Table of contents

Fluorescence correlation spectroscopy (FCS) in combination with the super-resolution imaging method STED (STED-FCS), and single-particle tracking (SPT) are able to directly probe the lateral dynamics of lipids and proteins in the plasma membrane of live cells at spatial scales much below the diffraction limit of conventional microscopy. However, a major disparity in interpretation of data from SPT and STED-FCS remains, namely the proposed existence of a very fast (unhindered) lateral diffusion coefficient, ⩾5 µm² s⁻¹, in the plasma membrane of live cells at very short length scales, ≈⩽ 100 nm, and time scales, ≈1–10 ms. This fast diffusion coefficient has been advocated in several high-speed SPT studies, for lipids and membrane proteins alike, but the equivalent has not been detected in STED-FCS measurements. Resolving this ambiguity is important because the assessment of membrane dynamics currently relies heavily on SPT for the determination of heterogeneous diffusion. A possible systematic error in this approach would thus have vast implications in this field. To address this, we have re-visited the analysis procedure for SPT data with an emphasis on the measurement errors and the effect that these errors have on the measurement outputs. We subsequently demonstrate that STED-FCS and SPT data, following careful consideration of the experimental errors of the SPT data, converge to a common interpretation which for the case of a diffusing phospholipid analogue in the plasma membrane of live mouse embryo fibroblasts results in an unhindered, intra-compartment, diffusion coefficient of  ≈0.7–1.0 µm² s⁻¹, and a compartment size of about 100–150 nm.

Large-area and uniform MoS₂ films are fabricated by using sulfurization of pre-deposited molybdenum (Mo) films. One- and three-layer MoS₂ films are obtained by sulfurizing 0.5 and 1.0 nm Mo films, respectively. The results have demonstrated the good layer number controllability of this growth technique down to single-layer MoS₂. By sequential sulfurization of 0.5 nm W, 0.5 nm Mo and 0.5 nm W under the same condition, three layers of the WS₂/MoS₂/WS₂ hetero-structure are established, which has demonstrated the potential of this growth technique for the establishment of 2D crystal hetero-structures.

Nanoscale spacing between the plasma membrane and the underlying cortical actin cytoskeleton profoundly modulates cellular morphology, mechanics, and function. Measuring this distance has been a key challenge in cell biology. Current methods for dissecting the nanoscale spacing either limit themselves to complex survey design using fixed samples or rely on diffraction-limited fluorescence imaging whose spatial resolution is insufficient to quantify distances on the nanoscale. Using dual-color super-resolution STED (stimulated-emission-depletion) microscopy, we here overcome this challenge and accurately measure the density distribution of the cortical actin cytoskeleton and the distance between the actin cortex and the membrane in live Jurkat T-cells. We found an asymmetric cortical actin density distribution with a mean width of 230 (+105/−125) nm. The spatial distances measured between the maximum density peaks of the cortex and the membrane were bi-modally distributed with mean values of 50  ±  15 nm and 120  ±  40 nm, respectively. Taken together with the finite width of the cortex, our results suggest that in some regions the cortical actin is closer than 10 nm to the membrane and a maximum of 20 nm in others.

The element distribution and the magnetic properties were investigated in (Ce,Nd)–Fe–B sintered magnets prepared by mixing Nd_13.5Fe₈₀B_6.5 and Ce₉Nd_4.5Fe₈₀B_6.5 powders with different mass ratios. Two main phases exist, but element diffusion is evident, and the chemical composition of the main phase is widely different from that of the master alloy. The Ce element tends to be expelled from the Ce-rich Re₂Fe₁₄B phase. Compared with the Ce-rich main phase, the Nd-rich Re₂Fe₁₄B phase is more stable in structure. Although the microstructure is inhomogeneous and the magnetocrystalline anisotropy is variable, the magnetization reversal is uniform in these dual main-phase magnets, which should ascribe to the existence of the exchange coupling, and magnetization reversal undergoes the nucleation of the reversed domain in irreversible magnetization. It is expected to further improve the coercivity by optimizing the distribution of the Nd-rich main phase in preparing the resource-saving (Ce,Nd)₂Fe₁₄B sintered magnets.

