bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Multi-Level Non-Volatile Memory in Au/Monolayer MoS2/Au Structures
Authors: Bhattacharjee Shubhadeep , Caruso Enrico , McEvoy Niall , Coileáain Cormac Ó , Ansari Lida , Nagle Roger , Cherkaoui Karim , Gity Farzan , Hurley P. K.
Published: May 2020

The wide range of electronic and optical properties exhibited by two dimensional semiconductors, and their variation physical thickness, opens up new possibilities to create ultra-short length transistors [1], steep-slope switches [2, 3], light detecting/emitting devices [4, 5] and chemical/physical sensors. Recently, it was demonstrated that monolayer 2D semiconductors can also display resistive switching [6]. In this work we demonstrate that a single layer of large area CVD-grown moly disulphide (MoS2) sandwiched between two metal electrodes can be tuned to exhibit multi-level non-volatile resistive memory, with resistance values separated by 5 orders of magnitude. The switching process is unipolar and thermochemically driven (TCM memory) requiring significant Joule heating in the RESET process. Temperature dependent electrical measurements will be presented which demonstrate the charge transport mechanism varies between the initial state (IS), the high resistive state (HRS) and low resistive state (LRS). The temperature dependent behavior of the SET, RESET process is consistent with the creation and passivation of sulfur vacancies in the MoS2 monolayer. Conductive AFM measurements confirm that the multi-filamentary resistive memory effects are inherent to a single crystalline MoS2 triangle and not necessarily dependent of grain boundaries. This work demonstrates that potential for 2 terminal, multi-state, resistive memories for next generation digital memory and neuromorphic applications.

[1] S. B. Desai et al., "MoS2 transistors with 1-nanometer gate lengths," Science, vol. 354, no. 6308, pp. 99-102, 2016.

[2] S. Bhattacharjee, K. L. Ganapathi, S. Mohan, and N. Bhat, "A sub-thermionic MoS2 FET with tunable transport," Applied Physics Letters, vol. 111, no. 16, p. 163501, 2017.

[3] D. Sarkar et al., "A subthermionic tunnel field-effect transistor with an atomically thin channel," Nature, vol. 526, no. 7571, p. 91, 2015.

[4] K. Roy et al., "Graphene–MoS 2 hybrid structures for multifunctional photoresponsive memory devices," Nature nanotechnology, vol. 8, no. 11, p. 826, 2013.

[5] X. Zhou et al., "2D Layered Material‐Based van der Waals Heterostructures for Optoelectronics," Advanced Functional Materials, vol. 28, no. 14, p. 1706587, 2018.

[6] R. Ge et al., "Atomristor: Nonvolatile Resistance Switching in Atomic Sheets of Transition Metal Dichalcogenides," Nano letters, vol. 18, no. 1, pp. 434-441, 2017.
Synthesis and Performance Evaluation of Exfoliated Graphene Nanoplatelet Hydrogels As Electrodes for Supercapacitors
Authors: Mypati Sreemannarayana , Sellathurai Andrew , Kontopoulou Marianna , Docoslis Aris , Barz Dominik P.J.
Published: May 2020

Graphene is an excellent material because of its high electrical conductivity, high surface area, and superior mechanical properties. Stable dispersions of graphene nanoplatelets (GNPs) can be only achieved in organic solvents while in polar solvents the GNPs tend to agglomerate. Therefore, covalent and non-covalent functionalization of the GNP, or the use of surfactants, is required to formulate stable dispersions. Unlike GNP, Graphene oxide (GO) can be readily dispersed in aqueous media because of the hydrophilic oxygen groups on the basal plane and edges. Consequently, GO has amphiphilic material characteristics like a surfactant, and we use it as a dispersing agent for GNP in aqueous solutions.

