is there a relationship between indexes and temporary file creation?

Greetings,
I have a table with 10s of millions of rows and I'm running a fairly
complex query with a lot of self joins.

This is an experimental db and the table structure needs to stay as it is.
I've noticed that some queries are not completed because postgres uses all
available space on disk for temporary data when doing complex joins.

The table has no indexes at the moment; I'm measuring performance with and
without indexes so I don't mind long query times. Running out of disk space
is a problem though.I can't think of a connection between indexes and the
temporary space needed for joins but I hope I can get some input from those
with (a lot) more knowledge about potgres internals.

Is there any possibility of indexing decreasing the required temporary disk
space when performing complex joins?

Best regards
Seref