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"Xue, Jingjing"
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Prospects for metal halide perovskite-based tandem solar cells
Over the past decade, metal halide perovskite photovoltaics have been a major focus of research, with single-junction perovskite solar cells evolving from an initial power conversion efficiency of 3.8% to reach 25.5%. The broad bandgap tunability of perovskites makes them versatile candidates as the subcell in a tandem photovoltaics architecture. Stacking photovoltaic absorbers with cascaded bandgaps in a multi-junction device can potentially overcome the Shockley–Queisser efficiency limit of 33.7% for single-junction solar cells. There is now intense activity in developing tandem solar cells that pair perovskite with either itself or with a variety of mature photovoltaic technologies such as silicon and Cu(In,Ga)(S,Se)2 (CIGS). In this review, we survey recent advances in the field and discuss its outlook.A discussion of the evolution, present status and future outlook for tandem solar cells employing perovskite materials.
Journal Article
A wireless network-enabled online english subjective assignment evaluation system using micro cloud environment
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.
Journal Article
The surface of halide perovskites from nano to bulk
The surface of a semiconductor often has a key role in determining its properties. For metal halide perovskites, understanding the surface features and their impact on the materials and devices is becoming increasingly important. At length scales down to the nanoscale regime, surface features become dominant in regulating the properties of perovskite materials, owing to the high surface-to-volume ratio. For perovskite bulk films in the micrometre range, defects and structural disorder readily form at the surface and affect device performance. Through concerted efforts to optimize processing techniques, high-quality perovskite thin films can now be fabricated with monolayer-like polycrystalline grains or even single crystals. Surface defects therefore remain the major obstacle to progress, pushing surface studies to the forefront of perovskite research. In this Review, we summarize and assess recent advances in the understanding of perovskite surfaces and surface strategies towards improving perovskite materials and the efficiency and stability of perovskite devices.
The surface features of metal halide perovskites have a crucial role in determining their properties. This Review introduces the recent advances in the understanding of perovskite surfaces and surveys the surface strategies towards improving the properties of perovskite materials and the performance of perovskite optoelectronic devices.
Journal Article
Oriented nucleation in formamidinium perovskite for photovoltaics
The black phase of formamidinium lead iodide (FAPbI
3
) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization
1
–
4
. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI
3
(refs.
5
,
6
). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm
2
, has achieved an impressive certified aperture efficiency of 21.4%.
The black phase of formamidinium lead iodide perovskite is used to make highly efficient solar cells, and a technique to improve its purity and stability by controlling crystal nucleation could make them even better.
Journal Article
Constructive molecular configurations for surface-defect passivation of perovskite photovoltaics
Surface trap–mediated nonradiative charge recombination is a major limit to achieving high-efficiency metal-halide perovskite photovoltaics. The ionic character of perovskite lattice has enabled molecular defect passivation approaches through interaction between functional groups and defects. However, a lack of in-depth understanding of how the molecular configuration influences the passivation effectiveness is a challenge to rational molecule design. Here, the chemical environment of a functional group that is activated for defect passivation was systematically investigated with theophylline, caffeine, and theobromine. When N-H and C=O were in an optimal configuration in the molecule, hydrogen-bond formation between N-H and I (iodine) assisted the primary C=O binding with the antisite Pb (lead) defect to maximize surface-defect binding. A stabilized power conversion efficiency of 22.6% of photovoltaic device was demonstrated with theophylline treatment.
Journal Article
Self-cleaning Spiro-OMeTAD via multimetal doping for perovskite photovoltaics
Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are usually achieved using organic spiro-OMeTAD. However, conventional doping with hygroscopic dopants (LiTFSI and tBP) leads to compromised device stability. We introduce a synergistic mixed doping strategy that utilizes a combination of metal-TFSI dopants—LiTFSI, KTFSI, NaTFSI, Ca(TFSI)
2
, and Mg(TFSI)
2
—to enhance doping efficiency while effectively removing hygroscopic contaminants from the Spiro-OMeTAD solution. This approach achieves PCEs exceeding 25% and significantly improves stability under harsh environmental conditions. Notably, Ca(TFSI)
2
and Mg(TFSI)
2
facilitate enhanced oxidative doping, while NaTFSI promotes interstitial doping in the bulk perovskite. Additionally, KTFSI serves as a catalytic agent, lowering the reaction energy barrier for the other dopants, thereby accelerating spiro-OMeTAD ion radical production. These findings underscore the potential of synergistic doping in optimizing the performance and longevity of photovoltaic devices.
