Higher Short-circuit Current Research Articles

Transient Characteristics Analysis of 500kV Parallel Circuit Breaker Based on Highly Coupled Split Reactor

With the continuous expansion of power system capacity, parallel high-voltage circuit breakers with a Highly Coupled Split Reactor (HCSR) have a potential application for limitation of high short-circuit current. However, as the parallel circuit breakers open at different time, the residual voltage of the split reactor on the post-open circuit breaker is higher and the stray capacitors of HCSR form high-order oscillating circuits, which may lead to serious transient recovery voltage (TRV). Therefore, it is necessary to analyze and simulate the transient characteristics of 500kV HCSR. Firstly, the equivalent model of HCSR circuit breakers is built in EMTP simulation plat-form, and its TRV generation is analyzed. Then, the TRV of parallel circuit breakers under different operating conditions and fault types is simulated and calculated. Finally, according to the statistical calculation results, the protection measure of 0.2uF shunt capacitance to limit rise rate of TRV is proposed.

Side chain triphenylamine-based conjugated polymers for the preparation of efficient heterojunction solar cells

A series of novel benzothiadiazole based triphenylamine polymers containing different electron-rich side chains (dithienosilole, dithienopyrrole, dithieno-cyclopentadiene derivatives) have been prepared and their photoelectric properties explored. These polymers have been characterized using UV–Vis absorption and fluorescence spectroscopy and their photo-electrochemical properties characterized using cyclic voltammetry. These new polymers exhibit high thermal decomposition temperatures and broad absorption spectra that enable them to absorb light across the entire visible region. The UV absorption response range electron of these polymers could be tuned by modifying their electron donating units, with the best polymer found to exhibit a long fluorescent lifetime. An P3:PC71BM device containing dithienocyclopentadiene electron donating side-chains was shown to give 3.6% photoelectric conversion efficiency for a high short-circuit current of 14.25 mA/cm2. The fluorescence intensity of this copolymer decayed rapidly, implying that effective charge transfer processes were occurring at its interface, which were associated with a relatively high short circuit current. This work clearly demonstrates that use of an appropriate electron donor unit can effectively broaden the polymers spectroscopic response range, thus increasing the rate of carrier transport at the interface, which leads to improved photoelectric conversion efficiency.

Rough versus planar interfaces: How to maximize the short circuit current of perovskite single and tandem solar cells

The short circuit current of perovskite/silicon tandem solar cells has to be increased to realize solar cells with energy conversion efficiencies exceeding the records of single junction solar cells. Photon management allows for increasing the short-circuit current and energy conversion efficiency of perovskite single junction and perovskite/silicon tandem solar cells due to improved light incoupling and/or light trapping. In this study, an electrically flat but optically rough solar cell design is investigated, which combines the benefit of reaching high short-circuit currents, while maintaining the integrity of perovskite films processed on planar substrates or surfaces. Consequently, the perovskite films exhibit electrical properties comparable to planar perovskite solar cells, which allows for achieving solar cells with high open circuit voltage and fill factors. Electrically flat but optically rough perovskite solar cell structures can be successfully implemented because the perovskite material system and the contact materials of the solar cells exhibit comparable refractive indices. This sets the perovskite material system with its low refractive index apart from other high refractive index materials like silicon or germanium. Hence the proposed design of an electrically flat but optically rough solar cell cannot be applied to silicon or germanium solar cells. The design of perovskite single junction solar cells is discussed, and electrically flat but optically rough solar cells are compared to electrically and optically rough solar cells. The design of perovskite/silicon tandem solar cells is investigated by using a hybrid approach, which combines Finite Difference Time Domain optical simulations of perovskite top and experimentally measured crystalline bottom solar cells. Detailed guidelines are provided on how to achieve high short-circuit currents.