Based on the equation of motion of an antiferromagnetic moment, taking into account a random field of thermal fluctuations, we propose a Monte Carlo (MC) scheme for the numerical simulation of the evolutionary dynamics of an antiferromagnetic particle, corresponding to the Langevin dynamics in the Kramers theory for the two-well potential. Conditions for the selection of the sphere of fluctuations of random deviations of the antiferromagnetic vector at an MC time step are found. A good agreement with the theory of Kramers thermal relaxation is demonstrated for varying temperatures and heights of energy barrier over a wide range of integration time steps in an overdamped regime. Based on the developed scheme, we performed illustrative calculations of the temperature drift of the exchange bias under the fast annealing of a ferromagnet–antiferromagnet structure, taking into account the random variation of anisotropy directions in antiferromagnetic grains and their sizes. The proposed approach offers promise for modeling magnetic sensors and spintronic memory devices containing heterostructures with antiferromagnetic layers.

(Co(0.4 nm)/Pt(0.7 nm))_x (x  =  10, 20, 30) multilayer antidot thin films (films with arrays of nanoholes) have been grown by dc sputtering onto self-assembled pores of anodic alumina membranes with a tailored diameter and a fixed inter-hole distance. The magnetic behavior has been quantified by vibrating sample magnetometry, and the surface magnetization patterns have been imaged by magnetic force microscopy. The magnetization reversal mechanism is characterized by two steps depending on the film thickness and antidot diameter. These steps are ascribed to the nucleation and demagnetization of magnetic stripe domains. Their presence confirms the perpendicular anisotropy of the multilayer antidot films. The coercivity of antidot thin film is larger than that of the continuous films due to additional pinning centers provided by antidots. The width of the stripe domains increases as a function of film thickness. The demagnetization is further investigated through micromagnetic simulations that are in agreement with the measured hysteresis loops and their features. Different reversal mechanisms and an increase of the domain width in antidot thin films are also confirmed as a function of the magnetic anisotropy, antidot diameter and thickness of the thin film. The presence of antidots with a designed geometry is revealed to be successful in tailoring the coercivity of the thin films and magnetic patterns, which is relevant for advances in nanoscale technologies.

Crystal structure and magnetic properties of polycrystalline Nd_1−xCa_xMnO₃ (x  =  0.0, 0.2, 0.3, 0.33, 0.4, 0.5, 0.6 and 0.8) manganites were investigated. The fine structural refinement using GSAS was found to undergo a transition from Pnma reflections to Pbnm reflections associated with the Ca substitution at x  =  0.3. The magnetic ordering of these compounds witnessed distinct magnetic phases with variations of Ca substitution. Magnetic ordering of the parent compound, NdMnO₃, was found as A-type antiferromagnetic (AFM) in accordance with the earlier reports, which progressively undergoes to canted A-type AFM for x  =  0.2, pseudo CE-type AFM for the intermediate compositions, i.e. x  =  0.3 to x  =  0.5 and CE-type AFM for x  >  0.5. The x  =  0.2 compound exhibited ferromagnetic like (weak AFM) behaviour, and the critical exponent study reinforced the magnetic inhomogeneity of the compound. Hysteresis curves of all the compounds measured at different temperatures implied the presence of metamagnetic like transitions for the intermediate compositions (0.3  ⩽  x  ⩽  0.5). Relative cooling power (RCP) value of Nd_0.8Ca_0.2MnO₃ was observed to be 900 J Kg⁻¹, at the higher magnetic field, making it a promising candidate for magnetic refrigeration applications.

