Performance Enhancement of Lead-Free 2D Tin Halide Perovskite Transistors by Surface Passivation and Its Impact on Non-Volatile Photomemory Characteristics.

Two-dimensional (2D) tin (Sn)-based perovskites have recently received increasing research attention for perovskite transistor application. Although some progress is made, Sn-based perovskites have long suffered from easy oxidation from Sn2+ to Sn4+ , leading to undesirable p-doping and instability. In this study, it is demonstrated that surface passivation by phenethylammonium iodide (PEAI) and 4-fluorophenethylammonium iodide (FPEAI) effectively passivates surface defects in 2D phenethylammonium tin iodide (PEA2 SnI4 ) films, increases the grain size by surface recrystallization, and p-dopes the PEA2 SnI4 film to form a better energy-level alignment with the electrodes and promote charge transport properties. As a result, the passivated devices exhibit better ambient and gate bias stability, improved photo-response, and higher mobility, for example, 2.96 cm2 V-1 s-1 for the FPEAI-passivated films-four times higher than the control film (0.76 cm2 V-1 s-1 ). In addition, these perovskite transistors display non-volatile photomemory characteristics and are used as perovskite-transistor-based memories. Although the reduction of surface defects in perovskite films results in reduced charge retention time due to lower trap density, these passivated devices with better photoresponse and air stability show promise for future photomemory applications.

Recent progress in layered metal halide perovskites for solar cells, photodetectors, and field-effect transistors.

Metal halide perovskite materials demonstrate immense potential for photovoltaic and electronic applications. In particular, two-dimensional (2D) layered metal halide perovskites have advantages over their 3D counterparts in optoelectronic applications due to their outstanding stability, structural flexibility with a tunable bandgap, and electronic confinement effect. This review article first analyzes the crystallography of different 2D perovskite phases [the Ruddlesden-Popper (RP) phase, the Dion-Jacobson (DJ) phase, and the alternating cations in the interlayer space (ACI) phase] at the molecular level and compares their common electronic properties, such as out-of-plane conductivity, crucial to vertical devices. This paper then critically reviews the recent development of optoelectronic devices, namely solar cells, photodetectors and field effect transistors, based on layered 2D perovskite materials and points out their limitations and potential compared to their 3D counterparts. It also identifies the important application-specific future research directions for different optoelectronic devices providing a comprehensive view guiding new research directions in this field.

Inorganic-Cation Pseudohalide 2D Cs2 Pb(SCN)2 Br2 Perovskite Single Crystal.

Most of the reported 2D Ruddlesden-Popper (RP) lead halide perovskites with the general formula of An +1 Bn X3 n +1 (n = 1, 2, …) comprise layered perovskites separated by A-site-substituted organic spacers. To date, only a small number of X-site-substituted RP perovskites have been reported. Herein, the first inorganic-cation pseudohalide 2D phase perovskite single crystal, Cs2 Pb(SCN)2 Br2 , is reported. It is synthesized by the antisolvent vapor-assisted crystallization (AVC) method at room temperature. It exhibits a standard single-layer (n = 1) Ruddlesden-Popper structure described in space group of Pmmn (#59) and has a small separation (d = 1.69 Å) between the perovskite layers. The SCN- anions are found to bend the 2D Pb(SCN)2 Br2 framework slightly into a kite-shaped octahedron, limiting the formation of a quasi-2D perovskite structure (n > 1). This 2D single crystal exhibits a reversible first-order phase transformation to 3D CsPbBr3 (Pm3m #221) at 450 K. It has a low exciton binding energy of 160 meV-one of the lowest for 2D perovskites (n = 1). A Cs2 Pb(SCN)2 Br2 -single-crystal photodetector is demonstrated with respectable responsivity of 8.46 mA W-1 and detectivity of ≈1.2 × 1010 Jones at a low bias voltage of 0.5 V.

Metal-Metalloligand Coordination Polymer Embedding Triangular Cobalt-Oxo Clusters: Solvent- and Temperature-Induced Crystal to Crystal Transformations and Associated Magnetism.

Reaction of the metalloligand IrIII(ppy-COOH)3 and the anisotropic paramagnetic CoII ion under solvothermal conditions resulted in a metal-metalloligand coordination polymer, [CoII3(µ3-O)(µ-OH2){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)4]·2DMF·xH2O (I). It consists of trimeric Co3O secondary building units (SBUs) bridged by pairs of Ir to form chains of alternate orthogonal squares. The compound undergoes two single-crystal to single-crystal transformations while retaining its general structural features. A chemical transformation occurs to give [CoII3(µ3-O){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)4(DMF)]·DMF·H2O (II) by soaking in acetone, where a bridging water molecule departs and the solvent DMF bonds to the vacant site of the Co center. Both I and II undergo a temperature-induced transformation to [CoII3(µ3-O){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)3(DMF)]·DMF (III), where one more coordinated water molecule is lost. The major difference in the three phases is in the Co coordination spheres, which have considerable consequences on the magnetism. Compound I displays paramagnetism down to 2 K, whereas II and III show weak ferromagnetism with TC values of 14 and 17 K, respectively.

