Improved Conversion Efficiency Research Articles

Research on Co-Combustion Behaviors of Binary and Ternary Blends of Coal, Walnut Shell, and Biochar by TGA

In this paper, the co-combustion behavior of the walnut shell, biochar, and coal, and the respective binary and ternary blends were investigated by thermogravimetric analysis (TGA) in the oxy-fuel atmosphere (21% O2/79% CO2). The combustion reactivity of coal was similar to biochar but lower than that of the walnut shell. The presence of the walnut shell improved the combustion performance of coal and biochar. The interaction between only biochar and coal was inhibited in the binary blends. The presence of the walnut shell in the ternary blend covered up the inhibition between biochar and coal. The average activation energy of each sample was obtained using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) kinetic models. The results of this study provide a reference for the rational utilization of biomass and biochar and the practical improvement of the thermal conversion efficiency of coal.

Oriented Crystal Growth during Perovskite Surface Reconstruction

Surface passivation has become a key strategy for an improvement in power conversion efficiency (PCE) of perovskite solar cells (PSCs) since PSCs experienced a steep increase in PCE and reached a comparably matured point. Recently, surface passivation using a mixed salt of fluorinated alkyl ammonium iodide and formamidinium bromide demonstrated a remarkable improvement in both performance and stability, which can be tuned by the length of the alkyl chain. Nevertheless, the role of the alkyl chain in manipulating surface-limited crystal growth was not fully understood, preventing a further progress in interface control. In this study, we found that the length of the fluorine-substituted alkyl chain governed the crystal formation dynamics by manipulating surface tensions of different crystal orientations. The overall enhancement of the (001) plane, being the most favored, commonly resulted from the surface reformation of the perovskite film regardless of the chain length, while the highly oriented (001) over (111) was monitored with a particular chain length. The enhanced crystal orientation during surface recrystallization was responsible for the low trap density and thus effectively suppressed charge recombination at the interface, resulting in a considerable increase in open-circuit voltage and fill factor.

Review on nanofluids and machine learning applications for thermoelectric energy conversion in renewable energy systems

This review is about applications of nanofluids technology and different machine learning algorithms on the potential improvement of system performance and computational efficiency of thermo-electric device installed systems. Brief information about the thermo-electric energy conversion principles, construction materials and different application areas in energy system technologies are presented. The applications of nanofluid technology in thermoelectric conversion starting from the basic information on the common nanofluid types, modeling aspects and thermophysical properties are presented. Potential of using nanofluid in diverse thermoelectric installed system on the conversion efficiency and performance improvements are discussed. Applications of different machine learning algorithms with the basic information on the most common applied ones are presented. The computational efficiency of using different machine learning methods have been analyzed. The gap in the present literature and future trends are discussed. As thermoelectric devices, which are among the clean energy technologies, gain importance with the many advantages they offer and draw attention with their adaptability to different systems, the results summarized here, and future aspects will be beneficial for efficient design and optimization of energy related technologies.

Tin Sulfide (SnS) Films Deposited by an Electric Field-Assisted Continuous Spray Pyrolysis Technique with Application as Counter Electrodes in Dye-Sensitized Solar Cells.

The deposition of tin sulfide (SnS) nanostructured films using a continuous spray pyrolysis technique is reported with an electric field present at the nozzle for influencing the atomization and the subsequent film deposition. In the absence of the electric field, the X-ray diffraction pattern shows the orthorhombic phase of SnS with a crystallographic preferred orientation along the (040) plane. The application of the electric field results in significant improvement in the morphology and a reduction in surface roughness (28 nm from 37 nm). The direct optical band gap of the films deposited with and without the electric field is estimated to be 1.5 and 1.7 eV, respectively. The photothermal deflection spectroscopy studies show a lower energetic disorder (no Urbach tail), which indicates an annealing effect in the SnS films deposited under the electric field. The improvement in the film properties is reflected in the expected improvement in the power conversion efficiency (PCE) of dye-sensitized solar cells fabricated using the SnS film as a counter electrode. An enhancement of PCE from 2.07% for the film deposited without the electric field to 2.89% for the film deposited with the electric field shows the role of the electric field in the fabrication of improved SnS films.

