Theoretical study on the neutral and ionic Cu(I) phosphorescent complexes with 2-(2′-quinolyl)benzimidazole and phosphine mixed ligand

The electronic structures and photophysical properties of a series of the neutral and ionic Cu(I) complexes with 2-(2′-quinolyl)benzimidazole and phosphine mixed ligand were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. To investigate the differences between the neutral and ionic complexes, the highest occupied molecular orbital (HOMO) energy, the lowest virtual molecular orbital (LUMO) energy, ΔE_H-L (the energy gap between HOMO and LUMO), the ionization potentials (IPs), electron affinities (EAs) and reorganization energies (λ) were computed. To explain the reason of the metal-to-ligand charge transfer (MLCT) hardly detection in the neutral complexes, the absorption and emission spectra were studied in detail. To evaluate the photoluminescence quantum yield (PLQY), the non-radiative and radiative decay rate constants (k_nr and k_r) were also presented. As a result, these calculations reveal that the structural distortion between the ground and excited states plays an important role in governing the PLQY. The charge transfer and the transport equilibrium property were markedly improved due to the lack of mobile counterions in the neutral form. Introducing the ether linkage together with the enhanced NˆN π-conjugation in 2b had obviously faster k_r but slower k_nr, which led to its higher PLQY relative to the introducing the ether linkage only or lacking of a proton and the counterions in complexes.     

Synthesis and characterization of highly efficient blue Ir(III) complexes by tailoring β-diketonate ancillary ligand for highly efficient PhOLED applications

We synthesized two new heteroleptic blue-emitting Ir(III) complexes tBuCN-FIrmMes and tBuCN-FIrdMes by using systematically tailored ancillary ligands 1-mesitylbutane-1,3-dione (mMes) and 1,3-dimesitylpropane-1,3-dione (dMes), respectively. Near-unity photoluminescence quantum yield (PLQY: 96 ± 3%) was achieved for tBuCN-FIrmMes in doped films with short phosphorescence lifetime and high horizontal dipole ratio (Θ: 76%) than the di-mesityl complex, tBuCN-FIrdMes (PLQY: 75 ± 3%, Θ: 71%). Here, introduction of mMes reduces the singlet-triplet splitting energy (ΔE_ST), permanent dipole moment (μ), and the symmetry of tBuCN-FIrmMes as compared with tBuCN-FIrdMes, these parameters can highly affect the PLQY and Θ values. As a result, the blue phosphorescent organic light-emitting diode (PhOLED) of tBuCN-FIrmMes exhibits high external quantum efficiency (EQE) of ≥ 20% throughout a wide luminance range 1000–10000 cd/m² with a very low efficiency roll-off, which is crucial for solid-state lighting applications.     

Photoelectrochemical cells based on ternary compounds CuIn2n + 1Se3n + 2 (n = 3–6)

Semiconductors - Single crystals of ternary CuIn2n + 1Se3n + 2 semiconductors with the composition index n = 3, 5, 6 were grown for the first time using the direct crystallization method. It was...     

Character of Interaction in the SnSb2Te4–SnBi2Te4 System and the Thermoelectric Properties of (SnSb2Te4)1 – x(SnBi2Te4)x Solid Solutions

Semiconductors - For the first time, the character of the interaction of components along the cut of SnSb2Te4–SnBi2Te4 is studied by various physicochemical methods in a wide temperature...     

Crystal Structure and Band Gap of (MnIn2S4)1–x • (AgIn5S8)x Alloys

Semiconductors - The (MnIn2S4)1–x • (AgIn5S8)x alloy single crystals are grown for the first time by the Bridgman method in the entire range of component concentrations. The composition...     

