Abstract
For kesterite copper zinc tin sulfide/selenide (CZTSSe) solar cells to enter the market, in addition to efficiency improvements, the technological capability to produce flexible and ...large-area modules with homogeneous properties is necessary. Here, we report a greater than 10% efficiency for a cell area of approximately 0.5 cm
2
and a greater than 8% efficiency for a cell area larger than 2 cm
2
of certified flexible CZTSSe solar cells. By designing a thin and multi-layered precursor structure, the formation of defects and defect clusters, particularly tin-related donor defects, is controlled, and the open circuit voltage value is enhanced. Using statistical analysis, we verify that the cell-to-cell and within-cell uniformity characteristics are improved. This study reports the highest efficiency so far for flexible CZTSSe solar cells with small and large areas. These results also present methods for improving the efficiency and enlarging the cell area.
Improving the efficiency of kesterite (Cu2ZnSn(S,Se)4; CZTSSe) solar cells requires understanding the effects of Na doping. This paper investigates these effects by applying a NaF layer at various ...positions within precursors. The NaF position is important because Na produces Na‐related defects in the absorber and suppresses the formation of intrinsic defects. By investigating precursors with various NaF positions, the sulfo‐selenization mechanism and the characteristics of defect formation are confirmed. Applying a NaF layer onto a Zn layer in a CZTSSe precursor limits Zn diffusion and suppresses Cu‐Zn alloy formation, thus changing the sulfo‐selenization mechanism. In addition, the surface NaF layer provides reactive Se and S to the absorber layer by generating Na2Sex and Na2Sx liquid phases during sulfo‐selenization, thus limiting the incorporation of Na into the absorber and reducing the Na effects. Efficiency values of 11.16% and 11.19% are obtained for a flexible CZTSSe solar cell by applying NaF between the Zn layer and back contact and between the Cu and Sn layers, respectively. This study presents methods for doping with alkali metals and improving the efficiency of photovoltaics.
Applying the NaF layer on a Zn layer in a CZTSSe precursor limits the diffusion of Zn and suppresses the formation of a Cu‐Zn alloy. An efficiency of 11.19% is obtained for the flexible CZTSSe solar cell by applying the NaF between the Cu and Sn layers.
A long-range wide area network (LoRaWAN) adapts the ALOHA network concept for channel access, resulting in packet collisions caused by intra- and inter-spreading factor (SF) interference. This leads ...to a high packet loss ratio. In LoRaWAN, each end device (ED) increments the SF after every two consecutive failed retransmissions, thus forcing the EDs to use a high SF. When numerous EDs switch to the highest SF, the network loses its advantage of orthogonality. Thus, the collision probability of the ED packets increases drastically. In this study, we propose two SF allocation schemes to enhance the packet success ratio by lowering the impact of interference. The first scheme, called the channel-adaptive SF recovery algorithm, increments or decrements the SF based on the retransmission of the ED packets, indicating the channel status in the network. The second approach allocates SF to EDs based on ED sensitivity during the initial deployment. These schemes are validated through extensive simulations by considering the channel interference in both confirmed and unconfirmed modes of LoRaWAN. Through simulation results, we show that the SFs have been adaptively applied to each ED, and the proposed schemes enhance the packet success delivery ratio as compared to the typical SF allocation schemes.
2D transition metal carbides and nitrides, namely MXenes, are normally synthesized in acidic solutions and are delaminated in basic solutions. This results in versatile materials with unique ...physical/chemical properties suitable for various practical applications. However, solution‐based chemical treatments can affect the chemical structures of MXenes, which accelerates the oxidation reactions and degrades their intrinsic properties. Here, long‐term stable Ti3C2Tx dispersion in deep eutectic solvents (DESs) that resisted oxidation degradation for up to 28 weeks is demonstrated. As an anti‐oxidative dispersion medium, DESs helped prevent oxidation of Ti3C2Tx layers due to hydrogen bond accepting and donating molecules passivated surface of the Ti3C2Tx. In addition, DES molecules in bulk solution can also be hydrated in the presence of water, which stabilizes reactive oxygen by forming stable DES‐water cluster. Therefore, the use of DESs enhanced the delamination of the Ti3C2Tx nanosheets, while preventing oxidation of the nanosheets in solution and even in their dried state. As a result, thick and thin films of Ti3C2Tx fabricated using DESs exhibited stable sheet resistance in comparison with pristine‐Ti3C2Tx. In addition, Ti3C2Tx dispersed in DESs can be applied as electrodes for electrochemical capacitors, in which they showed higher chemical stability and better performance than pristine Ti3C2Tx.
