Duo Queue - Are we punished for this?

My friend and I duo queue quite often, and when we aren't duo queuing, I play solo ranked in my free time.

Maybe I perceive this wrong, but over the course of this season, I have seen a pretty blatantly obvious trend:

When I queue solo, I win far far more games than when I duo queue with my friend. My friend also wins far more games solo queue than when we duo queue.

My question:

Are we punished for duo queuing? Is there something in the match making system to match our teammates lower than it normally would if we were solo queuing?

This isn't some notion, I climb easily when I'm solo queuing, and when I duo my rank just plummets.

If Riot encourages team play, then punishes us for it, why would I ever want to play with my friends?

I'm at the point now where we are looking for other games to play together and we just play league of legends as a 'single player' game. Because you can't duo queue at all. It isn't just one friend either. Every time any of my friends ask me to duo queue I will most often decline unless I've climbed out of the hole from the previous time I duo queued.