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It was argued that human energy consists of physical energy that related to metabolism in the human body and the invisible part represented by the human energy field (HEF). This energy can be generated by a person by using a special excercise. In term of Indian metaphysical theories this energy is called “Chakras” which represents an integrated energy centers. The paper investigates the measurement the Chakra energy by looking at the effect of this energy on the molecular structure of mineral water. The experiment is carried out by providing Chakra energy generated by varying Jurus to a water sample and measured in FTIR. The existence of Chakra energy then analyzed by its effect on the spectrum. The results show that Fourier transform infrared spectroscopy (FTIR) spectra of the mineral water has given Chakra energy have transmitance lower than normal mineral water. The Chakra energy reduce the transmittance but the majority of them does not change a pattern or shift the top of the spectrum. The explicit energy of molecular vibration will be studied by using the Fourier decomposition. This shows that a weakening of molecular vibration occurs to the higher Jurus with a decline in the amplitude of vibration almost half or less.

A facile sol–gel method is presented and used to optimize LixMn2-yTiyO4 spinel-type materials for Li-ion battery cathodes while maintaining nanostructured features and minimizing the formation of TiO2 impurities. LiMn1.8Ti0.2O4 exhibited the best initial specific capacity of 215 mA h g−1 at 30.8 mA g−1 in a window potential of 4.6 – 2.0 V vs. Li|Li+. The addition of Ti improved the specific capacity thanks to possibility of using both Mn4+|Mn3+ and Mn3+|Mn2+ transitions. However, capacity fading issues persist. The effect of Ti incorporation and degradation processes during cycling were studied by cyclic voltammetry, charge/discharge cycling and EIS, the latter was analyzed by seldom used distribution of relaxations times (DRT) and compared to the results obtained by fitting to equivalent electrical circuits. Cathode materials were characterized by XPS, Raman and BET surface area and at different cycling stages by XRD, Synchrotron XRD and SEM. The results showed undesired structure modifications for the transition Mn3+|Mn2+ and the formation of irreversible tetragonal phase that increased charge transfer resistances.

Perovskite light-emitting diodes have been gaining attention in recent years due to their high efficiencies. Despite of the recent progress made in device efficiency, the operation mechanisms of these devices are still not well understood, especially the effects of ion migration. In this work, the role of ion migration is investigated by measuring the transient electroluminescence and current responses, with both the current and efficiency showing a slow response in a time scale of tens of milliseconds. The results of the charge injection dynamics show that the slow response of the current is attributed to the migration and accumulation of halide ions at the anode interface, facilitating hole injection and leading to a strong charge imbalance. Further, the results of the charge recombination dynamics show that the slow response of the efficiency is attributed to enhanced charge injection facilitated by ion migration, which leads to an increased carrier density favoring bimolecular radiative recombination. Through a combined analysis of both charge injection and recombination dynamics, we finally present a comprehensive picture of the role of ion migration in device operation.

Similar to an electronic lattice determining the motion of electrons in solids, photonic crystals (PhCs) are periodic photonic nanostructures that determine the propagation of photons. By incorporating PhCs into organic light-emitting diodes (OLEDs), the device efficiency and emission spectra can be modified, which can be explained and predicted by the mode dispersion. In this work, we experimentally measure the mode dispersion of 1-D and 2-D PhC OLEDs at different azimuthal angles with angle-resolved electroluminescence spectra. The results are explained using an intuitive geometry approach, which shifts and slices the cone-shaped optical modes to obtain the mode dispersion of PhC OLEDs. We note that the weak cavity mode and a narrow photonic band gap are visible only after eliminating the intrinsic emitter spectrum in the air mode dispersion. In the end, we discuss the implication of mode dispersion on the OLED light extraction.

Power conversion efficiencies (PCEs) in organic solar cells (OSCs) have rapidly improved in the last 5 years owing largely to the development of novel small-molecule acceptors and polymer donors with several systems’ performances exceeding 17%. A key factor for these materials implementation into industrial relevant devices is their active layer thickness tolerance as solar cell performances are typically reported with thicknesses on the order of 100–150 nm, but thicker films (ca. 300 nm) are needed for printing and roll-to-roll processing. In this report, two PM7 isomeric derivatives were synthesized featuring a chlorinated benzodithiophene and ester functionalized terthiophene moieties for the incorporation into non-fullerene OSCs. The fundamental difference between the two isomeric polymers is the location of the ester side chains where the PM7 D1 esters are located on the outer thiophene units, whereas the esters on PM7 D2 are located on the central thiophene unit. This simple modification produced polymers with similar absorption profiles, electrochemical onsets, charge carrier mobilities when blended with ITIC-4F, and grazing-incidence wide-angle X-ray scattering patterns. Thin-film (100 nm) OSCs were fabricated resulting in average PCEs of 11.6% for PM7, 12.1% for PM7 D1, and 9.9% for PM7 D2 when blended with ITIC-4F. In contrast, large differences are observed in PCE when the active layer thickness is increased to 180 nm resulting in a decrease in average PCE for PM7 D2 (5.3%), whereas PM7 D1 was able to retain a 11.9% average PCE. The difference in active layer thickness tolerance between PM7 D1 and PM7 D2 is rationalized by extracting the energetic disorder (σ) for hole transport using temperature dependent space-charge limited current studies. In the end, this study conveys how small changes to polymer structure, such as side chain placement, may have a small effect on thin-film polymer properties and device performance, but significant differences are realized when charges are transported over longer distances (thicker films, >150 nm).