Characterization of two new (A–π)2–D–A type dyes with different central D unit and their application for dye sensitized solar cells

We report the photophysical, electrochemical and theoretical properties of two dyes with same acceptor, π-linker and anchoring acceptor unit and different TPA (D1) and pyran (D2) donor central unit. The change in the central unit resulted in corresponding different photophysical and electrochemical properties. The dye sensitized solar cell fabricated using dye D1 showed the higher incident photon to current efficiency of 54%, a short circuit current (J_sc) of 11.86 mA/cm², an open circuit voltage of 0.64 V, and fill factor (FF) of 0.68, corresponding an overall power conversion efficiency of 5.16% which is higher than that for D2 based DSSCs (4.42%). The difference in the PCE of DSSCs based on D1 and D2 is partly, due to the smaller amount of dye loading, higher dark current and charge recombination rate of D1 based DSSC. The electrochemical spectra of DSSCs demonstrated longer electron life time and charge recombination resistance and small charge transport resistance for D1 sensitized DSSC, results the higher PCE.     

Fabrication of polymer blend composites based on [PVA-PVP](1−x):(Ag2S)x (0.01 ≤ x ≤ 0.03) with small optical band gaps: Structural and optical properties

In this paper composite materials, based on polymer blends of polyvinyl alcohol (PVA): polyvinyl pyrrolidone (PVP) with small optical band gap, has been studied. Silver sulfide (Ag₂S) semiconductor particles have been synthesized in PVA:PVP blend host polymer, using in situ method. X-ray diffraction (XRD) analyses and Fourier transform infrared (FTIR) spectroscopy for the composite samples were carried out. From the XRD pattern, distinguishable crystalline peaks caused by the Ag₂S semiconductor particles were observed. From the result of FTIR spectroscopy, the intensity of the FTIR bands were shifted and increased, revealing the occurrence of interactions between the PVA:PVP blend system and Ag₂S particles. The composite samples were found to exhibit absorption spectra that cover UV–visible to near infrared regions. The absorption edge was found to be 5 eV for pure PVA:PVP system and shifted to 1.15 eV for incorporated PVA:PVP with 3 M of Ag₂S. The refractive index was also evaluated for the samples and observed to be increased from 1.15 to 1.52 as doping increased to the highest. A linear relationship between the refractive index and the filler fraction has been reported. Theoretical discussion of optical dielectric loss, which is a crucial parameter for the band gap estimation, was given. The achieved results reveal that spectra of the optical dielectric loss (ɛ_i) can be used to study the band gap structure and Tauc's model can be important in determining the types of electronic transition. The optical band gap was found to decrease from 5.2 eV for the pure PVA:PVP to 1.1 eV for doped PVA:PVP with 3 M of Ag₂S. Such reduction can be associated with the increase of optical dielectric constant. Finally, the correlation between optical dielectric constant and density of states was discussed.     

Two new D–A conjugated polymers P(PTQD-Th) and P(PTQD-2Th) with same 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b]bisthieno[2,3-f:3′,2′-h]quinoxaline-8,10(9H)-dione acceptor and different donor units for BHJ polymer solar cells application

We report the synthesis, characterization and photovoltaic properties of bulk heterojunction polymer solar cells of new donor–acceptor conjugated copolymers P(PTQD-Th) and P(PTQD-2Th) that incorporate same strong 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b]bisthieno[2,3-f:3′,2′-h]quinoxaline-8,10(9H)-dione as strong acceptor and different weak thiophene (Th) and bi-thiophene (2Th) as donors, respectively. Both the copolymers showed suitable unoccupied lowest molecular orbital (LUMO) energy levels, compatible with the LUMO of PC₇₁BM for efficient electron transfer from copolymer to PC₇₁BM in the blended copolymer: PC₇₁BM thin films. Moreover the deeper highest occupied molecular orbital (HOMO) energy levels of both copolymers ensures the high open circuit voltage (V_oc) of the BHJ polymer solar cells. The optimized P(PTQD-Th):PC₇₁BM and P(PTQD-2Th):PC₇₁BM with weight ratio of 1:2 processed with chloroform solvent showed PCE of 3.65% and 3.96%, respectively. The higher value of J_sc for the device processed with P(PTQD-2Th):PC₇₁BM as compared to that for P(PTQD-Th):PC₇₁BM, attributed to narrower optical bandgap and broader absorption profile for P(PTQD-2Th) as compared to P(PTQD-Th). The PCE values of polymer solar cells were further improved (5.54% and 5.67% for P(PTQD-Th):PC₇₁BM and P(PTQD-2Th):PC₇₁BM, respectively) when small amounts of solvent additive, i.e. 1,8-diiodoctane (DIO) were used for the processing of active layers. The improved PCE has been attributed to both the enhanced values of short circuit current (J_sc) and fill factor (FF) due to the better nanomorphology and charge transport, induced by the high boiling point of solvent additive.     

