Hybrid Organic-inorganic Semiconductors Research Articles

Alternative fabrication methodologies for two-dimensional self-assembled Inorganic-Organic hybrid semiconductors

This report presents the structural and optical properties of(R-NH 3 ) 2 PbI 4 type Inorganic-Organic (IO) hybrids, prepared from alternative fabrication techniques, without any excess usage of Iodine. The fabrication relies on common deposition techniques viz., thermal vacuum deposition, electrochemical deposition, and spincoating. The resulting two-dimensional (2D) structures are alternatively stacked-up along c-axis by inorganic (PbI 6 extended network) layers with organic (R–NH 3 ) - moieties as spacers. These hybrids show strong room-temperature exciton features confined within the lowest inorganic bandgap. The proposed methodologies are simple alternatives to the conventional multi-step fabrication methodologies and are directly applicable to varieties of IO hybrids of different dimensionalities for various optoelectronic applications. • Novel methodologies for IO hybrids without metal halide and excess of halide usage. • Efficient direct conversion of pure Pb metal films into perfect layered 2D IO hybrids. • Nano and microcrystal fabrication from lead acetate based electrodeposition. • Strong room-temperature exciton photoluminescence from IO hybrids is demonstrated.

Pentacene and tetracene molecules and films on H/Si(111): level alignment from hybrid density functional theory

The electronic properties of hybrid organic–inorganic semiconductor interfaces depend strongly on the alignment of the electronic carrier levels in the organic/inorganic components. In the present work, we address this energy level alignment from first principles theory for two paradigmatic organic–inorganic semiconductor interfaces, the singlet fission materials tetracene and pentacene on H/Si(111), using all-electron density functional theory calculations with a hybrid exchange–correlation functional. For isolated tetracene on H/Si(111), a type I-like heterojunction (lowest-energy electron and hole states on Si) is found. For isolated pentacene, the molecular and semiconductor valence band edges are degenerate. For monolayer films, we show how to construct supercell geometries with up to 1192 atoms, which minimize the strain between the inorganic surface and an organic monolayer film. Based on these models, we predict the formation of type II heterojunctions (electron states on Si, hole-like states on the organic species) for both acenes, indicating that charge separation at the interface between the organic and inorganic components is favored. The paper discusses the steps needed to find appropriate low-energy interface geometries for weakly bonded organic molecules and films on inorganic substrates from first principles, a necessary prerequisite for any computational level alignment prediction.

Real-time dynamic evolution monitoring of laser-induced exciton phase flips in 2D hybrid semiconductor (C12H25NH3)2PbI4

Real-time monitoring of room-temperature exciton photoluminescence (PL) while irradiated with ultrafast laser excitations (UV and infrared) in long alkyl-chain based (C12H25NH3)2PbI4 inorganic–organic hybrid semiconductors is presented. These naturally self-assembled 2D hybrid structures show strong room-temperature Mott-type excitons confined within the lowest inorganic bandgap, which are highly sensitive to structural phase flips. Under both one-photon (E1PA ≥ Eg) and two-photon (2E2PA ≥ Eg) laser excitations, the exciton PL of unstable phase-II appears initially, and with prolonged laser exposure, the PL peak switches to a new stable blueshifted phase-I peak position. This exciton phase flip demonstrates different laser-induced structural deformations in inorganic quantum wells (PbI6 extended network) associated with orthorhombic (phase-I) and monoclinic (phase-II) unit cells. One-photon absorption induced PL shows the various time dynamics of laser exposure depending on laser characteristics (continuous wave and ultrashort pulsed lasers), mostly influenced by localized heating, ablation effects, and third-order nonlinear effects such as saturation of linear absorption and exciton–exciton annihilation. However, in two-photon absorption induced PL, the near infrared laser excitation reveals the redshifted crumpled excitons from the deeper depth of the sample, which are induced by multiphoton absorption and avalanche ionization. A series of systematic linear and nonlinear steady-state and time-resolved PL studies are presented. A simplified kinetic model further provides an understanding of the real-time evolution of laser-induced excitons and their related phase flips. These laser-induced exciton phase flips and linear and nonlinear optical probing open a new avenue for novel functional properties and nonlinear absorption–based optoelectronic devices.

Flexible Inkjet-Printed Triple Cation Perovskite X-ray Detectors.