While there has been rapid progress made in the performance of organic photovoltaic (OPV) cells in recent years, the device stability remains a major bottleneck for commercialization. In this work, we blended a stable acceptor (O-IDTBR) with two photostable donors (PTB7-Th and PffBT4T-2OD) having different polymer crystallinity, and the resulting devices show a significant difference in the OPV degradation rate. The OPV devices employing a highly crystalline polymer PffBT4T-2OD as an active layer show a good resistance against light soaking, maintaining 80% of the initial power conversion efficiency (PCE) up to 100 hours, while the devices employing an amorphous polymer PTB7-Th as an active layer show a significant PCE loss in the initial 20 hours mainly due to a rapid loss of the fill factor. By carrying out a comprehensive analysis of the device degradation mechanisms, we conclude that the origin for the PTB7-Th:O-IDTBR device degradation is the formation of mid-gap states under continuous sunlight illumination, leading to a significant drop in electron mobility. Device simulation revealed that deep traps act as charge recombination centers and increase the trap-assisted recombination rate, lowering the FF and Jsc.

Results have been reported previously of a model describing the performance of photoelectrochemical reactors, which utilize semiconductor | liquid junctions. This model was developed and verified using SnIV-doped α-Fe2O3 as photoanodes. Hematite films were fully characterized to obtain parameter inputs to a model predicting photocurrent densities. Thus, measured photocurrents were described and validated by the model in terms of measurable quantities. The complete reactor model, developed in COMSOL Multiphysics, accounted for gas evolution and desorption in the system. Hydrogen fluxes, charge yields and gas collection efficiencies in a photoelectrochemical reactor were estimated, revealing a critical need for geometric optimization to minimize H2-O2 product recombination as well as undesirable spatial distributions of current densities and “overpotentials” across the electrodes. Herein, the model was implemented in a 3D geometry and validated using solid and perforated 0.1 × 0.1 m2 planar photoanodes in an up-scaled photoelectrochemical reactor of 2 dm3. The same model was then applied to a set of simulated electrode geometries and electrode configurations to identify the electrode design that would maximize current densities and H2 fluxes. The electrode geometry was modified by introducing circular perforations of different sizes, relative separations and arrangements into an otherwise solid planar sheet for the purpose of providing ionic shortcuts. We report the simulated effects of electrode thickness and the presence or absence of a membrane to separate oxygen and hydrogen gases. In a reactor incorporating a membrane and a photoanode at 1.51 V vs RHE and pH 13.6, an optimized hydrogen flux was predicted for a perforation geometry with a separation-to-diameter ratio of 4.5 ± 0.5; the optimal perforation diameter was 50 µm. For reactors without a membrane, this ratio was 6.5 and 8.5 for a photoanode in a “wired” (monopolar) and “wireless” (photo-bipolar) design, respectively. The results and methodologies presented here will serve as a framework to optimize composite photoelectrodes (semiconductor | membrane | electrolyte), and photoelectrochemical reactors in general, for the production of hydrogen (and oxygen) from water using solar energy.

OLEDs are thin-film devices consisting of multilayers of organic thin films sandwiched between a metal and an ITO electrodes. Because of the different refractive indices of the layers in the thin film stack, different optical modes are trapped in the device. In this talk, we will first discuss the physics of these optical modes and describe techniques to characterize them. We will then describe how to use various photonic structures to maximize the light output and manipulate these optical modes to control the polarization as well as directionality to achieve beam shaping.

Narrow bandgap lead sulfide (PbS) quantum dots (QDs) are solution-processed materials used for optoelectronic applications in the short-wavelength infrared (SWIR) range (1400 - 3000 nm). The PbS QDs based photodetector has achieved comparable detectivity with current commercial SWIR sensors. However, there are still obstacles towards commercialization in commonly used layer by layer (LbL) deposition, such as high material consumption and low reproducibility. Here, we developed a new ligand exchange strategy to prepare ligand exchanged QD inks for single-step PbS film deposition. Compared with LbL deposition, the EQE of PbS QD photodetector made by single-step deposition has improved from 31% to 53%. The EQE and responsivity can be further improved to 95% with IR transparent electrode.