In this work, we formulate highly-concentrated aqueous GO/GNP dispersions (5 mg/ml to 25 mg/ml). The stability of these dispersions mainly depends on the pH, concentrations of GO/GNP and lateral dimensions of the flakes. Stable dispersions are used to synthesize graphene hydrogels which are usually made from reduced graphene oxide (rGO), which is considerably more expensive than GNP obtained from mechanical/thermal exfoliation. Graphene hydrogels are a self-assembled microporous structure that incorporate a liquid phase. The graphene hydrogel matrix has a very high surface area, along with high electronic conductivity, which makes it a very suitable material for supercapacitor applications. The graphene hydrogels that we prepare from GNP, containing a small fraction of GO, are characterized by scanning electron microscopy, electrical conductivity measurements, X-ray diffraction, and Raman spectroscopy. The results indicate that a minimum GO/GNP ratio of 0.1 is required to stabilize the GNP flakes. The three-dimensional self-assembly is promoted due to the reduction of GO. The GNP hydrogels have better mechanical stability compared to a conventional rGO hydrogel; a 50 mg freeze-dried sample can sustain a load of 200 g of weight. A flexible supercapacitor is prepared from the GNP hydrogels. In detail, the symmetrical electrodes are prepared by pressing a 1 mm thick slice of hydrogel onto a carbon cloth current collector and two of these electrodes are separated by a filter paper soaked in a 2 M H2SO4 electrolyte. The supercapacitor is characterized by cyclic voltammetry, electrical impedance spectroscopy as well as galvanostatic charge and discharge measurements. The specific capacitance obtained at 1 A/g is 187 F/g, which is around 30% higher than that of comparable supercapacitor made from rGO hydrogels. Additionally, the specific capacitance and the coulombic efficiency at 10 A/g remains at almost 100% of the initial values, even after 3000 cycles.

Figure 1
Fast Nondestructive Battery Diagnostics with MRI and Magnetometry: Detect State of Health, State of Charge, and Current Distributions
Authors: Jerschow Alexej , Benders Stefan , Mohammadi Mohaddese , Schumacher Bret , Hu Yinan , Iwata Geoffrey , Blanchard John , Wickenbrock Arne , Budker Dmitry
Published: May 2020

Rechargeable batteries are notoriously difficult to assess. We are presenting new battery assessment technology based on MRI and magnetometry techniques, which allow non-destructive scanning of rechargeable cells. The techniques are fast, can detect changes in the electrode chemistry that occur as the battery is charged and discharged, or sense a range of different defects at early stages. In particular, we can determine site-resolved state-of-charge (where charge is stored in the cell), current distributions, as well as tiny transient effects. The vision is to use a benchtop-type instrument, which could be deployed in a variety of ways. The aim is to improve safety and performance, help in predicting battery life, clarify failure modes, and aid in the development of next-generation cells. Both MRI and magnetometry provide complementary measurement modalities with their strengths and limitations. MRI allows sensitive state of charge determination in a localized manner, and magnetometry allows to detect extremely weak electrical currents, both DC and AC at the level of nA in principle. Both these techniques provide new opportunities for battery diagnostics and research and could help reducuing the development cycle for new batteries and determining obscure battery failure modes.

Figure 1
Complementary Ex Situ, in Situ and Operando Spectroscopy, Diffraction and Electrochemistryto Deconvolute Productive and Parasitic Processes within Batteries
Authors: Marschilok Amy C. , Takeuchi Esther S , Takeuchi Kenneth J
Published: May 2020

Conceptually, there are two related electrochemical storage redox mechanisms for materials: insertion where the host structure is largely maintained, and conversion there is a chemical transformation leading to a formation of one or more new phases. For some materials, each of these mechanisms may participate at different stages of the electrochemical redox process, where the kinetics for ion and electron transport can play a determinstic role regarding which process dominates at a particular state of (dis)charge. Parasitic side reactions can also make significant contributions to the function of the energy storage system, through formation of resistive interfaces and consumption of redox active material/s. Progress towards distinguishing insertion and conversion processes, and decovoluting productive and parasitic processes within batteries will be discussed. Specifically, insight gained from complementary ex situ, in situ, and operando spectroscopy, diffraction and electrochemistry studies will be highlighted in this presentation.
A Bispyridinylidene Anolyte for an All-Organic Redox Flow Battery
Authors: Alkhayri Fahad , Dyker C. Adam
Published: May 2020

