MoO3 is a wide bandgap (> 2.7eV) n-type material. Even IGZO falls under the same category (BG > 3.4eV). Still, why MoO3 is not used as a channel material in general? In most reviews/articles its mentioned that MoO3 has a wide bandgap, and its thermal emission is less to operate FET. Whereas IGZO has a much wider gap, still we can find plenty of FETs based on IGZO.
However, I found one paper where MoO3 is used after modifying its BG. (DOI: 10.1002/adma.201203346)