In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense...

The mechanism was investigated of hydrogen sulfide splitting in alkaline aqueous solutions using spray-pyrolysed SnIV-doped α-Fe2O3 photo-anodes in a photo-electrochemical cell. In principle, hydrogen sulfide splitting can be used to treat hydrogen sulfide in natural and process gases and simultaneously to produce hydrogen using solar energy. A comparison with conventional water splitting demonstrated the lower energy requirements to achieve the same photocurrent densities, while producing soluble polysulfide ions and elemental sulfur from hydrogen sulfide oxidation. However, neither splitting process was spontaneous using SnIV-doped α-Fe2O3 photo-anodes without inputs of electrical energy; two judiciously chosen photo-electrodes are required to achieve that objective. The effects were also studied of stirring, hydrogen sulfide ion concentration, electrode potential and annealing of SnIV-doped α-Fe2O3 films on titanium substrates. Under potentiostatic conditions during photo-assisted electrolysis, the photo-anodes exhibited no compositional or morphological changes after 18 h. In a bench-scale reactor (0.1 dm3), stable photocurrent densities of ca. 12.5 A m−2 were recorded over 12 h at an electrode potential of 1.17 V vs. RHE and an effective irradiance of 2670 W m−2. Similarly, photocurrent densities corresponding to ca. 4.3 A m−2 were achieved in an up-scaled reactor under an effective irradiance of 457 W m−2. Charge yields for formation of polysulfide ions were close to unity when operating at optimised potentials and hydrogen sulfide ion concentrations. The shift towards lower electrode potentials of photocurrent densities for hydrogen sulfide splitting compared with those for water splitting was associated with increased charge transfer rates due to decreased interfacial electron-hole recombination rates. The potential dependences of sulfur coverage and oxygen evolution rates were also estimated.

ZnO is a potential replacement for TiO2 as an electron transport layer (ETL) used in low-temperature processed hybrid perovskite solar cells. However, poor thermal stability of perovskites on ZnO a...

The flat band potential is one of the key characteristics of photoelectrode performance. However, its determination on nanostructured materials is associated with considerable uncertainty. The complexity, applicability and pitfalls associated with the four most common experimental techniques used for evaluating flat band potentials, are illustrated using nanostructured synthetic hematite (α-Fe2O3) in strongly alkaline solutions as a case study. The motivation for this study was the large variance in flat band potential values reported for synthetic hematite electrodes that could not be justified by differences in experimental conditions, or by differences in their charge carrier densities. We demonstrate through theory and experiments that different flat band potential determination methods can yield widely different results, so could mislead the analysis of the photoelectrode performance. We have examined: (a) application of the Mott–Schottky (MS) equation to the interfacial capacitance, determined by electrochemical impedance spectroscopy as a function of electrode potential and potential perturbation frequency; (b) Gärtner–Butler (GB) analysis of the square of the photocurrent as a function of electrode potential; (c) determination of the potential of transition between cathodic and anodic photocurrents during slow potentiodynamic scans under chopped illumination (CI); (d) open circuit electrode potential (OCP) under high irradiance. Methods GB, CI and OCP were explored in absence and presence of H2O2 as hole scavenger. The CI method was found to give reproducible and the most accurate results on hematite but our overall conclusion and recommendation is that multiple methods should be employed for verifying a reported flat band potential.

Marked progress has been made in organometallic halide perovskite (OHP) solar cells, with their power conversion efficiency reaching up to 24.2% owing to the excellent optoelectronic properties such as high light absorption coefficients, long carrier diffusion lengths, and high carrier mobilities. Among the reported highly efficient devices, most were fabricated in a well-controlled inert environment. However, large-scale manufacturing requires ambient processing, which affects the crystallization process of OHP. Recently, considerable attention has been drawn to developing air-processed OHP solar cells, in terms of scientific understanding of the crystallization process and developing processes compatible with large volume manufacturing. This review article summarizes the recent progress made in air-processed OHP solar cells. Specifically, we focus on (1) the microscopic understanding of the impact of the ambient environment on the crystallization process of OHP composites, (2) the approaches to control the crystallization and morphology of OHP in ambient air, and (3) the fabrication processes to achieve highly efficient air-processed OHP solar cells. Finally, we will discuss the challenges and pathways toward commercialization of low-cost air-processed OHP solar cells.