6 μm thick AlInP 55Fe x-ray photovoltaic and 63Ni betavoltaic cells

Two 400 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiodes (6 μm i layer) were fabricated from a wafer grown by metalorganic vapour phase epitaxy (MOVPE) and then studied at temperatures from 140 °C to −20 °C for the development of temperature tolerant 55Fe x-ray photovoltaic and 63Ni betavoltaic microbatteries. The Al0.52In0.48P epitaxial layers are the thickest so far reported for this emerging application. At each temperature, the performances of the Al0.52In0.48P detectors were analysed in dark conditions, as well as under the illumination of a 182 MBq 55Fe radioisotope x-ray source and a 185 MBq 63Ni radioisotope source. An open circuit voltage as high as 1.13 V was found for both the Al0.52In0.48P x-ray photovoltaic cells at −20 °C; whilst an open circuit voltage of 0.47 V was found for the best 63Ni betavoltaic cell, at the same temperature. Maximum output powers of 1.44 and 1.36 pW were obtained from the two x-ray photovoltaic cells at −20 °C; combining the output powers of these two Al0.52In0.48P x-ray photovoltaic cells, a total maximum output power as high as 2.8 pW could be obtained at −20 °C. Maximum output powers of 0.18 pW and 0.13 pW were instead extracted from the two betavoltaic cells at −20 °C, these could lead to a total maximum output power as high as 0.3 pW at −20 °C. Conversion efficiencies of 2.2% and 0.06% were found, respectively, for the best Al0.52In0.48P x-ray photovoltaic and betavoltaic cells at −20 °C. With respect to previously reported Al0.52In0.48P x-ray photovoltaic cells with thinner i layers, the 6 μm Al0.52In0.48P x-ray photovoltaic cells had higher short circuit current, open circuit voltage, maximum output power, and conversion efficiency. The 6 μm Al0.52In0.48P betavoltaic cells instead presented similar performances to previously analysed Al0.52In0.48P betavoltaic cells.

Electric impulse spring-assisted contact separation mode triboelectric nanogenerator fabricated from polyaniline emeraldine salt and woven carbon fibers

In this article, we used modified woven carbon fiber mat (wCF-COOH), as one of the contact-electrification Triboelectric Nanogenerator (TENG) friction layer to generate high open circuit voltage (Voc) and short circuit current (Isc). We designed the contact-separation mode TENG which is functional using spring structure. The oxidation of wCF into wCF-COOH by Piranha solution followed by coupling of aniline through electrostatic interactions and in-situ oxidative polymerization to get woven carbon fiber-polyaniline emeraldine salt (wCF.PANI.ES) composite is a novel approach. The wCF-PANI.ES composite displays the surface resistivity of 0.324 Ω m and serves as a friction layer to generate charges by harvesting energy through vertical contact-separation mode TENG against PVDF membrane. The dynamic interactions of novel wCF-PANI.ES and PVDF membrane produced high Voc of 95 V, and Isc of 180 μA, respectively. In particular, wCF-PANI.ES-TENG has shown an enhancement of 498% of Voc with respect to wCF-COOH-TENG due to availability of PANI layer. In addition, it was observed that the proposed wCF-PANI.ES-TENG has shown the output power of 12.4 mW at 5 Hz, and the rectified current upto 180 μA. The novel wCF-PANI.ES is the potential candidate for fulfilling the need of optimized energy harvesting device as an alternate material option for contact-separation mode TENGs.

ZnO nanoflakes nanomaterials via hydrothermal process for dye sensitized solar cells

This work reports on the synthesis of well-crystalline zinc oxide nanoflakes (ZnO-Nfs) nanomaterials via hydrothermal process and preparation of photoanode for the fabrication of dye sensitized solar cells (DSSCs). A Well-defined flake like morphology was obtained which possessed the average thickness of ∼100 nm. The structural, crystalline and optical analysis revealed that the synthesized ZnO-Nfs exhibited a good crystal structure along with typical hexagonal wurtzite structure. The synthesized ZnO-Nfs was used as photoanode for the DSSC applications which expressed a good overall conversion efficiency (η) of ∼3.39%, high short circuit current (JSC) of 8.84 mA/cm2, and open circuit voltage (VOC) of 0.706 V with the fill factor (FF) of 0.54.

