“…Meanwhile, monovalent cations such as Ag + , Cu + , Cs + , and K + are commonly utilized in combination with Bi 3+ or Sb 3+ to form the double perovskite structures. ,− However, due to the large radius of iodide ions (I – ), the most common halogen anions in the reported three-dimensional (3D) Bi or Sb-based double perovskite structures are bromide or chloride ions (Cl – or Br – ). Therefore, it is challenging to combine I – with trivalent metal to form 3D double perovskite structures. − On the other side, the emergence of two-dimensional double perovskites such as [AE 2 T] 2 AgBiI 8 , (C 6 H 16 N 2 ) 2 AgBiI 8 ·H 2 O, (C 6 H 16 N 2 ) 2 CuBiI 8 ·0.5H 2 O, and (3AMPY) 2 AgBiI 8 ·H 2 O have made it possible to obtain hybrid double perovskite iodides (HDPIs) through the dimensional reduction strategy. ,,,− These HDPIs exhibit interesting material properties, such as ferroelectricity, − light detection, ,,, X-ray detection, ,− etc.…”