Many photoelectrodes produce a gaseous product, such as hydrogen or oxygen, from a liquid electrolyte and require light transmission directly through the two-phase mixture forming at the semiconductor–electrolyte interface. Consequently, incidence solar photons will be scattered and reflected from the bubbly mixture leading to an additional optical loss. In this work, these optical losses are quantified for a population of bubbles that evolved from the vertical surface of a transparent conductive electrode (F-SnO2) by measuring the amount of light transmitted. The transmitted photons were collected in an integrating sphere placed directly behind the 15 mm × 15 mm electrode to capture the forward scattered light. The empirical results were compared with a simple dimensionless model. Finally, mitigation strategies are suggested and critically discussed. With progress in the development of large scale prototype photoelectrochemical devices comes the need to understand, quantify, and potentially resolve the i...

Photoelectrodes enable simultaneous light absorption and catalysis of water splitting reactions. Their performance is established using electrochemical characterisation methods. Besides basic characterisation techniques such as voltammetry and chronoamperometry, employed in the dark or under illumination, more advanced techniques, including (photo-)electrochemical impedance spectroscopy, intensity-modulated impedance spectroscopy and transient absorption spectroscopy, can be used to evaluate key parameters and processes. For some of these techniques, data is often interpreted using over-simplified models, leading to the calculation of unreliable parameters. The values of the flat band potential and charge transfer efficiency depend heavily on the methods used to determine them, and it is recommended that the values are corroborated using multiple techniques. Lastly, certain ‘efficiencies’ defined in the literature for electrically biased systems should be revised.

There are many additives to be used to improve the performance of the mixture, especially to improve the performance of asphalt mixes and the resistance of asphalt concrete to hold repetitive loading on the road. The research uses plastic waste (low-quality polymer) as an added material. This study aims to determine the optimum conditions of the asphalt mixing process with PET plastic waste added in the model system, using RSM. The method used in this research is to use Response Surface Methodology (RSM), which in the calculation uses Expert design 8.0.6 (Stat-Ease, Inc., Minneapolis, MN, USA). By using Box Behnken Design and 3 factorial levels generated 17 trials run. The results showed that the independent variable (X factor) were investigated, respectively X1: the ratio between PET to Asbuton, X2: mixing temperature, and X3: mixing time. In response (Y) is the Marshall characteristic.

The performance of multijunction devices lags behind single-junction organic photovoltaics (OPVs) mainly because of the lack of suitable subcells. Here, we attempt to address this bottleneck and demonstrate efficient nonfullerene-based multijunction OPVs while at the same time highlighting the remaining challenges. We first demonstrate double-junction OPVs with power conversion efficiency (PCE) of 16.5%. Going a step further, we developed triple-junction OPVs with a PCE of 14.9%, the highest value reported to date for this triple-junction cells. Device simulations suggest that improving the front-cell's carrier mobility to >5 × 10-4 cm2 V-1 s-1 is needed to boost the efficiency of double- and triple-junction OPVs. Analysis of the efficiency limit of triple-junction devices predicts that PCE values of close to 26% are possible. To achieve this, however, the optical absorption and charge transport within the subcells would need to be optimized. The work is an important step toward next-generation multijunction OPVs.

Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.

Light-emitting diodes (LEDs) with directional and polarized light emission have many photonic applications, and beam shaping of these devices is fundamentally challenging because they are Lambertian light sources. In this work, using organic and perovskite LEDs (PeLEDs) for demonstrations, by selectively diffracting the transverse electric (TE) waveguide mode while suppressing other optical modes in a nanostructured LED, the authors first demonstrate highly directional light emission from a full-area organic LED with a small divergence angle less than 3° and a TE to transverse magnetic (TM) polarization extinction ratio of 13. The highly selective diffraction of only the TE waveguide mode is possible due to the planarization of the device stack by thermal evaporation and solution processing. Using this strategy, directional and polarized emission from a perovskite LED having a current efficiency 2.6 times compared to the reference planar device is further demonstrated. This large enhancement in efficiency in the PeLED is attributed to a larger contribution from the TE waveguide mode resulting from the high refractive index in perovskite materials.

Tandem structure provides a practical way to realize high efficiency organic photovoltaic (OPV) cells due to the limited optical absorption in organic semiconductors and tandem cells can be used to extend the wavelength coverage of the solar spectrum for light harvesting. The interconnecting layer (ICL) between subcells in a tandem solar cell plays a critical role in the reproducibility and the performance of tandem devices, and the processability of the ICL in a tandem cell has been a challenge. In this work we report on the fabrication of highly reproducible high efficiency tandem cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL. Comparing with the conventional PEDOT:PSS Al 4083, HSolar offers a better wettability on the underlying non-fullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT-M and PTB7-Th:IEICO-4F are used as the front cell and the back cells to fabricate the tandem solar cells, a power conversion efficiency (PCE) of 14.7% is achieved. To validate the processability of these tandem cells, three other research groups have successfully fabricated tandem cells using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, our device simulation results show that a PCE < 22% can be realized in tandem cells in the near future.

