Hafnium metallocene compounds used as cathode interfacial layers for enhanced electron transfer in organic solar cells

We have used hafnium metallocene compounds as cathode interfacial layers for organic solar cells [OSCs]. A metallocene compound consists of a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure. For the fabrication of the OSCs, poly[3,4-ethylenedioxythiophene]:poly(styrene sulfonate), poly(3-hexylthiophene-2,5-diyl) + [6,6]-phenyl C61 butyric acid methyl ester, bis-(ethylcyclopentadienyl)hafnium(IV) dichloride, and aluminum were deposited as a hole transport layer, an active layer, a cathode interfacial layer, and a cathode, respectively. The hafnium metallocene compound cathode interfacial layer improved the performance of OSCs compared to that of OSCs without the interfacial layer. The current density-voltage characteristics of OSCs with an interfacial layer thickness of 0.7 nm and of those without an interfacial layer showed power conversion efficiency [PCE] values of 2.96% and 2.34%, respectively, under an illumination condition of 100 mW/cm2 (AM 1.5). It is thought that a cathode interfacial layer of an appropriate thickness enhances the electron transfer between the active layer and the cathode, and thus increases the PCE of the OSCs

Dielectric properties of BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> ferroelectric thin film artificial lattice

Dielectric behavior on BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> artificial lattices has been investigated along with quantum mechanical simulation (first principles calculation). From the oxide artificial lattice approach, strain manipulation was performed to obtain a wide range of lattice deformation in the consisting BaTiO<SUB>3</SUB> and SrTiO<SUB>3</SUB> layers, which leads to two important consequences. First, we obtained enhanced dielectric constant and extremely large nonlinearity in the artificial lattices with very short stacking periods. Second, it is found that there exists a maximum dielectric constant in each BaTiO<SUB>3</SUB> lattice and SrTiO<SUB>3</SUB> lattice at a certain degree of lattice deformation. The first principles study successfully explains the dielectric behavior of strained BaTiO<SUB>3</SUB> and SrTiO<SUB>3</SUB> lattices, the existence of the maximum dielectric constant. The first principles study on BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> artificial lattices with very short stacking periods also reveals that the artificial lattice undergoes phase transition between the tetragonal and monoclinic phases with a misfit lattice strain and exhibits an anomalous dielectric behavior at the phase boundary. Optical phonon behavior of the BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> artificial lattice resembles that of strained SrTiO<SUB>3</SUB> lattice and optical phonon softening primarily derives the anomaly of the dielectric tensor at the phase boundary. The lattice deformation is a primary influencing factor to phonon and dielectric behaviors rather than interface layer effect in BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> artificial lattice with very short stacking periods

Polarization of strained BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> artificial superlattice: first-principles study

We performed first-principles calculation to investigate the effect of epitaxial strain on lattice instabilities and polarization behavior of BaTiO3/SrTiO3 artificial lattice with very short stacking period, i.e., BaTiO3 1 unit cell/SrTiO3 1 unit cell (BTO/STO). The structural analysis of BTO/STO artificial superlattice under in-plane compressive state showed enhanced stability of the tetragonal phase. On the other hand, the stability of monoclinic phase was enhanced when the BTO/STO was in the in-plane tensile state. The phase transition from tetragonal to the monoclinic phase occurs at the misfit strain of -0.25%. As the misfit strain of BTO/STO superlattice increases from -0.25% to -1.5% (in-plane compressive state), the tetragonal superlattice exhibits an increasing polarization along the [001] direction. In the monoclinic phase, the polarization of the superlattice rotates progressively toward [110] direction with increasing the misfit strain, and the magnitude of the polarization simultaneously increases with the rotation. The first-principles study shows that the phase stability and polarization vector is sensitively influenced by the lattice misfit strain

Structural transition and dielectric response of an epitaxially strained BaTiO<SUB>3</SUB>/SrTiO<SUB>3</SUB> superlattice: a first-principles study

We determine the structure and static dielectric response of the BaTiO3 1 unit cell/SrTiO3 1 unit cell (BTO/STO) superlattice as a function of epitaxial strain using first-principles density functional theory (DFT) calculations based on pseudopotentials and a plane-wave basis. We find a structural transition from the tetragonal phase at compressive strains to the monoclinic phase at tensile strains, with a nonzero in-plane component of polarization in the monoclinic phase as its order parameter. For the stable structures determined as a function of in-plane strain, we obtained optical phonon frequencies, Born effective charges and static dielectric constants using DFT linear response. Our calculations predict a large zero-temperature dielectric response with a strong anisotropy, whose origin is traced to soft phonons of the superlattice