Back-contact perovskite solar cells with honeycomb-like charge collecting electrodes

Back-contact electrodes have been broadly applied to silicon photovoltaics to enhance their performance and avoid parasitic absorption from window materials and charge collection grids [1,2]. Here we introduce an innovative back-contact design for perovskite solar cells (PSCs) derived from our recently described quasi-interdigitated back-contact architecture [3]. The back contact consists of a top electrode, which has a honeycomb-like grid geometry, that is separated from the underlying planar bottom electrode by a similarly shaped insulating Al2O3 layer. This new design has higher structural robustness, as well as better defect tolerance, resulting in the highest short-circuit current (~ 16.4 mA/cm2) and stabilized power output (~ 4%) for a back-contact PSC to date. The improved performance was attributed to an increased charge collecting efficiency, with photocurrent mapping revealing what electrode dimensions are required for optimum efficiency.

Oligothiophenes and alkyl side-chain arrangement the structure-property study of their diketopyrrolopyrrole copolymers for organic photovoltaics

Abstract We have synthesized and characterized a series of diketopyrrolopyrrole (DPP)-oligothiophene copolymers, of which the number of regioregular oligothiophene ring (2T, 3T and 4T) and the arrangement of the alkyl side-chain on regioirregular quarterthiophene (4T0, 4T1 and 4T2) are variable. The side chains with regioregular lead to more planar copolymer backbones and higher short circuit current (JSC), but backbone torsion (due to regioirregular side chains) generates greater open-circuit voltages (VOC) for DPP-oligothiophene copolymers. The increasing thiophene ring progressively raises HOMO energy level of copolymers but marginally affects their band gaps. Additionally, the HOMO energy level was found declined significantly with side-chain regioirregularity, because of reducing length of π-conjugation. The HDDPP4T0 exhibits the strongest absorption, extensive network structure, and high hole mobility (μh = 6.04 × 10−4 cm2 V-1 s-1). These characteristics contribute to the exceptional high JSC of 18.96 mA/cm2 for OPV with PCE = 6.12%. However, the HDDPP4T1 having an optimal combination of π-conjugation and energy level affords the second highest VOC (0.73 V) and the third highest JSC (16.89 mA/cm2), resulting the best PCE of 7.51% among all. X-ray scattering, transmission electron microscopy, atomic force microscopy, and space-charge-limited-current (SCLC) measurements reveal that the solvent additive of diphenylether (DPE) enables PC71BM-blended copolymers thin film in crystallinic fibril with enhanced hole mobility.

Numerical Investigations of ReBCO Conductors With High Limitation Electric Field for HVDC SFCL

Superconducting fault current limiters (SFCL) are already in operation in alternative current medium voltage applications and their use in HVDC grids is very promising due to their capability of reducing high short-circuit currents. In the European project FASTGRID, started in January 2017, a 50-kV DC SFCL demonstrator will be built and tested. This limiter is expected to be made with state-of-the-art ReBCO conductors with a critical current of 1000 A/cm (at 65 K, self-field) and a limitation electric field of 150 V/m. To investigate the architecture of the conductor, a numerical model has been developed and confronted to experimental results. To increase the normal resistance of the conductor, various steps have been investigated such as the alloying of the silver layer and the addition of a highly resistive shunt. Two bonding techniques (solder or glue) have been considered to assemble the shunt on the conductor. This paper compares theoretical results of different architectures of conductors to be tested in small SFCL pancakes.

Highly Efficient Perovskite Solar Cells with Gradient Bilayer Electron Transport Materials.

