A frequency‐dependent droop scheme for parallel control of ups inverters

Abstract

This paper presents a frequency‐dependent droop scheme for paralleling UPS inverters with no control interconnection, so the inverters can be tightly connected with the load. At the fundamental frequency, the reference voltage of the inverter is generated as a reactor connected between the inverter and the load. The intention is to control the real and reactive power sharing of inverters with the Q‐V and P‐ω droop scheme employed in the power system without needing a true transfer reactor. At the harmonic frequency, the reference voltage is generated as a resistor connected between the inverter and the load. The intention is that the load harmonic current can be shared equally and the voltage waveform distortion will be low. Two 1KVA single‐phase inverters are designed and implemented, some simulation and experimental results are provided for demonstrating the effectiveness of the proposed approach.     

Fast,accurate measurement of path difference with white light

Abstract

An interferometric system is described for measuring phase distributions with white light at a speed limited by the CCD frame rate using a simple phase shifting algorithm where the phase is recovered from quadrature fringe sets. The technique used is almost immune to vibration, and highly accurate. A phase measurement system is implemented using a polarizing Michelson-type interferometer together with geometric phase modulation. The measured phase distributions enabled the recovery of path differences with an accuracy of better than about λ _m /70 where λ _m is the mean wavelength.     

Fine Multi‐Phase Alignments in 2D Perovskite Solar Cells with Efficiency over 17% via Slow Post‐Annealing

Layered Ruddlesden–Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non‐eliminable quantum well effect. Here, a slow post‐annealing (SPA) process is proposed for BA₂MA₃Pb₄I₁₃ (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open‐circuit voltage, short‐circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi‐3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley–Read–Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA‐processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N₂ environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.     

Dynamics analysis of LFR model for a single‐stage high power factor correction diagonal half‐bridge flyback ac/dc converter

Abstract

By means of a graft scheme, a buck‐boost cell and a wide range diagonal half‐bridge flyback cell are combined to create a novel single‐stage high power factor correction (HPFC) diagonal half‐bridge flyback ac/dc converter in this paper. When both of the two cells operate in discontinuous conduction mode, the proposed converter exhibits high power factor and low bulk capacitor voltage stress independent of the load variations. Based on the Loss‐Free Resistor (LFR) model, a new technique, referred to as ac‐dc balancing method, is also proposed. It is useful to determine the dc values, voltage ripples, and phase angle shifts of the bulk capacitor and output voltage of the converter. Moreover, the component values are well designed according to the operation conditions and design specifications of the converter. Finally, a prototype of the proposed converter with output voltage 48 V and power 100 W is built to test the theoretical analysis. It is successfully validated by IsSpice simulations and experimental results.     

Over 15.7% Efficiency of Ternary Organic Solar Cells by Employing Two Compatible Acceptors with Similar LUMO Levels

Efficient organic solar cells (OSCs) are fabricated using polymer PM6 as donor, and IPTBO‐4Cl and MF1 as acceptors. The power conversion efficiency (PCE) of IPTBO‐4Cl based and MF1 based binary OSCs individually arrive to 14.94% and 12.07%, exhibiting markedly different short circuit current density (J_SC) of 23.18 mA cm^?2 versus 17.01 mA cm^?2, fill factor (FF) of 72.17% versus 78.18% and similar open circuit voltage (V_OC) of 0.893 V versus 0.908 V. The two acceptors, IPTBO‐4Cl and MF1, have similar lowest unoccupied molecular orbital levels, which is beneficial for efficient electron transport in the ternary active layer. The PCE of optimized ternary OSCs arrives to 15.74% by incorporating 30 wt% MF1 in acceptors, resulting from the simultaneously increased J_SC of 23.20 mA cm^?2, V_OC of 0.897 V, and FF of 75.64% in comparison with IPTBO‐4Cl based binary OSCs. The gradually increased FFs of ternary OSCs indicate the well‐optimized phase separation and molecular arrangement with MF1 as morphology regulator. This work may provide a new viewpoint for selecting an appropriate third component to achieve efficient ternary OSCs from materials and photovoltaic parameters of two binary OSCs.     