Flexible direct conversion X-ray detectors enable a variety of novel applications in medicine, industry, and science. Hybrid organic-inorganic perovskite semiconductors containing elements of high atomic number combine an efficient X-ray absorption with excellent charge transport properties. Due to their additional cost-effective and low-temperature processability, perovskite semiconductors represent promising candidates to be used as active materials in flexible X-ray detectors. Inspired by the promising results recently reported on X-ray detectors that are based on either triple cation perovskites or inkjet-printed perovskite quantum dots, we here investigate flexible inkjet-printed triple cation perovskite X-ray detectors. The performance of the detectors is evaluated by the X-ray sensitivity, the dark current, and the X-ray stability. Exposed to 70 kVp X-ray radiation, reproducible and highly competitive X-ray sensitivities of up to 59.9 μC/(Gyaircm2) at low operating voltages of 0.1 V are achieved. Furthermore, a significant dark current reduction is demonstrated in our detectors by replacing spin-coated poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) with sputtered NiOx hole transport layers. Finally, stable operation of a flexible X-ray detector for a cumulative X-ray exposure of 4 Gyair is presented, and the applicability of our devices as X-ray imaging detectors is shown. The results of this study represent a proof of concept toward flexible direct conversion X-ray detectors realized by cost-effective and high-throughput digital inkjet printing.

Synthesis, Structural, Linear, and Nonlinear Optical Studies of Inorganic–Organic Hybrid Semiconductors (R–C6H4CHCH3NH3)2PbI4, (R = CH3, Cl)

Synthesis, crystal structure, and optical properties of two-dimensional (2D) layered structurally slightly different inorganic–organic (IO) hybrid semiconductors (R–C6H4C2H4NH3)2PbI4 (R = CH3, Cl) are presented. They are naturally self-assembled systems where two (RNH3)+ moieties are sandwiched between two infinitely extended 2D layers of the [PbI6]4– octahedral network and treated as natural IO multiple quantum wells. While the former compound crystallizes into an orthorhombic system in the Cmc21 space group, the latter crystallizes into a monoclinic system in the space group P21/c. As a thin film, they are well-oriented along the (l00) direction. Both single crystals and thin films show strong room-temperature Mott type exciton features that are highly sensitive to the self-assembly and crystal packing. Linear (one-photon) and nonlinear (two-photon) optical probing of single crystals for exciton photoluminescence imaging and spectral spatial mapping provide deep insight into the layered re-arrangement and structural crumpling due to organic conformation. The strongly confined excitons, within the lowest band gap of inorganic, show distinctly different one- and two-photon excited photoluminescence peaks: free excitons from perfectly aligned 2D self-assembly and energy down-shifted excitons originated from the locally crumpled layered arrangement. Their structural aspects are successfully presented with proper correlation that emphasize various differences in physical and optical properties associated between these novel IO hybrids.

Coated and Printed Perovskites for Photovoltaic Applications.

Hybrid organic-inorganic metal halide perovskite semiconductors provide opportunities and challenges for the fabrication of low-cost thin-film photovoltaic devices. The opportunities are clear: the power conversion efficiency (PCE) of small-area perovskite photovoltaics has surpassed many established thin-film technologies. However, the large-scale solution-based deposition of perovskite layers introduces challenges. To form perovskite layers, precursor solutions are coated or printed and these must then be crystallized into the perovskite structure. The nucleation and crystal growth must be controlled during film formation and subsequent treatments in order to obtain high-quality, pin-hole-free films over large areas. A great deal of understanding regarding material engineering during the perovskite film formation process has been gained through spin-coating studies. Based on this, significant progress has been made on transferring material engineering strategies to processes capable of scale-up, such as blade coating, spray coating, inkjet printing, screen printing, relief printing, and gravure printing. Here, an overview is provided of the strategies that led to devices deposited by these scalable techniques with PCEs as high as 21%. Finally, the opportunities to fully close the shrinking gap to record spin-coated solar cells and to scale these efficiencies to large areas are highlighted.