Shell-shaped active layers for omnidirectional organic photovoltaic cells

For the employment of organic photovoltaic cells in wearable electronic systems, improvements in energy conversion efficiency and omnidirectionality (angular coverage) are highly appreciated. This study aims at those improvements by introducing shell-shaped active layers. The proposed device structures enhance light absorption and angular range through light coupling to guided modes in the active layer. Two shapes, i.e., a triangle and a semicircle, are examined for the shell cross-sections. Numerical simulation using finite-element analysis and finite-difference time-domain methods demonstrates that the devices with the triangular-shell-shaped active layers exhibit an average absorption enhancement of up to 63% for transverse electric (TE)-polarization and up to 32% for transverse magnetic (TM)-polarization when compared with the flat active layers of the same thicknesses. The average enhancements of the semicircular-shell-shaped active layers are found to be slightly lower than those values, with 60% for TE and 28% for TM. The examined structures also show good omnidirectionality with decent absorption up to an 81 deg incidence angle for the triangular-shell-shaped device and up to a 76 deg angle for the semicircular one when TM polarization is considered. These absorption enhancements and improved angular coverages make the proposed structures highly attractive for wearable electronic system applications.

Ethylammonium Bromide- and Potassium-Added CH3NH3PbI3 Perovskite Solar Cells

Perovskite solutions with added potassium iodide (KI) and ethylammonium bromide (EABr) were used to fabricate perovskite solar cells in ordinary air at 190 °C. The addition of EABr and KI induced (100)-oriented perovskite crystals, which resulted in the improvement in short-circuit current densities and conversion efficiencies. The short-circuit current density, open circuit voltage, and conversion efficiency of the best device were 21.0 mA cm−2, 0.942 V, and 12.88%, respectively. First-principles calculations also indicated a decrease in total energy per cell and an increase in energy gaps, which agreed with the improved results of device stabilities and photovoltaic properties.

Improvement in the energy conversion efficiency for silicon heterojunction solar cells due to SiOx inserted with conducting filaments

Patterning an insulator to make electrical contact between the front electrode and the emitter is essential in solar cells, resulting in an increase in manufacturing cost. In this paper, conducting filaments (CFs) are applied to the silicon heterojunction (SHJ) solar cell with an SiOx/ITO structure for the first time. The self-assembled CFs in SiOx of 200 × 200 nm2 on the SHJ solar cell are directly observed via current-atomic force microscopy. Low series resistance of 2.2 Ω cm2 for the SHJ solar cell with SiOx is formed by the self-assembled CFs. In addition, high efficiency up to 20.24 % is achieved by the SHJ solar cell with CFs in SiOx without an additional patterning process. We thereby expect that the proposed technology will provide a tipping point from which a revolution in the solar cell industry can ensue.

Two‐wavelength excitation–driven robust operation of green up‐conversion emission in Er3+‐doped oxyfluoride glass–ceramic

AbstractEfficient optical modulation enables a significant improvement of optical conversion efficiency and regulation of optical response rate, showing great potential for optoelectronics applications. However, the weak interaction between photons poses a strong obstacle for manipulating photon–photon interactivity. Here, upon simultaneous excitation of 850 and 1550 nm, a fast–slow optical modulation of green up‐conversion (UC) luminescence in oxyfluoride glass ceramics containing NaYF4:Er3+ nanocrystals can be achieved. Compared with the sum of luminescence intensity excited by the two single‐wavelengths, green UC luminescence excited by simultaneous two‐wavelength presents an obvious increase by approximate six times. Interestingly, the response rate of green UC luminescence relies on the pump strategy of two‐wavelength excitation, showing as high as two times of the fast–slow response difference. The fast–slow optical modulation of green UC luminescence under two‐wavelength excitation is promising for emerging applications in all‐optical switching.

