the X axis. The black BTO line has a minimum of around 1x10^-10 at 2.8 eV, which is the energy of a photon in 450 nm blue light, and the red SBC222 line has a minimum of around 1x10^-7. Yes, the difference between 10^-10 and 1…
I absolutely don't understand all the physics but are "barium titanate" and "strontium titanate" rare stuff ?
Looking at the elemental abundances you can see that titanium and strontium are fairly high, above both gallium and arsenic, another solar cell pair. Barium is in the ballpark of gallium and arsenic.
https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_el...