An AlGaAs/GaAs oxide‐stripe double‐heterostructure laser

Abstract

An AlGaAs/GaAs oxide‐stripe double‐heterostructure (DH) laser is fabricated by liquid‐phase epitaxy (LPE) successfully. This laser consists of four epilayers, i.e., (N) Al_0.35Ga_0.65As cladding layer, (p) Al_0.05Ga_0.95As active layer, (P) Al_0.35Ga_0.65As cladding layer and (p) Al_0.05Ga_0.95As contact layer, and a top SiO₂ insulating layer. The stripe window opened through the SiO₂ layer is either 5 or 10 μm wide. The emission properties of the laser diodes were all measured under pulse mode. The lowest threshold current measured is 95 mA for a 10, μm‐wide stripe laser which corresponds to a threshold current density of 3,200 A/cm². The best power output is more than 30 mW per facet with a differential quantum efficiency of 10% per facet. In addition, the single filament operation is also observed in a 5 μm‐wide stripe laser. The lasing wavelength is centered around 8,500 Å.     

Temperature and voltage sensings by mode‐mode interference in polarization‐maintaining optical fibers

Abstract

Two optic fiber sensing systems for temperature and voltage have been developed which utilize the mode‐mode interference of the two orthogonally polarized modes, HE^x _II and HE^y _II, in two commencal polarization‐maintaining fibers (bow‐tie and elliptical core fibers). A package of controlled programs in a Macintosh computer, which can record and process all related data automatically, is established for temperature sensing. The signal drifting problem in voltage sensings has been investigated, and the elimination of signal drifting is obtained by the phase tracking with direct current technology The agreement between the sensing results for temperature and dynamic voltage and those predicted by experimental principles is satisfactory, which confirms the validity of the developed sensing systems.     

Normal form for Mueller Matrices in Polarization Optics

Abstract

The normal (canonical) form for Mueller matrices in polarization optics is derived: it is shown that a non-singular real 4 × 4 matrix M qualifies to be the bona fide Mueller matrix of some physical system if and only if it has the canonical form M = L′ ΛL, where L and L′ are elements of the proper orthochronous Lorentz group L ^↑ ₊, and where Λ = diag (λ₀, λ₁, λ₂, λ₃) with λ₀ ≥ ¦λ_j¦ > 0. It is further shown that λ₁ and λ₂ can be taken to be positive so that the signature of λ₃ is the same as that of det M. Several experimentally measured Mueller matrices are analysed in the light of the normal form. The case of singular Mueller matrices is briefly discussed as a limiting case.     

FA0.88Cs0.12PbI3−x(PF6)x Interlayer Formed by Ion Exchange Reaction between Perovskite and Hole Transporting Layer for Improving Photovoltaic Performance and Stability

Interface engineering to form an interlayer via ion exchange reaction is reported. A FA_0.88Cs_0.12PbI₃ formamidinium (FA) perovskite layer is first prepared, then FAPF₆ solution with different concentrations is spin‐coated on top of the perovskite film, which leads to a partial substitution of iodide by PF₆^? ion. The second phase with nominal composition of FA_0.88Cs_0.12PbI_3?x(PF₆)_x is grown at the grain boundary, which has island morphology and its size depends on the FAPF₆ solution concentration. The lattice is expanded and bandgap is reduced due to inclusion of larger PF₆^? ions. The power conversion efficiency (PCE) is significantly enhanced from 17.8% to 19.3% as a consequence of improved fill factor and open‐circuit voltage (V_oc). In addition, current–voltage hysteresis is reduced. Post‐treatment with FAPF₆ reduces defect density and enhances carrier lifetime, which is responsible for the improved photovoltaic performance and reduced hysteresis. The unencapsulated device with post‐treated perovskite film demonstrates better stability than the pristine perovskite, where the initial PCE retains over 80% after 528 h exposure under relative humidity of around 50–70% in the dark and 92% after 360 h under one sun illumination.     