Defect Passivation by a Sulfur‐Containing Lewis Base for Efficient Printable Mesoscopic Perovskite Solar Cells

In the rapid development of perovskite solar cells (PSCs), additive engineering has played a significant role for perovskite crystallization and passivation. The high density of defects at perovskite grain boundaries in the mesoporous scaffold leads to severe nonradiative recombination, which results in severe voltage loss. Herein, a sulfur‐containing Lewis base 2‐(methylthio)ethylamine hydrochloride (MTEACl) is applied in the perovskite precursor solution for printable mesoscopic PSCs with triple‐mesoscopic layer structure. Due to the strong electron donating ability of sulfur, the MTEACl can strongly interact with Pb2+, which can effectively passivate the defects of the perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

(Invited) Design of Ceramic Fuel Electrode for Solid Oxide Cells for Direct Oxidation of Hydrocarbon Fuels and for Direct CO2 Electrolysis

Large scale consumption of fossil fuels has led to the rapid increase in the atmospheric CO2 concentration, resulting in very adverse environmental concerns and frequent natural disasters. There is a grand challenge to improve conversion efficiency of fossil fuels and mitigate CO2 emmissions for terrestial applications. To enable long-term manned space exploration, there are critical needs in recycling CO2 to oxygen for life support and in situ generation of propellants using CO2 feedstock for ascent vehicles. Solid oxide cells (SOCs) have a great promise for energy conversion and storage for both terrestrial applications and space explorations. In the fuel cell mode, SOCs can convert chemical energy to electrical energy with high efficiency and fuel flexibility. In the electrolysis mode, SOCs can efficiently utilize CO2 as feedstock for chemical synthesis. The conventional Ni-based fuel electrode is vulnerable to deactivation by carbon build-up (coking) from direct oxidation of hydrocarbon fuels or for direct electrolysis of CO2, and suffers volume instability on redox cycling. This talk will report novel heterogeneous functional materials as SOC fuel electrodes that possess a combined property of good coking resistance and redox cyclability, enabling SOCs to be operated on hydrocarbon fuels for electricity generation in the fuel cell mode and for direct CO2 electrolysis for fuel synthesis in the electrolysis mode.The general philosophy to design novel SOC fuel electrodes is to develop ceramic materials that are redox-stable, possess mixed ionic and electronic mixed conductivity, and have catalytic activities for fuel oxidation and CO2 splitting reaction. Different types of ceramic fuel electrode materials have been explored and characterized as SOC fuel electrodes. The phase formation, redox-stability, electrical conductivity, electrochemical performance, and tolerance to coking and redox-cycling have been systematically evaluated. By judicious design of ceramic-based heterogeneous functional materials, high performance redox-flexible ceramic fuel electrodes can be achieved for direct oxidation of hydrocarbon fuels and for direct CO2 electrolysis. Acknowledgements Financial support from the U.S. Department of Energy (DE-EE0009427), National Science Foundation (DMR–1832809) and NASA EPSCoR (Grant # 80NSSC20M0233) is greatly appreciated.

