active layers
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2022 ◽  
Author(s):  
Pablo B. Pinto ◽  
Kimberly C. T. da Cruz ◽  
Eufrânio Nunes da Silva Júnior ◽  
Luiz Alberto Cury

Abstract Dropcast films produced from blends solutions of phenazine 1,2,3-triazole molecules in very low concentrations in a 1,3-Bis (N-carbazolyl) benzene (mCP) matrix were investigated at room temperature. The mCP acts as an optically inert matrix, having no influence on the emission properties of the guest molecules. Its conductive properties also ensure that blend films, within a completely organic character, are formed as truly active layers. The fluorescent and phosphorescent emission properties of the phenazine molecules, depending on their conformational states, allowed relatively intense emissions in blue, green, red and also in white, without the need to mix different materials. Although the results of absorption of the blended films have shown no characteristics of the guest molecules, due to their relatively low concentrations, the excitation of them occurs directly by the incident laser beam. The steady-state spectroscopy for the monomer and dimer singlet fluorescence states of respective blue and green emissions of the films were investigated. The analysis of their temporal decays were done using a different approach based on the Exponentially Modified Gaussian (EMG) function. The phosphorescent emissions of the triplet steady-states, occurring in the orange or in the red wavelength regions, were observed to be correlated, respectively, to the formation of guest monomers or to the guest dimers singlet states.


Author(s):  
Thomas Chaney ◽  
Maged A. Abdelsamie ◽  
Hongping Yan ◽  
Sebastian Schneider ◽  
Ismail Alperen Ayhan ◽  
...  

Improving the morphology of bulk heterojunction active layers remains a primary challenge for organic photovoltaics (OPVs), and much research has been devoted to achieving this through modifying OPV casting solutions...


Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 84
Author(s):  
Anna Maria Ferretti ◽  
Marianna Diterlizzi ◽  
William Porzio ◽  
Umberto Giovanella ◽  
Lucia Ganzer ◽  
...  

The use of water-processable nanoparticles (WPNPs) is an emerging strategy for the processing of organic semiconducting materials into aqueous medium, dramatically reducing the use of chlorinated solvents and enabling the control of the nanomorphology in OPV active layers. We studied amphiphilic rod-coil block copolymers (BCPs) with a different chemical structure and length of the hydrophilic coil blocks. Using the BCPs blended with a fullerene acceptor material, we fabricated NP-OPV devices with a sustainable approach. The goal of this work is to clarify how the morphology of the nanodomains of the two active materials is addressed by the hydrophilic coil molecular structures, and in turn how the design of the materials affects the device performances. Exploiting a peculiar application of TEM, EFTEM microscopy on WPNPs, with the contribution of AFM and spectroscopic techniques, we correlate the coil structure with the device performances, demonstrating the pivotal influence of the chemical design over material properties. BCP5, bearing a coil block of five repeating units of 4-vinilpyridine (4VP), leads to working devices with efficiency comparable to the solution-processed ones for the multiple PCBM-rich cores morphology displayed by the blend WPNPs. Otherwise, BCP2 and BCP15, with 2 and 15 repeating units of 4VP, respectively, show a single large PCBM-rich core; the insertion of styrene units into the coil block of BCP100 is detrimental for the device efficiency, even if it produces an intermixed structure.


Author(s):  
Zolile Wiseman Dlamini ◽  
Sreedevi Vallabhapurapu ◽  
Olamide Abiodun Daramola ◽  
Potlaki Foster Tseki ◽  
Rui Werner Macedo Krause ◽  
...  

In this paper, we report on the resistive switching (RS) and conduction mechanisms in devices consisting of CdTe/CdSe core–shell quantum dots embedded chitosan composites active layer. Two devices with active layers sandwiched between (1) Al and Ag, and (2) ITO and Ag electrodes were studied. Both devices exhibited bipolar memory behavior with [Formula: see text] V and [Formula: see text][Formula: see text]V, for the Al-based device, while [Formula: see text] V and [Formula: see text][Formula: see text]V were observed for the ITO-based device, enabling both devices to be operated at low powers. However, the switching mechanisms of both devices were different, i.e., RS in Al device was attributed to conductive bridge mechanism, while space-charge-limited driven conduction filament attributed the switching mechanism of the ITO device. Additionally, the Al-based device showed long retention ([Formula: see text][Formula: see text]s) and a reasonable large ([Formula: see text]) ON/OFF ratio. Additionally, for this device, we also observed sweeping cycle-induced reversal of voltage polarity of the [Formula: see text] and [Formula: see text]. In contrast, we observed that increasing sweeping cycles resulted in an exponential decrease of the OFF-state resistance of the ITO-based device.


Author(s):  
Elisabeth Ramm ◽  
Chunyan Liu ◽  
Per Ambus ◽  
Klaus Butterbach-Bahl ◽  
Bin Hu ◽  
...  