In this work, we demonstrated that through the addition of large organic cation PEABr, the quality of cesium lead halide thin films has been enhanced by controlling the crystallization process and thus the domain size and morphology. As a result, by increasing the PEABr concentration to 40%, the perovskite thin films with a small domain size, highly oriented crystal structure and low defect density demonstrated a lowest amplified spontaneous emission threshold of 7 µJ/cm2. However, further increasing PEABr concentration will result in a slower energy transfer, which limits the population inversion process and thus showed a higher ASE threshold. Using this strategy, by tuning the halide ratio, the ASE emissions were observed over the broad visible range (from 490 nm to 680 nm), demonstrating its wide wavelength-tunability.

Lead sulfide (PbS) quantum dots (QDs) exhibiting the narrow bandgap (Eg < 0.9 eV) provide a promising avenue to high performance, inexpensive shortwave infrared (SWIR) photodetector. However, most PbS-QD based SWIR photodiodes suffers from low responsivity and low external quantum efficiency (EQE) in the IR range due to insufficient ligand exchange. Here, we report a precursor engineering strategy that facilitates the commonly used Tetrabutylammonium iodide (TBAI) ligand exchange. We synthesized the PbS QDs from Lead Oxide (PbO) and lead acetate trihydrate (PbAc2·3H2O). Compared with PbS QDs photodiode based on PbO, the responsivity and EQE of PbS QDs photodiode based on PbAc2·3H2O have been improved from 0.15 to 0.586A/W and 12.35 to 47.27%.

A typical top-emitting organic light-emitting diode (OLED) has a strong microcavity effect because of the two reflective electrodes. The cavity effect causes a serious color shift with the viewing angles and restricts the organic layer thickness. To overcome these drawbacks, we design a multi-mode OLED structure with dual-dielectric spacer layers, which extend the cavity length by more than 10 times. This design completely eliminates the intrinsic cavity effect caused by the top and bottom boundaries and provides freedom for the organic layer thickness. We demonstrate these effects in a white multi-mode OLED using a white emitter, which shows a negligible angular chromaticity shift of Δuv = 0.006 from 0 to 70° and a Lambertian emission profile. The simple design and the perfect angular color profiles make the multi-mode OLED structure promising in large-area displays and solid-state lighting applications.

It has been developed successfully of multi-frequency bio-impedance devices using the AD9850 module. The devices are composed of AD9850 sin-wave generator module, High Pass Filter, VCCS, AD620A Instrument amplifier, AC to DC AD536A and Arduino Nano. The performance of the devices was tested with 10 variations of the load containing elements R and C. The results of the measurements were compared with the theoretical at frequencies less than 110 kHz resulting error less than 10%. The device can be used to calculate electrical impedance accurately from 10 Hz to 100 kHz.

The electrochemical properties of photoelectrodes must be measured accurately and precisely to enable better comparisons between different materials. Along with the flat band potential, the interfacial charge transfer efficiency, which is the ratio between charge transfer rate at the photoelectrode surface and rate of charge carrier generation in the photoelectrode, can be used to predict the current density response at a given photon flux and electrode potential. The most widely used techniques for measuring charge transfer efficiencies are Photo-Electrochemical Impedance Spectroscopy (PEIS), current density ratios in the presence and absence of hole/electron scavengers, chrono-amperometry and Intensity Modulated Photocurrent Spectroscopy (IMPS). Charge transfer efficiencies can be estimated from PEIS and IMPS spectra either by using raw data (graphically), by fitting equivalent electrical circuits or by computing the Distribution of Relaxation Times (DRT). However, these techniques have their own drawbacks and impracticalities, that require researchers to make a choice between measuring accurately or pragmatically. Hitherto, the theoretical and experimental details of these techniques have not been summarised collectively and comprehensively. Here, we report the benefits and drawbacks, the accuracy, precision and best experimental recommendations when employing different techniques for photon-driven charge transfer efficiency determination.

We report the effects of the growth temperature on the structural and electrical properties of the InAlGaN/GaN heterostructures grown on c-plane sapphire substrates. X-ray Photoelectron Spectroscopy and Atomic Force Microscopy measurements results indicate that the InAlGaN layer properties is strongly dependent on the growth temperature. It is observed that the Gallium incorporation increases with the increase of the growth temperature. Meanwhile, the surface roughness decreases from 0.49 nm to 0.34 nm with the increase of growth temperature. The variation of structural properties, composition and surface morphology influences the transport properties of the InAlGaN/GaN heterostructures. High 2DEG electron density, low sheet resistance and good C-V response with a steep slope for InAlGaN/GaN HEMT were achieved at an optimized growth temperature window between 900 °C and 950 °C.