(Keynote) New Materials and Spectroscopies for Colloidal Quantum Dot Solar Cells

Colloidal quantum dots (CQDs) are an attractive third-generation material for photovoltaics due to their solution-processability, lightweight and flexible nature, and bandgap tunability, allowing them to be used as infrared materials for multi-junction solar cells. Here, we describe several methods for building new lead sulfide-based CQD materials and thin films for improving efficiencies in both single-junction and multi-junction solar cells.First, we demonstrate that the power conversion efficiency in single-junction PbS CQD solar cells is limited in part by the performance of the hole transport layer (HTL), traditionally made from ethanedithiol-passivated lead sulfide CQDs, due to the sub-optimal carrier mobility and doping density in this material. We use sulfur doping of the HTL, as well as incorporation of 2D transition metal dichalcogenide nanoflakes to address these issues and demonstrate absolute power conversion efficiency improvements of greater than 1% in single-junction devices.Next, we demonstrate a micrometer-resolution 2D characterization method with millimeter-scale field of view for assessing CQD solar cell film quality and uniformity. Our instrument simultaneously collects photoluminescence spectra, photocurrent transients, and photovoltage transients. We use this high-resolution morphology mapping to quantify the distribution and strength of the local optoelectronic property variations in CQD solar cells due to film defects, physical damage, and contaminants across nearly the entire test device area, and the extent to which these variations account for overall performance losses. We also use the massive data sets produced by this method to train machine learning models that take as input simple illuminated current-voltage measurements and output complex underlying materials parameters, greatly simplifying the characterization process for optoelectronic devices.Finally, we use artificial photonic band engineering as a method for achieving spectral selectivity in absorbing PbS CQD thin films for applications in multi-junction photovoltaics. We show that a structured periodic CQD thin film is able to maintain a photonic band structure, including the existence of a reduced photonic density of states, in the presence of weak material absorption, enabling modification of the absorption, transmission, and reflection spectra. We use a machine learning-based inverse design process to generate CQD thin film photonic structures with targeted absorption, transmission, and reflection spectra for multi-junction photovoltaics and narrow bandwidth photodetectors.

Hydrophobic long alkyl chain organic cations induced 2D/3D heterojunction for efficient and stable perovskite solar cells

Designing post-formed two-dimensional (2D) perovskite on the surface of three-dimensional (3D) perovskite with matched energy levels and high stability is crucial for improving the performance and stability of perovskite solar cells (PSCs). Herein, a long alkyl chain dodecylammonium bromide (DABr) was applied to react with excessive lead iodide (PbI2) on the grain boundary of metal halide perovskite preferentially, forming DA2PbI4 (n = 1) to constitute a clear 2D/3D heterojunction. The existence of heterojunction increases the intensity of the built-in electric field of the device to enhance carrier separation and extraction, and the amino group of dodecylammonium cation passivates defects, which jointly contribute to the improvement of the power conversion efficiency (PCE) from 20.35 to 21.81%. The long alkyl chain endows the 2D perovskite with good hydrophobic properties, improving the humidity and thermal stability of the device. The unencapsulated device can maintain 64% of its initial efficiency after 1065 h storage in ambient air.

48-Pulse Voltage-Source Converter Based on Three-Level Neutral Point Clamp Converters for Solar Photovoltaic Plant

The demand for high-power converters for use in large-scale solar photovoltaic (PV) plants increases as the plant size continues to grow. The multipulse voltage-source converter (VSC) configurations are the viable option for high-power solar PV converter applications because they improve conversion efficiency due to low switching losses and allow direct integration with a medium-voltage (MV) grid. In this article, a 48-pulse VSC based on the fundamental frequency switching (FFS) three-level neutral point clamp (NPC) converter with a start–delta transformer configuration is used for large-scale solar PV plant application. It is also used as a PV-static synchronous compensator (STATCOM) to provide the required reactive power support to the grid to regulate the voltage. The solar PV plant configuration for a 100-MW capacity is modeled in MATLAB and implemented in the real-time OPAL-RT platform to verify its design and controls. The harmonics, static, and dynamic performances are demonstrated in detail.

Enhancement of catalytic converter performance to reduce cold start emissions with thermal energy storage – An experimental study

A “Thermal Energy Storage” (TES) system can assist in solving the cold start emission problem associated with the catalytic converter. “Phase change materials” (PCMs) can be used in the TES system to absorb heat from the exhaust gases, liquefy it and store it as latent heat. This makes it possible to store the exhaust heat during the engine running conditions and to release it on the catalyst substrate during the off-engine and low temperature start. A catalytic converter is integrated with a TES unit with Mg70Zn24.9Al5.1 as PCM having melting point in range of 310 °C & 157 kJ/kg as heat of fusion. This paper presents Experimental investigation of Catalytic Converter for exhaust temperature, conversion efficiency with and without TES unit. The investigation includes the heat storage and retention time during engine operation. Test cycle of 150 min with each load were run including idle events in between at 2000 rpm for different load conditions. Results showcased maximum average conversion efficiency improvement for 60 %, 53 % and 30 % for HC, NOx and CO respectively at No load condition during cold start. Heat Retention time was found higher for high loads, 100 % & 75 % load temperature was observed to remain above 100 0C for nearly 350 min.

