查看更多>>摘要：Perovskite solar cells (PSCs) show great promise for scalable application owing to the advantages of high conversion efficiency and solution processable fabrication. However, the material cost and device stability greatly hinder the development of PSC technology. Counter electrodes, as one of the indispensable components in PSCs, play critical roles in charge collection and device protection. However, the commonly used noble metals (Ag or Au) are unaffordable for the scalable application of PSCs, and the interfacial instability caused by metal corrosion has significantly threatened the reliability of PSCs. Here we provide a comprehensive review of the development of counter electrodes in the aspects of materials, interfaces and device stability. Firstly, the fundamental understanding of the roles and limitations of counter electrodes are summarized, including the basic requirements and influencing factors for counter electrodes. Moreover, different degradation mechanisms and various interfacial characterization methods have been discussed. Furthermore, recent development of alternative counter electrodes and their photovoltaic performance are reviewed. This review provides a comprehensive understanding of the fundamental material limitations and guides the design of robust and efficient counter electrodes for PSCs.
查看更多>>摘要：Monolayer molecular crystals (MMCs) have attracted worldwide research interest due to their unique properties toward their bulk counterparts. The lower contact resistance of MMCs over their bulk counterparts makes them ideal carriers for studying the intrinsic properties of organic semiconductors. Anisotropic charge transport is an important characteristic of organic single crystals and also one of the primary factors induced in device performance fluctuation; however, related studies based on MMCs are still rare. MMC materials with a weak charge transport anisotropic property would be urgently needed and is of great significance for realizing high performance device arrays with low device-to-device variation. The major difficulty regarding anisotropic charge transport study in MMCs lies in the non-destructive preparation of electrodes on MMCs. Here, by taking advantage of the varied adhesion forces between substrates/gold electrodes/polymer films, the prepatterned fan-shaped electrodes could be readily transferred to target MMCs for the anisotropy study. By this non-destructive dry transferring of top electrodes, anisotropic charge transport properties of typical 2,6-bis(4-hexylphenyl) anthracene (C6-DPA) and 1,4-bis((5′-hexyl-2,2′-bithiophen-5-yl)ethynyl)benzene (HTEB) MMCs were obtained with an anisotropic ratio of 1.15 and 2.15, respectively. The low anisotropic ratio of C6-DPA would facilitate the future applications in MMC OFET arrays without considering the influence of crystal orientation.
查看更多>>摘要：With the continuous development of science and technology, people have an urgent demand for wearable flexible sensors. Therefore, how to obtain high performance wearable sensors at low cost has become an urgent problem to be solved. In this work, a method for surface modification of sensors based on electron irradiation is proposed. Hydroxylated multi-walled carbon nanotube (hydroxylated MWCNT)/ecoflex composite flexible sensors were irradiated under the synergistic effect of 1 MeV electron irradiation and temperature to improve their performance. It is found that under the synergistic effect of low temperature, more defects and active functional groups were introduced into the irradiated sensor, and thus its sensitivity was higher. At the maximum strain, the gauge factor (GF) of the irradiated sensor was 3.7 times that of the original. And when the irradiation fluence was 1 × 1014 e cm−2, the response time and recovery time of the sensor were reduced by 57.1% and 75.0%, respectively. This synergistic modification method of electron irradiation and low temperature provides a new idea for obtaining wearable sensors with high performance.
查看更多>>摘要：Millimeter waves have recently spread to wireless communication and imaging fields. In particular, millimeter waves at 81, 94, and 140 GHz are essential from the viewpoint of practical applications. Herein we report an external magnetic field effect on the millimeter wave absorption of ε-GaxFe2−xO3 nanomagnets with x = 0.46 (1), 0.29 (2), and 0.19 (3) and ε-AlxFe2−xO3 nanomagnets with x = 0.47 (4), 0.23 (5), and 0.16 (6). Terahertz time-domain spectroscopy (THz-TDS) measurements show that these materials display a zero-field ferromagnetic resonance in the millimeter wave range of 76–144 GHz. The ferromagnetic resonance was measured by applying an external magnetic field (Hex) to the sample along the remnant magnetization parallelly or antiparallelly. Switching the Hex value between +3.5 kOe and −3.5 kOe shifts the resonance frequency by 8–12 GHz (e.g., 70 ↔ 81 GHz (1), 94 ↔ 106 GHz (4), and 139 ↔ 147 GHz (6)). For example, a millimeter wave switch effect on the absorption intensity appears by changing the Hex value due to the magnetic field–induced resonance frequency shift, i.e., from 2 to 11 dB at 81 GHz for 1. Theoretical calculations of the ferromagnetic resonance based on Landau–Lifshitz–Gilbert theory reproduce the magnetic field–induced switching.
