Halide Containing Short Organic Monocations in n = 1–4 2D Multilayered Halide Perovskite Thin Films and Crystals

Low electronic band gap 2D multilayered (n = 3,4) lead-iodide perovskites with formulas A′2An–1PbnI3n+1 A″An–1PbnI3n+1 are of great interest for photovoltaics, with recent demonstrations of stable solar cell operation based on 2D/3D bilayered heterostructures. Still, the difficulty in achieving optimal phase control, with potential formation of mixed n-domains, is a limiting factor for the photovoltaic performance of 2D/3D heterostructures, and the current choice for multi n-layered compounds is limited. Here, we report synthesis and XRD characterization of novel (I-EA)2MAn–1PbnI3n+1 (n = 1–4) compound series, along with the (Br-EA)2PbBr4 (n = 1) compound, incorporating iodo-ethylammonium (I-EA) and bromo-ethylammonium (Br-EA) spacers. These halide-featuring spacers lead to a small lattice mismatch between the inorganic and organic components, which explains the successful formation of multi n-layered compounds. The presence of bromine or iodine in the interlayer space impacts on the dielectric and electronic properties of these materials. Periodic DFT simulations predict vertical hole effective mass for n = 1 (I-EA)2PbI4 as small as 1.8 me, comparable to popular organic semiconductors, like rubrene. UV–vis characterization sets the optical absorption onset of these materials around 1.71 eV for n = 3 and 4, hence suggesting that they can be successfully implemented in 2D/3D photovoltaic architectures.