Inhibiting the Growth of 1D Intermediates in Quasi‐2D Ruddlesden−Popper Perovskites

AbstractQuasi‐2D perovskite solar cells have recently emerged as a highly prospective and inexpensive solution for sustainable energy due to their intrinsic optoelectronic properties and stability. The qualities of these promising quasi‐2D perovskite cells are generally affected by different intermediates derived from the precursor solution during film fabrication processing. However, efficient solutions to inhibit intermediates remain insufficient to date. Here, an effective strategy is prsented to inhibit the growth of 1D solvate intermediate during the fabricating process of quasi‐2D perovskite films by introducing a guanidinium thiocyanate (GUASCN) inhibitor. Theoretical calculations reveal that the SCN− anions spontaneously replace the iodide ions in the inorganic framework [PbI6]3− and induce the decomposition of the solvate intermediate. The resulted perovskite solar cells exhibit a significant improvement in power conversion efficiency (PCE), benefiting from the reduced trap‐state density and enhanced carrier mobilities. The unencapsulated devices retain 91% and 95% of the original PCEs under 45 ± 10% humidity in air or under continuous light irradiation at 100 mW cm−2 and 45 °C in a nitrogen atmosphere for 1000 h. Particularly, devices without electron‐transporting layers maintain 85% of the peak PCE under maximum power point tracking at 45 °C for 1000 h.

High-brightness and high-efficiency diode laser module based on double wavelength division multiplexing external cavities.

In this Letter, a new, to the best of our knowledge, external cavity structure based on double wavelength division multiplexing external cavities is proposed and demonstrated. The electro-optical conversion efficiency is improved and the brightness of the spectral beam combining diode lasers is enhanced. One wavelength division multiplexing external cavity is placed on the rear-side of the laser emitters to provide the strong optical feedback for wavelength locking and the other wavelength division multiplexing external cavity is placed on the front-side of laser emitters to combine three emitter beams to one beam. A maximum output power of up to 7.5 W is obtained and the brightness of the laser diode is 100 MW cm-2 sr-1 with an electro-optical conversion efficiency of 46.5%. Compared with a standard cavity for spectral beam combining, the use of double wavelength division multiplexing external cavities results in an electro-optical conversion efficiency improvement of 6.5%. The whole structure provides a new technology to achieve high-brightness and high electro-optical conversion efficiency for a laser diode source.

Suppressing Nickel Oxide/Perovskite Interface Redox Reaction and Defects for Highly Performed and Stable Inverted Perovskite Solar Cells.

The inorganic hole transport layer of nickel oxide (NiOx ) has shown highly efficient, low-cost, and scalable in perovskite photovoltaics. However, redox reactions at the interface between NiOx and perovskites limit their commercialization. In this study, ABABr (4-(2-Aminoethyl) benzoic acid bromide) between the NiOx and different perovskite layers to address the issues has been introduced. How the ABABr interacts with NiOx and perovskites is experimentally and theoretically investigated. These results show that the ABABr molecule chemically reacts with the NiOx via electrostatic attraction on one side, whereas on the other side, it forms a strong hydrogen bond via the NH3 + group with perovskites layers, thus directly diminishing the redox reaction between the NiOx and perovskites layers and passivating the layer surfaces. Additionally, the ABABr interface modification leads to significant improvements in perovskite film morphology, crystallization, and band alignment. The perovskites solar cells (PSCs) based on an ABABr interface modification show power conversion efficiency (PCE) improvement by over 13% and maintain over 90% of its PCE after continuous operation at maximum power point for over 500 h. The work not only contributes to the development of novel interlayers for stable PSCs but also to the understanding of how to prevent interface redox reactions.

