Decent Power Research Articles

Electrostatic energy harvesting device with dual resonant structure for wideband random vibration sources at low frequency.

In this paper, we present design and test of a broadband electrostatic energy harvester with a dual resonant structure, which consists of two cantilever-mass subsystems each with a mass attached at the free edge of a cantilever. Comparing to traditional devices with single resonant frequency, the proposed device with dual resonant structure can resonate at two frequencies. Furthermore, when one of the cantilever-masses is oscillating at resonance, the vibration amplitude is large enough to make it collide with the other mass, which provides strong mechanical coupling between the two subsystems. Therefore, this device can harvest a decent power output from vibration sources at a broad frequency range. During the measurement, continuous power output up to 6.2-9.8 μW can be achieved under external vibration amplitude of 9.3 m/s2 at a frequency range from 36.3 Hz to 48.3 Hz, which means the bandwidth of the device is about 30% of the central frequency. The broad bandwidth of the device provides a promising application for energy harvesting from the scenarios with random vibration sources. The experimental results indicate that with the dual resonant structure, the vibration-to-electricity energy conversion efficiency can be improved by 97% when an external random vibration with a low frequency filter is applied.

In Situ Growth of Highly Adhesive Surface Layer on Titanium Foil as Durable Counter Electrodes for Efficient Dye-sensitized Solar Cells.

Counter electrodes (CEs) of dye-sensitized solar cells (DSCs) are usually fabricated by depositing catalytic materials on substrates. The poor adhesion of the catalytic material to the substrate often results in the exfoliation of catalytic materials, and then the deterioration of cell performance or even the failure of DSCs. In this study, a highly adhesive surface layer is in situ grown on the titanium foil via a facile process and applied as CEs for DSCs. The DSCs applying such CEs demonstrate decent power conversion efficiencies, 6.26% and 4.37% for rigid and flexible devices, respectively. The adhesion of the surface layer to the metal substrate is so strong that the photovoltaic performance of the devices is well retained even after the CEs are bended for 20 cycles and torn twice with adhesive tape. The results reported here indicate that the in situ growth of highly adhesive surface layers on metal substrate is a promising way to prepare durable CEs for efficient DSCs.

Solubilized 5,6-bis(octyloxy)benzoxadiazole as a versatile acceptor block for designing novel (-X-DADAD-)n and (-X-DADADAD-)n electron donor copolymers for bulk heterojunction organic solar cells

Three novel conjugated polymers incorporating extended DADAD and DADADAD building blocks with the 5,6-bisalkoxybenzoxadiazole acceptor (A) and the electron donor (D) thiophene units were synthesized and fully characterized. The application of the benzoxadiazole instead of benzothiadiazole resulted in a significant increase in the open circuit voltage of organic solar cells based on such polymers. The best performing material delivered a decent solar light power conversion efficiency of 5.5% in organic bulk heterojunction solar cells using PC71BM as an electron acceptor component. The obtained results revealed a high potential of using different acceptor building blocks in the design of novel (-X-DADAD-)n polymers with tailored optoelectronic and photovoltaic properties.

Coherent polyaniline/graphene oxides/multi-walled carbon nanotubes ternary composites for asymmetric supercapacitors

A coherent polyaniline (PANI)/graphene oxides (GOs)/multi-walled carbon nanotubes (MWCNTs) composite was prepared by in-situ solution polymerization as a positive electrode of supercapacitors. The orderly growth of PANI nano-dots on GOs led to the formation of the nano-ravines that can enhance ions diffusion efficiency. MWCNTs surrounded by PANI connected all components, and thus the conductivity with the increasing electron transfer rate was improved. The results showed that the electrode exhibited the outstanding electrochemical performances with the specific capacitance up to 696Fg−1 at 20mVs−1. The KOH-activated GOs/MWCNTs were used as a negative electrode to assemble an asymmetric supercapacitor (ASC). The ASC possessed an extended working potential (1.6V), a good rate capability (58% capacitance retention even after the current density being increased by 10 times), an excellent cycling stability (89% capacitance retention after 3000 cycles), and a decent average energy and power density (69Wh/kg and 6.4kW/kg).

