Things I have thought of till now:

  1. Acetonitrile with HI additive
  2. Acetonitrile with DMSO additive

The problem with the first would be that HI is in an around 55% aqueous solution and water doesn't play well with the perovskite. Meanwhile, the second might end up needing enough DMSO to drastically increase the boiling point. I am not sure about the second and intend to try it out and will post updates when I am done.