Global warming associated with CO2 emissions caused by the excessive use of fossil fuels has become a worldwide concern. The use of renewable energy resources as an alternative power source can help reduce the amount of CO2 in air. Redox flow batteries (RFBs) have attracted a lot of attention recently as promising systems for energy storage from intermittent renewable resources and to allow integration with the power grid. Most RFBs are based on metallic active species in aqueous media, however there is a growing interest around the use of soluble organic redox couples in non-aqueous solvents to achieve higher energy density. Organic compounds with high redox potentials (catholyte) are readily available, but new organic compounds that undergo multi-electron redox processes at a low redox potential (anolyte) are needed to boost the energy density of RFBs. This presentation will outline efforts to demonstrate a new bispyridinylidene-based anolyte that undergoes a reversible two-electron oxidation (-1.69 V vs. ferrocene) and assess its applicability in a RFB. In addition to stability tests for the bispyridinylidene, an all-organic non-aqueous RFB employing 2,2,6,6-tetramethyl-1-piperidinyloxy and bispyridinylidene as cathodic and anodic active materials, respectively has been investigated.
An Artificial Interface (AI) to Open the Window for Aqueous Electrolytes
Authors: Olarte Marco , Menu Marie-Joelle , Simon Patrice , Gressier Marie , Taberna Pierre-Louis
Published: May 2020

Devices with high power density which can store energy with a fast rate charge-discharge, the supercapacitors are suitable in different applications where high power is needed. That because it stores charge by fast surface process, i.e. ion adsorption of an electrolyte into the electrochemical double layer at the electrode/electrolyte interface. Nevertheless, in order to extend their autonomy beyond few seconds, its energy density has to be increased. For this aspect, in recent years many teams around the world have set up different strategies as a combination of a carbon electrode with a faradic type electrode (battery electrode or pseudocapacitive) or through the development of new active materials, including the development of new electrolytes. The main significant achievements are more on the active material side. Even though some works have been successful in increasing the cell voltage, thanks to the use of new ionic liquids, they are still room for improvement regarding the increase of the cell voltage.

To address this point, we have targeted to obtain an aqueous-based high voltage supercapacitor. Our strategy consists in using an Artificial Interface (AI) by depositing an ionogel onto a carbon electrode, the AI is composed of an inorganic matrix and an ionic liquid, in order to form a passivation layer at the electrode/electrolyte interface; a better electrochemical and thermal stability of this interface is thus expected. The IA has got to be electronically insulating but ionic conductive, limiting or even preventing the transfer of electronic charge to the electrode / electrolyte interface.1,2

First things first, the study have been carried out on glassy carbon where AI has been deposited and the linear sweep voltammetry tests in an aqueous electrolyte based on EMI+ HSO4
- and H2SO4 indicate, in both cases, an increase in the potential window: the onset potential for water reduction is shifted toward more cathodic potentials. Going further, tests in the presence of a redox probe (Ferri-Ferro potassium cyanide) demonstrate the absence of electron transfer at the electrode/electrolyte interface. On the other hand, it appears, thanks to measurements carried out by electrochemical impedance spectroscopy, since within the IA is embedded EMI+ TFSI-, better ionic conduction is obtained when the electrolyte is made of EMI+ HSO4
-, sharing the same cation than the one of IA. As we will be showing, a better transference number is achieved for EMI+ cations than for H+ still further works are needed to improve the selectivity of the IA to improve its stability over cycling.

1. Z. H. Zhang et al., Sci. Rep., 8, 1–12 (2018).

2. M. D. Elola and J. Rodriguez, J. Phys. Chem. C, 123, 3622–3633 (2019).
Nanostructured Manganese Oxides for Energy Storage: Synthetic Control Leading to Improved Electrochemistry
Authors: Takeuchi Kenneth J , Takeuchi Esther S , Marschilok Amy C.
Published: May 2020

Manganese is desirable due to its high environmental abundance and low cost. Some manganese oxides (α-MnO2, Mn8O16) possess a tunneled structure comprised of one-dimensional 2 × 2 tunnels formed by corner and edge sharing manganese octahedral [MnO6] units which can be substituted in the central tunnel by a variety of cations of varying size, providing a robust framework for ion insertion and (de)insertion. Control of composition, crystallite size, and defect through scalable synthesis approaches will be described in this presentation. Impact of nanostructure and mesoscale electrode structure on capacity, rate capability, and capacity retention in lithium and beyond lithium batteries will be discussed. Specific improvements in capacity retention realized through targeted elemental substitution will be highlighted. Mechanistic differences in aqueous and non-aqueous battery systems will be described. The use of x-ray absorption spectroscopy to gain insight into mechanism and the evolution of local coordination environment in these systems will be reviewed.
Integration of Thermo-Electrochemical Conversion into Forced Convection Cooling
Authors: Ikeda Yutaka , Fukui Kazuki , Murakami Yoichi
Published: May 2020

In our present civilization, forced convection cooling is used in wide-ranging situations from cooling of microprocessors in data centers to that of power turbines and automobile engines. Active cooling is essential in such situations. However, active transfer of heat or thermal energy across a large temperature difference promptly destroys the free-energy component of the thermal energy called “exergy”. This issue has remained unaddressed despite widespread use of forced convection cooling. In this study, to partially recover presently lost exergy in such situations in the form of electric power, we integrate thermo-electrochemical conversion, which has been mostly studied for stationary conditions, into forced convection cooling. The proposed concept is graphically illustrated in Fig. 1.