Fabrication of lanthanum strontium cobalt ferrite (LSCF) cathodes for high performance solid oxide fuel cells using a low price commercial inkjet printer

In this study, we investigate a method to fabricate high quality lanthanum strontium cobalt ferrite (LSCF) cathodes for solid oxide fuel cells (SOFCs) using a commercial low price inkjet printer. The ink source is synthesized by dissolving the LSCF nanopowder in a water-based solvent with a proper amount of surfactants. Microstructures of the LSCF layer, including porosity and thickness per printing scan cycle, are adjusted by grayscale in the printing image. It is successfully demonstrated that anode-supported SOFCs with optimally printed LSCF cathodes can produce decent power output, i.e., a maximum peak power density of 377 mW cm−2 at 600 °C, in our experiment. We expect that this approach can support the quick and easy prototyping and evaluating of a variety of cathode materials in SOFC research.

Nd2(S, Se, Te)3 Colloidal Quantum Dots: Synthesis, Energy Level Alignment, Charge Transfer Dynamics, and Their Applications to Solar Cells

Novel and less toxic quantum dot (QD) semiconductors are desired for developing environmentally benign colloidal quantum dot solar cells. Here, the synthesis of novel lead/cadmium‐free neodymium chalcogenide Nd2(S, Se, Te)3 QDs via solution‐processed method is reported for the first time. The results show that small‐bandgap semiconductor QDs with a narrow size distribution ranging from 2 to 8 nm can be produced, and the wide absorption band can be achieved by the redshift owing to the size quantization effect by controlling the initial loading of chalcogenide precursors. By analyzing the band structure of QDs and the energy level alignment between QDs and TiO2, the influence of energy offset between the conduction band edges of QDs and TiO2 on the charge transfer dynamics and photovoltaic performance of QD solar cells (QDSCs) is investigated. It is revealed that among the three types of QDs studied, Nd2Se3 QDSCs with the smallest energy offset exhibit the best performances and a decent power conversion efficiency of 3.19% is achieved. This work clearly demonstrates the promising potentials of novel rare earth chalcogenide quantum dots in photovoltaic applications.

In situ synthesis of crosslinked-polyaniline nano-pillar arrays/reduced graphene oxide nanocomposites for supercapacitors

Crosslinked-polyaniline (CPA) nano-pillar arrays adsorbed on the surface of reduced graphene oxide (RGO) sheets were synthesized by in situ solution polymerization through two steps of reduction. The electrochemical analyses demonstrated that the befittingly reduced CPA/RGO composite exhibited high performance as electrode materials for supercapacitors. The CPA/RGO composite showed very high specific capacitance of 1532 F g−1 at a scan rate of 10 mV s−1 or 694 F g−1 at a current density of 2 A g−1 in 1 M H2SO4 electrolyte, as well as great energy density of 61.4 W h kg−1 at a current density of 2 A g−1. The electrode material also had decent power density of 4 kW kg−1 at a current density of 10 A g−1, and good cycling stability of 92.5 % capacitance retained after 500 cycles of cyclic voltammetry at 500 mV s−1. The neat microstructures and super electrochemical properties suggest the potential use of the composites in supercapacitors.

A CMOS–MEMS arrayed resonant-gate field effect transistor (RGFET) oscillator

A high-frequency CMOS–MEMS arrayed resonant-gate field effect transistor (RGFET) fabricated by a standard 0.35 μm 2-poly-4-metal CMOS–MEMS platform is implemented to enable a Pierce-type oscillator. The proposed arrayed RGFET exhibits low motional impedance of only 5 kΩ under a purely capacitive transduction and decent power handling capability. With such features, the implemented oscillator shows impressive phase noise of −117 dBc Hz−1 at the far-from-carrier offset (1 MHz). In this work, we design a clamped–clamped beam (CCB) arrayed resonator utilizing a high-velocity mechanical coupling scheme to serve as the resonant-gate array. To achieve a functional arrayed RGFET, a corresponding FET array is directly placed underneath the resonant gate array to convert the motional current on the resonant-gate array into a voltage output with a tunable transconductance gain. To understand the behavior of the proposed device, an equivalent circuit model consisting of the resonant unit and FET is also provided. To verify the effects of the post-CMOS process on device performance, a conventional MOS ID current measurement is carried out. Finally, a CMOS–MEMS arrayed RGFET oscillator is realized by utilizing a Pierce oscillator architecture, showing decent phase noise performance that benefits from the array design to alleviate the nonlinear effect of the resonant gate.

