Hole Charge Carriers Research Articles

Hole-Transporting Organic Salt Induced Surface-2D/Bulk-3D Hierarchy Perovskite for Efficient and Stable Photovoltaic Devices

Here, we report a novel hole-transporting organic salt (HTOS) based on (4'-(bis(4-methoxyphenyl)amino)-[1,1'-biphenyl]-4-yl)methanaminium bromide, which facilely forms a hole-transporting 2D perovskite on the top surface of 3D perovskite via a spin-coating procedure. This capping 2D perovskite can significantly reduce interface trap densities and enhance hole-extracting abilities of heterojunction region between 3D perovskite and hole-transporting layer (HTL), owing to its spatially and potentially confined hole-charge carriers, simultaneously. This interfacial HTOS induced 2D perovskite can effectively suppress nonradiative recombination, which leads to an increase in the photovoltage of perovskite solar cells (PSC) to more than 1.20 V. As a result, the n-i-p planar PSC can achieve a champion power conversion efficiency of 20.71% as well as excellent operational stability exhibiting 92% of initial efficiency after 500 h continuous illumination without encapsulation. This work provides a facile approach to fabricate hole-transporting surface-2D and light-harvesting bulk-3D hierarchy perovskite structure, which delivers significantly enhanced efficiency and stability of PSCs.

Descriptors for Electron and Hole Charge Carriers in Metal Oxides.

Metal oxides can act as insulators, semiconductors, or metals depending on their chemical composition and crystal structure. Metal oxide semiconductors, which support equilibrium populations of electron and hole charge carriers, have widespread applications including batteries, solar cells, and display technologies. It is often difficult to predict in advance whether these materials will exhibit localized or delocalized charge carriers upon oxidation or reduction. We combine data from first-principles calculations of the electronic structure and dielectric response of 214 metal oxides to predict the energetic driving force for carrier localization and transport. We assess descriptors based on the carrier effective mass, static polaron binding energy, and Fröhlich electron-phonon coupling. Numerical analysis allows us to assign p- and n-type transport of a metal oxide to three classes: (i) band transport with high mobility; (ii) small polaron transport with low mobility; and (iii) intermediate behavior. The results of this classification agree with observations regarding carrier dynamics and lifetimes and are used to predict 10 candidate p-type oxides.

Gate-Defined Quantum Dots in Ge/SiGe Quantum Wells as a Platform for Spin Qubits

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel spin qubits. In contrast to the weak spin-orbit interaction found in Si, strong spin-orbit coupling in Ge may allow purely electrical spin control using the electric field component of a microwave drive signal applied to a confinement gate, without the need for additional components such as microwave stripline antennas or micromagnets. A crucial aspect in the search for alternative semiconductor qubit host materials is the need to maintain the advantages of existing platforms such as Si: low disorder, long coherence times, extensibility, and semiconductor foundry compatibility. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells that can serve as hosts for hole spin qubits. These quantum wells consist of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below, grown by reduced pressure chemical vapor deposition. Isotopic enrichment is possible if required. The heavy hole charge carriers are characterized by a small effective mass m* ~ 0.08m 0 (about 2.4x lighter than for electrons in Si), high mobility μ ≥ 1E5 cm2/Vs, and highly anisotropic g-factors. The small effective mass should allow relatively large and easily-coupled quantum dots. The next-nearest light hole band is theoretically predicted to be on the order of ~ 100 meV below the heavy hole band. The p-orbital character of the hole wavefunction may provide an advantage in minimizing contact hyperfine interactions with nonzero-spin lattice nuclei. There is both theoretical and experimental evidence of a cubic Rashba-type spin-orbit interaction in this material, whose large strength is manifest as a spin-orbit length on the order of 1 micrometer. An additional advantage over Si is that the two-dimensional band structure of Ge quantum wells does not feature valley states, which can present difficulties for qubit operations. Here, we will describe our ongoing efforts to prepare spin qubits in this platform, including development of gated device architectures, device tuning protocols, and charge-sensing capabilities. Initial work focused on single-layer gate layouts, in which lithographically-defined single and double quantum dots were demonstrated at dilution refrigerator temperatures. Charging energies of ~ 1.7 meV were observed. These devices featured a broad and shallow potential landscape, and only a small number of holes could be confined to a quantum dot. Although adjacent quantum dots could be coupled to one another, this coupling was not easily tuned using this gate design. These limitations in the confinement and control of quantum dots motivated the subsequent adoption of multilayer gate-stack architectures, similar to what has been demonstrated in Si. Our three-layer devices feature gate electrodes designed for accumulation of holes, local depletion to form quantum dots, and selective isolation/screening of electric fields. Device structures feature Ti/Pt gates, ALD oxide dielectrics, and implanted ohmic contacts. Symmetrically constructed devices comprise two gated channels for quantum dot confinement, one to be used as the quantum dot under study and the other operated as a local charge sensor. By monitoring the conductance of the charge sensor as the quantum dot is tuned, we can remotely determine the dot’s occupation number, in principle down to the last hole. Iterative cycles of device fabrication and measurement, combined with numerical modeling, have allowed continuous improvements to the device design. Early three-layer device designs suffered from poor isolation between the upper and lower mirror-symmetric device channels. Numerical modeling showed (and measurements have confirmed) that an additional isolation gate could allow improved autonomy of the two channels while maintaining their electrostatic coupling needed for charge sensing. Ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a qubit demonstration, will be discussed. This work was funded, in part, by the Laboratory Directed Research and Development Program and performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in this article do not necessarily represent the views of the US Department of Energy or the United States Government. The work at NTU was supported by the Ministry of Science and Technology (107-2622-8-002-018-). Figure 1