Highly Efficient Ternary‐Blend Polymer Solar Cells Enabled by a Nonfullerene Acceptor and Two Polymer Donors with a Broad Composition Tolerance

In this work, highly efficient ternary‐blend organic solar cells (TB‐OSCs) are reported based on a low‐bandgap copolymer of PTB7‐Th, a medium‐bandgap copolymer of PBDB‐T, and a wide‐bandgap small molecule of SFBRCN. The ternary‐blend layer exhibits a good complementary absorption in the range of 300–800 nm, in which PTB7‐Th and PBDB‐T have excellent miscibility with each other and a desirable phase separation with SFBRCN. In such devices, there exist multiple energy transfer pathways from PBDB‐T to PTB7‐Th, and from SFBRCN to the above two polymer donors. The hole‐back transfer from PTB7‐Th to PBDB‐T and multiple electron transfers between the acceptor and the donor materials are also observed for elevating the whole device performance. After systematically optimizing the weight ratio of PBDB‐T:PTB7‐Th:SFBRCN, a champion power conversion efficiency (PCE) of 12.27% is finally achieved with an open‐circuit voltage (V _oc) of 0.93 V, a short‐circuit current density (J _sc) of 17.86 mA cm^?2, and a fill factor of 73.9%, which is the highest value for the ternary OSCs reported so far. Importantly, the TB‐OSCs exhibit a broad composition tolerance with a high PCE over 10% throughout the whole blend ratios.     

A high performance step up/down three phase AC to DC converter

Abstract

In this paper, a new three phase AC to DC converter is proposed to achieve a sinusoidal current waveform and the unity power factor at the input, and clean DC at the output. Control of the converter is so simple that only one PWM control circuit with fixed switching frequency is required. In addition, the new converter has both step‐up and step‐down capabilities. Also, no current sensor is required for the current control. The small signal model and some design considerations are also presented. Finally, some experimental results are provided for the purposes of demonstration.     

Novel Tunnel‐Contact‐Controlled IGZO Thin‐Film Transistors with High Tolerance to Geometrical Variability

Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al₂O₃ layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (V_{D_SAT} ≈ 3 V), change in V_{D_SAT} with a gate voltage of only 0.12 V V^?1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.     

Enhanced Open‐Circuit Voltage in Colloidal Quantum Dot Photovoltaics via Reactivity‐Controlled Solution‐Phase Ligand Exchange

The energy disorder that arises from colloidal quantum dot (CQD) polydispersity limits the open‐circuit voltage (V_OC) and efficiency of CQD photovoltaics. This energy broadening is significantly deteriorated today during CQD ligand exchange and film assembly. Here, a new solution‐phase ligand exchange that, via judicious incorporation of reactivity‐engineered additives, provides improved monodispersity in final CQD films is reported. It has been found that increasing the concentration of the less reactive species prevents CQD fusion and etching. As a result, CQD solar cells with a V_OC of 0.7 V (vs 0.61 V for the control) for CQD films with exciton peak at 1.28 eV and a power conversion efficiency of 10.9% (vs 10.1% for the control) is achieved.     

Field Electron Emission from Single‐Walled Carbon Nanotube Layers

Abstract

Field emission characteristics of single‐walled carbon nanotube layers have been investigated at room and low temperatures. For these layers the emission current density of 10 mA/cm² was obtained at the average field E _av = 1.6–3.8 V/µm. Current–voltage characteristics in Fowler–Nordheim coordinates have a break at emission current about 10^?8 A. Cooling of samples only insignificantly changed the form of current–voltage characteristics. This indicates, that investigated single‐walled nanotubes have the metal type conductivity.     

A novel driver with adjustable frequency and phase for traveling‐wave type ultrasonic motor

Abstract

This paper describes the design of a traveling‐wave ultrasonic motor (TWUSM) drive circuit, intended to simultaneously employ both driving frequency and phase modulation control. The operating principles and a detailed analysis of the proposed driving circuit, consisting of voltage‐controlled oscillator (VCO), voltage‐controlled phase‐shifter circuit and non‐resonant power amplifier converter, are introduced. To drive the USM effectively, a two‐phase power amplifier converter using non‐resonant output was designed to provide a balanced two‐phase voltage source. Two‐phase output driving voltages could be maintained at the same peak voltage value as the driving frequency under varying phase‐modulation processes. Detailed experimental results are provided to demonstrate the effectiveness of the proposed driving circuit.     

Europium and Acetate Co‐doping Strategy for Developing Stable and Efficient CsPbI2Br Perovskite Solar Cells

All‐inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed‐halide inorganic CsPbI₂Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI₂Br perovskites limit the open‐circuit voltage (V_oc < 1.2 V), short‐circuit current density (J_sc < 15 mA cm^?2), and fill factor (FF < 75%) of CsPbI₂Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI₂Br perovskite is doped by Eu(Ac)₃ to obtain a high‐quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable V_oc of 1.25 V, a reasonable J_sc of 15.44 mA cm^?2, and a high FF of 79.00% are realized for CsPbI₂Br solar cells. Moreover, the CsPbI₂Br solar cells with Eu(Ac)₃ doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35–40%) for 30 days.     

