Organic–inorganic perovskites have made tremendous progress in recent years due to exceptional material properties such as high panchromatic absorption, charge carrier diffusion lengths, and a sharp ...optical band edge. The combination of high‐quality semiconductor performance with low‐cost deposition techniques seems to be a match made in heaven, creating great excitement far beyond academic ivory towers. This is particularly true for perovskite solar cells (PSCs) that have shown unprecedented gains in efficiency and stability over a time span of just five years. Now there are serious efforts for commercialization with the hope that PSCs can make a major impact in generating inexpensive, sustainable solar electricity. In this Review, we will focus on perovskite material properties as well as on devices from the atomic to the thin film level to highlight the remaining challenges and to anticipate the future developments of PSCs.
Perovskite solar cells have emerged as a low‐cost, thin‐film technology with unprecedented efficiency gains that challenge the quasi‐paradigm that high efficiency photovoltaics must come at high costs. Perovskites can be processed via inexpensive solution methods and have exceptional material properties that are comparable to established materials such as CdTe, GaAs, or Si. Remarkably, perovskites have a continuously tuneable band gap from 1 to 3 eV enabling applications far beyond photovoltaics.
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The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1% in a few years’ time. At this stage of their development, the key issues concern how to achieve further ...improvements in efficiency and long-term stability. We review recent developments in the quest to improve the current state of the art. Because photocurrents are near the theoretical maximum, our focus is on efforts to increase open-circuit voltage by means of improving charge-selective contacts and charge carrier lifetimes in perovskites via processes such as ion tailoring. The challenges associated with long-term perovskite solar cell device stability include the role of testing protocols, ionic movement affecting performance metrics over extended periods of time, and determination of the best ways to counteract degradation mechanisms.
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Grain boundaries (GBs) play an important role in most polycrystalline solar cells. In perovskite solar cells, the research community is just starting to understand their effects on performance and ...long‐term durability. In this essay, three important questions are explored: Do GBs affect: 1) recombination and thus open‐circuit voltage? Not dramatically, if at all; 2) current–voltage hysteresis? Most studies show that hysteresis is dominated by defects at GBs; and 3) long‐term durability? Yes, GBs definitely help increase the rate of perovskite degradation. In this essay, the latest reports are summarized and the authors' perspective on this very important subject is given.
Grain boundaries (GBs) play an important role in most polycrystalline solar cells. In this essay, three important questions are explored: Do GBs affect: 1) recombination and thus open‐circuit voltage? Not dramatically, if at all; 2) current–voltage hysteresis? Most studies show that hysteresis is dominated by defects at GBs; and 3) long‐term durability? Yes, GBs definitely help increase the rate of perovskite degradation.
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Lead halide perovskites have attracted considerable interest as photoabsorbers in PV-applications over the last few years. The most studied perovskite material achieving high photovoltaic performance ...has been methyl ammonium lead iodide, CH sub(3)NH sub(3)PbI sub(3 ). Recently the highest solar cell efficiencies have, however, been achieved with mixed perovskites where iodide and methyl ammonium partially have been replaced by bromide and formamidinium. In this work, the mixed perovskites were explored in a systematic way by manufacturing devices where both iodide and methyl ammonium were gradually replaced by bromide and formamidinium. The absorption and the emission behavior as well as the crystallographic properties were explored for the perovskites in this compositional space. The band gaps as well as the crystallographic structures were extracted. Small changes in the composition of the perovskite were found to have a large impact on the properties of the materials and the device performance. In the investigated compositional space, cell efficiencies, for example, vary from a few percent up to 20.7%. From the perspective of applications, exchanging iodide with bromide is especially interesting as it allows tuning of the band gap from 1.5 to 2.3 eV. This is highly beneficial for tandem applications, and an empirical expression for the band gap as a function of composition was determined. Exchanging a small amount of iodide with bromide is found to be highly beneficial, whereas a larger amount of bromide in the perovskite was found to cause intense sub band gap photoemission with detrimental results for the device performance. This could be caused by the formation of a small amount of an iodide rich phase with a lower band gap, even though such a phase was not observed in diffraction experiments. This shows that stabilizing the mixed perovskites will be an important task in order to get the bromide rich perovskites, which has a higher band gap, to reach the same high performance obtained with the best compositions.