Synthesis,optical and electrochemical properties new donor–acceptor (D–A) copolymers based on benzo[1,2-b:3,4-b′:6,5-b″] trithiophene donor and different acceptor units: Application as donor for photovoltaic devices

Two new conjugated D–A polymers P3 (PBTT-d-BTT) and P4 (PBTT-d-TPD) based on same benzo[1,2-b:3,4-b′:6,5-b″] trithiophene (BTT) donor and different acceptors monomers 5,8-dibromo-2-dodecanoylbenzo[1,2-b:3,4-b′:6,5-b″] trithiophene (d-BTT), and 1,3-dibromo-5-(2-ethylhexyl)thieno[3,4]pyrrol-4,6-dione (d-TPD) respectively, were synthesized by Stille cross-coupling reaction and characterized by gel permeation chromatography (GPC), ¹H NMR, UV–Vis absorption, thermal analysis and electrochemical cyclic voltammetry (CV) tests. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC₇₁BM as acceptor with a weight ratio of polymer:PC₇₁BM 1:1, 1:2 and 1:2.5. The optimized photovoltaic device was fabricated with an active layer of a blend P3:PC₇₁BM and P4:PC₇₁BM with a blend ratio of 1:2 showed PCE 3.16% and 2.42%, respectively under illumination of AM 1.5 at 100 mW/cm² with solar simulator. The PCE of the device based on P3:PC₇₁BM processed with DIO/o-DCB has been further improved up to 4.64% with J_sc of 10.52 mA/cm² and FF of 0.58 attributed to the increase in crystalline nature of active layer and more balanced charge transport in the device, induced by DIO additive.     

Organic donor-σ-acceptor molecules based on 1,2,4,5-tetrakis((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)benzene and perylene diimide derivative and their application to photovoltaic devices

Donor-σ-acceptor molecules of HPBT-n(PDI) (n = 1, 2, and 4) containing perylene diimide (PDI) and π-extended 1,2,4,5-tetrakis((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)benzene (HPBT) have been successfully synthesized for studying the self-organization of each moiety and their applications in photovoltaic devices. Interesting features were found in these molecules: the aggregation-induced crystallization in the HPBT moieties enhanced the power conversion efficiency (PCE) in the photovoltaic cell. By incorporating HPBT as the donor and PDI as the acceptor moiety, we anticipated that their high degree of independent aggregation-induced crystallization would yield electron/hole transport channels and high mobility in the desired direction of charge transport. In a photovoltaic device, HPBT-1(PDI) gave a PCE of 0.22% with an open circuit voltage ranging from 0.62 to 0.63 V. When the HPBT moiety was more hindered by the PDI moiety, less PCE was observed in HPBT-2(PDI). Addition of methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) resulted in enhancement of the PCE due to enhanced visible absorption. The device bearing HPBT-1(PDI) and PCBM (1:4 mol ratio) demonstrate much higher PCE to be around 1.60%.     

Enhanced electrochromic write–erase efficiency of a device with a novel viologen: 1,1′-bis(2-(1H-indol-3-yl)ethyl)-4,4′-bipyridinium diperchlorate