Graphite/SiO2 film electrode modified with hybrid organic-inorganic perovskites: Synthesis, optical, electrochemical properties and application in electrochemical sensing of losartan

Hybrid organic-inorganic semiconductors (HOIS) still remain as research focus due to their exceptional optoelectronics properties, placing them as ideal candidates for use in the field of light emitting diodes and photovoltaics. In the present work, HOIS have been synthesized, characterized as well as adsorbed onto graphite/silica film electrodes (GSiHE), the latter used as simple, low cost, yet sensitive, electrochemical sensors. These composite electrodes have been specifically characterized with electrochemical methods and have been applied in the development of prototype electrochemical drug sensors; a paradigm is provided for simple, efficient, sensitive and relatively specific sensing of an antihypertensive drug, losartan (LOS). The electrochemical behavior of GSiHE film modified with HOIS was examined by cyclic voltammetry, while its morphology, structural and spectroscopic properties were investigated by field emission scanning electron microscopy, X-ray diffraction, porosimetry, optical and luminescence spectroscopies. Under optimized conditions, the modified film electrode demonstrated excellent electrocatalytic activity towards oxidation of LOS in the linear response range for concentrations from 4 × 10−5 M to 3.2 × 10−4 M (correlation coefficient 0.989) with the limit of detection computed at 3 × 10−6 M. The sensor takes advantage of the ability of ions to interact with the HOIS lattice on the GSiHE film; this type of sensor has demonstrated good repeatability, reproducibility and stability and was found to be applicable for use in determining pharmaceutical tablet sample concentrations.

Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites.

Hybrid organic-inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (≲50 cm-1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.

Strongly luminescent inorganic–organic hybrid semiconductors with tunable white light emissions by doping

Tunable white light emissions from copper bromide based inorganic–organic hybrid semiconductors have been observed upon doping.

Highly efficient and very robust blue-excitable yellow phosphors built on multiple-stranded one-dimensional inorganic-organic hybrid chains.

Inorganic-organic hybrid semiconductors are promising candidates for energy-related applications. Here, we have developed a unique class of multiple-stranded one-dimensional (1D) structures as very robust and efficient lighting phosphors. Following a systematic ligand design strategy, these structures are constructed by forming multiple coordination bonds between adjacent copper iodide inorganic building units Cu m I m (m = 2, 4, 6) (e.g. dimer, tetramer and hexamer clusters) and strong-binding bidentate organic ligands with low LUMO energies which give rise to infinite 1D chains of high stability and low bandgaps. The significantly enhanced thermal/photostability of these multiple-stranded chain structures is largely attributed to the multi-dentate nature and enhanced Cu-N bonding, and their excellent blue excitability is a result of using benzotriazole based ligands with low-lying LUMO energies. These facts are confirmed by Density Functional Theory (DFT) calculations. The luminescence mechanism of these compounds is studied by temperature dependent photoluminescence experiments. High internal quantum yields (IQYs) are achieved under blue excitation, marking the highest value reported so far for crystalline inorganic-organic hybrid yellow phosphors. Excellent thermal- and photo-stability, coupled with high luminescence efficiency, make this class of materials promising candidates for use as rare-earth element (REE) free phosphors in energy efficient general lighting devices.

Tunable Semiconductors: Control over Carrier States and Excitations in Layered Hybrid Organic-Inorganic Perovskites.

For a class of 2D hybrid organic-inorganic perovskite semiconductors based on π-conjugated organic cations, we predict quantitatively how varying the organic and inorganic component allows control over the nature, energy, and localization of carrier states in a quantum-well-like fashion. Our first-principles predictions, based on large-scale hybrid density-functional theory with spin-orbit coupling, show that the interface between the organic and inorganic parts within a single hybrid can be modulated systematically, enabling us to select between different type-I and type-II energy level alignments. Energy levels, recombination properties, and transport behavior of electrons and holes thus become tunable by choosing specific organic functionalizations and juxtaposing them with suitable inorganic components.

Coherent Spin and Quasiparticle Dynamics in Solution-Processed Layered 2D Lead Halide Perovskites.