Electron transport layers (ETLs) with suitable energy level alignment for facilitating charge carrier transport as well as electron extraction are essential for planar heterojunction perovskite solar cells (PSCs) to achieve high open-circuit voltage ( VOC) and short-circuit current. Herein we systematically investigate band offset between ETL and perovskite absorber by tuning F doping level in SnO2 nanocrystal. We demonstrate that gradual substitution of F- into the SnO2 ETL can effectively reduce the band offset and result in a substantial increase in device VOC. Consequently, a power conversion efficiency of 20.2% with VOC of 1.13 V can be achieved under AM 1.5 G illumination for planar heterojunction PSCs using F-doped SnO2 bilayer ETL. Our finding provides a simple pathway to tailor ETL/perovskite band offset to increase built-in electric field of planar heterojunction PSCs for maximizing VOC and charge collection simultaneously.

Design and Fabrication of Multifunctional Portable Bi2Te3-Based Thermoelectric Camping Lamp

Camping lamps have been widely used in the lighting, power supply, and intelligent electronic equipment fields. However, applications of traditional chemical and solar camping lamps are largely limited by the physical size of the source and operating conditions. A new prototype multifunctional portable Bi2Te3-based thermoelectric camping lamp (TECL) has been designed and fabricated. Ten parallel light-emitting diodes were lit directly by a Bi2Te3-based thermoelectric generator (TEG). The highest short-circuit current of 0.38 A and open-circuit voltage of 4.2 V were obtained at temperature difference of 115 K. This TECL is attractive for use in multifunctional and extreme applications as it integrates a portable heat source, high-performance TEG, and power management unit.

Synthesis and Photovoltaic Properties of 2D-Conjugated Polymers Based on Alkylthiothienyl-Substituted Benzodithiophene and Different Accepting Units.

Two new low bandgap conjugated polymers, PBDTS-ID and PBDTS-DTNT, containing isoindigo (ID) and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT), respectively, as an electron-deficient unit and alkylthiothienyl-substituted benzodithiophene (BDTS) as an electron-rich unit, were designed and synthesized by palladium-catalyzed Stille polycondensation. Both polymers showed good thermal stability up to 330 °C and broad absorption ranging from 300 to 842 nm. Electrochemical measurement revealed that PBDTS-ID and PBDTS-DTNT exhibited relatively low-lying highest occupied molecular orbital energy levels at −5.40 and −5.24 eV, respectively. These features might be beneficial for obtaining reasonable high open-circuit voltage and high short-circuit current. Polymer solar cells (PSCs) were fabricated with an inverted structure of indium-tin oxide/poly(ethylenimine ethoxylate)/polymer:PC71BM/MoO3/Ag. As a preliminary result, the PSCs based on PBDTS-ID and PBDTS-DTNT exhibited moderate power conversion efficiencies of 2.70% and 2.71%, respectively.

Piper Ornatum and Piper Betle as Organic Dyes for TiO2 and SnO2 Dye Sensitized Solar Cells

Dye sensitized solar cell (DSSC) mimics the principle of natural photosynthesis are now currently investigated due to low manufacturing cost as compared to silicon based solar cells. In this report, we utilized Piper ornatum (PO) and Piper betle (PB) as sensitizer to fabricate low cost DSSCs. We compared the photovoltaic performance of both sensitizers with Titanium dioxide (TiO2) and Tin dioxide (SnO2) semiconductors. The results show that PO and PB dyes have higher Short circuit current (Jsc) when applied in SnO2 compared to standard TiO2 photo-anode film even though the Open circuit voltage (Voc) was hampered on SnO2 device. In conclusion, from the result, higher electron injections can be achieved by choosing appropriate semiconductors with band gap that match with dyes energy level as one of strategy for further low cost solar cell.

Cesium-Doped Vanadium Oxide as the Hole Extraction Layer for Efficient Perovskite Solar Cells.

In this study, we report the utilization of low-temperature solution-processed Cs-doped VOX thin films as the hole extraction layers (HELs) in perovskite solar cells (PSCs). It is found that the VOX:yCs (where y is the mole ratio of Cs versus V and y = 0.1, 0.3, and 0.5) thin films possess better electrical conductivities than that of the pristine VOX thin film. As a result, the PSCs incorporated with the VOX:yCs HEL exhibit large fill factors and high short-circuit currents, with consequently high power conversion efficiencies, which is more than 30% enhancement as compared with pristine VOX HEL. Our studies provide a facial way to enhance the electrical conductivity of the hole extraction layer for boosting device performance of perovskite solar cells.

