Write a draft of the introduction now, containing ...
Leave it while you write the rest.
- what are you trying to achieve? why is it important?
After you finish the rest, come back and re-write it ...
- significance/importance of the general topic area
- brief review of current state-of-the-art in the area
- the aim of your study and what are its implications
- summary of the main results and implications
- structure of rest of thesis; what does each chapter give