Structure and Optical Properties of Hybrid-Layered-Double Perovskites (C8H20N2)2AgMBr8 (M = In, Sb, and Bi).

The Pb-free hybrid-layered-double perovskites (HLDPs) have been proposed as green and stable semiconducting materials for optoelectronic devices, but the synthesized members are still limited. Here, we report the synthesis of three new HLDPs, (C8H20N2)2AgMBr8 (M = In, Sb, and Bi), by a solution method using 1,4-bis(ammoniomethyl)cyclohexane (C8H20N22+) as the organic spacing cation. All three of these HLDPs show ⟨100⟩-oriented layered structures with Ag and In/Sb/Bi order arranged in corner-sharing octahedral layers. The first-principle calculations indicate the indirect-gap nature of (C8H20N2)2AgInBr8 and (C8H20N2)2AgSbBr8, while their Bi counterpart shows a direct band gap after considering spin-orbit coupling. The band gaps obtained by diffuse-reflectance spectroscopy are 3.11, 2.60, and 2.70 eV for M = In, Sb, and Bi, respectively. (C8H20N2)2AgInBr8 shows a broadband red emission centered at 690 nm, and it is mainly attributed to the self-trapped-excitons mechanism. Our results not only provide a series of new "Pb-free" HLDPs with chemical diversity but also help us to further understand the structure-property relationships of HLDP materials.