Examination of a relationship between atmospheric blocking and seismic events in the Middle East using a new seismo-climatic index

This study statistically examines the role of atmospheric blocking as a precursor of major seismic events. Atmospheric blocking archive and earthquake databases for the Middle East region are compiled for 2000–2013. Correlations between atmospheric blocking events and seismicity are examined based on defined seismo-climatic index (SCI) based on variations of earthquake frequency and magnitude before and after blocking events. Limiting the SCI index to values > 6, 16 out of 26 major earthquakes (M > 6), i.e. 62%, are shown to have occurred within 14 days after blocking events over their respective epicentral regions. The correlation between blocking events and subsequent seismicity falls into a range of 0.694–0.803. Additional blocking-related atmospheric anomalies such as cyclogenesis, cloud coverage, and anomalous rainfall prior to major earthquakes can be understood as processes that take place in the Earth’s crust and at the ground-to-air interface as a result of the stress activation of positive hole charge carriers at depth, in the hypocentral rock volume, and their rapid migration to the Earth’s surface. Hence, atmospheric blocking events in a seismically active region may be categorized as an earthquake precursory phenomenon.

Equilibrium of Defects and Electrical Conductivity of Cation-Deficient Double Cobaltites

The crystal structure, oxygen nonstoichiometry, and electrical conductivity in PrBa1 – xCo2O6 – δ cobaltites with double perovskite structure are studied. It is shown that defective cobaltites within region of homogeneity 0 < х ≤ 0.1 have a tetragonal structure (space group P4/mmm) with parameters ap × аp × 2аp, where аp ~ 3.8 A. Coulometric titration is used to measure the content of oxygen in oxides over a wide range of temperatures and oxygen pressures in the gas phase, to calculate the concentrations of electronic defects, and to determine the limits of the thermodynamic stability of composition х = 0.1. It is established that increasing the concentration of cationic vacancies in the barium sublattice reduces the mobility of the hole charge carriers and contributes to a drop in the thermal expansion coefficient.

Pressure tuning of the electrical transport properties in the Weyl semimetal TaP

We investigated the pressure evolution of the electrical transport in the almost compensated Weyl semimetal TaP. In addition, we obtained information on the modifications of the Fermi-surface topology with pressure from the analysis of pronounced Shubnikov-de Haas (SdH) quantum oscillations present in the Hall-effect and magnetoresistance data. The simultaneous analysis of the Hall and longitudinal conductivity data in a two-band model revealed an only weak decrease in the electron- and hole charge-carrier densities up to 1.2 GPa, while the mobilities are essentially pressure independent along the a-direction of the tetragonal crystal structure. Only weak changes in the SdH frequencies for B||a and B||c point at a robust Fermi-surface topology. In contrast to the stability of the Fermi-surface topology and of the density of charge carriers, our results evidence a strong pressure variation of the magnitude of transverse magnetoresistance for B||a contrary to the results for B||c. We can relate the former to an increase in the charge-carrier mobilities along the crystallographic c-direction.

