  Density functional theory screening of the hybrid double perovskites
(MA)2BIBiX6 (BI=K,Cu,Ag,Tl; X=Cl,Br,I) shows that systems with band gaps
similar to those of the MAPbX3 lead compounds can be expected for BI=Cu,Ag,Tl.
Motivated by these findings, (MA)2TlBiBr6, isoelectronic with MAPbBr3, was
synthesised and found to have a band gap of ~2.0eV.