A novel cathodically coloring viologen electrochrome: 1,1′-bis(2-(1H-indol-3-yl)ethyl)-4,4′-bipyridinium diperchlorate (IEV), comprising of a 4,4′-bipyridyl core, sandwiched between two indole moieties, was synthesized using 3-(2-bromoethyl)-indole. An electrochromic device (ECD) was assembled using an electrolyte containing an imidazolium imide ionic liquid and characterized by a large electrical conductivity, thermal stability upto 150 °C, and an electrochemical potential stability range of ∼3.6 V. The IEV viologen was dissolved in the electrolyte and Prussian blue was used as the anodic electrochrome. The indole moieties of the IEV²⁺ salt owing to their electron donating tendency can act like bleaching agents and bleach the viologen faster (IEV⁺ → IEV²⁺) and this hypothesis was used for the improved write–erase efficiency of the device. The device switched between colorless and dark violet–blue hues under applied potentials of ±1.5 V. A large transmission modulation (52%, λ = 605 nm), a high electrochromic coloring efficiency of 533 cm² C⁻¹ at 605 nm and switching times of ∼2 s and good stability during 2000 cycles were reported herein. The electrochemical activity of the ECD improved when it was maintained at an elevated temperature of 70 °C, with no sign of thermal degradation. Furthermore, we also present the ability of this new viologen to function as an excellent redox mediator as we achieved an 86% enhancement in the power conversion efficiency of a solution processed solar cell, by its’ addition in the electrolyte. Our studies demonstrate this new viologen to be a highly versatile electroactive material which can be useful for both electrochromics and photovoltaics.     

Design and Directional Growth of (Mg1−xZnx)(Al1−yCry)2O4 Single-Crystal Fibers for High-Sensitivity and High-Temperature Sensing Based on Lattice Doping Engineering and Acoustic Anisotropy

High-performance temperature sensors for the harsh environment are vital components for meeting the increasing demands for the development of existing and emerging technologies. In this study, specifically oriented (Mg_1−xZn_x)(Al_1−yCr_y)₂O₄ single-crystal fibers (SCF) are grown by the laser-heated pedestal growth technique and used as acoustic waveguides for ultrasonic temperature sensors (UTS) for the first time. The anisotropic sensor performance of the MgAl₂O₄ SCF-UTS are investigated under a longitudinal wave and transverse wave conditions, and the [110]-oriented MgAl₂O₄ SCF-UTS is found to have the highest sensitivity and resolution among all the MgAl₂O₄ SCF-UTS. On this basis, a unit sensitivity of 40.38–67.50 ns °C⁻¹ m⁻¹ and a resolution of 1.24–0.74 °C are achieved for the [110]-oriented (Mg_0.9Zn_0.1)(Al_0.995Cr_0.005)₂O₄ SCF-UTS in the range of 20–1200 °C, both of which represent the best sensor performance achieved by a SCF-UTS to date. The positive temperature-dependent sensor performance, accompanied by a high working temperature (≈2000 °C) and outstanding anti-oxidation, indicates that the [110]-oriented (Mg_0.9Zn_0.1)(Al_0.995Cr_0.005)₂O₄ SCF-UTS is a promising candidate for ultra-high temperature sensors. This study demonstrates a feasible strategy for the rational design of high-performance temperature sensors through a combination of crystal design, acoustic anisotropy, and lattice doping engineering.     

The effect of temperature on the growth of Ag2O nanoparticles and thin films from bis(2-hydroxy-1-naphthaldehydato)silver(I) complex by the thermal decomposition of spin–coated films

Bis(2-hydroxy-1-naphthaldehydato)silver(I) complex (Ag-HNA) was prepared through the reaction of the ligand and silver nitrate. Silver oxide nanoparticles were synthesized via thermal decomposition at different temperatures by calcinating Ag complex inside a ceramic boat. The same metal precursor was used to prepare Ag₂O thin films at different temperatures by spin coating onto a glass substrate. The prepared silver complex was characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis, nuclear magnetic resonance (NMR) and thermogravimetric (TGA) analysis. The effects of decomposition temperatures (150, 200, 250 and 300 °C) and of the annealing temperatures for the films at 200, 250, 300 and 350 °C were studied. The surface morphologies, structural and optical properties of the nanoparticles and films were investigated. The results shows that the temperature plays a significant role in controlling nature of the nanoparticles and thin films. The X-Ray diffraction patterns of Ag₂O nanoparticles and the prepared thin films prepared revealed the face-centred cubic structures.     