Enhanced structural, optical, electrochemical and magnetic behavior on manganese doped tin oxide nanoparticles via chemical precipitation method

A series of Sn1−xMnxO2 (X = 0.00, 0.015, 0.025, 0.035 and 0.045 mol%) nanoparticles have been synthesized by effective chemical precipitation method. In this work to explore the structural, morphological, optical, electrochemical and magnetic properties of the pure and Manganese doped SnO2 nanoparticles are characterized on the TG/DTA, XRD, SEM/EDX, HR-TEM, FTIR, UV–DRS, PL, CV, and VSM analysis. XRD indicates that the tetragonal crystal structure, with the crystallite size of range from 37 to 11 nm. The structure, size, shape, and morphology analysis by SEM and HR-TEM was spherical shape is observed. FTIR studies on functional group analysis of pure and Manganese doped SnO2 nanoparticles. The peak appeared at 619 cm−1 due to O–Sn–O stretching vibration of clearly indicates the formation of SnO2 phase. UV–DRS absorption measures were the optical band gap energies decreasing with increasing Mn (0.00%, 0.015%, 0.025%, 0.035% and 0.045%) concentration from 3.89 to 3.75 eV. UV–DRS analyzed the mechanisms of electron–hole recombination and charge carriers separation. Further, the electrochemical properties were subsequently characterized by cyclic voltammetry. From the CV performance of the supercapacitor application was analyzed, the higher capacitance value of pure and Manganese (0.045%) doped SnO2 electrode 156.7 Fg−1 and 285.2 Fg−1 observed in the scan rate of 5 mV s−1 for the product calcinated at 700 °C. The M–H loop of pure SnO2 nanoparticles showed diamagnetism, Manganese doped SnO2 nanoparticles show weak ferromagnetic and paramagnetic behavior at room temperature as measured by VSM. A tin oxide with lower manganese concentration show larger magnetization and with increasing manganese concentration the retentivity and coercivity are found to decrease. The magnetic parameters such as saturation magnetization (MS), coercivity (HC) and retentivity (MR) are obtained from VSM data.

Collectively Exhaustive Electrodes Based on Covalent Organic Framework and Antagonistic Co‐Doping for Electroactive Ionic Artificial Muscles

AbstractIn this study, high‐performance ionic soft actuators are developed for the first time using collectively exhaustive boron and sulfur co‐doped porous carbon electrodes (BS‐COF‐Cs), derived from thiophene‐based boronate‐linked covalent organic framework (T‐COF) as a template. The one‐electron deficiency of boron compared to carbon leads to the generation of hole charge carriers, while sulfur, owing to its high electron density, creates electron carriers in BS‐COF‐C electrodes. This antagonistic functionality of BS‐COF‐C electrodes assists the charge‐transfer rate, leading to fast charge separation in the developed ionic soft actuator under alternating current input signals. Furthermore, the hierarchical porosity, high surface area, and synergistic effect of co‐doping of the BS‐COF‐Cs play crucial roles in offering effective interaction of BS‐COF‐Cs with poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), leading to the generation of high electro‐chemo‐mechanical performance of the corresponding composite electrodes. Finally, the developed ionic soft actuator based on the BS‐COF‐C electrode exhibits large bending strain (0.62%), excellent durability (90% retention for 6 hours under operation), and 2.7 times higher bending displacement than PEDOT:PSS under extremely low harmonic input of 0.5 V. This study reveals that the antagonistic functionality of heteroatom co‐doped electrodes plays a crucial role in accelerating the actuation performance of ionic artificial muscles.

Thermoelectric Properties of Ca₃Co2-xMnxO₆ (x = 0.05, 0.2, 0.5, 0.75, and 1).