To investigate this concept, we design a test cell (Fig. 2a) in which an electrolyte liquid is forced through a channel formed between two parallel electrodes (Fig. 2b) and the hot-side electrode simulates an object to be cooled. We use cobalt redox couple CoII/III(bpy)3(NTf2)2/3 (Fig. 2c) dissolved in an ionic liquid as the coolant (electrolyte) for this purpose.

Our experimental investigations show that the narrower interelectrode channels afford higher cooling and power generation performances. The mass transfer resistance is the most dominant type of resistance for all the conditions tested and the charge transfer kinetics is controlled by electrolyte viscosity. The dependence of the generated power on the flow rate is caused by the change in the diffusion coefficient of redox species with temperature. As an evaluation measure for such forced-flow thermo-electrochemical cells, the “gain”—defined as the ratio of the generated power to the hydrodynamic pumping work required to force the liquid through the cell—is introduced. The gain is found to be above unity in a certain flow rate region. This demonstrates that such a system can generate more electric power than the hydrodynamic pump work required to drive the liquid through the cell, supporting our concept to address aforementioned unresolved issue in the situations of forced-convection cooling.

Reference:

Ikeda, K. Fukui, and Y. Murakami, Phys. Chem. Chem. Phys., 2019, in press, DOI: 10.1039/c9cp05028k; arxiv.org/abs/1908.08646.

Figure 1
Effect of the Electron Transport Layer on the Photovoltaic Properties of Hybrid Organic Inorganic Perovskites Solar Cells: Cross-Section of Optics, Morphology, Composition and Quality
Authors: Demopoulos George P. , Yekani Rana , Yasin Amrita , Dagdeviren Omur , Dragomir Vlad , Leonelli Richard , Grutter Peter
Published: May 2020

Ever since their dawn in 2009 1, hybrid organic–inorganic perovskite materials have been experiencing an ever increase in research investment to finally emerge as a strong alternative for high power conversion efficiency (PCE) photovoltaic devices at low costs. One of the main challenges that is currently impeding the upscaling of these solar cells is the phenomenon of hysteresis on their j–V response that has been correlated with slow ion migration which, in turn, affects their photovoltaic properties. Although hysteresis has been described to some extent of detail, the precise role of the external contacts remains under debate. Furthermore, there has been a great deal of focus on materials and interface design while less attention has been given to optical aspects of these cells. Our work highlights the role of electron transport layer (ETL) of different compositions and synthesized through various routes on the hysteresis response of these systems. We show that there’s a clear correlation between thickness, morphology and composition of the ETL on the photovoltaic response these systems. To better elucidate such a response, we have utilized photoluminescence, electroluminescence, absorption and kelvin probe force microscopy to get a substantial grasp of the optoelectronic phenomena occurring at the interfaces in perovskite solar cells.

Acknowledgments: This research was supported by a Hydro-Quebec/NSERC CRD grant and the McGill Sustainability Systems Initiative (MSSI).

1- Kojima, A., Teshima, K., Shirai, Y. and Miyasaka, T., 2009. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American Chemical Society, 131(17), pp.6050-6051.
(Invited) Oxygen Reduction Reactivity at Fe- and Cu-Codoped Carbon Nanostructures
Authors: Yagi Ichizo , Fujibayashi Natsuki , Abe Daiki , Yasuda Satoshi , Kato Masaru
Published: May 2020

Polymer electrolyte fuel cells (PEFCs), which can efficiently convert hydrogen into electricity without using fossil fuels, are a promising energy conversion device. At the cathodes of PEFCs, oxygen reduction reaction (ORR) occurs via 4-electrons' and 4-protons' transfer. Due to its low reaction rate limiting the performance of PEFCs, the electrocatalysts are necessary and the platinum-based electrocatalysts for ORR are mainly used because of its highest electrocatalystic activity in the metals. Since platinum metal is expensive and rare, there is a need to develop non-platinum-based electricatalysts based on iron and/or copper with high ORR activity1,2,3,4).

