Wireless networks have various applications in different sectors of life, such as industries, entertainment, agriculture, education, etc. However, its role cannot be ignored in the education sector, ...particularly in online teaching content sharing and online assignment submission systems. Wireless networks can offer real-time progress tracking and insights into student involvement and participation, especially in group assignments, and also help teachers identify the students who need more supervision and assistance. Keeping the significance of wireless networks in consideration, in this study, we investigated the usage of wireless networks for online subjective English assignments. We find out that wireless network-based online assignments provide prompt feedback; however, they fall short when compared to offline assignments in terms of depth, coherence, reflection, and review. To solve this problem, we proposed a convolutional neural network (CNN)-based solution for better text recognition that can successfully extract and identify English assignments from uploaded photographs. To be more precise, we developed an object-based under-representation (OUR) CNN model for the classification or labeling of input data, i.e., an English assignment. These techniques allow us to develop a system that automatically rectify English assignments by combining data matching and information extraction approaches. For the deployment of the proposed system, we used a wireless remote micro-cloud platform, which allow us to create an efficient and comprehensive online learning environment for both teachers and students, which is more scalable and flexible in terms of adjusting new students, teachers, and teaching contents. The experimental results show that the proposed OUR-CNN and information extraction techniques, along with the usage of wireless networks and micro-cloud platforms, assist both the students in improving their learning skills and the teachers in identifying the weak students and helping them to increase their learning capabilities.
In this review, the factors influencing the power conversion efficiency (PCE) of perovskite solar cells (PSCs) is emphasized. The PCE of PSCs has remarkably increased from 3.8% to 23.7%, but on the ...other hand, poor stability is one of the main facets that creates a huge barrier in the commercialization of PSCs. Herein, a concise overview of the current efforts to enhance the stability of PSCs is provided; moreover, the degradation causes and mechanisms are summarized. The strategies to improve device stability are portrayed in terms of structural effects, a photoactive layer, hole‐ and electron‐transporting layers, electrode materials, and device encapsulation. Last but not least, the economic feasibility of PSCs is also vividly discussed.
In parallel with the tremendous progress in the efficiency of perovskite solar cells, research on the issue of instability has attracted enormous attention. In this review, the strategies to enhance the stability from the perspectives of the device structure, the photoactive layer, hole‐ and electron‐transporting layers, electrode materials, and device encapsulation are portrayed.
Metal halide perovskites have been in the limelight in recent years due to their enormous potential for use in optoelectronic devices, owing to their unique combination of properties, such as high ...absorption coefficient, long charge‐carrier diffusion lengths, and high defect tolerance. Perovskite‐based solar cells and light‐emitting diodes (LEDs) have achieved remarkable breakthroughs in a comparatively short amount of time. As of writing, a certified power conversion efficiency of 22.7% and an external quantum efficiency of over 10% have been achieved for perovskite solar cells and LEDs, respectively. Interfaces and defects have a critical influence on the properties and operational stability of metal halide perovskite optoelectronic devices. Therefore, interface and defect engineering are crucial to control the behavior of the charge carriers and to grow high quality, defect‐free perovskite crystals. Herein, a comprehensive review of various strategies that attempt to modify the interfacial characteristics, control the crystal growth, and understand the defect physics in metal halide perovskites, for both solar cell and LED applications, is presented. Lastly, based on the latest advances and breakthroughs, perspectives and possible directions forward in a bid to transcend what has already been achieved in this vast field of metal halide perovskite optoelectronic devices are discussed.
The latest breakthroughs in interface and defect engineering as applied to metal halide perovskite solar cells and light‐emitting diodes (LEDs) are reviewed in order to shed light on their necessity and importance in tuning the optoelectronic properties of devices in an attempt to realize the best‐performing solar cells and LEDs.