The structural, morphological, electrical and optical properties of In-rich Al_xIn_1−xN (0  <  x  <  0.39) layers grown by reactive radio-frequency (RF) sputtering on sapphire are investigated as a function of the deposition parameters. The RF power applied to the aluminum target (0 W–150 W) and substrate temperature (300 °C–550 °C) are varied. X-ray diffraction measurements reveal that all samples have a wurtzite crystallographic structure oriented with the c-axis along the growth direction. The aluminum composition is tuned by changing the power applied to the aluminum target while keeping the power applied to the indium target fixed at 40 W. When increasing the Al content from 0 to 0.39, the room-temperature optical band gap is observed to blue-shift from 1.76 eV to 2.0  eV, strongly influenced by the Burstein–Moss effect. Increasing the substrate temperature, results in an evolution of the morphology from closely-packed columnar to compact. For a substrate temperature of 500 °C and RF power for Al of 150 W, compact Al_0.39In_0.61N films with a smooth surface (root-mean-square surface roughness below 1 nm) are produced.

The degradation of conductivity with increased Mg content for Mg_xZn_1−xO wide bandgap materials has always been a fundamental application-motivated research issue. Herein, the study of self-compensating defects in Mg_xZn_1−xO:F (0  ⩽  x  ⩽  0.29) thin films was performed to reveal their influence on increased resistivity. Our observations solidly evidence that the degradation of conductivity is mainly owing to the increased concentration of Zn vacancy (V_Zn)-related compensating defects in Mg_xZn_1−xO alloys. The formation enthalpy of intrinsic V_Zn defects decreases as Mg content (x) increases. Thus, the compensation ratio increases from 0.23 at x  =  0 to 0.47 at x  =  0.29, resulting in deteriorated conductivity in Mg_xZn_1−xO alloys. Cathodoluminescence (CL) spectra further confirm higher V_Zn concentrations with increased Mg content. The electron transport is demonstrated to be dominated by an ionized scattering mechanism. Formation of $F_{\text{O}}^{+}$–$V_{\text{Zn}}^{2-}$ complexes could reduce the concentration of ionized scattering centers and thus increase mobility. These results clarify the reason of increasingly high resistivity in Mg_xZn_1−xO, which is a long-sought-after physics problem in this area, and provide crucial information on controlling the conductivity of Mg_xZn_1−xO alloys.

The dissociation of charge-transfer (CT) states into free charge carriers at donor–acceptor (DA) interfaces is an important step in the operation of organic solar cells and related devices. In this paper, we show that the effect of DA morphology and architecture means that the directions of CT states (where a CT state's direction is defined as the direction from the electron to the hole of the CT state) may deviate from the direction of the applied electric field. The deviation means that the electric field is not fully utilized to assist, and could even hinder the dissociation process. Furthermore, we show that the correct charge carrier mobilities that should be used to describe CT state dissociation are the actual mobilites at DA interfaces. The actual mobilities are defined in this paper, and in general are not the same as the mobilities that are used to calculate electric currents which are the mobilites along the direction of the electric field. Then, to correctly describe CT state dissociation, we modify the widely used Onsager–Braun (OB) model by including the effect of DA morphology and architecture, and by employing the correct mobilities. We verify that when the modified OB model is used to describe CT state dissociation, the fundamental issues that concern the original OB model are resolved. This study demonstrates that DA morphology and architecture play an important role by strongly influencing the CT state dissociation as well as the mobilites along the direction of the electric field.

In this study we present a method for measuring bulk traps using deep-level spectroscopy techniques in metal–insulator–semiconductor (MIS) structures. We will focus on deep-level transient spectroscopy (DLTS), although this can be extended to deep-level optical spectroscopy (DLOS) and similar techniques. These methods require the modulation of a depletion region either from a Schottky junction or from a highly asymmetric p–n junction, junctions that may not be realizable in many current material systems. This is the case of wide-bandgap semiconductor families that present a doping asymmetry or have a high residual carrier concentration or surface carrier accumulation, such as InGaN or ZnO. By adding a thin insulating layer and forming an MIS structure this problem can be circumvented and DLTS/DLOS can be performed under certain conditions. A model for the measurement of bulk traps in MIS structures is thus presented, focusing on the similarities with standard DLTS, maintaining when possible links to existing knowledge on DLTS and related techniques. The model will be presented from an equivalent circuit point of view. The effect of the insulating layer on DLTS is evaluated by a combination of simulations and experiments, developing methods for the measurement of these type of devices. As a validation, highly doped ZnO:Ga MIS devices have been successfully characterized and compared with a reference undoped sample using the methods described in this work, obtaining the same intrinsic levels previously reported in the literature but in material doped as high as $1\times {{10}^{18}}$ cm⁻³.