From a layered iridium(iii)-cobalt(ii) organophosphonate to an efficient oxygen-evolution-reaction electrocatalyst.

Bimetallic MOF precursors can produce a homogeneous distribution of mixed-metal oxides after calcination, and thus may provide high efficiency as electrocatalysts in the water splitting process. We designed a layered bimetallic-organophosphonate containing Ir, Co and P because the metal-oxides are well-known for their efficiency in the oxygen-evolution reaction (OER), especially when the phosphate acts as a proton carrier. We describe the structure of the MOF and characteristics of the calcined form, which has outstanding OER characteristics in 1.0 M KOH with an overpotential of 317.7 mV at 10 mA cm-2 and a low Tafel slope of 59.1 mV dec-1.

Iridium(III)-Based Metal-Organic Frameworks as Multiresponsive Luminescent Sensors for Fe3+, Cr2O72-, and ATP2- in Aqueous Media.

Three iridium(III)-based metal-organic frameworks (MOFs), namely [Cd3{Ir(ppy-COO)3}2(DMF)2(H2O)4]·6H2O·2DMF (1), [Cd3{Ir(ppy-COO)3}2(DMA)2(H2O)2]·0.5H2O·2DMA (2), and [Cd3{Ir(ppy-COO)3}2(DEF)2(H2O)2]·8H2O·2DEF (3) (ppy-COOH = methyl-3-(pyridin-2-yl)benzoic acid, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide, DEF = N,N-diethylformamide), have been synthesized and characterized. Single-crystal structural determinations reveal that compounds 1-3 are isostructural, showing a three-dimensional framework structure with (3,6) connected rtl topologyin whose trimers of {Cd3(COO)6} are cross-linked by Ir(ppy-COO)33-. The structures are completely different from those of other Ir(III)-based MOFs. Compound 1 was selected for a detailed study on sensing properties. The excellent luminescence as well as good water stability of 1 makes it a highly selective and sensitive multiresponsive luminescent sensor for Fe3+ and Cr2O72-. The detection limits are 67.8 and 145.1 ppb, respectively. Compound 1 can also be used as an optical sensor for selective sensing of adenosine triphosphate (ATP2-) over adenosine diphosphate (ADP2-) and adenosine monophosphate (AMP2-) in aqueous solution. This is the first example of iridium(III)-based MOFs for the optical detection of Fe3+, Cr2O72-, and ATP2-. More interestingly, the luminescent composite film doped with 1% (w/w) of compound 1, 1@PMMA (PMMA = poly(methyl methacrylate)), can be successfully prepared, which endows efficient sensitivity for Fe3+ and Cr2O72- detection and thus provides great potential for future applications.

Defective Metal-Organic Frameworks Incorporating Iridium-Based Metalloligands: Sorption and Dye Degradation Properties.

Artificial control and engineering of metal-organic framework (MOF) crystals with defects can endow them with suitable properties for applications in gas storage, separation, and catalysis. A series of defective iridium-containing MOFs, [Zn4 (µ4 -O)(Ir-A)2(1-x) (Ir-B)2x ] (ZnIr-MOF-dx ), were synthesized by doping heterostructured linker Ir-BH3 into the parent [Zn4 (µ4 -O)(Ir-A)2 ] (ZnIr-MOF), in which Ir-AH3 represents [Ir(ppy-COOH)3 ] (ppyCOOH=3-(pyridin-2-yl)benzoic acid) and Ir-BH3 is [Ir(ppy-COOH)2 (2-pyPO3 H)] (2-pyPO3 H2 =2-pyridylphosphonic acid). Samples with different degrees of defects were characterized by SEM, IR and NMR spectroscopy, powder XRD measurements, and thermal and elemental analyses. ZnIr-MOF-d0.3 was selected as a representative for gas (N2 , CO2 ) or vapor (H2 O, alcohol) sorption studies. The results demonstrate that defective ZnIr-MOF-d0.3 possesses multiple pore size distributions, ranging from micro- to mesopores, unlike the parent material, which shows a uniform micropore distribution. The hydrophilicity of the interior surface is also increased after defect engineering. As a result, ZnIr-MOF-d0.3 shows an enhanced adsorption capability toward n-butanol, relative to that of the parent compound. Optical studies reveal that both ZnIr-MOF and ZnIr-MOF-d0.3 have low band gaps (2.35 and 2.40 eV), corresponding to semiconductors. ZnIr-MOF-d0.3 exhibits dramatically increased photocatalytic efficiency for dye degradation.