PbS Quantum-Dot Depleted Heterojunction Solar Cells Employing CdS Nanorod Arrays as the Electron Acceptor with Enhanced Efficiency.

Depleted heterojunction (DH) solar cells have shown great potential in power conversion. A 3-D DH structure was first designed and fabricated through a layer-by-layer spin-coating technique to increase the interfacial contact of p-type PbS quantum dots (QDs) and n-type CdS nanorod arrays. As a result, a decent power conversion efficiency of 4.78% in this structure was achieved, which is five times the efficiency of a planar heterojunction structure of a similar thickness. In the 3-D DH structure, n-type CdS nanorod arrays (NRs) were grown vertically as electron acceptors, on which p-type PbS quantum dots were deposited as absorbing materials in a layer-by-layer spin-coating fashion. The results are discussed in view of effective transportation of electrons through CdS NRs than the hopping transportation in large nanoparticle-based CdS film, the enlarged interfacial area, and shortened carrier diffusion distance.

New Semiconducting Polymer Based on Benzo[1,2‐b:4,5‐b′]diselenophene Donor and Diketopyrrolopyrrole/Isoindigo Acceptor Unit: Synthesis, Characterization and Photovoltaics

AbstractTwo new D‐A type polymers PBDSe‐DPP and PBDSe‐ID were synthesized to explore new ideal semiconducting polymers, by conjugating acceptor unit diketopyrrolopyrrole/isoindigo to a donor unit benzo[1,2‐b:4,5‐b′]diselenophene, which is designed by substituting the sulfur atom with a selenium atom in the benzo[1,2‐b:4,5‐b′]dithiophene. The thermal, optical, electrochemical, photoelectric and photovoltaic properties of the two polymers were studied systematically. Relatively high open circuit voltage (0.7 and 0.75 V) and fill factor (>65%) were demonstrated for both polymers. Huge increase (by 64% and 120%) of the short circuit current density was achieved for both polymer based devices by using additive compared to the corresponding reference without additive, resulting in decent power conversion efficiency of 3.7% and 2.5% respectively with only simple optimizing consideration. We believe this class of BDSe polymer possesses a good potential to be alternatives of active material for photovoltaic applications.

Inverted quantum-dot solar cells with depleted heterojunction structure employing CdS as the electron acceptor

Colloidal quantum-dot (QD) solar cells have emerged as one of the most promising photovoltaic techniques. Herein, we report an inverted PbS QD solar cells employing solution-processed CdS as the electron acceptor materials. Chemical bath deposition – one featuring ease of fabrication and compatibility with a low-temperature process – was employed to prepare CdS film on FTO glass, followed by deposition of PbS QDs as absorbing layer in a layer-by-layer fashion, thereby forming a depleted heterojunction structure. The results suggested that the thickness of CdS layer can be a key factor for determining the photovoltaic performance. After systematical optimization, an inverted FTO/CdS/PbS QDs/MoO3/Ag structure with an ultra-thin CdS film of 40nm delivered a decent power conversion efficiency of 5.22%. The maximum temperature is ~85°C via device fabrication demonstrates potential large-scale production process.

Inverted planar heterojunction perovskite solar cells employing polymer as the electron conductor.