A model that universally describes the characteristics of photocurrent in molybdenum disulphide (MoS₂) thin-film transistor (TFT) photosensors in both 'light on' and 'light off' conditions is presented for the first time. We considered possible material-property dependent carrier generation and recombination mechanisms in layered MoS₂ channels with different numbers of layers. We propose that the recombination rates that are mainly composed of direct band-to-band recombination and interface trap-involved recombination change on changing the light condition and the number of layers. By comparing the experimental results, it is shown that the model performs well in describing the photocurrent behaviors of MoS₂ TFT photosensors, including the photocurrent generation under illumination and a hugely long time persistent trend of the photocurrent decay in the dark condition, for a range of MoS₂ layer numbers.

Chemical solution deposition is a low cost, scalable and high performance technique to obtain metal oxide thin films. Recently, solution combustion synthesis has been introduced as a chemical route to reduce the processing temperature. This synthesis method takes advantage of the chemistry of the precursors as a source of energy for localized heating. According to the combustion chemistry some organic solvents can have a dual role in the reaction, acting both as solvent and fuel. In this work, we studied the role of 2-methoxyethanol in solution based synthesis of ZTO thin films and its influence on the performance of ZTO TFTs. The thermal behaviour of ZTO precursor solutions confirmed that 2-methoxyethanol acts simultaneously as a solvent and fuel, replacing the fuel function of urea. The electrical characterization of the solution based ZTO TFTs showed a slightly better performance and lower variability under positive gate bias stress when urea was not used as fuel, confirming that the excess fuel contributes negatively to the device operation and stability. Solution based ZTO TFTs demonstrated a low hysteresis (ΔV  =  −0.3 V) and a saturation mobility of 4–5 cm² V⁻¹ s⁻¹.

DNA-based small molecules of guanine, cytosine, thymine and adenine are adopted for the charge injection layer between the Au electrodes and organic semiconductor, heptazole (C₂₆H₁₆N₂). The heptazole-channel organic field effect transistors (OFETs) with a DNA-based small molecule charge injection layer showed higher hole mobility (maximum 0.12 cm² V⁻¹ s⁻¹) than that of a pristine device (0.09 cm² V⁻¹ s⁻¹). We characterized the contact resistance of each device by a transfer length method (TLM) and found that the guanine layer among all DNA-based materials performs best as a hole injection layer leading to the lowest contact resistance. Since the guanine layer is also known to be a proper channel passivation layer coupled with a thin conformal Al₂O₃ layer protecting the channel from bias stress and ambient molecules, we could realize ultra-stable OFETs utilizing guanine/Au contact and guanine/Al₂O₃ bilayer on the organic channel.

Silicon carbide (SiC) is a semiconductor with excellent mechanical and physical properties. We study the thermal transport in SiC by using non-equilibrium molecular dynamics simulations. The work is focused on the effects of twin boundaries and temperature on the thermal conductivity of 3C-SiC. We find that compared to perfect SiC, twinned SiC has a markedly reduced thermal conductivity when the twin boundary spacing is less than 100 nm. The Si–Si twin boundary is more effective to phonon scattering than the C–C twin boundary. We also find that the phonon scattering effect of twin boundary decreases with increasing temperature. Our findings provide insights into the thermal management of SiC-based electronic devices and thermoelectric applications.

