Designing Hole Transport Materials with High Hole Mobility and Outstanding Interface Properties for Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) have attracted much attention due to their rapid increase in power conversion efficiencies (PCEs), and many efforts are devoted to further improving the PCEs. Designing highly efficient hole transport materials (HTMs) for PSCs may be one of the effective ways. Herein we theoretically designed three new HTMs (FDT−N, FDT−O, and FDT−S) by introducing a nitrogen-phenyl group, an oxygen atom, and a sulfur atom into the spiro core of an experimentally synthesized HTM (FDT), respectively. And then we performed quantum chemical calculation to study their application potential. The results show that the devices with FDT−O and FDT−S instead of FDT may have higher open circuit voltages owing to their lower highest occupied molecular orbital (HOMO) energy levels. Moreover, FDT−S exhibits the best hole transport performance among the studied HTMs, which may be due to the significant HOMO-HOMO overlap in the hole hopping path with the largest transfer integral. Furthermore, the results on interface properties indicate that introducing oxygen and sulfur atoms can enhance the MAPbI₃/HTM interface interaction. The present work not only offers two promising HTMs (FDT−O and FDT−S) for PSCs but also provides theoretical help for subsequent research on HTMs.     

Organic electroluminescent device with aromatic amine-containing polymer as a hole transport layer (II): Poly(arylene ether sulfone)-containing tetraphenylbenzidine

Organic electroluminescent devices were fabricated using a poly(arylene ether sulfone)-containing tetraphenylbenzidine (PTPDES) and tris(8-quinolinolato)-aluminum(III) complex, Alq, as the hole transport layer and the electron-transporting emitter layer, respectively. A device structure of glass substrate/indium—tin oxide (ITO)/PTPDES/Alq/Mg : Ag was employed. Hole injection from ITO through the PTPDES layer to the Alq layer and concomitant electroluminescence from the Alq layer were observed. Bright green light with a luminance of 14,000 cd/m² was observed at a drive voltage of 14 V, indicating that the polymer possesses a high hole mobility and a high electron-blocking capability.     

Quinoid-Aromatic Resonance for Very Small Optical Energy Gaps in Small-Molecule Organic Semiconductors: A Naphthodithiophenedione-oligothiophene Triad System

Organic semiconductors with very small optical energy gaps have attracted a lot of attention for near-infrared-active optoelectronic applications. Herein, we present a series of donor-acceptor-donor (D−A−D) organic semiconductors consisting of a highly electron-deficient naphtho[1,2-b:5,6-b′]dithiophene-2,7-dione quinoidal acceptor and oligothiophene donors that show very small optical energy gaps of down to 0.72 eV in the solid state. Investigation of the physicochemical properties of the D−A−D molecules as well as theoretical calculations of their electronic structures revealed an efficient intramolecular interaction between the quinoidal acceptor and the aromatic oligothiophene donors in the D−A−D molecules; this significantly enhances the backbone resonance and thus reduces the bond length alternation along the π-conjugated backbones. Despite the very small optical energy gaps, the D−A−D molecules have low-lying frontier orbital energy levels that give rise to air-stable ambipolar carrier transport properties with hole and electron mobilities of up to 0.026 and 0.043 cm² V⁻¹ s⁻¹, respectively, in field-effect transistors.     

Novel Metal Complexes Unit of Phenanthroline Derivative for Being Used as Auxiliary Electron Acceptor in Dye Sensitizer Molecules

Donor-acceptor-π bridge-acceptor (D−A−π−A) motif dyes are promising dye sensitizers in dye-sensitized solar cells (DSSCs). In this study, to strengthen with-drawing electron force of the auxiliary electron acceptors(A) in D−A−π−A motif dye sensitizers, the metal complexes unit is be used as auxiliary electron acceptor(A) instead of organic electron-withdrawing monomer. The four polymeric metal complexes were designed, synthesized, and characterized, which used metal complexes of phenanthroline derivatives as auxiliary acceptors (A), benzodithiophene-dithiophene derivatives (BDTT) as donors (D), and 8-hydroxyquinoline derivatives as π-bridges and acceptors of the dye sensitizers, and have been used for dye sensitizers. Under AM 1.5 G (100 mW cm⁻²), the photovoltaic test results indicated that the short-circuit photocurrent density (J_sc) of the DSSCs based four polymeric metal complexes are 11.26, 13.68, 14.42 and 15.57 mA cm⁻² and power conversion efficiency (PCE) are 5.96 %, 7.83 %, 8.07 %, 9.28 % respectively. Both J_sc and PCE value of the four polymeric metal complexes increased in order. This may be due to the fact that larger radius of metal ion under the same change number can enhance the coordination bond and cause stronger electron-withdrawing ability of auxiliary acceptor and stronger charge-transfer ability between the donor and the acceptor, which results in higher J_sc and higher PCE of the polymeric complex dye sensitizer.     