High-temperature instability of the Ca3Co4−yO9+δ and CaMnO3−δ direct p-n junction causing the formation of Ca3Co2−xMnxO6 has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca3Co2−xMnxO6 with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca3CoMnO6 (x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S·cm−1 at 900 °C for x = 0.05. The material Ca3Co1.8Mn0.2O6 (x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca3Co2−xMnxO6 layers between Ca3Co4−yO9+δ and CaMnO3−δ open for new geometries and designs of oxide-based thermoelectric generators.

Synthesis and characterization of photo-crosslinkable coumarin-containing polymer dielectric for organic transistors

Abstract Herein, a photo-crosslinkable coumarin-containing polymer, poly(7-(4-vinyl-benzyloxyl)-4-methylcoumarin) or PVBMC, was prepared, and its physicochemical and electrical properties as a gate dielectric in organic electronic devices, such as organic thin-film transistor (OTFT) and inverter, was evaluated. The crosslinking of PVBMC by exposure to UV light (365 nm) over time was characterized using Fourier-transform IR and UV–visible spectroscopy. The measured capacitance of the cross-linked PVBMC thin film in a metal-insulator-metal-type capacitor was as high as 36.4 pF/mm2. Pentacene-based OTFT and load-type inverter with the cross-linked PVBMC gate dielectric were prepared, and their electrical responses were evaluated under ambient conditions. The OTFT showed dominant hole charge carrier transport behavior with a field-effect mobility of 1.52 × 10−1 cm2/Vs and negligible hysteresis. The load-type inverter based on the OTFT exhibited moderate static and dynamic switching responses to the applied electrical pulse. These results suggest the potential application of photo-crosslinked PVBMC as a gate dielectric in the fabrication of high-performance OTFT-based devices.

Thermo-transport properties of Zn-substituted layered Li-nickel oxide, $$\hbox {LiNiO}_{2}$$ LiNiO 2

The layered Li-TM-\(\hbox {O}_{2}\) materials have been investigated extensively due to their application as cathodes in Li batteries. The electrical properties of these oxides can be tuned or controlled either by non-stoichiometry or substitution. Hence the thermo-transport properties of Zn-substituted \(\hbox {LiNi}_{1-x}\hbox {Zn}_{x}\hbox {O}_{2}\) for \(0 \le x \le 0.16\) have been investigated in the temperature range of 300–900 K for potential application as a high-temperature thermoelectric material. For \(x < 0.08\), the compounds were of single phase belonging to the space group R-3mH while for \(x > 0.08\) an additional minority phase, ZnO forms together with the main layered phase. All the compounds exhibit a semiconducting behaviour with electrical resistivity, varying in the range of \(\sim 10^{-4}\) to \(10^{-2}\,\,\Omega \hbox {m}\) between 300 and 900 K. The electrical resistivity is found to increase with increasing Zn-substitution predominantly due to a decrease in the charge carrier hole mobility. The activation energy remains constant, \(\sim \)10 meV, with Zn-substitution. The Seebeck coefficient of the compounds is found to decrease with increasing temperature and increase with increasing Zn-substitution. The Seebeck coefficient decreases from \(\sim \)95 to \(35\ \upmu \hbox {V K}^{-1}\) and the corresponding power factor is \(\sim \)12\(\ \upmu \hbox {W m}^{-1}\ {\hbox {K}}^{-2}\) for the \(x = 0.16\) compound.

Does Polaronic Self-Trapping Occur at Anatase TiO2 Surfaces?

The behavior of electron and hole charge carriers at surfaces of titanium dioxide (TiO2) controls performance for important applications, including photocatalysts and solar cells. Although anatase TiO2 exhibits high electron mobility in the bulk, a commonly held belief is that strong coupling between electrons and phonons can lead to electron trapping at anatase surfaces. However, direct evidence is scarce, and the nature of the trapping sites and electronic properties remains unclear. To address this question, we investigate the trapping of electrons and holes at low and high index surfaces of anatase TiO2 using an accurate hybrid density functional theory approach. We find that, as in the bulk, electrons do not trap on the low index planes (001, 100, 101, 110, 112) of anatase crystals. For the higher index planes (103, 105, 107) that contain structural step defects, we find that electrons do trap at the low-coordinated Ti cations present on the steps. The trapping of holes at the surfaces of anatase TiO...