A cytochrome c oxidase (CcO), which is a metalloenzyme and contains iron and copper metal ions, catalyzes the ORR efficiently to produce ATP in mitochondria5) and its activity is higher than that of artificial platinum-based electrocatalysts6). Metalloenzymes are not practical because of their stability, size, and difficulty to isolate and purify.

In this study, iron and copper co-doped carbon electrocatalysts, synthesized from the mixtures of Fe and/or Cu complexes and carbon nanotubes in heat treatment inspired by the CcO’s active center, were developed. Synthetic conditions of Fe : Cu metal ratios and heating temperatures were optimized. The ORR activity was evaluated by hydrodynamic voltammetry using a rotating ring disk electrode in 0.05 M sulfuric acid aqueous solution saturated with oxygen. The activity of Fe/Cu/CNT catalyst was compared with two catalysts: iron-doped carbon carbon catalyst (Fe/CNT) and copper-doped carbon catalyst (Cu/CNT). The Fe/Cu/CNT catalyst showed more positive onset potential for the oxygen reduction in acidic media than Fe/CNT and Cu/CNT, indicating that Fe/Cu/CNT is more active, and we figure out that the coexistence of iron and copper in CNTs contributes to the improvement of ORR activity.

References:

1. Kato et al., Chem. Lett.
45, 1213–1215 (2016).

2. Kato et al., ACS Appl. Energy Mater. 1, 2358–2364 (2018).

3. Chung et al., Science
357, 479–484 (2017).

4. Yasuda et al., Adv. Funct. Mater. 26, 738–744 (2016).

5. Sakamoto et al., PNAS
108, 12271–12276 (2011).

6. Kjaergaard et al., Inorg. Chem. 49, 3567–3572 (2010).
Functionalized Carbon Nanotubes for Lithium-Organic Batteries
Authors: Kamaleddine Hanine , Charrier Gaëlle , Jousselme Bruno , Cornut Renaud , Gutel Thibaut , Barchasz Céline , Campidelli Stephane
Published: May 2020

Lithium batteries are among the most promising systems for electrochemical energy storage. However, their capacity and cost-efficiency have to be improved for further applications.1 Lithium/organic batteries offer an interesting alternative to the classical Li-ion systems due to the low molecular weight of organic materials, their potential low cost and recyclability. However, two major roadblocks currently prevent the industrial development in these kind of batteries: (i) the progressive dissolution of the active material in the electrolyte, which hinders the cyclability of the devices and (ii) the electrical insulating nature of organic materials.2

Here, we develop a new positive electrode material avoiding the dissolution of the active material in the electrolyte upon cycling, by grafting new diazonium derivatives containing active groups onto multi-walled carbon nanotubes (MWNTs) at different ratios between the carbon nanotubes and the active material.3 The MWNTs insure a well distributed electronic conductivity inside the positive electrode and serve as a support for a covalent immobilization of the organic active species.

References

[1] Cheng, F., Liang, J., Tao, Z., and Chen, J. Adv. Mater, 2011, 23, 1695-1715.

[2] C. Barchasz, F. Mesguich, J. Dijon, J.-C. Leprêtre, S. Patoux and F. Alloin, J. Power Sources. 2012, 211, 19-26.

[3] G. Charrier, H. Kamaleddine, C. Barchasz, R. Cornut, B. Jousselme and S. Campidelli, ChemElectroChem. 2018, 5, 1732-1737.
Charge Transport and Transfer Mechanisms for Solid State Metal Complex Systems
Authors: Hamann Thomas
Published: May 2020