In this article, it is found that polarized deep eutectic solvent (DES) molecules can also act as an effective intercalant to delaminate MXene. Moreover, the hydrogen bond accepting and donating molecules in DESs, which have strong interactions with the oxygen functional groups and unsaturated Ti vacancies in the defect sites of Ti3C2Tx not only have the superb ability to disperse Ti3C2Tx sheets, but also prevent oxidation in both the solution and dried phase.
The suitable materials, metal nitrides, are a promising class of electrocatalyst materials for a highly efficient oxygen evolution reaction (OER) because they exhibit superior intrinsic conductivity ...and have higher sustainability than oxide-based materials. To our knowledge, for the first time, we report a designable synthesis of three-dimensional (3D) and mesoporous Co
3
N@amorphous N-doped carbon (AN-C) nanocubes (NCs) with well-controlled open-framework structures via monodispersed Co
3
Co(CN)
6
2
Prussian blue analogue (PBA) NC precursors using
in situ
nitridation and calcination processes. Co
3
N@AN-C NCs (2 h) demonstrate better OER activity with a remarkably low Tafel plot (69.6 mV·dec
−1
), low overpotential of 280 mV at a current density of 10 mA·cm
−2
. Additionally, excellent cycling stability in alkaline electrolytes was exhibited without morphological changes and voltage elevations, superior to most reported hierarchical structures of transition-metal nitride particles. The presented strategy for synergy effects of metal-organic frameworks (MOFs)-derived transition-metal nitrides-carbon hybrid nanostructures provides prospects for developing high-performance and advanced electrocatalyst materials.
Aspergilli known as black- and white-koji molds which are used for awamori, shochu, makgeolli and other food and beverage fermentations, are reported in the literature as A. luchuensis, A. awamori, ...A. kawachii, or A. acidus. In order to elucidate the taxonomic position of these species, available ex-type cultures were compared based on morphology and molecular characters. A. luchuensis, A. kawachii and A. acidus showed the same banding patterns in RAPD, and the three species had the same rDNA-ITS, β-tubulin and calmodulin sequences and these differed from those of the closely related A. niger and A. tubingensis. Morphologically, the three species are not significantly different from each other or from A. niger and A. tubingensis. It is concluded that A. luchuensis, A. kawachii and A. acidus are the same species, and A. luchuensis is selected as the correct name based on priority. Strains of A. awamori which are stored in National Research Institute of Brewing in Japan, represent A. niger (n = 14) and A. luchuensis (n = 6). The neotype of A. awamori (CBS 557.65 = NRRL 4948) does not originate from awamori fermentation and it is shown to be identical with the unknown taxon Aspergillus welwitschiae. Extrolite analysis of strains of A. luchuensis showed that they do not produce mycotoxins and therefore can be considered safe for food and beverage fermentations. A. luchuensis is also frequently isolated from meju and nuruk in Korea and Puerh tea in China and the species is probably common in the fermentation environment of East Asia. A re-description of A. luchuensis is provided because the incomplete data in the original literature.
A long-range wide area network (LoRaWAN) is one of the leading communication technologies for Internet of Things (IoT) applications. In order to fulfill the IoT-enabled application requirements, ...LoRaWAN employs an adaptive data rate (ADR) mechanism at both the end device (ED) and the network server (NS). NS-managed ADR aims to offer a reliable and battery-efficient resource to EDs by managing the spreading factor (SF) and transmit power (TP). However, such management is severely affected by the lack of agility in adapting to the variable channel conditions. Thus, several hours or even days may be required to converge at a level of stable and energy-efficient communication. Therefore, we propose two NS-managed ADRs, a Gaussian filter-based ADR (G-ADR) and an exponential moving average-based ADR (EMA-ADR). Both of the proposed schemes operate as a low-pass filter to resist rapid changes in the signal-to-noise ratio of received packets at the NS. The proposed methods aim to allocate the best SF and TP to both static and mobile EDs by seeking to reduce the convergence period in the confirmed mode of LoRaWAN. Based on the simulation results, we show that the G-ADR and EMA-ADR schemes reduce the convergence period in a static scenario by 16% and 68%, and in a mobility scenario by 17% and 81%, respectively, as compared to typical ADR. Moreover, we show that the proposed schemes are successful in reducing the energy consumption and enhancing the packet success ratio.
Planar CH3NH3PbI3 perovskite solar cells with constant 17.2% average power conversion efficiency irrespective of the scan rate are described. These properties are attributed to the formation of a ...pure CH3 NH3 PbI3 thin film by the introduction of a HI solution. Thereby, charge‐injection/separation efficiency, charge‐collection efficiency, diffusion coefficient, carrier lifetime, and traps are improved.
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