In  an  effort  to  identify lead-free  2D  hybrid  organic-inorganic perovskites (HOIPs), double perovskites (DPs) with mixed-valent dual metals  such  as  Ag  and  Bi  are  attractive.  Additionally,  replacing chloride  and  bromide  anions  with  iodide  represents  an  important target in these systems, due to associated lower bandgaps. So far iodide  2D  DPs  have  proven  inaccessible  in  bulk  form  when  using traditional spacer cations, due to intrinsic instability or formation of competing non-perovskite phases.

By using a specifically designed bifunctionalized oligothiophene cation, (bis-aminoethyl)bithiophene (AE2T), we have synthesized the first example of a 2D Ag−Bi iodide DP with a direct bandgap of 2 eV, templated  by  the  collective  influence  of  aromatic  interactions, hydrogen  bonding,  bidentate  tethering,  and  the  structural  rigidity associated with the oligothiophene cation.

Our  work  highlights  new  avenues  for  exploring  specifically designed  organic  cations  to  stabilize  otherwise  inaccessible  2D HOIPs, with associated potential applications for optoelectronics.