Layered 2D halide perovskites with their alternating organic and inorganic atomic layers that form a self‐assembled quantum well system are analogues of the purely inorganic 2D transition metal dichalcogenides. Within their periodic structures lie a hotbed of photophysical phenomena such as dielectric confinement effect, optical Stark effect, strong exciton–photon coupling, etc. Detailed understanding into the strong light–matter interactions in these hybrid organic–inorganic semiconductor systems remains modest. Herein, the intricate coherent interplay of exciton, spin, and phonon dynamics in (C6H5C2H4NH3)2PbI4 thin films using transient optical spectroscopy is explicated. New insights into the hotly debated origins of transient spectral features, relaxation pathways, ultrafast spin relaxation via exchange interaction, and strong coherent exciton–phonon coupling are revealed from the detailed phenomenological modeling. Importantly, this work unravels the complex interplay of spin–quasiparticle interactions in these layered 2D halide perovskites with large spin–orbit coupling.

Defect Variants Based on the 2D Hybrid Organic–Inorganic Low-Dimensional Semiconductor (4-Fluoro-phenethylamine-H)2PbBr4 for Fabrication of Single-Layer Deep Blue LEDs

The low-cost and self-assembled hybrid organic–inorganic semiconductors (HOIS) appear lately to be ideal for novel optoelectronic devices due to their inherent stable excitonic states, even at room temperature. 2D HOIS, superlattices of alternating layers of amines and of corner sharing lead halide octahedra, exhibit dielectrically confined bound excitonic states that are ideal for light emitting diodes (LEDs). HOIS-based deep blue LEDs are rarely reported, in which cases HOIS is usually deposited between electron and hole transport layers. Here, in the quest of suitable 2D HOIS for single layer LEDs (SLLEDs), we report on the synthesis and characterization of (4-fluoro-phenethylamine-H)2PbBr4 and its defect variations (DV), formed by nonstoichiometric synthesis. The DV thin films, deposited on conducting transparent anodes, allow for easy and simple fabrication of SLLEDs, using a Ga/In droplet cathode. The pristine iodine analogue readily provides green SLLEDs, while here only the DVs or pristine materia...

Polystyrene based perovskite light emitting diode

Hybrid organic–inorganic semiconductors (HOIS) based on lead halides exhibit unique optoelectronic properties even at room temperature, immediately assigning these for potential applications as optical and active device materials, where most common applications have been light emitting diodes (LED), solar cell devices and X-ray detectors. In this work, a low cost and simple prototype single layer LED emitting green light under low voltage, is presented. The main advantage in this work's LED is that the active layer is based on a blend of low dimensional (LD) perovskites entrapped in a polystyrene film, never reported before. The HOIS blend is formed by the admixture of two-dimensional (2D) (C6H5CH2CH2NH3)2PbBr4, one dimensional (1D) CH3NH3CdBr3, while the blend's entrapment is afforded by mixing it with dissolved polystyrene powder. It is found that final composite contains a blend of quasi two-dimensional (quasi-2D) perovskites, that exhibits green luminescence and electroluminescence, assisted by energy funneling phenomena toward the blend's moiety with the smallest energy band gap. The addition of Cd++ is reported as a paradigm for several effects; its addition is not inhibiting the electroluminescence, while also polystyrene successfully prevents even cadmium halide's degradation by moisture. Moreover, successful doping of the LED active material portrays possibilities for enhancing perovskite-based devices, as it has been shown that cation dopants enhance the photoluminescence or transfer energy toward the dopant's light emission energy bands.

Production and identification of highly photoconductive CdSe-based hybrid organic-inorganic multi-layer materials

Highly photoconductive thin multi-layers of new hybrid organic-inorganic semiconductors have been developed. They result by the combination of an inorganic semiconductor with ferrocene, a commercially available compound, applying the electrodeposition and spin coating techniques, introducing sodium oxalate as an additive in the electrolytic bath. The organic layer of the hybrid system is enveloped between two inorganic layers in a sandwich-like structure. The full characterization of the final products by XRD, SEM-EDAX, band gap and photo electro chemical cell (PEC) measurements confirmed the development of the hybrid semiconducting system. The outer electrodeposited CdSe layer of the sandwich-like materials exhibits a definite hexagonal structure, whereas, as derived from the XRD and band gap data, the development of a new semiconducting compound has been confirmed. Thus, due to a synergic action, the three-layer materials present a remarkably improved photoresponse compared to that of the pure cubic CdSe electrodeposited in the presence of the oxalate additive as well as the three-layer hybrid CdSe-based products developed in our previous work in additive-free electrolytic baths.