Inverted planar heterojunction perovskite solar cells employing different polymers, poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), poly{[N,N'-bis(alkyl)-1,4,5,8-naphthalene diimide-2,6-diyl-alt-5,5'-di(thiophen-2-yl)-2,2'-(E)-2-(2-(thiophen-2-yl)vinyl)thiophene]} (PNVT-8), and PNDI2OD-TT as electron-transporting material (ETM) have been investigated for the first time. The best device performance was obtained when N2200 was applied as the ETM, with JSC of 14.70 mA/cm2, VOC of 0.84 V, and fill factor (FF) of 66%, corresponding to a decent power conversion efficiency (PCE) of ∼ 8.15%. Which is very competitive to the parameters (JSC 14.65 mA/cm2, VOC 0.83 V, FF 70%, and PCE 8.51%) of the reference device employing conventional PCBM as the ETM. The slightly lower FF could be mainly accounted for by the increased recombination in the polymer contained devices. This work demonstrated that polymeric materials can be used as efficient ETM in perovskite solar cells, and we believe this class of polymeric ETMs will further promote the performance of perovskite photovoltaic cells after extended investigation.

A way of achieving a low $/W and a decent power output from a thermoelectric device

While most research concerning thermoelectrics has focused on the enhancement of the thermoelectric figure of merit, zT, the $/W is a direct indication of its practical use. It is suggested that in the conventional device architecture, it is better to reduce thermoelectric material consumption rather than to increase zT for higher conversion efficiency, i.e., higher power output with given heat input for lower costs, in certain cases. As a result of this, a thermoelectric device with low $/W suffers from its low power output. Here, we present another way to lower the $/W value, while maintaining a decent power output of a thermoelectric device by changing the device architecture. In the analytical expression which we deduced, we demonstrated that the $/W value can be reduced to around 10% while maintaining ∼65–70% of the maximum possible power output with a given zT. The device architecture we propose should be useful to recover low quality waste heat, which is abundant and could be harvested as long as the $/W value is low enough in general.

Low-temperature performance of yttria-stabilized zirconia prepared by atomic layer deposition

We report on the performance of thin-film yttria-stabilized zirconia (YSZ) synthesized by atomic layer deposition (ALD) at temperatures of 50–525 °C. Electrochemical impedance spectroscopy (EIS) was used for conductivity measurements. Relatively high conductivity values were observed in the low-temperature region when compared to reference values of YSZ synthesized by other methods. To investigate the conduction mechanism, various experimental variables were modified during the electrical measurements, including the ratio of yttria to zirconia in the ALD YSZ films and the atmospheric conditions. To relate the electrical properties to the structural characteristics, the crystallinity and microstructure were investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Finally, the suitability of an ALD YSZ membrane as the electrolyte of micro solid oxide fuel cells was evaluated. An open circuit voltage of almost 1 V and decent power output were successfully measured below 100 °C.

Thermoelectric transport properties of boron-doped nanocrystalline diamond foils

Natural diamond is known for its outstanding thermal conductivity and electrical insulation. However, synthetic production allows for doping and tailoring microstructural and transport properties. Despite some motivation in the literature and the ongoing search for abundant and non-toxic thermoelectric materials, the first experimental study on a set of eight substrate-free boron-doped nanocrystalline diamond foils is presented herein. All transport coefficients were determined in the same direction within the same foils over a broad temperature range up to 900°C. It is found that nanostructuring reduces the thermal conductivity by two orders of magnitude, but the mobility decreases significantly to around 1cm2V−1s−1, too. Although degenerate transport can be concluded from the temperature dependence of the Seebeck coefficient, charge carriers notably scatter at grain boundaries where sp2-carbon modifications and amorphous boron-rich phases form during synthesis. A detailed analysis of doping efficiency yields an acceptor fraction of only 8–18at%, meaning that during synthesis excess boron thermodynamically prefers electrically inactive sites. Decent power factors above 10−4Wm−1K−2 at 900°C are found despite the low mobility, and a Jonker-type analysis grants a deeper insight into this issue. Together with the high thermal conductivity, the thermoelectric figure of merit zT does not exceed 0.01 at 900°C.

A fused-ring acceptor unit in d-a copolymers benefits photovoltaic performance.

Pentacyclic lactam acceptor unit TPTI invented by our group is proved to be a good building block for efficient D-A copolymers used in organic solar cells. Here, two D-A copolymers PBTTPTI and PTTTPTI are developed by copolymerizing TPTI with 2,2'-bithiophene (BT) or thieno[3,2-b]thiophene (TT). PBTTPTI and PTTTPTI exhibit good solubility and strong interchain π-π interaction even in dilute solution. They possess deep HOMO levels (ca. -5.3 eV), partial crystallinity, and good hole mobilities. Blending with PC71 BM, PBTTPTI and PTTTPTI give decent power conversion efficiencies (PCE) up to 6.83% and 5.86%, with outstanding fill factors (FF) of 74.3% and 71.3%, respectively.