Metal halide perovskite absorber materials are about to emerge as a high-efficiency photovoltaic technology. At the same time, they are suitable for high-throughput manufacturing characterized by a ...low energy input and abundant low-cost materials. However, a further optimization of their efficiency, stability and reliability demands a more detailed optoelectronic characterization and understanding of losses including their evolution with time. In this work, we analyze perovskite solar cells with different architectures (planar, mesoporous, HTL-free), employing temperature dependent measurements (current–voltage, light intensity, electroluminescence) of the ideality factor to identify dominating recombination processes that limit the open-circuit voltage (
V
oc
). We find that in thoroughly-optimized, high-
V
oc
(≈1.2 V) devices recombination prevails through defects in the perovskite. On the other hand, irreversible degradation at elevated temperature is caused by the introduction of broad tail states originating from an external source (
e.g.
metal electrode). Light-soaking is another effect decreasing performance, though reversibly. Based on FTPS measurements, this degradation is attributed to the generation of surface defects becoming a new source of non-radiative recombination. We conclude that improving long-term stability needs to focus on adjacent layers, whereas a further optimization of efficiency of top-performing devices requires understanding of the defect physics of the nanocrystalline perovskite absorber. Finally, our work provides guidelines for the design of further dedicated studies to correctly interpret the diode ideality factor and decrease recombination losses.
Multimodal Assessment of Parkinson's Disease: A Deep Learning Approach Vasquez-Correa, Juan Camilo; Arias-Vergara, Tomas; Orozco-Arroyave, J. R. ...
IEEE journal of biomedical and health informatics,
2019-July, 2019-07-00, 2019-7-00, 20190701, Volume:
23, Issue:
4
Journal Article
Peer reviewed
Open access
Parkinson's disease is a neurodegenerative disorder characterized by a variety of motor symptoms. Particularly, difficulties to start/stop movements have been observed in patients. From a ...technical/diagnostic point of view, these movement changes can be assessed by modeling the transitions between voiced and unvoiced segments in speech, the movement when the patient starts or stops a new stroke in handwriting, or the movement when the patient starts or stops the walking process. This study proposes a methodology to model such difficulties to start or to stop movements considering information from speech, handwriting, and gait. We used those transitions to train convolutional neural networks to classify patients and healthy subjects. The neurological state of the patients was also evaluated according to different stages of the disease (initial, intermediate, and advanced). In addition, we evaluated the robustness of the proposed approach when considering speech signals in three different languages: Spanish, German, and Czech. According to the results, the fusion of information from the three modalities is highly accurate to classify patients and healthy subjects, and it shows to be suitable to assess the neurological state of the patients in several stages of the disease. We also aimed to interpret the feature maps obtained from the deep learning architectures with respect to the presence or absence of the disease and the neurological state of the patients. As far as we know, this is one of the first works that considers multimodal information to assess Parkinson's disease following a deep learning approach.
Organometal halide perovskite solar cells have demonstrated high conversion efficiency but poor long-term stability against ultraviolet irradiation and water. We show that rapid light-induced ...free-radical polymerization at ambient temperature produces multifunctional fluorinated photopolymer coatings that confer luminescent and easy-cleaning features on the front side of the devices, while concurrently forming a strongly hydrophobic barrier toward environmental moisture on the back contact side. The luminescent photopolymers re-emit ultraviolet light in the visible range, boosting perovskite solar cells efficiency to nearly 19% under standard illumination. Coated devices reproducibly retain their full functional performance during prolonged operation, even after a series of severe aging tests carried out for more than 6 months.
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Despite the fact that perovskite solar cells (PSCs) have a strong potential as a next‐generation photovoltaic technology due to continuous efficiency improvements and the tunable properties, some ...important obstacles remain before industrialization is feasible. For example, the selection of low‐cost or easy‐to‐prepare materials is essential for back‐contacts and hole‐transporting layers. Likewise, the choice of conductive substrates, the identification of large‐scale manufacturing techniques as well as the development of appropriate aging protocols are key objectives currently under investigation by the international scientific community. This Review analyses the above aspects and highlights the critical points that currently limit the industrial production of PSCs and what strategies are emerging to make these solar cells the leaders in the photovoltaic field.
From laboratories to production plants: Large‐scale manufacturing techniques and cheaper materials can push perovskite solar cells towards commercialization soon. This Review analyses the limits and challenges of this photovoltaic technology that is emerging as a leader in the solar energy scene.
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The so-called index of economic complexity, based on nations’ exports, was initially proposed as an alternative to traditional macroeconomic metrics just as the scientific productivity of countries ...which has also been deemed as a better predictor of economic growth. Adequate scrutiny to the relationship between these two factors, however, remains little explored. This paper aims to examine the relationship between economic complexity and scientific production while identifying which areas of knowledge hold to this relationship best. By applying panel data techniques to a sample of 91 countries between 2003 and 2014, we found that scientific productivity in basic sciences and engineering has a significant positive effect on the economic complexity of countries. This relationship, however, only remains stable for high-income countries, where university-industry-government capabilities interact to stimulate and generate innovation and strategies for economic growth of firms.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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