Tightly bound indirect exciton in single-layer hybrid organic-inorganic perovskite semiconductor

We theoretically study the direct and indirect excitons (IXs) in a single-layer hybrid organic-inorganic perovskite (HOIP) semiconductor. Due to the 2D nature, the single-layer HOIP supports the large binding energy of IXs and direct excitons over a wide range of applied electric fields, which exceed the thermal energy of room temperature. Moreover, the ground-state IX has a lower energy than that of direct exciton, which will extend the coherence and relaxation time of IXs. This is beneficial to optoelectronic applications and excitonic information processing devices of IXs.

Light emitting diodes based on blends of quasi-2D lead halide perovskites stabilized within mesoporous silica matrix

The effective synthesis and embedding of semiconducting perovskite blends inside the pores of different mesoporous silica matrices is reported, as well as the implementation of these composites for the first time, as the single and active layer in light emitting diodes. The reported perovskites are blends of quasi-two dimensional hybrid organic-inorganic semiconductors based on lead halides. These blends have been synthesized within the pores of calcined or non-calcined MCM-41 hosts, of two different types, and were optically characterized with UV and PL spectroscopies, as well as structurally with XRD, BET, TEM and SEM techniques. Perovskites reside within the pores of the final dried samples, where degradation protection is provided from chemicals, including water. Moreover, the final white powder like composites exhibit naked-eye visible luminescence as well as electroluminescence under daylight.

Energy transfer yellow light emitting diodes based on blends of quasi-2D perovskites

The new class of hybrid organic-inorganic semiconductor (HOIS) materials, based on metal halide perovskites, is constantly being pursued for applications such as light emitting diodes (LEDs), solar cells or even single photon emitters, due to their momentous optoelectronic properties. In this work, we present a single layer LED that operates due to energy transfer effects as well as a simple, instant and low cost method for its fabrication. The active LED layer is based on the reaction of zero dimensional (CH3NH3)4PbI6, two dimensional (F-C6H4CH2CH2NH2)2PbI4 and three dimensional (CH3NH3)PbI3 HOIS, which yields a mixture of quasi-two dimensional HOIS and is presented for the first time. The final material manifests simple, yet unique energy transfer effects, while its electroluminescence exhibits excitonic recombination bright yellow light, peaked at 592nm. Utilizing appropriate mixtures is possible to create films containing such phases that multi-color EL emission is observed, here presented as yellow/green, yellow/red or yellow/red/deep-red. LED device fabricated under ambient air, readily functions at room temperature and low voltages, while the active layer exhibited substantial film continuity with any deposition method.

Nanostructuring methylammonium lead iodide perovskite by ultrafast nano imprinting lithography

We report the nanopatterning of the methylammonium lead iodide (MAPbI3) perovskite, a polycrystalline hybrid organic-inorganic semiconductor with very promising perspectives for photovoltaic and optoelectronic applications. Nanopatterning of MAI is obtained via Pulsed-NIL technology, an ultrafast version of the thermal nanoimprint lithography (NIL) based on stamps with integrated heaters. By Pulsed-NIL we were able to replicate onto the hybrid perovskite structures with details at the sub-100nm scale, in spite of its crystalline nature. This work shows a new possibility for the exploitation of organo-metal halide perovskites in optoelectronic devices with more complex architectures than just planar films.

Production and identification of highly photoconductive CdSe-based hybrid organic-inorganic multi-layer materials

Highly photoconductive thin multi-layers of new hybrid organic-inorganic semiconductors have been developed. They result by the combination of an inorganic semiconductor with ferrocene, a commercially available compound, applying the electrodeposition and spin coating techniques, introducing sodium oxalate as an additive in the electrolytic bath. The organic layer of the hybrid system is enveloped between two inorganic layers in a sandwich-like structure. The full characterization of the final products by XRD, SEM-EDAX, band gap and photoelectrochemical cell (PEC) measurements confirmed the development of the hybrid semiconducting system. The outer electrodeposited CdSe layer of the sandwich-like materials exhibits a definite hexagonal structure, whereas, as derived from the XRD and band gap data, the development of a new semiconducting compound has been confirmed. Thus, due to a synergic action, the three-layer materials present a remarkably improved photoresponse compared to that of the pure cubic CdSe electrodeposited in the presence of the oxalate additive as well as the three-layer hybrid CdSe-based products developed in our previous work in additive-free electrolytic baths. DOI: 10.21883/0000000000