Kinetic simulation of the effect of 3.6 eV and 4.2 eV photon excitation on the optical absorption energy spectrum of 137 Cs gamma irradiated LiF:Mg,Ti (TLD-100)

Abstract The effect of photon excitation on the optical absorption (OA) energy spectrum of LiF:Mg,Ti (TLD-100) following gamma ray irradiation to a dose-level of 2500 Gy are presented. Photon energies of 3.6 eV and 4.2 eV were chosen to selectively excite the trapping centers (TCs) associated with the 3.8 eV and 4.3 eV OA bands. The TCs associated with these OA bands are believed to give rise to the electron-only and electron-hole components of composite glow peak 5 in the thermoluminescence (TL) of TLD-100. Kinetic modeling is shown capable of simulating the changes in the optical density of the OA bands induced by the two photon energies with the same values of the recombination coefficients. This result is in contrast to a previous investigation which could not simulate the OA following both gamma irradiation and photon bleaching with the same values of the recombination coefficients. The results reported herein are consistent with : (i) the interpretation of the e-only and e-h charge configurations giving rise to the 3.8 eV and 4.3 eV OA bands and (ii) the possibility that the recombination processes following gamma irradiation occur not only following thermalization of the electron and hole charge carriers but at higher energies as well.

Improving the Charge Carrier Transport and Suppressing Recombination of Soluble Squaraine-Based Solar Cells via Parallel-Like Structure.

Small molecule organic solar cells (SMOSCs) have attracted extensive attention in recent years. Squaraine (SQ) is a kind of small molecule material for potential use in high-efficiency devices, because of its high extinction coefficient and low-cost synthesis. However, the charge carrier mobility of SQ-based film is much lower than other effective materials, which leads to the pretty low fill factor (FF). In this study, we improve the performance of SQ derivative-based solar cells by incorporating PCDTBT into LQ-51/PC71BM host binary blend film. The incorporation of PCDTBT can not only increase the photon harvesting, but also provide an additional hole transport pathway. Through the charge carrier mobility and transient photovoltage measurement, we find that the hole mobility and charge carrier lifetime increase in the ternary system. Also, we carefully demonstrate that the charge carrier transport follows a parallel-like behavior.

Role of Co3O4 Nanoparticles in Dielectric Properties of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ Superconducting Phase

Cobalt oxide (Co3O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase were prepared by sol–gel and solid-state reaction methods, respectively. Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223, x = 0–2.0 wt.%, nanoparticles–superconductor composites. The unchanged crystal structure of the host CuTl-1223 superconducting phase (i.e. tetragonal) revealed that Co3O4 nanoparticles were settled at the grain boundaries. Superconducting properties of the CuTl-1223 phase were overall suppressed due to hole–charge carriers interaction at the grain boundaries. The dielectric properties of (Co3O4)x/CuTl-1223 composites were investigated by varying the test frequencies from 40 Hz to 100 MHz and operating temperatures from 77 to 298 K. The values of dielectric properties were found maximal at lower frequencies and started to decrease at higher frequencies. So, the dielectric properties of the CuTl-1223 superconducting phase can be tuned by varying the contents of (Co3O4) nanoparticles, test frequencies as well as operating temperatures.

Earthquake chemical precursors in groundwater: a review

We review changes in groundwater chemistry as precursory signs for earthquakes. In particular, we discuss pH, total dissolved solids (TDS), electrical conductivity, and dissolved gases in relation to their significance for earthquake prediction or forecasting. These parameters are widely believed to vary in response to seismic and pre-seismic activity. However, the same parameters also vary in response to non-seismic processes. The inability to reliably distinguish between changes caused by seismic or pre-seismic activities from changes caused by non-seismic activities has impeded progress in earthquake science. Short-term earthquake prediction is unlikely to be achieved, however, by pH, TDS, electrical conductivity, and dissolved gas measurements alone. On the other hand, the production of free hydroxyl radicals (•OH), subsequent reactions such as formation of H2O2 and oxidation of As(III) to As(V) in groundwater, have distinctive precursory characteristics. This study deviates from the prevailing mechanical mantra. It addresses earthquake-related non-seismic mechanisms, but focused on the stress-induced electrification of rocks, the generation of positive hole charge carriers and their long-distance propagation through the rock column, plus on electrochemical processes at the rock-water interface.