Plasma-polymerized carbon disulfide films as a hole transport layer in organic electroluminescent devices

Electroluminescent devices were fabricated using plasma-polymerized carbon disulfide films, poly(CS₂), and tris(8-quinolinolato)aluminum(III) complex, Alq, as the hole transport layer and the emitting layer, respectively. A cell structure of glass substrate/indium–tin–oxide/poly(CS₂/Alq/Mg/Ag) was employed. Smooth hole injection from the electrode through the poly(CS₂) layer and concomitant electroluminescence from the Alq layer were observed. Green emission with a luminance of 250 cd/m² was achieved at a drive voltage of 14 V.     

Electrocatalytic oxidation of alcohols on carbon electrodes modified by functionalized polypyrrole–RuO2 films

The electrocatalytic activity of several types of polypyrrole films bearing cationic pendant group [tris(bipyridyl)ruthenium(II) complexes, viologen, ammonium] and containing dispersed microparticles of RuO₂ towards the oxidation of alcohols to aldehydes or ketones has been investigated. Best results are obtained with polypyrrole films substituted by a tris(bipyridyl)ruthenium(II) complex, the latter acting as an electron relay for the electrogeneration of the strong oxidizing species RuO₄²⁻. The influence of several parameters such as base, supporting electrolyte, electrolysis potential and catalyst amount on the efficiency of the electrocatalysis has been examined. Under optimum conditions a maximum turnover of 10 900 was reached. In all cases the lifetime of these electrode materials was limited by the slow release of the RuO₄²⁻ species.     

Dominant Role of Hole Transport Pathway in Achieving Record High Photoconductivity in Two-Dimensional Metal–Organic Frameworks

Metal–organic frameworks (MOFs) with mobile charges have attracted significant attention due to their potential applications in photoelectric devices, chemical resistance sensors, and catalysis. However, fundamental understanding of the charge transport pathway within the framework and the key properties that determine the performance of conductive MOFs in photoelectric devices remain underexplored. Herein, we report the mechanisms of photoinduced charge transport and electron dynamics in the conductive 2D M−HHTP (M=Cu, Zn or Cu/Zn mixed; HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) MOFs and their correlation with photoconductivity using the combination of time-resolved terahertz spectroscopy, optical transient absorption spectroscopy, X-ray transient absorption spectroscopy, and density functional theory (DFT) calculations. We identify the through-space hole transport mechanism through the interlayer sheet π–π interaction, where photoinduced hole state resides in HHTP ligand and electronic state is localized at the metal center. Moreover, the photoconductivity of the Cu−HHTP MOF is found to be 65.5 S m⁻¹, which represents the record high photoconductivity for porous MOF materials based on catecholate ligands.     

Manipulation of the Buried Interface for Robust Formamidinium-based Sn−Pb Perovskite Solar Cells with NiOx Hole-Transport Layers

Low band gap tin-lead perovskite solar cells (Sn−Pb PSCs) are expected to achieve higher efficiencies than Pb-PSCs and regarded as key components of tandem PSCs. However, the realization of high efficiency is challenged by the instability of Sn²⁺ and the imperfections at the charge transfer interfaces. Here, we demonstrate an efficient ideal band gap formamidinium (FA)-based Sn−Pb (FAPb_0.5Sn_0.5I₃) PSC, by manipulating the buried NiO_x/perovskite interface with 4-hydroxyphenethyl ammonium halide (OH-PEAX, X=Cl⁻, Br⁻, or I⁻) interlayer, which exhibits fascinating functions of reducing the surface defects of the NiO_x hole transport layer (HTL), enhancing the perovskite film quality, and improving both the energy level matching and physical contact at the interface. The effects of different halide anions have been elaborated and a 20.53 % efficiency is obtained with OH-PEABr, which is the highest one for FA-based Sn−Pb PSCs using NiO_x HTLs. Moreover, the device stability is also boosted.     

