The uviquity 220 nm SHG chips are super cool--they're perfectly monochromatic (though maybe with some blue light leakage) and I hear from their tech lead that they expect to get up to 10% WPE. I think that approach is definitely going to be relevant much sooner than far-UVC LEDs, but they're still early days, it's going to be a long road. Krypton-chloride excimer lamps are more or less the only game in town for commercial far-UV, at least for now.

Full report here if you want more solid state far UV info: https://www.convergentresearch.org/resources/convergent/soli...