Transition from single to multiple axial potential structure (MAPS) formation is reported in expanding helicon plasma. This transition is created by forming a cusp magnetic field at the downstream after the expansion throat. Two distinct potential drops are separated by a uniform axial potential zone. Non-uniform axial density distribution exists in expanding helicon systems. A cusp-like field nourishes both the axial density gradients sufficient enough for the formation of these two distinct potential drops. It is also shown that both single and multiple axial potential structures are observed only when both geometric and magnetic expansions closely coincide with each other. Coexistence of these two expansions at the same location enhances plasma expansion which facilitates deviation from Boltzmann distribution and violates quasi-neutrality locally.

A kinetic description for electronic excitation of helium for principal quantum number n$\leqslant$ 4 has been included into a particle-in-cell (PIC) simulation utilizing direct simulation Monte Carlo (DSMC) for electron-neutral interactions. The excited electronic levels radiate state-dependent photons with wavelengths from the extreme ultraviolet (EUV) to visible regimes. Photon wavelengths are chosen according to a Voigt distribution accounting for the natural, pressure, and Doppler broadened linewidths. This method allows for reconstruction of the emission spectrum for a non-thermalized electron energy distribution function (EEDF) and investigation of high energy photon effects on surfaces, specifically photoemission. A parallel plate discharge with a fixed field (i.e. space charge neglected) is used to investigate the effects of including photoemission for a Townsend discharge. When operating at a voltage near the self-sustaining discharge threshold, it is observed that the electron current into the anode is higher when including photoemission from the cathode than without even when accounting for self-absorption from ground state atoms. The photocurrent has been observed to account for as much as 20% of the total current from the cathode under steady-state conditions.

Interactions between an arc and external fields are crucially important for the design and the optimization of modern plasma torches. Multiple studies have been conducted to help better understand the behavior of DC and AC current arcs exposed to external and 'self-induced' magnetic fields, but the theoretical foundations remain very poorly explored. An analytical investigation has therefore been carried out in order to study the general behavior of DC and AC arcs under the effect of random cross-fields.

A simple differential equation describing the general behavior of a planar DC or AC arc has been obtained. Several dimensionless numbers that depend primarily on arc and field parameters and the main arc characteristics (temperature, electric field strength) have also been determined. Their magnitude indicates the general tendency pattern of the arc evolution. The analytical results for many case studies have been validated using an MHD numerical model.

The main purpose of this investigation was deriving a practical analytical model for the electric arc, rendering possible its stabilization and control, and the enhancement of the plasma torch power.

Epoxy-based model insulators were manufactured and fluorinated under a F₂/N₂ mixture (12.5% F₂) at 50 °C and 0.1 MPa for 15 min and 60 min. Surface charge accumulation and decay behavior were studied with and without dc voltage application. The effect of direct fluorination on surface charge migration as well as on flashover voltage was verified. The obtained results show that the charge decay of epoxy-based insulators is a slow process, but the decay rate increases when an outer dc electric field is applied. The surface charge distribution is changed when a streamer is triggered on the insulator surface. The existence of heteropolarity surface charges can decrease the dc surface flashover voltage to some extent, while the surface flashover voltage is almost unchanged when charges of the same polarity accumulate on the insulator surface. The short time fluorinated insulator can modify the surface resistivity, and the rate of surface charge dissipation is greatly increased under a dc electric field.

In this study, numerical approaches were applied to theoretically investigate the influence of process parameters, such as the incident angle and the deposition rate, on the nanostructural formation of thin films by oblique angle deposition (OAD). A continuum model was first developed, and the atomic diffusion, shadowing effect and steering effect were incorporated in the formation mechanisms of the surface morphology and nanostructure of the deposited films. A characteristic morphology of columnar nanorods corresponding to an OAD was well reproduced through this kinetic model. With the increase of the incident angle, the shadowing effect played a significant role in the columnar structures and the ratio of the surface area to volume was raised, implying a high level of voids in the nanostructures. When the deposition rate decreased, the porosity was notably suppressed due to the atomic diffusion in the growth process. These simulation results coincide well with many experimental observations. With the manipulation of the numerical simulations, the underlying mechanisms of the morphological formation during OAD were revealed, which also provided plentiful information to stimulate the process designs for manufacturing advanced materials.