High-performance organic transistors based on solution-processed rubrene crystals directly grown on a polymeric dielectric

Abstract High-quality rubrene crystals were directly grown on a polymeric gate dielectric-coated ITO/glass substrate by a simple solution process. Organic field-effect transistors were fabricated based on these rubrene crystals, and their electrical performance was investigated. Atomic force micrographs of the rubrene crystal reveal that its surface has a conventional terrace structure, confirming the well-ordered rubrene molecules. The organic transistor with the rubrene crystal shows the highest charge carrier hole mobility of 3.74 cm2/V·s that can be attributed to the strong π-π overlap between the adjacent rubrene molecules. The device shows a stable static and dynamic electrical stress response under ambient conditions. For evaluating the applicability of the transistor in a logic circuit, a simple load-type inverter is fabricated by combining the rubrene transistor and a 10 MΩ load-resistor, to achieve a clear dynamic switching response up to 100 Hz.

Toward Quantitative Electrochemical Nanomachining of III-Nitrides

In this paper, a comprehensive quantitative investigation is conducted on III-N electrochemical nanomachining to explore the underlying mechanisms. An electric circuit model is proposed for the etching system to interpret the various distinct etching dynamics. Factors such as the geometry of patterning, charge transfer and mass transport properties are taken into consideration as nonlinear lumped elements, which compete for voltage with the GaN/electrolyte interface during etching, thus change the etching behaviors. Quantitative study of nanoporous morphologies suggests that the anodic etching is driven by net voltage bias on the GaN/electrolyte interface and the high electric field in GaN, both related to the generation of charge carrier holes. And by three-dimensional analysis of the electrical field, the etching phase diagram is reconstructed. This study not only offers a mechanistic understanding of GaN anodic etching, but also provides a systematical prospective in constructing nanostructures on a broad range of semiconductor materials using electrochemical method.

Study of the Contributions of Donor and Acceptor Photoexcitations to Open Circuit Voltage in Bulk Heterojunction Organic Solar Cells

One of the key parameters in determining the power conversion efficiency (PCE) of bulk heterojunction (BHJ) organic solar cells (OSCs) is the open circuit voltage . The processes of exciting the donor and acceptor materials individually in a BHJ OSC are investigated and are found to produce two different expressions for . Using the contributions of electron and hole quasi-Fermi levels and charge carrier concentrations, the two different expressions are derived as functions of the energetics of the donor and acceptor materials and the photo-generated charge carrier concentrations, and calculated for a set of donor-acceptor blends. The simultaneous excitation of both the donor and acceptor materials is also considered and the corresponding , which is different from the above two, is derived. The calculated from the photoexcitation of the donor is found to be somewhat comparable with that obtained from the photoexcitation of the acceptor in most combinations of the donor and acceptor materials considered here. It is also found that the calculated from the simultaneous excitations of donor and acceptor in BHJ OSCs is also comparable with the other two . All three thus derived produce similar results and agree reasonably well with the measured values. All three depend linearly on the concentration of the photoexcited charge carriers and hence incident light intensity, which agrees with experimental results. The outcomes of this study are expected to help in finding materials that may produce higher and hence enhanced PCE in BHJ OSCs.

Controlling charge balance using non-conjugated polymer interlayer in quantum dot light-emitting diodes

The balance of electron–hole charge carriers in quantum dot (QD) light-emitting diodes (QLEDs) is an important factor to achieve high efficiency. However, poor interfacial properties between QDs and their adjacent layers are likely to deteriorate the electron–hole charge balance, resulting in the poor performance of a QLED. In this paper, we report an enhanced efficiency in red-emitting inverted QLEDs by modifying the interface properties between QDs and ZnO electron transport layer (ETL) using a thin layer of non-conjugated polymer, poly(4-vinylpyridine) (PVPy). Based on the precise control of the electrical properties with PVPy, the maximum efficiency of the QLED is enhanced by 30% compared to the device without a PVPy layer. In particular, the efficiency at low current density region is significantly increased. We investigate the effect of the PVPy interlayer on the performance of QLEDs and find that this thin layer not only shifts the energy levels of the underlying ZnO ETL, but also effectively blocks the leakage current at the ETL/QD interface.