From Zero- to One-Dimensional, Opportunities and Caveats of Hybrid Iodobismuthates for Optoelectronic Applications

International audienceThe association of the electron acceptor 4,4’-amino-bipyridinium (AmV(2+)) dication and BiI(3) in an acidic solution affords three organic-inorganic hybrid materials, (AmV)(3)(BiI(6))(2) (1), (AmV)(2)(Bi(4)I(16)) (2), and (AmV)BiI(5) (3), whose structures are based on isolated BiI(6)(3-) and Bi(4)I(16)(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)BiI(5) 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 corner-shared octahedra, for (AmV)BiI(5), 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 6p(x) 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)BiI(5). Further insight is provided for trans- and cis-MI(5) 1D model structures (M = Bi or Pb) based on DFT investigations

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

International audienceLow electronic band gap 2D multilayered (n=3,4) lead-iodide perovskites with formula A’2An‑1PbnI3n+1 and 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 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 (Br‑EA)2PbBr4 (n=1) compound, incorporating iodo-ethylammonium (I-EA) and bromo-ethylammonium (Br-EA) spacers. These halide-featuring spacers lead to small lattice mismatch between the inorganic and organic components, that 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 these compounds can be successfully implemented in 2D/3D photovoltaic architectures

Halide Containing Short Organic Monocations in <i>n</i> = 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

Quasi 3D electronic structures of Dion-Jacobson layered perovskites with exceptional short interlayer distances.

International audienceIn the field of perovskite solar cells (PSCs), 3D/2D heterostructures are a promising route to obtain highly efficient and stable devices. Herein, inspired by dications which have afforded rare layered perovskites called Dion-Jacobson (DJ), with short interlayer distances, we designed and synthesized the new 2-iodopropane-1,3-diamonium dication (DicI), and we successfully obtained multi-n 2D layered perovskites (DicI)(MA)n- 1PbnI3n+1 (n= 1-4, MA+= methylammonium). As a result of a suitable size of the dication which well fits, in projection to the layer planes, in the square defined by four adjacent apical iodides, as well as halogen bonding between organic iodine and apical iodides (I(ap)) of perovskite layers, a perfect eclipsed configuration between adjacent layers takes place, yielding unprecedented short I(ap)….I(ap) distances, as small as 3.882 Å in (DicI)(MA)2Pb3I10. Density Functional Theory (DFT) calculations highlight unusually strong valence band dispersion along the the →Z direction. Effective masses for out-of-plane motions of holes are estimated on par with values computed for 3D perovskites, and similar to in-plane effective masses in 2D multilayered perovskites. This indicates these layered compounds feature quasi 3D electronic structures, hence appearing as promising candidates for PSCs heterostructure