Abstract The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system of permafrost ecosystems we show that gross ammonification and nitrification rates in active layers were of similar magnitude and showed a similar dependence on soil organic carbon (SOC) and total nitrogen (TN) concentrations as observed in temperate and tropical systems. Moreover, high protein depolymerization rates and only marginal effects of C:N stoichiometry on gross N turnover provided little evidence for N limitation. Instead, the rather short period when soils are not frozen is the single main factor limiting N turnover. High gross rates of mineral N cycling are thus facilitated by released protection of organic matter in active layers with nitrification gaining particular importance in N-rich soils, such as organic soils without vegetation. Our finding that permafrost-affected soils show vigorous N cycling activity is confirmed by the rich functional microbial community which can be found both in active and permafrost layers. The high rates of N cycling and soil N availability are supported by biological N fixation, while atmospheric N deposition in the Arctic still is marginal except for fire-affected areas. In line with high soil mineral N production, recent plant physiological research indicates a higher importance of mineral plant N nutrition than previously thought. Our synthesis shows that mineral N production and turnover rates in active layers of permafrost-affected soils do not generally differ from those observed in temperate or tropical soils. We therefore suggest to adjust the permafrost N cycle paradigm, assigning a generally important role to mineral N cycling. This new paradigm suggests larger permafrost N climate feedbacks than assumed previously.


2021 ◽  
Vol 8 (12) ◽  
pp. 125001
Author(s):  
Bilal Zaarour

Abstract Enhancing the electrical outputs of energy harvesters is a great demand for researchers in recent years. In this work, the effect of the plasticizer treatment (Tetrahydrofuran [THF]) on the β phase content (F[β]) of electrospun polyvinylidene fluoride (PVDF) fiber webs which are used as active layers to directly make a piezoelectric nanogenerator (PENG) is demonstrated. The results showed that during the plasticizer treatment, the F(β) of the web increases when the initial length of the web (L0) equals the distance between the two ends of the solid support (L) which the web fixed on it, whereas the F(β) decreases when L < L0 resulting in the formation of crimped fibers. Furthermore, the electrical outputs of the PENG based on the pristine web, and treated webs at different lengths are investigated. We believe this work can be used as a good reference for enhancing the electrical outputs of the PENG by enhancing the F (β) of PVDF nanofiber webs using a plasticizer treatment.


2021 ◽  
Vol 19 (1) ◽  
pp. 016201
Author(s):  
Natalia V Kryzhanovskaya ◽  
Fedor I Zubov ◽  
Eduard I Moiseev ◽  
Anna S Dragunova ◽  
Konstantin A Ivanov ◽  
...  

Abstract Characteristics of a compact III–V optocoupler heterogeneously integrated on a silicon substrate and formed by a 31 µm in diameter microdisk (MD) laser with a closely-spaced 50 µm × 200 µm waveguide photodetector are presented. Both optoelectronic devices were fabricated from the epitaxial heterostroctructures with InGaAs/GaAs quantum well-dot layers. The measured dark current density of the photodetector was as low as 2.1 µA cm−2. The maximum link efficiency determined as the ratio of the photodiode photocurrent increment to the increment of the microlaser bias current was 1%–1.4%. The developed heterogeneous integration of III–V devices to silicon boards by Au-Au thermocompression bonding is useful for avoiding the difficulties associated with III–V epitaxial growth on Si and facilitates integration of several devices with different active layers and waveguides. The application of MD lasers with their lateral light output is promising for simplifying requirements for optical loss at III–V/Si interface.


2021 ◽  
Author(s):  
Joo-Hong Lee ◽  
June-Mo Yang ◽  
So-Yeon Kim ◽  
Sungpyo Baek ◽  
Sungjoo Lee ◽  
...  

Abstract Organic-inorganic or inorganic metal halide materials have emerged as a promising candidate for a resistive switching material owing to its capability to achieve low operating voltage, high on/off ratio and multi-level switching. However, the high switching variation, limited endurance and poor reproducibility of the device hinder practical use of the memristors. Here, we report a universal approach to relieve the issues by using a van der Waals metal contacts (vdWC). By transferring the pre-deposited metal contact onto the active layers, an intact junction between the metal halide and contact layer is formed without unintended damage in the active layer that has been caused by a conventional physical deposition process of the metal contacts. Compared to the thermally evaporated metal contact (EVC), the vdWC did not degrade optoelectronic quality of the underlying layer to enable memristors with reduced switching variation, significantly enhanced endurance and reproducibility relative to those based on the EVC. By adopting various metal halide active layers, versatile utility of the vdWC is demonstrated. Thus, this vdWC approach can be a useful platform technology for development of high-performance and reliable memristors for future computing.


2021 ◽  
Author(s):  
Yanming Sun ◽  
Yunhao Cai ◽  
Qian Li ◽  
Guanyu Lu ◽  
Hwa Sook Ryu ◽  
...  

Abstract The development of high-performance organic solar cells (OSCs) with thick active layers is of crucial importance for the roll-to-roll printing of large-area solar panels. Unfortunately, increasing the active layer thickness usually results in a significant reduction in efficiency. Herein, we fabricated efficient thick-film OSCs with an active layer consisting of one polymer donor and two non-fullerene acceptors. The two acceptors were found to possess enlarged exciton diffusion length in the mixed phase, which is beneficial to exciton generation and dissociation. Additionally, layer by layer approach was employed to optimize the vertical phase separation. Benefiting from the synergetic effects of enlarged exciton diffusion length and graded vertical phase separation, a record high efficiency of 17.31% (certified value of 16.9%) was obtained for the 300 nm-thick OSC, with an unprecedented short-circuit current density of 28.36 mA cm−2, and a high fill factor of 73.0%. Moreover, the device with an active layer thickness of 500 nm also shows a record efficiency of 15.21%. This work provides new insights into the fabrication of high-efficiency OSCs with thick active layers.


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