Fabrication of Pb1‐xSnxTe/PbTe heterojunctions by liquid phase epitaxy

Abstract

Pb_1‐x Sn _x Te epitaxial layers were successfully grown on PbTe substrates by liquid phase epitaxy (LPE) technique. The compositions and surface morphology of the epitaxial Pb_1‐x Sn _x Te layers were controlled in the LPE growth, and p‐Pb_1‐x Sn _x Te/n‐PbTe heterodiodes with a good junction‐perfection factor were made.     

The Impact of Grain Alignment of the Electron Transporting Layer on the Performance of Inverted Bulk Heterojunction Solar Cells

This report presents a new strategy for improving solar cell power conversion efficiencies (PCEs) through grain alignment and morphology control of the ZnO electron transport layer (ETL) prepared by radio frequency (RF) magnetron sputtering. The systematic control over the ETL's grain alignment and thickness is shown, by varying the deposition pressure and operating substrate temperature during the deposition. Notably, a high PCE of 6.9%, short circuit current density (J_sc) of 12.8 mA cm^?2, open circuit voltage (V_oc) of 910 mV, and fill factor of 59% are demonstrated using the poly(benzo[1,2‐b:4,5‐b′]dithiophene–thieno[3,4‐c]pyrrole‐4,6‐dione):[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester polymer blend with ETLs prepared at room temperature exhibiting oriented and aligned rod‐like ZnO grains. Increasing the deposition temperature during the ZnO sputtering induces morphological cleavage of the rod‐like ZnO grains and therefore reduced conductivity from 7.2 × 10^?13 to ≈1.7 × 10^?14 S m^?1 and PCE from 6.9% to 4.28%. An investigation of the charge carrier dynamics by femtosecond (fs) transient absorption spectroscopy with broadband capability reveals clear evidence of faster carrier recombination for a ZnO layer deposited at higher temperature, which is consistent with the conductivity and device performance.     

Perovskite Solar Cells on Corrugated Substrates with Enhanced Efficiency

Organometallic halide perovskites solar cells are fabricated on nano‐scaled corrugated substrates using a sequential deposition method. The corrugated substrates are fabricated using colloidal lithography followed by reactive ion etching. The corrugated structure is found to accelerate the chemical reaction between the sequentially deposited lead iodide (PbI₂) and methyl ammonium iodide layers to form stoichiometric perovskite films, and the corrugated morphology is preserved at the interface of the hole transport layer (HTL) and the perovskite layer. The shunt resistance of the corrugated devices is found to be higher than that of the planar devices, leading to a higher open circuit voltage (V_OC) and fill factor (FF) in the corrugated devices. Finite‐difference time‐domain simulation is carried out on both planar and corrugated devices. The results revealed that light absorption is enhanced in the corrugated devices due to the corrugated HTL/perovskite interface, resulting in a significantly higher short circuit current (J_SC) observed in the corrugated devices. As a result, the average power conversion efficiency increases from 8.7% for the planar devices to 13% for the corrugated devices.     

High Efficiency Nonfullerene Polymer Solar Cells with Thick Active Layer and Large Area

In this work, high‐efficiency nonfullerene polymer solar cells (PSCs) are developed based on a thiazolothiazole‐containing wide bandgap polymer PTZ1 as donor and a planar IDT‐based narrow bandgap small molecule with four side chains (IDIC) as acceptor. Through thermal annealing treatment, a power conversion efficiency (PCE) of up to 11.5% with an open circuit voltage (V _oc) of 0.92 V, a short‐circuit current density (J _sc) of 16.4 mA cm^?2, and a fill factor of 76.2% is achieved. Furthermore, the PSCs based on PTZ1:IDIC still exhibit a relatively high PCE of 9.6% with the active layer thickness of 210 nm and a superior PCE of 10.5% with the device area of up to 0.81 cm². These results indicate that PTZ1 is a promising polymer donor material for highly efficient fullerene‐free PSCs and large‐scale devices fabrication.