查看更多>>摘要：Ceramic/polymer nanocomposites are promising materials for energy storage applications. The most common approach to optimize energy storage properties relies on combining a ceramic and a polymer having the highest possible dielectric permittivity and breakdown strength, respectively. It is also known that another significant factor is the aspect ratio of nanofillers where a higher aspect ratio gives rise to a higher effective dielectric permittivity of the composite. There is thus a duality between the dielectric permittivity of the ceramic and its aspect ratio that we propose to study in this paper. To achieve this, high-k nanocomposites were designed based on biodegradable polymer matrix polylactic acid (PLA) and different inorganic nanofillers having different shapes (spherical, rod and wire) and dielectric properties. The effects of the aspect ratio, core–shell structure, dielectric permittivity and volume fraction of the nanofillers on the dielectric and energy storage performances of PLA-based nanocomposites were assessed. An enhanced energy storage density and recovered energy density of 3.63 and 1.80 J cm−3, respectively, were obtained in nanocomposites based on rod-like fillers. We discussed, from a theoretical model, that, below the percolation threshold, the obtained properties resulted from a compromise between both the dielectric permittivity and the aspect ratio of the ceramic. This investigation provides an exciting opportunity to advance our knowledge of ceramic/polymer nanocomposites for energy storage applications.
Yang Dong-ChunEglitis Roberts I.Yi Zhi-JunLiu Chun-Sheng...
10页
查看更多>>摘要：A novel two-dimensional (2D) carbon allotrope, named C2mm-graphyne, is predicted with the aid of the first-principles calculations. Its lattice dynamic and thermodynamic stabilities have been confirmed by evaluating its phonon dispersion relation and the trajectory from the ab initio molecular dynamics (AIMD) simulation at 1000 K. The unique network consists of sp–sp2 hybridized carbons. This 2D carbon allotrope possesses a direct quasi-particle (QP) band gap of 3.06 eV at the Γ point, which is close to the value of rutile. Significantly, some of its extended structures containing B and N dopants possess direct or quasi-direct QP band gaps in the range of 1.37–2.42 eV, which are falling into the visible light region. More exciting, their band arrangements just meet the requirements of photocatalytic water splitting. Furthermore, the HER and the OER are clearly discussed.
Gielen SamGómez Virginia CuestaBrebels SonnyQuill Tyler James...
7页
查看更多>>摘要：Natural porphyrins play a key role in a range of vital functions such as oxygen transport in the bloodstream and the conversion of light to chemical energy in plants. Likewise, synthetic porphyrin derivatives can be used to detect light and convert it into an electrical current in photodiodes. The versatility of porphyrinoid chemistry allows to extend the absorptivity (and hence detectivity) to the near-infrared while maintaining good solubility, suitable electrochemical properties, and compatibility with the electron acceptor molecules required to achieve a reasonable photocurrent. Here, our efforts on the design and synthesis of novel push–pull type meso-ethynyl-extended porphyrin compounds, both of A–D–A and D–A–D type (D = donor, A = acceptor), and their evaluation in prototype near-infrared organic photodetector devices are presented. The push–pull design with strongly electron-deficient building blocks results in absorption onsets up to 1200 nm, translating in an optical gap approaching 1 eV. Both A–D–A and D–A–D small molecules show good photodetector performance, with a peak specific detectivity near 2 × 1011 and 4 × 1011 Jones at 1000 nm (at −2 V bias), respectively. These values are among the best reported so far for small molecule based near-infrared organic photodetectors.
查看更多>>摘要：The power conversion efficiency (PCE) of organic solar cells (OSCs) is limited by the large non-radiation energy loss (ΔEnr), which is due to the low fluorescence quantum efficiency (φF) of typical organic/polymer photovoltaic materials. In this manuscript, we report a polymer acceptor containing a B ← N unit with strong red fluorescence. The polymer, PBN-16, is the alternating copolymer of an electron-withdrawing B ← N-bridged bipyridine (BNBP) unit and an electron-donating 2,5-dithienyl-1,4-dichlorophenylene unit. PBN-16 exhibits φF of as high as 11% in thin film because of the near-unity φF of BNBP itself and the twisted configuration of the polymer backbone. Its all-polymer photovoltaic device shows an open-circuit voltage (VOC) of 1.33 V and a PCE of 6.0% under AM 1.5G illumination as well as a VOC of 1.17 V and a PCE of 15.4% under indoor light-emitting diode illumination. Organic light-emitting diode devices using PBN-16 as an emissive material emit pure red light with a luminance efficiency of 0.99 cd A−1 and CIE coordinates of (0.67, 0.32). These results confirm that conjugated polymers or small molecules containing a B ← N unit are promising for organic solar cells with minimized energy loss and high PCE.
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