Molecular Engineering of Chalcogen-Embedded Anthanthrenes via peri-Selective C−H Activation: Fine-Tuning of Crystal Packing for Organic Field-Effect Transistors

Disclosed herein is a RhCl₃-catalyzed peri-selective C−H/C−H oxidative homo-coupling of 1-substituted naphthalenes, which provides a highly efficient and streamlined approach to chalcogen-embedded anthanthrenes from readily available starting materials. Introducing O, S, and Se into the anthanthrene skeleton leads to gradually increased π–π stacking distances but significantly enhanced π–π overlaps with the growth of the hetero-atom radius. Moderate π–π distance, overlap area, and intermolecular S−S interactions endow S-embedded anthanthrene ( PTT ) with excellent 2D charge-transport properties. Moreover, the transformation of p-type to n-type S-embedded anthanthrenes is realized for the first time via the S-atom oxidation from PTT to PTT-O4 . In organic field-effect transistor devices, PTT derivatives exhibit hole transport with mobilities up to 1.1 cm² V⁻¹ s⁻¹, while PTT-O4 shows electron transport with a mobility of 0.022 cm² V⁻¹ s⁻¹.     

Infrared and mössbauer investigations on dimethyltin(IV) complexes with potentially tridentate dianionic ligands

Dimethyltin(IV) complexes with formulae Me₂Sn(IMDA)·H₂O, Me₂Sn(ODA)· H₂O and [Me₂Sn(OH)]₂(TDA) [IMDA²⁻ = iminodiacetate²⁻ (NOO); ODA²⁻ = oxydiacetate²⁻ (OOO); and TDA²⁻ = thiodiacetate²⁻ (SOO donor atoms)] have been obtained and their solid state coordination investigated. Infrared and Mössbauer spectroscopic evidence would suggest tridentate behaviour of the ligands in polymeric trans-dimethyl structures for Me₂Sn(IMDA)·H₂O and Me₂Sn(ODA)·H₂O with bridging carboxylate groups; polymeric tetrahedral environments around the two tin(IV) atoms could be inferred with TDA acting as bidentate dianionic ligand through ester type carboxylate groups in [Me₂Sn(OH)]₂(TDA), without involvement of the sulfur atom in coordination.     

Organic light‐emitting diodes with multiple photocrosslinkable hole‐transport layers

We report on photocrosslinkable hole‐transport polymers and their use as photodefinable hole‐transport layers in organic light‐emitting diodes. The polymers were obtained by copolymerization of bis(diarylamino)biphenyl‐based acrylate monomers with cinnamate‐functionalized acrylate moieties. Polymers with a range of redox potentials were obtained by varying the substitution patterns of the bis(diarylamino)biphenyl units. The 2 + 2 cycloaddition of the cinnamate moieties following UV irradiation renders the material insoluble. This allows for patterning of the polymer and simultaneously enables the fabrication of multilayer structures from solution. Hole mobilities were measured in these copolymers with the time‐of‐flight technique. Their performance as hole‐transport layers in light‐emitting diodes, with tris(8‐hydroxyquinolinato)aluminum as the emitter and electron‐transport layer, is evaluated. Electroluminescent devices with multiple hole‐transport layers having different ionization potentials were fabricated from solution, and the quantum efficiency of these devices was greater than that for devices based on a single hole‐transport layer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2726–2732, 2003     

A Multifunctional Polymer as an Interfacial Layer for Efficient and Stable Perovskite Solar Cells

Metal-cation defects and halogen-anion defects in perovskite films are critical to the efficiency and stability of perovskite solar cells (PSCs). In this work, a random polymer, poly(methyl methacrylate-co-acrylamide) (PMMA-AM), was synthesized to serve as an interfacial passivation layer for synergistically passivating the under-coordinated Pb²⁺ and anchor the I^- of the [PbI₆]⁴⁻ octahedron. Additionally, the interfacial PMMA-AM passivation layer cannot be destroyed during the hole transport layer deposition because of its low solubility in chlorobenzene. This passivation leads to an enhancement in the open-circuit voltage from 1.12 to 1.22 V and improved stability in solar cell devices, with the device maintaining 95 % of the initial power conversion efficiency (PCE) over 1000 h of maximum power point tracking. Additionally, a large-area solar cell module was fabricated using this approach, achieving a PCE of 20.64 %.     