A STUDY OF THE CHARACTERISTICS OF ORGANIC–INORGANIC HYBRID PLASMA-POLYMER THIN FILMS BY CO-DEPOSITION OF TOLUENE AND TEOS

We investigated the interaction of varied plasma power with ultralow-κ Toluene–TEOS hybrid plasma-polymer thin films, as well as changes in electrical and mechanical properties with various mixture ratios of toluene and TEOS (tetraethoxysilane). Using the plasma enhanced chemical vapor deposition (PECVD) method, organic–inorganic hybrid polymer thin films were deposited on silicon(100) substrates under 150°C of wall temperature and a ratio of TEOS to toluene. Toluene and TEOS were utilized as organic and inorganic precursors, and hydrogen and argon were used as bubbler and carrier gases, respectively. In order to compare the differences in the electrical and the mechanical properties of plasma polymerized thin films, we grew the hybrid polymer thin films under 30 W of RF (radio frequency using 13.56 MHz) power with various ratios of toluene to TEOS. The as-grown polymerized thin films were first analyzed by Fourier Transform Infrared (FT-IR) spectroscopy, and Atomic Force Microscopy (AFM). The results of FT-IR showed that the hybrid polymer thin films were totally fragmented and polymerized with increasing RF power. AFM showed that polymer films with smooth surface could be grown under various deposition conditions. An impedance analyzer was utilized for the measurements of capacitance values for dielectric constants and the thin films were analyzed for hardness and Young's modulus using a nanoindenter.Low-κ, PECVD, mechanical and electronic properties

Novel plasma-polymerized coating facilitates HeLa cell spheroid formation, exerting necroptosis via β-cyclodextrin-encapsulated resveratrol

Abstract Beta-cyclodextrins (β-CDs) comprise a pore for accommodating resveratrol (Res), thereby boosting its bioavailability. Res-incorporated β -CD (Res/CD) may be cytotoxic against both normal and cancer cells. Herein, we examined whether Res/CD exhibits anticancer activity against tumor spheroids, similar to in vivo tumor mass. To prepare three-dimensional spheroids, 1,1,1,3,5,7,7,7 octamethyl-3,5-bis(trimethylsiloxyl) tetrasiloxane (OMBTSTS) was deposited to the surface of the culture dish via plasma polymerization. We observed that HeLa cells grew as spheroids on the OMBTSTS-deposited surface at 20 W plasma power. Res/CD was delivered to the hypoxic core of the spheroid, inducing necrosis, whereas Res was not. Consistently, 10 μM Res alone was not cytotoxic to two-dimensional HeLa cells grown on a culture dish and three-dimensional spheroids. However, Res/CD promoted the necroptosis of spheroids, which were split into small fragments, ultimately inducing cell spheroid death. Collectively, our data suggest that nontoxic levels of Res/CD were efficiently delivered to the hypoxic core of tumor spheroids, promoting cell death. Therefore, Res/CD can be used as an effective anticancer drug. Moreover, the plasma-polymerized OMBTSTS modification technique provides insights into the efficient formation of spheroids in various cancer cell lines

Optimization of Gas-Sensing Properties in Poly(triarylamine) Field-Effect Transistors by Device and Interface Engineering

In this study, we investigated the gas-sensing mechanism in bottom-gate organic field-effect transistors (OFETs) using poly(triarylamine) (PTAA). A comparison of different device architectures revealed that the top-contact structure exhibited superior gas-sensing performance in terms of field-effect mobility and sensitivity. The thickness of the active layer played a critical role in enhancing these parameters in the top-contact structure. Moreover, the distance and pathway for charge carriers to reach the active channel were found to significantly influence the gas response. Additionally, the surface treatment of the SiO2 dielectric with hydrophobic self-assembled mono-layers led to further improvement in the performance of the OFETs and gas sensors by effectively passivating the silanol groups. Under optimal conditions, our PTAA-based gas sensors achieved an exceptionally high response (>200%/ppm) towards NO2. These findings highlight the importance of device and interface engineering for optimizing gas-sensing properties in amorphous polymer semiconductors, offering valuable insights for the design of advanced gas sensors