Recently there have been excited reports that copper-based molecular redox couples can be effective hole collection and transport materials when dissolved in liquid as well as in the solid state. The mechanism of charge transport in the solid state system is not understood, however, which inhibits further improvements or the development of design rules for intentionally made solid state DSSCs utilizing molecular redox complexes. In this talk, a change of diffusion mechanism for copper redox complexes will be presented during the solidification by an in-situ electrochemical analysis. The modified Dahms-Luff equation, which was partially substituted by the viscosity term, was used to evaluate the overall mechanism, and it was confirmed that the calculated self-exchange rate constant varies with phase and the viscosity-dependent value. Eventually, as the solidification progressed, the transport mechanism dominating was changed from ionic to electrical diffusion, which led to an increase in the apparent diffusion coefficient, indicating a high conductivity and a high self-exchange rate constant. However, in the case of cobalt complexes, which are often used in the liquid state, the transport mechanism continued to be dominated by ionic diffusion during solidification with a decrease in apparent diffusion and device performance. In addition to charge transport, the solidification affects rates of heterogeneous charge transfer and ultimately the performance in DSSCs, which will also be described. Finally, the results will be interpreted in design rules for metal complexes as solid state hole transport materials.
(Invited) Beta, Beta-Functionalized Push-Pull Opp-Dibenzoporphyrins As Sensitizers for Dye-Sensitized Solar Cells: The Role of the Phenylethynyl Bridge and the Tertiary Amine Push Group
Authors: Wang Hong , Hu Yi , Thomas Michael , Alsaleh Ajyal , D'Souza Francis
Published: May 2020

Significant progress has been made on dye-sensitized solar cells sensitized by push-pull porphyrins in recent years.1-3 An effective way to significantly enhance power conversion efficiencies of porphyrin dyes is through installation of push (electron-donating) and pull (electron-withdrawing) groups at porphyrin meso-positions.4-6 In this presentation, we present a different strategy to install push and pull groups at porphyrin b-positions. Three series of novel opp-dibenzoporphyrins were prepared using this strategy. Our studies show significant push-pull effects for these porphyrins.7 DFT calculations suggest that the inclusion of ethynylphenyl bridge between the donating group and the porphyrin core significantly segregate the frontier orbitals, which is a much-favored feature for sensitizers in DSSC. It has also been found that dimethylaminophenyl group cause dye decomposition on solar cells. To solve the dye degradation problem, porphyrin dyes with tertiary arylamine groups serving as the donor groups were prepared. Our studies show that tertiary arylamine groups are able to stabilize the dyes adsorbed on the solar cells. The electronic and optical properties of these p-extended porphyrins were measured using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, cyclic voltammetry and transient spectroscopy. Their photovoltaic performances were tested in dye-sensitized solar cells.

Reference

1. T. Higashino and H. Imahori, Dalton Trans., 2015, 44, 448-463.

2. M. Urbani, M. Gratzel, M. K. Nazeeruddin and T. Torres, Chem. Rev., 2014, 114, 12330-12396.

3. L. L. Li and E. W. Diau, Chem. Soc. Rev., 2013, 42, 291-304.

4. A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science, 2011, 334, 629-634.

5. S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. F. Curchod, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin and M. Gratzel, Nat. Chem., 2014, 6, 242-247.

6. G. Di Carlo, A. O. Biroli, F. Tessore, S. Caramori and M. Pizzotti, Coord. Chem. Rev., 2018, 358, 153-177.

7. Y. Hu, S. Yellappa, M. B. Thomas, R. G. W. Jinadasa, A. Matus, M. Shulman, F. D'Souza and H. Wang, Chem Asian J, 2017, 12,
(Invited) Charge Carrier Dynamics of Inorganic Perovskite Quantum Dots Showing Water Treatment Effect of Photoluminescence Efficiency
Authors: Furube Akihiro , Mori Koki , Chen Shih-Hsuan , Chen Liang-Yih
Published: May 2020

All-inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) exhibit a high photoluminescence quantum yield, and is attracting attention due to the increasing demand for optoelectronic devices such as solar cells and light-emitting diodes (LEDs). In this study, we prepared a solution of CsPbBr3 QD synthesized by hot injection method and performed femtosecond transient absorption spectroscopy. In particular, we investigated the change in transient absorption during the process of improving luminous efficiency by water treatment.

To study the luminescence increment mechanism, a two-layer structure of oleylamine (OAm) aqueous solution (in the lower part) and CsPbBr3 QD hexane solution (in the upper part) was made, and transient absorption measurement under 400 nm excitation was performed for 8 hours.