Side-chain sequence enabled regioisomeric acceptors, bearing different side-chain sequences on the same conjugated backbone, are herein reported. Two regioregular polymers PTBI-1 and PTBI-2 and one regiorandom polymer PTBI-3 were synthesized from these two regioisomeric acceptors for a comparative study. UV–vis–NIR absorption spectroscopy and electrochemical study confirmed similar frontier molecular orbital levels of the three polymers in their solid state. More intriguingly, absorption profiles suggest that the sequence of side chains greatly governs the aggregation behaviors. Furthermore, the PTBI-2 film shows larger ordered domains than PTBI-1 and PTBI-3 films, as supported by AFM and GIWAXS measurements. As a result, PTBI-2-based FET devices achieved an average hole mobility of 1.37 cm2 V–1 s–1, much higher than the two polymers with other side-chain sequences. The regiorandom PTBI-3 exhibited the lowest average hole mobility of 0.27 cm2 V–1 s–1. This study highlights the significant impact of side-c...

A GaN metal-insulator-semiconductor-high electron mobility transistor (HEMT) using hybrid ferroelectric charge trap gate stack (FEG-HEMT) is demonstrated for normally-OFF operation. The ferroelectric (FE) polarization increases the number of trapped charges in the HfON charge trapping layer, leading to high positive threshold voltage ( ${V}_{\textsf {th}}$ ) shift for the normally-OFF device. Besides, under the positive bias temperature instability (PBTI) test, the internal electric field induced by FE polarization causes smoother slope of the conduction band in FE gate stack, resulting in better ${V}_{\textsf {th}}$ stability. With the proposed hybrid FE charge trap gate stack, the device exhibits a high ${V}_{\textsf {th}}$ of +2.71 V at ${I}_{\textsf {DS}} = \textsf {1}\,\,\mu \text{A}$ /mm, a high maximum current density of 820 mA/mm and low on-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) of 11.1 $\Omega \cdot \textsf {mm}$ . The FE device also shows good ${V}_{\textsf {th}}$ –temperature stability compared to the non-FE device results. Besides, a high current device with 40 A is also fabricated in this letter to demonstrate the feasibility of the proposed FEG-HEMT device for high power device application.

As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to p...

Vertical organic light-emitting transistor (VOLET) having an organic light-emitting diode integrated with a vertical thin-film transistor is promising for transparent electronics because the vertical device structure potentially offers a display with a large aperture ratio and a low power consumption. However, making a transparent VOLET has been challenging due to the requirements for all transparent electrodes including fabrication of a porous source electrode for current modulation in the device. Here, we report a semi-transparent VOLET with a large modulation of light emitted through the top and bottom electrodes using a nano-porous indium-tin oxide (ITO) source electrode, a Mg:Ag drain electrode, and an ITO gate electrode. The porous ITO source electrode is not only important for luminance modulation, but the nano-textured film morphology also enhances light extraction from the device. Finally, we show that the off current of the VOLET can be suppressed with an electron transporting layer (C60), leading to a large luminance on/off ratio of 104.

We demonstrate the electrical performances of the quaternary InAlGaN/GaN MIS-HEMTs with high quality SiNx gate dielectric and surface passivation layer deposited by low pressure chemical vapor deposition (LPCVD) at 780 °C. Excellent LPCVD-SiNx/InAlGaN interface and SiNx film quality were obtained, resulting in very high output current density, a very small threshold voltage hysteresis and steep subthreshold slope. The LPCVD-SiNx/InAlGaN/GaN MIS-HEMT device exhibited high on/off current ratio, large gate voltage swing, high breakdown voltage, and very low dynamic on-resistance (RON) degradation, meaning effective current collapse suppression compared to the plasma enhanced chemical vapor deposition -SiNx/InAlGaN/GaN MIS-HEMTs. The corresponding specific on-resistance (RON,sp) for LPCVD-SiNx device was as low as 0.98 mΩ·cm2, yielding a high figure of merit of 737 MW/cm2. These results demonstrate a great potential of the LPCVD-SiNx/InAlGaN/GaN MIS-HEMTs for high-power switching applications.