The performance of organic photovoltaics (OPVs) has rapidly improved over the past years. Recent work in material design has primarily focused on developing near‐infrared nonfullerene acceptors with ...broadening absorption that pair with commercialized donor polymers; in the meanwhile, the influence of the morphology of the blend film and the energy level alignment on the efficiency of charge separation needs to be synthetically considered. Herein, the selection rule of the donor/acceptor blend is demonstrated by rationally considering the molecular interaction and energy level alignment, and highly efficient OPV devices using both‐fluorinated or both‐nonfluorinated donor/acceptor blends are realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, the devices based on the PBDB‐T‐F/Y1‐4F blend and PBDB‐T‐F/Y6 exhibit champion power conversion efficiencies as high as 14.8% and 15.9%, respectively.
By rationally tuning the molecular interaction and energy level alignments of the donors and acceptors, when both donor and acceptor are fluorinated or both are not fluorinated, high‐performance organic photovoltaics can be realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, devices based on the PBDB‐T‐F/Y1‐4F blend and PBDB‐T‐F/Y6 exhibit power conversion efficiencies as high as 14.8% and 15.9%, respectively.
The ideal charge transport materials should exhibit a proper energy level, high carrier mobility, sufficient conductivity, and excellent charge extraction ability. Here, a novel electron transport ...material was designed and synthesized by using a simple and facile solvothermal method, which is composed of the core–shell ZnO@SnO2 nanoparticles. Thanks to the good match between the energy level of the SnO2 shell and the high electron mobility of the core ZnO nanoparticles, the PCE of inorganic perovskite solar cells has reached 14.35% (J SC: 16.45 mA cm–2, V OC: 1.11 V, FF: 79%), acting core–shell ZnO@SnO2 nanoparticles as the electron transfer layer. The core–shell ZnO@SnO2 nanoparticles size is 8.1 nm with the SnO2 shell thickness of 3.4 nm, and the electron mobility is seven times more than SnO2 nanoparticles. Meanwhile, the uniform core–shell ZnO@SnO2 nanoparticles is extremely favorable to the growth of inorganic perovskite films. These preliminary results strongly suggest the great potential of this novel electron transfer material in high-efficiency perovskite solar cells.
Postfabrication surface treatment strategies have been instrumental to the stability and performance improvements of halide perovskite photovoltaics in recent years. However, a consensus ...understanding of the complex reconstruction processes occurring at the surface is still lacking. Here, we combined complementary surface-sensitive and depth-resolved techniques to investigate the mechanistic reconstruction of the perovskite surface at the microscale level. We observed a reconstruction toward a more PbI2-rich top surface induced by the commonly used solvent isopropyl alcohol (IPA). We discuss several implications of this reconstruction on the surface thermodynamics and energetics. Particularly, our observations suggest that IPA assists in the adsorption process of organic ammonium salts to the surface to enhance their defect passivation effects.
A graphene quantum dots (GQDs)–chitosan (CS) composite film was prepared via successive electrodeposition of GQDs and CS on the surface of a glassy carbon electrode (GCE). The strong interactions ...between GQDs and CS resulted in the formation of a regular and uniform film, which can be applied in the electrochemical chiral recognition of tryptophan (Trp) enantiomers. CS in the composite film provides a chiral microenvironment, meanwhile, GQDs can amplify the electrochemical signals and improve the recognition efficiency. Due to the synergetic effect of GQDs and CS, chiral recognition of Trp enantiomers is achieved successfully. Compared with previous reports utilizing GQDs in photoluminescent research, this work opens a new avenue for broadening the applications of GQDs in the electrochemically chiral sensors.
Chitosan provides a chiral microenvironment, meanwhile, graphene quantum dots can amplify the electrochemical signals. Due to the synergetic effect of chitosan and graphene quantum dots, chiral recognition of tryptophan enantiomers is achieved successfully. Display omitted
•GQDs–CS composite film was prepared via successive electrodeposition of GQDs and CS.•CS in the composite film provides a chiral microenvironment.•GQDs can amplify the electrochemical signals and improve the recognition efficiency.•Due to the synergetic effect of GQDs and CS, recognition of l- and d-Trp is achieved.•It opens a new avenue for broadening the applications of GQDs in chiral sensors.
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