Two Heteromorphic Crystals of Antimony-Based Hybrids Showing Tunable Optical Band Gaps and Distinct Photoelectric Responses

Organic-inorganic hybrid perovskites, most markedly CH3NH3PbI3, have attracted extensive interest because of their potential use in optoelectronic and photovoltaic applications. Nevertheless, the toxicity of lead restricts their further application. Here, we successfully synthesized two lead-free heteromorphic hybrids, (C7H18N2O)3Sb4I18·H2O (1) and (C7H18N2O)Sb2I8·H2O (2, C7H18N2O2+ is N-aminopropylmorpholinium), both of which belong to the zero-dimensional tetranuclear perovskite-like structure. However, the inorganic [Sb4I18] cluster of 1 adopts a tetragonal topology, while 2 features the distorted [Sb4I16] motif; this disparity leads to a significant distinction between their electronic structures as well as an optical band gap ( Eg). Their absorption cutoffs are measured to be 708 nm (for 1, Eg = 1.71 eV) and 578 nm (for 2, Eg = 2.11 eV), respectively. In particular, 1 exhibits a stronger photoelectric response in a wider optical region compared to that of 2, and the "on/off" ratio of conductivity of 1 is estimated to ∼300 under sunlight illumination. Density functional theory calculation discloses that different inorganic motifs make greater contributions to their electronic structure and photoelectric response. It is believed that the heteromorphic method allows a potential pathway for construction of new lead-free hybrid materials as light absorbers for photoelectric application.