Efficient hole extraction with Eu3+-doped CsPbBr3 QD interface modification for HTL-free CH3NH3PbI3:Na perovskite solar cells

Hole transport layer free perovskite solar cells (HTL-Free PSCs) have attracted extensive attention due to their advantages of simple structure and low cost. However, due to the serious energy level mismatch caused by the direct contact between the perovskite layer and the opposite electrode, the space for improving the efficiency of HTL-Free PSCs is greatly limited. We use Eu3+ doped CsPbBr3 quantum dots (QD) to modify the interface between MAPbI3:Na layer and C electrode, and study its effect on the surface defect passivation, interface energy level arrangement and carrier transport behavior in the device. It was found that compared with the interfacial modification of CsPbBr3 QD alone, the interfacial modification of CsPbBr3:Eu QD could effectively solve the problem of energy level mismatch in HTL-Free PSCs, resulting in a remarkable improvement of conversion efficiency from 9.01 % to 12.95 %. Furthermore, electron beam induced current (EBIC) was used to prove that CsPbBr3:Eu QD interface modification significantly improved the hole collection ability. This provides an experimental basis and theoretical guidance for the optimization of the efficiency of other types of transport layer free photovoltaic devices.

CuBiSe2 Quantum Dots as Ecofriendly Photosensitizers for Solar Cells

Cu-based ternary chalcogenides have shown high promise as low-cost ecofriendly alternatives to heavy-metal based photosensitizers. The successive ionic layer adsorption and reaction (SILAR) processed CuBiSe2 quantum dots possess an optimal bandgap, appealing photoresponsivity (excellent absorption coefficient of (10)5 cm–1), and photostability. Because of these advantageous properties, they have been investigated as photoabsorber materials for solar cells in this work for the first time. Use of such nontoxic and nonscarce materials, paired with low-temperature solution processing can address both concerns of environmental regulation and fabrication costs. The performance of the prototype solar cell developed has been satisfactory as a new emerging material (power conversion efficiency (PCE) of 2%) unlike the reported CuBiS2 showing a PCE of 0.68%. A further increase in efficiency was observed with the formation of a heterostructure CuBiSe2/CuBiS2 that exhibits a type-1 heterostructure and enables improvement in power conversion efficiency up to 2.6%. CuBiS2 acts as a passivation layer (reducing surface defects and recombination losses) and also as an absorber, facilitating confinement and longer lifetime of charge careers. A detailed investigation of these Cu based selenium quantum dots and the insights provided into their electronic structure and dynamics in this work would significantly influence the future research of these materials into other optoelectronic applications.

Thermal and energy benefits of rooftop photovoltaic panels in a semi-arid city during an extreme heatwave event

Rooftop photovoltaic panels (RPVPs) implementation is one of the effective strategies to mitigate urban heat island and relieve urban energy demand with renewable energy resources, which is in need, especially during extreme heatwave events. However, the effects of RPVPs on cooling the urban thermal environment and saving energy have not been fully investigated in terms of RPVPs coverage (CV) and conversion efficiency (CE). To address this question, this study conducted a numerical evaluation of RPVPs on the thermal environment, cooling energy consumption (EC) in buildings, and electricity production (EP) during an extreme heatwave event in a semi-arid Chinese city using the WRF model coupled with building effects parameterization and building energy model. Simulations of twelve scenarios with four CVs and three CEs were conducted. The results indicated that RPVPs implementation could generally lower the 2-m air temperature, due to RPVPs’ higher effective albedo and higher emissivity. An increase in RPVPs CV and CE resulted in stronger cooling effects and larger cooling areas, where the RPVPs with a CV of 100 % and a CE of 0.3 could lower the 2-m air temperature by 0.4 – 0.7 °C, and significantly contributed to a decrease of cooling EC by 14.74 %. The EP could offset and even exceed the cooling EC, with the EP/EC reaching 182.61 %, 135.77 %, and 123.37 % in 100 % coverage (CE = 0.3), 75 % coverage (CE = 0.3) and 100 % coverage (CE = 0.2) scenarios, respectively, indicating that RPVPs could potentially generate enough electricity to compensate cooling EC in semi-arid cities. Our findings have practical implications for the RPVPs implementation and the necessity of improving conversion efficiency for better thermal and energy benefits.