Features of Protonation of the Simplest Weakly Basic Molecules,SO2, CO,N2O,CO2, and Others by Solid Carborane Superacids

An experimental study on protonation of simple weakly basic molecules (L) by the strongest solid superacid, H(CHB₁₁F₁₁), showed that basicity of SO₂ is high enough (during attachment to the acidic H atoms at partial pressure of 1 atm) to break the bridged H‐bonds of the polymeric acid and to form a mixture of solid mono‐ LH⁺⋅⋅⋅An⁻, and disolvates, L−H⁺−L. With a decrease in the basicity of L=CO (via C), N₂O, and CO (via O), only proton monosolvates are formed, which approach L−H⁺−An⁻ species with convergence of the strengths of bridged H‐bonds. The molecules with the weakest basicity, such as CO₂ and weaker, when attached to the proton, cannot break the bridged H‐bond of the polymeric superacid, and the interaction stops at stage of physical adsorption. It is shown here that under the conditions of acid monomerization, it is possible to protonate such weak bases as CO₂, N₂, and Xe.     

An organic electroluminescent device with a molecularly doped polymer hole transport layer

Electroluminescent(EL) devices have been fabricated using four different polymers with different glass transition temperatures (T_g) dispersed with N,N′-bis-(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) as a hole transport layer and tris(8-hydroxyquinoline) aluminum (Alq₃) as an emitting layer. It was found that the higher the T_g of the polymer, the longer the lifetime of the device. From observations of TPD-doped polymer films with optical microscope and atomic force microscope, dispersing TPD in the polymers was found to suppress the crystallization that causes the roughness of the film surface. It was also observed that the higher the T_g of the host polymers, the more difficult TPD crystallization was. The property of the EL device with polyethersulfone (PES) dispersed with TPD was also investigated. The lifetime of EL device with the TPD doped PES film was improved more than five times at a current density below 10 mA/cm² compared with the device with a conventional TPD hole transport layer. © 1997 John Wiley & Sons, Ltd.     

Intrinsic Stress-strain in Barium Titanate Piezocatalysts Enabling Lithium−Oxygen Batteries with Low Overpotential and Long Life

Rechargeable lithium−oxygen (Li−O₂) batteries with high theoretical energy density are considered as promising candidates for portable electronic devices and electric vehicles, whereas their commercial application is hindered due to poor cyclic stability caused by the sluggish kinetics and cathode passivation. Herein, the intrinsic stress originated from the growth and decomposition of the discharge product (lithium peroxide, Li₂O₂) is employed as a microscopic pressure resource to induce the built-in electric field, further improving the reaction kinetics and interfacial Lithium ion (Li⁺) transport during cycling. Piezopotential caused by the intrinsic stress-strain of solid Li₂O₂ is capable of providing the driving force for the separation and transport of carriers, enhancing the Li⁺ transfer, and thus improving the redox reaction kinetics of Li−O₂ batteries. Combined with a variety of in situ characterizations, the catalytic mechanism of barium titanate (BTO), a typical piezoelectric material, was systematically investigated, and the effect of stress-strain transformation on the electrochemical reaction kinetics and Li⁺ interface transport for the Li−O₂ batteries is clearly established. The findings provide deep insight into the surface coupling strategy between intrinsic stress and electric fields to regulate the electrochemical reaction kinetics behavior and enhance the interfacial Li⁺ transport for battery system.     

Using Ylide Functionalization to Stabilize Boron Cations

The metalated ylide YNa [Y=(Ph₃PCSO₂Tol)⁻] was employed as X,L‐donor ligand for the preparation of a series of boron cations. Treatment of the bis‐ylide functionalized borane Y₂BH with different trityl salts or B(C₆F₅)₃ for hydride abstraction readily results in the formation of the bis‐ylide functionalized boron cation [Y−B−Y]⁺ ( 2 ). The high donor capacity of the ylide ligands allowed the isolation of the cationic species and its characterization in solution as well as in solid state. DFT calculations demonstrate that the cation is efficiently stabilized through electrostatic effects as well as π‐donation from the ylide ligands, which results in its high stability. Despite the high stability of 2 [Y−B−Y]⁺ serves as viable source for the preparation of further borenium cations of type Y₂B⁺←LB by addition of Lewis bases such as amines and amides. Primary and secondary amines react to tris(amino)boranes via N−H activation across the B−C bond.     