As time passed, the OAm and/or water molecules moved up to the upper QD surface, and the increase in the photoluminescence occurred. Previous experiments have shown that the emission quantum yield increases from about 30% to about 70%. In the measurement of transient absorption, transient bleaching was confirmed to grow little by little 2 hours after the preparation of the two-layer structure. The bleaching reached its maximum amplitude after 3 or 4 hours, and gradually decreased till 8 hours. Since the bleaching intensity is proportional to the number of excitons generated, it was found that the excitation efficiency was increased by the water treatment. Ultrafast exciton quenching probably by the QD surface seems to be the main reason of the low emission quantum yield before the water treatment.
Donor-Acceptor-Donor-Type Cyclopenta[2,1-b;3,4-b’]Dithiophene Derivatives As a New Class of Hole Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells
Authors: Abate Seid Yimer , Lin Yan-Duo , Chung Hsin-Cheng , Liau Kang-Ling , Chow Tahsin J. , Sun Shih-Sheng , Tao Yu-Tai
Published: May 2020

Three new donor-acceptor-donor-type (D-A-D) hole-transporting materials (HTMs), YC-1–YC-3, based on 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b’]dithiophene (DiCN-CPDT) core structure endowed with two arylamino-based units as peripheral groups were designed, synthesized and applied in perovskite solar cells (PSCs). Hole mobility, steady-state photoluminescence, thin-film surface morphology on top of perovskite layer, and photovoltaic performances for the YC series were systematically investigated and compared with that of Spiro-OMeTAD. It was found that YC-1 exhibited more efficient hole transport and extraction characteristics at the perovskite/HTM interface. Meanwhile, the film of YC-1 showed a homogeneous and dense capping layer coverage on perovskite layer without any pinholes, leading to the improvement of the fill factor and open circuit voltage. PSC device based on YC-1 as HTM exhibited a high power conversion efficiency (PCE) of 18.03%, which is comparable to that of the device based on the benchmark Spiro-OMeTAD (18.14%),1 and also a better long-term stability, with 85% of the initial efficiency retained after 500 hours storage under the condition of 30% relative humidity, presumably due to the hydrophobic nature of the material. This work demonstrates that the dicyanomethylene-CPDT-based derivatives are promising HTMs for efficient and stable PSCs.

Y. S. Lin, S. Y. Abate, K. W. Lai, C. W. Chu, Y. D. Lin, Y. T. Tao, & S. S Sun, ACS Appl. Mater. Interfaces,
2018,
10, 41439.

Figure 1
(Invited) Catalyst Design and Development for Highly Selective Photocatalytic Conversion of CO2 By H2o As an Electron Donor
Authors: Teramura Kentaro
Published: May 2020

The reduction in human-induced emissions of CO2 from automobiles, factories, power stations etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock to build a sustainable society. Linear CO2 molecules adsorbed on the surface of the solid bases are converted into unique structures, such as bicarbonate and carbonate species possessing lattice oxygen atoms. We believe that the process involves the capture and distortion of CO2 upon adsorption on a solid base through activation by photoirradiation. These days, we succeeded in designing highly selective photocatalytic conversion of CO2 by H2O as the electron donor, by the simultaneous use of an inhibitor of the production of H2 and a material for CO2 capture and storage. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of O2 were generated together with CO.
(Invited) Ultrafast Solar Energy Conversion with Earth-Abundant Complexes
Authors: Chabera Pavel , Lindh Linnea , Rosemann Nils , Warnmark Kenneth , Yartsev Arkady , Sundstrom Villy , Persson Petter
Published: May 2020

Transition-metal complexes are widely used as photosensitizers and photocatalysts, and in light-emitting devices.[1] We have studied ultra-fast processes in a variety of DSSC and photocatalytic applications.[2,3] More recently we demonstrated the first iron complex [FeIII(btz)3]3+ exhibiting room temperature photoluminescence from a CT state and show that it has a 100 ps excited state CT lifetime which is unprecedented for any iron complex.[4] This was characterized as a rare low-spin FeIII
d5
complex with emission from a long-lived doublet ligand-to-metal charge transfer (2LMCT) state. Absence of intersystem crossing (ISC) in this complex avoids significant excited state energy losses as encountered in the prevailing class of d6
TM complexes of e.g. FeII and RuII. Furthermore, we have also shown [FeII(btz)3]2+ low-spin complex [5], a FeII analogue to [FeIII(btz)3]3+. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a 3MLCT state with a 528 ps excited state lifetime in CH3CN solution that is more than one order of magnitude longer compared to the MLCT lifetime of any previously reported FeII complex. Together, these results show that the FeII and FeIII oxidation states of the same Fe(btz)3 complex feature long lived MLCT and LMCT states, respectively. This demonstrates the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of photophysical and photochemical applications, and on-going efforts for further improvements of the excited state dynamics of such systems will be outlined, including the very latest development of an iron compound [Fe(phtmeimb)2]+ with an excited state stable enough to emit luminescence with unprecedented 2 ns lifetime and with the ability to engage in bi-molecular electron transfer [6].