We report on an extensive and detailed study of the silicide reaction of Ni–W alloys on Si(1 0 0). The solid phase reaction when studied over the full composition range reveals the substantial impact of composition and microstructure on the silicide reaction properties, such as the phase formation sequence and formation temperatures. It was found that the microstructure of the as-deposited film depends crucially on the alloy composition, being polycrystalline below 45 at.% W and amorphous above 45 at.% W. The microstructure affects the elemental mobility substantially, resulting in a drastic increase in the silicide reaction temperature in the case of an amorphous thin film. To further investigate the effect of elemental mobility, Si was premixed in the as-deposited alloy, thereby excluding the need for long-range diffusion. As a result, the silicide reaction temperatures were lowered. However, what was more striking was the observation of a bilayer structure for epitaxial NiSi₂ in contact with the Si substrate and a W-rich layer residing at the outermost layer at a temperature of only 300 °C. The results stress the importance of the composition and crystalline nature of the as-deposited film, with these being decisive for the reaction sequence.

Based on first-principles calculations, a new-type of edge reconstruction with remarkable stability is predicted for zigzag phosphorene nanoribbons. Such a new-type of edge reconstruction is named as θ-edge according to its θ-like configuration, in which all edge atoms are fully self-passivated with a coordination number of 3. In ZZ nanoribbons, θ-edge is energetically more stable than the bare case and as stable as the previously proposed ZZ'-o reconstruction. In ZZ₅₄ nanoribbons, θ-edge is energetically more stable than the metastable Δ-edge spontaneously formed in normal VASP optimization, and it is the most stable one among all these edge reconstructions. Further investigation shows that zigzag phosphorene nanoribbons with θ-edge are semiconductors with band gaps varying inversely with ribbon width.

We have critically evaluated the deposition parameter space of very high frequency plasma-enhanced chemical vapour deposition discharges near the amorphous to crystalline transition for intrinsic a-Si:H passivation layers on Si (1 1 1) wafers. Using a low silane concentration in the SiH₄–H₂ feedstock gas mixture that created amorphous material just before the transition, we have obtained samples with excellent surface passivation. Also, an a-Si:H matrix was grown with embedded local epitaxial growth of crystalline cones on a Si (1 1 1) substrate, as was revealed with a combined scanning electron and high-resolution transmission electron microscopy study. This local epitaxial growth was introduced by a decrease of the silane concentration in the feedstock gas or an increase in discharge power at low silane concentration. Together with the samples on Si (1 1 1) substrates, layers were co-deposited on Si (1 0 0) substrates. This resulted in void-rich, mono-crystalline epitaxial layers on Si (1 0 0). The epitaxial growth on Si (1 0 0) was compared to the local epitaxial growth on Si (1 1 1). The sparse surface coverage of cones seeded on the Si (1 1 1) substrate is most probably enabled by a combination of nucleation at steps and kinks in the {1 1 1} surface and intense ion bombardment at low silane concentration. The effective carrier lifetime of this sample is low and does not increase upon post-deposition annealing. Thus, sparse local epitaxial growth on Si (1 1 1) is enough to obstruct crystalline silicon surface passivation by amorphous silicon.

Recent studies of photoalignment of liquid crystals (LCs) on chalcogenide surfaces have a rich variety of mechanisms responsible for the photoalignment on these materials. Both chalcogenide surface-mediated and LC bulk-mediated photoalignment were observed. We report on investigation toward understanding the origin of the chalcogenide surface-mediated photoalignment. The contributions of light-induced optical and surface morphological anisotropy of the chalcogenide surface were studied. Light-induced optical anisotropy in the film was observed by polarization interferometry and the surface anisotropy was measured by high-resolution x-ray reflectivity. The data reveals the lack of a strong anisotropy in the surfaces' morphology after irradiation with polarized blue light. At the same time, an evident correlation between the anchoring energy and the quality of the photoalignment was observed. This allows us to conclude that the photoalignment of LCs on chalcogenide surfaces is mainly determined by a light-induced anisotropic distribution of the glass structural elements in the bulk and on the chalcogenide surface.

