Two-dimensional semiconducting Cs(i)/Bi(iii) bimetallic iodide hybrids for light detection

Lead-based semiconducting organic-inorganic halides such as CH3NH3PbI3 are promising materials for optoelectronic applications. However, the toxicity of lead and the instability of these materials could raise environmental issues if they are applied on a large scale. Herein, two new 2D lead-free bimetallic iodide-based hybrid compounds are presented, namely (C12H30N4)Cs3BiI8 (CsBiI-1) and (C14H35N4)CsBiI7 (CsBiI-2), using different amines: C6H14N2 = cyclohexane-1,4-diamine (CDA) and C7H16N2 = 2-piperidinoethylamine (PDA). These two compounds show optical band gaps of 2.18 eV and 2.39 eV for CsBiI-1 and CsBiI-2, respectively. Both materials yield high surface coverage films from spin-coating. Moreover, CsBiI-1 and CsBiI-2 are stable under moisture and present photocurrent responses. Thus, these materials have the potential for use in light detection.