The tandem structure provides a practical way to realize high-efficiency organic solar cells (OSCs). It overcomes several bottlenecks in single-junction OSCs such as thermalization loss, transmission loss, and inefficient light absorption. In tandem OSCs, the interconnecting layer (ICL) electrically connects two subcells and it plays a critical role in determining the device performance and reproducibility. In this review paper, we first give a brief introduction to the working mechanism and the requirements for ICLs. We then compare three classes of ICLs based on their optical, mechanical, and chemical properties. Finally, the possible paths forward for tandem OSCs are discussed.

Since the invention of organic light emitting diodes (OLEDs), great research efforts have been dedicated to improving their efficiency and lifetime. For high-brightness applications, tandem OLED structures have advantages because of the lower current densities required to achieve high brightness. With the successful development of highly efficient charge generation layers, high brightness tandem OLEDs are used in displays and lighting. However, the major challenge for tandem OLEDs is the low light extraction efficiency, because about 50% of the light is trapped inside the device as waveguide modes. In this Perspective, we first review the recent works done on light extraction, analyze different waveguide mode extraction structures, and then identify the key factors determining the extraction efficiencies in tandem OLEDs.

The understanding and control of the emission zone in organic light emitting diodes (OLEDs) is crucial to the device operational stability. Using the photoluminescence and electroluminescence degradation data, we have developed a modeling methodology to quantitatively determine the length of the emission zone and correlate that with the degradation mechanism. We first validate the modeling results by studying the emitter concentration effect on operational stability of devices using the well-studied thermal activated delayed fluorescent (TADF) emitter (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), and our results are consistent with previous published data. We further applied this methodology to study the emitter concentration effect using another TADF emitter, 4-carbazolyl-2-methylisoindole-1,3-dione (dopant 1). The results show that the emission zone of the dopant 1 devices is narrower than the 4CzIPN device, leading to faster degradation. While a higher emitter concentration does not result in widening of the emission zone, we were able to widen the emission zone and hence extend the device lifetime using a mixed host.

Non-wetting hole transport materials (HTMs) have great potential in facilitating large-sized perovskite crystal growth and enhancing device stability by opposing moisture ingress, However, the severe non-wetting issue limits the wide application of these materials in low-temperature solution-processed inverted planar perovskite solar cells (PVSCs), and corresponding devices are rarely reported. Here, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. By carefully controlling the UVO modification time, the surface wettability of poly-TPD can be tuned without affecting the bulk properties of the film, hence perovskite films with desired grain size and excellent coverage can be deposited via a one-step spin-coating method. Benefiting from the high-quality perovskite, well-matched energy level alignment and hydrophobic property of poly-TPD, the resulting PVSCs show a champion power conversion efficiency of 18.19% with significantly enhanced stability as compared to the PEDOT:PSS counterparts. Moreover, the UVO modification approach also demonstrates its validity when being extended to other hydrophobic HTMs. This work not only provides a general strategy to broaden the selection pool of HTMs for solution-processed inverted planar PVSCs, but also may triggers the exploration of more advanced strategies to make non-wetting HTMs applicable in solution-processed inverted planar PVSCs.

Fluorinated conjugated polymers leading to enhanced photovoltaic device performance has been widely observed in a variety of donor–acceptor copolymers; however, almost all these polymers have fluorine substituents on the acceptor unit. Building upon our previously reported PBnDT-FTAZ, a fluorinated donor–acceptor conjugated polymer with impressive device performance, we set this study to explore the effect of adding the fluorine substituents onto the flanking thiophene units between the donor unit (BnDT) and the acceptor unit (TAZ). We developed new synthetic approaches to control the position of the fluorination (3′ or 4′) on the thiophene unit, and synthesized four additional PBnDT-TAZ polymers incorporating the fluorine-substituted-thiophene (FT) units, 3′-FT-HTAZ, 4′-FT-HTAZ, 3′-FT-FTAZ, and 4′-FT-FTAZ. We discover that relocating the fluorine substituents from the acceptor to the flanking thiophene units have a negligible impact on the device characteristics (short circuit current, open circuit volta...

NH3 flow rate during AlGaN barrier layer growth not only affects the growth efficiency and surface morphology as a result of parasitic reactions but also influences the concentration of carbon impurity in the AlGaN barrier. Carbon, which decomposes from metal precursors, plays a role in electron compensation for AlGaN/GaN HEMT. No 2-dimensional electron gas (2-DEG) was detected in the AlGaN/GaN structure if grown with 0.5 slm of NH3 due to the presence of higher carbon impurity (2.6 × 1019 cm−2). When the NH3 flow rate increased to 6.0 slm, the carbon impurity reduced to 2.10 × 1018 atom cm−3 and the 2 DEG electron density recovered to 9.57 × 1012 cm−2.