Conventional doping with hygroscopic dopants could lead to compromised device stability in perovskite solar cells. Here, the authors employ a combination of metal salt dopants to enhance doping efficiency and remove hygroscopic contaminants, realizing efficiency of over 25% for stable devices.
Journal Article
Strain regulates the photovoltaic performance of thick-film perovskites
Perovskite photovoltaics, typically based on a solution-processed perovskite layer with a film thickness of a few hundred nanometres, have emerged as a leading thin-film photovoltaic technology. Nevertheless, many critical issues pose challenges to its commercialization progress, including industrial compatibility, stability, scalability and reliability. A thicker perovskite film on a scale of micrometres could mitigate these issues. However, the efficiencies of thick-film perovskite cells lag behind those with nanometre film thickness. With the mechanism remaining elusive, the community has long been under the impression that the limiting factor lies in the short carrier lifetime as a result of defects. Here, by constructing a perovskite system with extraordinarily long carrier lifetime, we rule out the restrictions of carrier lifetime on the device performance. Through this, we unveil the critical role of the ignored lattice strain in thick films. Our results provide insights into the factors limiting the performance of thick-film perovskite devices.
The power conversion efficiencies of thick-film perovskite solar cells lag behind those with nanometre film thickness. Here, the authors rule out the restrictions of carrier lifetime on device performance and reveal the critical role of lattice strain in micron-scale thick perovskite films.
Journal Article
Cooperative Control of Multiple Dynamic Positioning Vessels with Input Saturation Based on Finite-time Disturbance Observer
This paper presents a new cooperative control strategy for dynamic positioning of multiple surface vessels subject to unknown time-varying environmental disturbances and input saturation. The vessels are assumed interconnected through a directed topology rather than bidirectional. Two control objectives are considered in this paper. The first one is to make these vessels track desired positions and headings, and the other control objective is to hold the desired formation. For these purposes, we propose a cooperative control which consists of finite-time disturbance observer, auxiliary dynamic system and dynamic surface control technique. A nonlinear finite-time observer is developed to estimate unknown time-varying disturbance. To tackle the input saturation problem, an auxiliary dynamic system is constructed. It is also proved that all signals in the closed-loop control system converge to a small neighborhood of equilibrium state via Lyapunov analysis. Simulation results are given to validate the effectiveness of the proposed control strategy.
Journal Article
The diagnostic value of two-dimensional ultrasound Su-RADS combined with shear wave elastography for benign and malignant lesions of the gastric wall
Objective
This study explored the value of stomach ultrasound reporting and data system (Su-RADS) and two-dimensional shear wave elastography (2D-SWE) in the diagnosis of benign and malignant lesions of the gastric wall, evaluating the feasibility of combining the two methods for the diagnosis of gastric wall lesions.
Methods
113 patients with gastric wall lesions were examined after oral gastric ultrasound contrast agent, and the grades of the gastric wall lesions were classified according to Su-RADS. Moreover, 2D-SWE was performed to measure the E value of the lesions. ROC curves were constructed to evaluate the diagnostic efficacy of Su-RADS, 2D-SWE and their combination for gastric wall lesions.
Results
The cutoff values for Emean and Emax were 8.01 kPa and 11.08 kPa, respectively. The sensitivity and specificity of 2D-SWE were 70.59%, 93.67% and 85.69%, 88.61%, respectively. The diagnostic sensitivity and specificity of Su-RADS were 91.18% and 82.28%, respectively. The AUC of combination of two methods was 0.951, which was greater than that of Su-RADS (0.940) or 2D-SWE alone (0.853, 0.903), and the sensitivity and specificity were 82.35% and 94.94%. The sensitivity and specificity of the combination of the two methods for the diagnosis of malignant gastric lesions were 82.35% and 94.94%, respectively. The AUC was 0.951, and the Youden index was 0.8064. The DeLong test was used to determine the AUC between the combination of two methods and 2D-SWE was
P
< 0.05.
Conclusion
Compared with Su-RADS or 2D-SWE alone, the combination of the two methods is more effective at diagnosing of gastric wall.And improved the specificity in the diagnosis of gastric wall lesions.
Journal Article