Core-shell coaxially structured triboelectric nanogenerator for energy harvesting and motion sensing.

Converting sustainable human motion energy into electric energy has become an urgent task for the advancement of next-generation wearable and portable electronics. Herein, a core–shell coaxially structured triboelectric nanogenerator (CSTN) was fabricated by inserting an inner hollow circular tube into an outer hollow circular tube, and a gasbag is constructed within the space between the inner and outer tubes. Both Ni-coated polyester conductive textile and the conductive silicone rubber were used as effective electrode materials. The CSTN has excellent properties, including flexibility, light weight, sustainability and biological compatibility due to its unique structural design and materials selection. The CSTN can convert various forms of human motion energy, such as pressing, bending and twisting motion, into electric energy. A high short-circuit current of 11 μA and an open-circuit voltage of 380 V can be obtained from a CSTN with a length of 6 cm, corresponding to a high peak power of 1.638 mW at a load resistance of about 10 MΩ. When six such CSTNs are connected in parallel and placed under shoes, the electric energy output by normal walking can light up 60 LEDs connected serially and power up a competition-timer. The device can also sense different bending angles or twisting angles according to its signal outputs under different deformation angles. This study indicates the promising application prospects of the CSTN for next-generation devices, including self-powered illuminating devices, portable electronics, body motion sensing and health monitoring.

Enhancing efficiency of planar structure perovskite solar cells using Sn-doped TiO2 as electron transport layer at low temperature

Sn-doped TiO2 films were successfully deposited by low-temperature solution method as electron transport layer (ETL), whose influence on the performance of perovskite solar cell (PSC) was investigated. In this work, X-ray photoelectron spectroscopy and X-ray diffraction revealed that Sn4+ was successfully incorporated into the TiO2 lattice as an effective metal ion dopant without forming secondary phases. Compared with pristine TiO2, the Sn-doped TiO2 is more efficient for photogenerated electron extraction and transport, showing lower trap-state density and higher conductivity. Higher short-circuit current (Jsc) is obtained due to the enhanced carrier transport velocity and improved charge collection efficiency, leading to a higher fill factor (FF) and better energy transfer efficiency. Our optimized planar solar cell using such a Sn-doped TiO2 ETL has achieved power conversion efficiency (PCE) of 17.2%, which was almost 29.3% higher than that of sample using the undoped TiO2. To the best of our knowledge, this is the lowest processing temperature for Sn-dope TiO2 film at present, which provides an effective route towards flexible high-performance PSCs.

Cu2ZnSnSe4 Thin Film Solar Cell with Depth Gradient Composition Prepared by Selenization of Sputtered Novel Precursors

In this study, we proposed a new method for the synthesis of the target material used in a two stage process for preparation of a high quality CZTSe thin film. The target material consisting of a mixture of CuxSe and ZnxSn1-x alloy was synthesized, providing a quality CZTSe precursor layer for highly efficient CZTSe thin film solar cells. The CZTSe thin film can be obtained by annealing the precursor layers through a 30 min selenization process under a selenium atmosphere at 550 °C. The CZTSe thin films prepared by using the new precursor thin film were investigated and characterized using X-ray diffraction, Raman scattering, and photoluminescence spectroscopy. It was found that diffusion of Sn occurred and formed the CTSe phase and CuxSe phase in the resultant CZTSe thin film. By selective area electron diffraction transmission electron microscopy images, the crystallinity of the CZTSe thin film was verified to be single crystal. By secondary ion mass spectroscopy measurements, it was confirmed that a double-gradient band gap profile across the CZTSe absorber layer was successfully achieved. The CZTSe solar cell with the CZTSe absorber layer consisting of the precursor stack exhibited a high efficiency of 5.46%, high short circuit current (JSC) of 37.47 mA/cm2, open circuit voltage (VOC) of 0.31 V, and fill factor (F.F.) of 47%, at a device area of 0.28 cm2. No crossover of the light and dark current-voltage (I-V) curves of the CZTSe solar cell was observed, and also, no red kink was observed under red light illumination, indicating a low defect concentration in the CZTSe absorber layer. Shunt leakage current with a characteristic metal/CZTSe/metal leakage current model was observed by temperature-dependent I-V curves, which led to the discovery of metal incursion through the CdS buffer layer on the CZTSe absorber layer. This leakage current, also known as space charge-limited current, grew larger as the measurement temperature increased and completely overwhelmed the diode current at a measurement temperature of 200 °C. This is due to interlayer diffusion of metal that increases the shunt leakage current and decreases the efficiency of the CZTSe thin film solar cells.