Light harvesting in the near-infrared part of the solar spectrum is important to achieve high efficiency polymer solar cells (PSCs). In this work, we demonstrate that we take an existing polymer:fullerene blend and extend its spectral response into the near-IR region by adding a small amount near-IR absorbing dye in the blend. The polymer studied in this work is Poly[ N -9′-heptadecanyl-2,7-carbazole- alt -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). By adding only 2.5% squaraine dye to the blend, we were able to extend the spectral response of the resulting devices 100 nm into the near-IR spectral region. We show that the enhanced light harvesting is due to efficient Forster resonance energy transfer (FRET) between PCDTBT and the squaraine dye, resulting in an increase in power conversion efficiency. This type of ternary polymer solar cells is unique in that it allows the use of a small amount of selected dyes to extend light harvesting in infrared region.

Fabric-based microfluidic fuel cells (MFCs) serve as a novel, cost-efficient alternative to traditional FCs and batteries, since fluids naturally travel across fabric via capillary action, eliminating the need for an external pump and lowering production and operation costs. Building on previous research with Y-shaped paper-based MFCs, fabric-based MFCs mitigate fragility and durability issues caused by long periods of fuel immersion. In this study, we describe a microfluidic fabric-based direct formate fuel cell, with 5 M potassium formate and 30% hydrogen peroxide as the anode fuel and cathode oxidant, respectively. Using a two-strip, stacked design, the optimized parameters include the type of encasement, the barrier, and the fabric type. Surface contact of the fabric and laminate sheet expedited flow and respective chemical reactions. The maximum current (22.83 mA/cm2 ) and power (4.40 mW/cm2 ) densities achieved with a 65% cotton/35% polyester blend material are a respective 8.7% and 32% higher than previous studies with Y-shaped paper-based MFCs. In series configuration, the MFCs generate sufficient energy to power a handheld calculator, a thermometer, and a spectrum of light-emitting diodes.

Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties. However, NFA-based solar cells often have a decreased short-circuit current (Jsc) and fill factor (FF) compared to their fullerene-based counterparts. Here, we investigate the fundamental causes of this decrease in the performance of solar cells using a non-fullerene acceptor (SF-PDI2) paired with two polymer donors, FTAZ and PyCNTAZ, compared with their fullerene-based counterparts. Through a number of experimental techniques and morphological studies, we show that the SF-PDI2-based solar cells suffer from insufficient charge generation, transport, and collection when compared with the PCBM-based solar cells. The SF-PDI2-based solar cells show increased bimolecular recombination, which, together with other recombination loss mechanisms in these cells, causes a significant decrease in their Jsc and FF. Notably, the less pure domains, low electron mobility (on the order of 10−5 cm2 V−1 s−1), and imbalanced mobility (in regard to the hole mobility) further explain the low FF. On the other hand, the higher open-circuit voltage (Voc) in the SF-PDI2 devices is mainly due to the increase in the CT state energy. It is worth mentioning that the PyCNTAZ-based devices show an ultralow charge separation energy (ΔECS), close to 0 eV. Our results demonstrate that further increasing the mobility (both of electrons and holes) in these NFA-based solar cells would be a viable approach to further enhance the efficiency of these new types of solar cells, ideally, without losing the high Voc of such cells.

The performance of polymer–fullerene bulk heterojunction (BHJ) solar cells is highly affected by the morphology of the blend film. Though the structure of the BHJ morphology is well-understood, the relationship between relevant material interactions and BHJ morphological evolutions is poorly understood and seldom explored. In this report, we discuss the impact of polymer molecular weight (MW) on thermodynamic and kinetic phenomena which have a drastic influence on the nanoscale BHJ morphology. The blend film comprises a highly aggregating low bandgap diketopyrrolopyrrole-based polymer PDPP3T and the fullerene electron acceptor molecule PC71BM, cast from a 1,2-dichlorobenzene (DCB) solution with and without the additive 1,8-diiodooctane (DIO). The pair-wise interactions among the components were evaluated by Flory–Huggins interaction parameters (χ). The BHJ blend of PDPP3T and PC71BM exhibited liquid–liquid (L–L) phase separation as a result of strong polymer–fullerene interactions (large χPDPP3T–fullerene) in DCB solution. In contrast, addition of 3% DIO into the DCB solution is found to stimulate polymer aggregation which gives rise to liquid–solid (L–S) phase separation. Large χPDPP3T–fullerene and χPDPP3T–solvent were observed as a result of increasing polymer MW, and these changes promote strong L–L phase separation and polymer aggregation in the blend solution, respectively. The latter interactions have led to low molecular mobility, with an end result of reduced crystallinity and smaller domain size of the BHJ films. The observed dramatic MW-dependent morphological changes were also manifested in solar cell outputs as well as charge carrier dynamics calculated by transient absorption measurements.