[jerf]

Going from 99% black to 99.999% black turns out not to represent that much more efficiency. It's the difference between absorbing 99 of 100 joules of energy vs 99.999 of 100 joules of energy; unless the rest of your system is effectively 100% efficient, it may not even be a noticeable change. It is very likely that other engineering concerns, not least of which is price, is going to dominate this question.

[Zelizz]

The article does mention that it's more durable than vantablack, so perhaps more suitable for a space-based project (if it turns out a really black material is useful for a solar panel of sorts).