Powerful tests for structural changes in volatility

Detecting structural changes in volatility is important for understanding volatility dynamics and stylized facts observed for financial returns such as volatility persistence. We propose modified CUSUM and LM tests that are built on a robust estimator of the long-run variance of squared series. We establish conditions under which the new tests have standard null distributions and diverge faster than standard tests under the alternative. The theory allows smooth and abrupt structural changes that can be small. The smoothing parameter is automatically selected such that the proposed test has good finite-sample size and meanwhile achieves decent power gain.

Synthesis, Molecular and Photovoltaic Properties of Donor–Acceptor Conjugated Polymers Incorporating a New Heptacylic Indacenodithieno[3,2-b]thiophene Arene

We have developed a new multifused indacenodithieno[3,2-b]thiophene arene (IDTT) unit where the central phenylene is covalently fastened with the two outer thieno[3,2-b]thiophene (TT) rings, forming two cyclopentadiene rings embedded in a heptacyclic structure. This rigid and coplanar IDTT building block was copolymerized with electron-deficient acceptors, 4,7-dibromo-2,1,3-benzothiadiazole (BT), 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole (FBT) and 1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD) via Stille polymerization, respectively. Because the higher content of the thienothiophene moieties in the fully coplanar IDTT structure facilitates π-electron delocalization, these new polymers show much improved light-harvesting abilities and enhanced charge mobilities compared to PDITTBT copolymer using hexacyclic diindenothieno[3,2-b]thiophene (DITT) as the donor moieties. The device using PIDTTBT:PC71BM (1:4, w/w) exhibited a decent power conversion efficiency (PCE) of 3.8%. Meanwhile, the solar cell using PIDTTFBT:PC71BM (1:4 in wt %) blend exhibited a greater Voc value of 0.9 V and a larger Jsc of 10.08 mA/cm2, improving the PCE to 4.2%. The enhanced Voc is attributed to the lower-lying of HOMO energy level of PIDTTFBT as a result of fluorine withdrawing effect on the BT unit. A highest PCE of 4.3% was achieved for the device incorporating PIDTTTPD:PC71BM (1:4 in wt %) blend.

A novel test of informative missingness using inconsistent linkage disequilibrium signals between case-parent triads and incomplete data

In general, multiple issues are examined before the analysis of genetic data such as Hardy-Weinberg Equilibrium and Mendelian errors. Although missing genotypes are commonly observed in genetic studies, potential bias due to informative missingness is usually overlooked. Therefore, the Test of Informative Missingness (TIM) was the first attempt to determine whether or not parental genotypes are missing informatively. The TIM is a useful tool for genetic data cleaning. For example, excluding single-nucleotide polymorphisms that appear to be missing informatively may further improve the quality of genetic data. Although the TIM has decent power, its performance is discernibly weaker when the minor allele/genotype introduces informative missingness. In an effort to avoid such reduced power, the newly proposed strategy detects informative missingness by comparing inconsistent linkage disequilibrium signals between intact case-parent triads and incomplete data. Computer simulations revealed that the new method was robust to population stratifications and more powerful than the TIM in most situations. In addition, the new method demonstrated decent power in the genome-wide association study, even if the most conservative correction for multiple testing was adopted.

New A-A-D-A-A-Type Electron Donors for Small Molecule Organic Solar Cells

Two A-A-D-A-A-type molecules (BCNDTS and BDCDTS), where two terminal electron-withdrawing cyano or dicyanovinylene moieties are connected to a central dithienosilole core through another electron-accepting 2,1,3-benzothiadiazole block, have been synthesized, characterized, and employed as electron donors for small molecule organic solar cells. Vacuum-deposited bilayer and planar mixed heterojunction devices based on BCNDTS and fullerene acceptors (C(60) or C(70)) exhibited decent power conversion efficiencies of 2.3% and 3.7%, respectively.