The association of the electron acceptor 4,4'-amino-bipyridinium (AmV 2+ ) dication and BiI3 in an acidic solution affords three organic−inorganic hybrid materials, (AmV)3(BiI6)2 ( 1), (AmV)2(Bi4I16) (2), and (AmV)BiI5 (3), whose structures are based on isolated BiI6 3− and Bi4I16 4− anion clusters in 1 and 2, respectively, and on a one-dimensional (1D) chain of trans-connected corner-sharing octahedra in 3. In contrast with known methylviologen-based hybrids, these compounds are more soluble in polar solvents, allowing thin film formation by spin-coating. (AmV)BiI5 exhibits a broad absorption band in the visible region leading to an optical bandgap of 1.54 eV and shows a PV effect as demonstrated by a significant open-circuit voltage close to 500 mV. The electronic structure of the three compounds has been investigated using first-principles calculations based on density functional theory (DFT). Unexpectedly, despite the trans-connected cornershared octahedra, for (AmV)BiI5, the valence state shows no coupling along the wire direction, leading to a high effective mass for holes, while in contrast, the strong coupling between Bi 6px orbitals in the same direction at the conduction band minimum suggests excellent electron transport properties. This contributes to the low current output leading to the low efficiency of perovskite solar cells based on (AmV)BiI5. Further insight is provided for trans-and cis-MI5 1D model structures (M = Bi or Pb) based on DFT investigations.

Low electronic band gap 2D multilayered (n = 3,4) leadiodide perovskites with formulas A′ 2 A n−1 Pb n I 3n+1 A″A n−1 Pb n I 3n+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 ndomains, 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) 2 MA n−1 Pb n I 3n+1 (n = 1−4) compound series, along with the (Br-EA) 2 PbBr 4 (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 nlayered 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) 2 PbI 4 as small as 1.8 m e , 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.

Lead free organic-inorganic hybrid perovskites have attracted increasing attention because of their variety of applications such as photovoltaics or lighting. Here, we reported a new iodobismuthate organic-inorganic perovskite (PyrCO 2 H) 2 BiI 5 where PyrCO 2 H + is the 4-carboxy-1-methylpyridinium. In the room temperature orthorhombic phase, the one-dimensional (1D) inorganic framework which consists of cis-connected corner-sharing BiI 6 octahedra, exhibits a sinusoidal deformation along the chain axis, while a regular chain leading to a sub-cell is found in the high temperature phase (T > 390 K). An original structural feature is the relative position of consecutive 1D chains in planes leading to a layered character of this organicinorganic compound. The electrical properties as function frequencies and temperatures have been studied in particular allowing the extraction of R g and further the calculation of σ g = f(T). Interestingly, a change of activation energy is detected at the phase transition temperature (390 K). The higher value of activation energy above 390 K can be attributed to change of the conduction mechanism involving ionic conduction.