We have carried out a comparative study of plausible non-180° domain configurations in the two- and three-phase states of lead-free ferroelectrics Ba(Ti_1−xZr_x)O₃ (0.02  ⩽  x  ⩽  0.08) and (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃, respectively, using the elastic matching approach. The phase contents and stress-relief conditions in Ba(Ti_0.93Zr_0.07)O₃ and (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ strongly depend on domain types in the rhombohedral R3m phase, whereas domains of the orthorhombic Amm2 phase influence two-phase states in Ba(Ti_0.98Zr_0.02)O₃. Changes in unit-cell parameters of (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ at poling lead to the complete stress relief in three-phase (P4mm  +  Amm2  +  R3m) structures by increasing the volume fraction of the R3m phase. A link between the heterophase/domain structures and high piezoelectric activity in (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ is discussed. Based on our results, we state that equal or almost equal volume fractions of the domain types at the three-phase coexistence in (Ba_0.85Ca_0.15)^..(Ti_0.90Zr_0.10)O₃ can lead to an enhanced contribution from domain-wall displacements and therefore, to the large piezoelectric response in this important lead-free ferroelectric compound.

Poly(3,4-ethylendioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on a fluoride-doped tin oxide glass substrate using a heuristic method to fabricate platinum-free counter electrodes for dye-sensitized solar cells (DSSCs). In this heuristic method a thin layer of PEDOT:PPS is obtained by spin coating the PEDOT:PSS on a Cu substrate and then removing the substrate with FeCl₃. The characteristics of the deposited PEDOT:PSS were studied by energy dispersive x-ray analysis and scanning electron microscopy, which revealed the micro-electronic specifications of the cathode. The aforementioned DSSCs exhibited a solar conversion efficiency of 3.90%, which is far higher than that of DSSCs with pure PEDOT:PSS (1.89%). This enhancement is attributed not only to the micro-electronic specifications but also to the HNO₃ treatment through our heuristic method. The results of cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and Tafel polarization plots show the modified cathode has a dual function, including excellent conductivity and electrocatalytic activity for iodine reduction.

This research assessed the effects of various chemical structures and molecular sizes on the simulated geometric parameters, electron structures, and spectroscopic properties of single-chain complex alternating donor–acceptor (D–A) monomers and copolymers that are intended for use as photoactive layer in a polymer solar cell by using Kohn–Sham density functional theory with B3LYP exchange-correlation functional. The 3-hexylthiophene (3HT) was selected for electron donor, while eight chemicals, namely thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT), thiadiazolothieno-pyrazine (TPD), oxadiazole (OXD) and 5-diphenyl-1,2,4-triazole (TAZ), were employed as electron acceptor functional groups. The torsional angle, bridge bond length, intramolecular charge transfer, energy levels, and molecular orbitals were analyzed. The simulation results reveal that the geometry and electron structure of donor–acceptor monomer and copolymer are significantly impacted by heterocyclic rings, heteroatoms, fused rings, degree of steric hindrance and coplanarity of the acceptor molecular structure. Planar conformation was obtained from the D copolymer, and a pseudo-planar structure with the TD copolymer. The TAZ acceptor exhibited strong steric hindrance due to its bulky structure and non-planarity of its structure. An analysis of the electron structures indicated that the degree of intramolecular electron-withdrawing capability had the rank order TAZ  <  Z  <  D  <  TPD  <  OXD  <  TP  <  BT  <  TD. The TD is indicated as the most effective acceptor among those that were simulated. However, the small energy gaps of TD as well as TPD copolymer indicate that these two copolymers can be used in transparent conducting materials. The copolymer based on BT acceptor exhibited good intramolecular charge transfer and absorbed at 656 nm wavelength which is close to the maximum flux of solar spectrum. Hence, the BT acceptor functional group provides a compromise in the characteristics of a donor–acceptor copolymer, useful in a polymeric candidate material for the photoactive layer in a polymer solar cell.