According to DnD 5e wizard evoker subclass lvl 2 feature Sculpt Spell, you could prevent 1 friendly adjacent creature from taking damage from a Thunderclap cast by your evoker (it would automatically save the CON save and suffer no damage).
Also, according to evoker lvl 6 feature Potent Cantrip, cantrips that would normally do no damage on a failed save now do half damage (including, I’m assuming, thunderclap). Taken to the letter, this would mean that getting the lvl 6 feature Potent Cantrip would be detrimental to your character, at least with regard to the casting of Thunderclap, since the spell would now harm your friend near you? Am I getting this right?
It may well be the case, but it seems a little bit unfair. Could you choose to apply the Potent Cantrip feature only to your enemies when casting a Thunderclap? Could you choose not to apply Potent Cantrip to a given Thunderclap cantrip casting at all to prevent friendly fire?