Organic electroluminescent device with an aromatic amine-containing polymer as a hole transport layer (I): Poly[N-[p-N′ -phenyl-N′-[1,1′-biphenyl-4′-[N″-phenyl-N″-(2-methylphenyl)amino]-4-amino]]phenyl methacrylamide]

Electroluminescent devices were fabricated using a holetransporting polymer, poly[N-[p-N′ -phenyl-N′-[1,1′-biphenyl-4′-[N″-phenyl-N″-(2-methylphenyl)amino]-4-amino]]phenyl methacrylamide] (PTPDMA), and tris(8-quinolinolato)aluminum(III) complex, Alq, as the hole transport layer and the emitter layer, respectively. A device structure of glass substrate/indium–tin–oxide/PTPDMA/Alq/Mg:Ag was employed. Hole injection from the electrode through the PTPDMA layer to the Alq layer and concomitant electroluminescence from the Alq layer were observed. Bright green luminescence with a luminance of 20,000 cd/m² was obtained at a drive voltage of 14 V.     

Yttrium Doped Copper (II) Oxide Hole Transport Material as Efficient Thin Film Transistor

This work reports development of yttrium doped copper oxide (Y−CuO) as a new hole transport material with supplemented optoelectronic character. The pure and Y-doped CuO thin films are developed through a solid-state method at 200 °C and recognized as high performance p-channel inorganic thin-film transistors (TFTs). CuO is formed by oxidative decomposition of copper acetylacetonate, yielding 100 nm thick and conductive (40.9 S cm⁻¹) compact films with a band gap of 2.47 eV and charge carrier density of ∼1.44×10¹⁹ cm⁻³. Yttrium doping generates denser films, Cu₂Y₂O₅ phase in the lattice, with a wide band gap of 2.63 eV. The electrical conductivity increases nine-fold on 2 % Y addition to CuO, and the carrier density increases to 2.97×10²¹ cm⁻³, the highest reported so far. The TFT devices perform remarkably with high field-effect mobility (μ_sat) of 3.45 cm² V⁻¹ s⁻¹ and 5.3 cm² V⁻¹ s⁻¹, and considerably high current-on/off ratios of 0.11×10⁴ and 9.21×10⁴, for CuO and Y−CuO films, respectively (at −1 V operating voltage). A very small width hysteresis, 0.01 V for CuO and 1.92 V for 1 % Y−CuO, depict good bias stability. Both the devices work in enhancement mode with stable output characteristics for multiple forward sweeps (5 to −60 V) at −1V_g.     

Tricaesium tris(oxalato‐κ2O1,O2)chromate(III) dihydrate

The title compound, Cs₃[Cr(C₂O₄)₃]·2H₂O, has been synthesized for the first time and the spatial arrangement of the cations and anions is compared with those of the other members of the alkali metal series. The structure is built up of alternating layers of either the d or l enantiomers of [Cr(oxalate)₃]³⁻. Of note is that the distribution of the [Cr(oxalate)₃]³⁻ enantiomers in the Li⁺, K⁺ and Rb⁺ tris(oxalato)chromates differs from those of the Na⁺ and Cs⁺ tris(oxalato)chromates, and also differs within the corresponding BEDT‐TTF [bis(ethylenedithio)tetrathiafulvalene] conducting salts. The use of tris(oxalato)chromate anions in the crystal engineering of BEDT‐TTF salts is discussed, wherein the salts can be paramagnetic superconductors, semiconductors or metallic proton conductors, depending on whether the counter‐cation is NH₄⁺, H₃O⁺, Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺. These materials can also be superconducting or semiconducting, depending on the spatial distribution of the d and l enantiomers of [Cr(oxalate)₃]³⁻.     

Heterogeneous Aromatic Amination of Aryl Halides with Arylamines in Water with PS‐PEG Resin‐Supported Palladium Complexes

Catalytic aromatic amination is achieved in water under heterogeneous conditions by the use of immobilized palladium complexes coordinated with the amphiphilic polystyrene‐poly(ethylene glycol) resin‐supported di(tert‐butyl)phosphine ligand. Aromatic amination of aryl halides with diphenylamine and N,N‐double arylation of anilines with bromobenzene were found to proceed in water with broad substrate tolerance to give the triarylamines in high yield with high recyclability of the polymeric catalyst beads. Very little palladium leached from the polymeric catalyst under the water‐based reaction conditions to provide a green and clean (metal‐uncontaminated) protocol for the preparation of triarylamines, including the optoelectronically active N,N,N′,N′‐tetraaryl‐1,1′‐biphenyl‐4,4′‐diamines (TPDs).