The 'rear' delts were mentioned. I think doing power cleans definitely thickens everything on the upper back. The rear delts aren't especially involved in the pull, but in the catch they have to be braced hard to rack the bar in a solid, strong position (elbows up). But I guess you could say that during powercleans, ALL muscles are braced to some extent
And as was said, the movement should be primarily hip/glute. If you do them properly, do them with squats.