Discovery of the (In2S3)x(MnIn2S4)1 ? x solid solutions and fabrication of photosensitive structures based on them

A technology of growing single crystals of (In₂S₃) _x (MnIn₂S₄)_{1 − x} solid solutions that provides control over their atomic composition in the entire concentration range 0 ≤ x ≤ 1 is developed. It is shown that, in the range x = 0–1, the single crystals have the cubic spinel structure and the unit cell parameter a follows the linear dependence on x. The exponential character of the temperature dependence of resistivity of solid solutions, on which the first photosensitive Cu/(In₂S₃)x(MnIn₂S₄)_{1 − x} structures are obtained, is revealed. The first photosensitivity spectra of these structures are obtained, and, based on these spectra, dependences of energy of the direct and indirect band-to-band transitions on the composition x are determined. The possibility of applying these structures in broad-band photoconverters of optical radiation is concluded.     

Quaternary (FeIn2S4)x(MnIn2S4)1 ? x alloys and photosensitive structures on their basis

Using directional crystallization of the melt of the (FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} alloy, homogeneous crystals of a similar atomic composition are grown over the entire range of compositions 1 ≥ x ≥ 0. It is established that the crystals of the continuous series of quaternary alloys in the range x = 0–1 crystallize in the spinel structure and lattice parameter a linearly depends on x. It is established that it is possible to obtain In(Al)/(FeIn₂S₄) _x (MnIn₂S₄)_1–x photosensitive structures. Room-temperature spectra of relative quantum efficiency of photoconversion of the In(Al)/(FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} structures fabricated for the first time are obtained. From the analysis of these spectra, activation energies of direct and indirect band-to-band transitions for the crystals of the (FeIn₂S₄) _x (MnIn₂S₄)_1–x alloys are determined and the dependence of these parameters on the composition of the position-disordered phases of mentioned alloys is discussed. It is concluded that the crystals of the (FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} alloys can be used in broadband photoconverters of optical radiation.     

Effect of Fe doping on structural and magnetic properties of La2/3Ca1/3Mn1−yFeyO3 (y=0–0.03) thin films

We have characterized the magnetic and structural properties of pure and ⁵⁷Fe-doped La_2/3Ca_1/3MnO₃ thin films and targets, substituted with 1% and 3% of ⁵⁷Fe on the Mn site. The films were prepared via high O₂-pressure (500 mTorr) by DC magnetron sputtering on (1 0 0) SrTiO₃ and (1 0 0) LaAlO₃ single-crystal substrates. Mössbauer spectra measured at room temperature confirm the presence of Fe³⁺ with octahedral coordination, thus indicating that Fe is incorporated into the structure by substituting Mn. Structural analysis by X-ray diffraction (XRD) shows that the films are single phase and c-axis oriented and that the Fe doping gives rise to a relaxation of the epitaxial strain. Interestingly, the Curie temperature and the magnetoresistance (MR) show a non-monotonic behavior with Fe doping. This indicates that initially the strain relaxation induced by the Fe doping is more important than the reduction of ferromagnetic coupling due to the Fe incorporation.     

I–V characteristic of p-n structures based on a continuous solid solutions (Si2)1 ? xx(CdS)x

The I–V characteristics of the p-Si-n-(Si₂) _{1 − x} (CdS) _x (0 ≤ x ≤ 0.01) structures are investigated at various temperatures. It is found that the I–V characteristic of such structures has a sublinear portion of the current growth with voltage V ≈ V ₀exp(JaW). The experimental results can be explained on the basis of the theory of the injection depletion effect. It is shown that the mobility of the minority carrier (hole) decreases with an increasing temperature. Original Russian Text ? A.S. Saidov, A.Yu. Leyderman, Sh.N. Usmonov, K.T. Kholikov, 2009, published in Fizika i Tekhnika Poluprovodnikov, 2009, Vol. 43, No. 4, pp. 436–438.     

Effects of annealing technique and TiO2 seed layer on the phase composition of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 film

The lead magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO₂ seed layer were prepared by a pulsed laser deposition (PLD) deposited on Pt/Ti/SiO₂/Si substrates. The films were treated by two-step annealing and normal annealing with rapid thermal annealing (RTA). The effects of two-step annealing and the TiO₂ seed layer on the phase composition of PMN–PT films were studied. The results show that the PMN–PT film with TiO₂ seed layer can gain a pure perovskite phase with a high (1 0 0) preferential orientation after the two-step annealing technique.