Charge Generation and Recombination in an Organic Solar Cell with Low Energetic Offsets

AbstractOrganic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short‐circuit currents (JSC) and fill factors (FF). However, it is necessary to reduce the energetic offsets to achieve high open‐circuit voltages (VOC). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl‐C61‐butyric acid methyl ester (PC61BM), that achieves a high VOC (0.9 V) with very low energy losses (Eloss = 0.52 eV) from the energy of absorbed photons, a respectable JSC (13 mA cm−2), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field‐dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge‐carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC61BM. These results hold promise that given the appropriate morphology, the JSC, VOC, and FF can all be improved, even with very low energetic offsets.

Technical and Economic Analysis of the R-Type SFCL for HVDC Grids Protection

Mainly used in ac grids, resistive-type superconducting fault current limiters may be still more interesting for dc systems due to their capability to reduce high short circuit currents appearing in case of dc cable fault. This limiter reduces the breaking capability, speed, and energy requirements of the required dc circuit breaker allowing the implementation of electromechanical breakers for fault current interruption. These breakers have lower breaking capability, on-load losses, and investment costs in comparison with hybrid circuit breakers based on power electronics. This paper presents a technical and economic analysis of a superconducting fault current limiter used in a radial three-terminal high voltage dc grid to protect a cable link. Based on simulation studies using an electromagnetic transient program, an effective system protection will be demonstrated with special attention to the continuity of power flow through healthy parts of the grid.

Designing 1,5‐Naphthyridine‐2,6‐dione‐Based Conjugated Polymers for Higher Crystallinity and Enhanced Light Absorption to Achieve 9.63% Efficiency Polymer Solar Cells

AbstractHighly crystalline conjugated polymers represent a key material for producing high‐performance thick‐active‐layer polymer solar cells (PSCs). However, despite their potential, a limited number of crystalline polymers are used in PSCs because of the lack of highly coplanar acceptor building blocks and insufficient light absorptivity (α < 105) of most donor (D)–acceptor (A)‐type polymers. This study reports a series of novel 3,7‐di(thiophen‐2‐yl)‐1,5‐naphthyridine‐2,6‐dione (NTDT) acceptor‐based conjugated polymers, PNTDT‐2T, PNTDT‐TT, and PNTDT‐2F2T, synthesized with 2,2′‐bithiophene (2T), thieno[3,2‐b]thiophene (TT), and 3,3′‐difluoro‐2,2′‐bithiophene (2F2T) donor units, respectively. PNTDT‐2F2T exhibits superior polymer crystallinity and a much higher absorption coefficient than those of PNTDT‐2T or PNTDT‐TT because of adequate matching between highly coplanar A (NTDT) and D (2F2T) building blocks. A bulk heterojunction solar cell based on PNTDT‐2F2T exhibits a power conversion efficiency of up to 9.63%, with a high short circuit current of 18.80 mA cm−2 and fill factor of 0.70, when a thick active layer (>200 nm) is used, without postfabrication hot processing. The findings demonstrate that the polymer crystallinity and absorption coefficient can be effectively controlled by selecting appropriate D and A building blocks, and that NTDT is a novel and versatile A building block for highly efficient thick‐active‐layer PSCs.