Have you considered melatonin? Quoting gwern:

Melatonin allows us a different way of raising the cost, a physiological & self-enforcing way. Half an hour before we plan to go to sleep, we take a pill. The procrastinating effect will not work - half an hour is so far away that our decision-making process & willpower are undistorted and can make the right decision (viz. following the schedule). When the half-hour is up, the melatonin has begun to make us sleepy. Staying awake ceases to be free, to be the default option; now it is costly to fight the melatonin and remain awake.

I use it for exactly this reason and it works brilliantly.