Yep, the very high efficiency cells are typically reserved for highly specialized areas where cost doesn’t matter.. You’ll see Boeing’s name a lot near the top of the efficiency list for the exotic cell types, their lab’s website should clue everyone in to what their main purpose is: https://www.spectrolab.com

They list 31% efficiencies for their cells that can fly today which must be near the limit of commercialization / certification. Still pretty good though, that’s 50% more efficient than a standard panel, and at several $10s of thousands per kg into space, clearly worth it!

28/30% cells are common in spacecraft and have been for more than five years, but they are expensive. A little less than 10k for something like 1 square meter only for the cells wouldn't be crazy.

It looks like Boeing's latest multijunction line ships at 30.7% efficient:

https://www.spectrolab.com/photovoltaics.html#cells_cics

Which seems about right, but what I didn't realize is that they're shipping >40% concentrators too. That's pretty great!

https://www.spectrolab.com/photovoltaics.html#cells_cics

(That last link was supposed to be for the concentrator section at the bottom of that page, but I don't think it's a normal # bookmark)

These cells should be available for everyone and not just the 1%.

These things aren't expensive just for fun. They're usually made of very exotic materials or very difficult to manufacture, hence the prices. They'll go down if they become easier to make.

Although in this case those ultra-expensive cells are being built by Boeing for space use. That no doubt includes a lot of flight certification and similar checks. If you were making a version for domestic use the price could probably be significantly reduced.

That said, they would only make sense in places where space is at a premium so people are willing to pay extra for something a bit smaller. That's not especially common in home use.