References:

1 Ponseca, C. S., Jr.; Chabera, P.; Uhlig, J.; Persson, P.; Sundstrom, V. Ultrafast Electron Dynamics in Solar Energy Conversion.
Chem Rev
2017, 117 (16), 10940.

2 H. Imahori et al, Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO2 Electrodes: The Key Role of Charge Recombination for Solar Cell Performance,
J. Phys. Chem. A
2011, 115, 16, 3679-3690

3 M. Yamamoto et al, Visible light-driven water oxidation with a subporphyrin sensitizer and a water oxidation catalyst,
Chem. Commun.
2016,52, 13702-13705

4 Chabera, P. et al. A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 2017, 543 (7647), 695.

5 Chabera, P. et al. Fe(II) Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime, J Phys Chem Lett 2018, 9, 459−463.

6 Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 2019, 363 (6424), 249-253.

Figure caption:

Photoluminescent iron complex [6]

Figure 1
(Invited) Alchemy in Nanoplasmonics: New Class of Plasmonic Alloy Nanoparticles
Authors: Teranishi Toshiharu
Published: May 2020

It has been believed for more than 150 years that, in the form of spherical nanoparticles (NPs), only the group 11 elements (Cu, Ag, Au) show the localized surface plasmon resonance in the visible region. It is well known that chemical conversion of inorganic NPs via element replacement reactions, such as ion exchange reactions and galvanic replacement reactions, can overcome the difficulties associated with controlling the size, shape, chemical composition, and crystal structure in conventional syntheses [1-3]. Especially, alloying enables us to drastically modulate the electronic properties of metallic NPs. The retained shape of the parent-NPs in element replacement reactions provides an opportunity to obtain non-equilibrium unique structures and even new structures of inorganic NPs, these final structures being known as “pseudomorphs”. Here the nano-pseudomorphic chemistry to give unique alloy NPs, which possess the localized surface plasmon resonance in visible-to-near infrared region, is presented [4]. This is an alchemy in nanoplasmonics in the sense that the plasmonic properties of group 11 elements are reproduced by using non-group 11 elements. [1] Saruyama, M.; So, Y.-G.; Kimoto, K.; Taguchi, S.; Kanemitsu, Y.; Teranishi, T. J. Am. Chem. Soc. 2011, 133, 17598. [2] Kanehara, M.; Arakawa, H.; Honda, T.; Saruyama, M.; Teranishi, T. Chem. Eur. J. 2012, 18, 9230. (Frontispiece) [3] Wu, H.-L.; Sato, R.; Yamaguchi, A.; Kimura, M.; Haruta, M.; Kurata, H.; Teranishi, T. Science 2016, 351, 1306. [4] Sato, R.; Teranishi, T. et al., to be submitted.
(Invited) Ordered Semiconductor Through-Hole Membranes with Controlled Geometrical Structures by Anodization Processes
Authors: Yanagishita Takashi , Masuda Hideki
Published: May 2020

The semiconductor materials with naturally occurring self-ordered nanostructures have attracted growing interest for the preparation of functional nanodevices for energy conversion.1 To obtain the nanodevices with optimized performance, control of the geometrical structure of semiconductors is essential. For example, the fabrication of highly ordered structures of semiconductors contributes to the efficient absorption of the incident light and also enhance the charge separation in the interfaces. Anodization process of metals is an effective method for the preparation of ordered hole array structures of metal oxides. One advantageous point of this process is controllability of the geometrical structures of the obtained porous structures based on the anodization conditions.2 In addition, the naturally occurring self-ordered ordered nanoporous structures can be obtained under the appropriate anodization conditions. In our previous reports, we described that ordered nanothrough-hole membranes can also be obtained effectively by two-layer anodization process.3,4 This process allows repeated preparation of ordered through-hole membranes from a single metal substrate by repetition of the process. As an application to semiconductor through-hole membranes, ordered TiO2 through-hole membranes were obtained by two-layer anodization using an electrolyte containing fluoride ions.5 The hole period of the obtained TiO2 membranes could be controlled by changing the anodizing voltage. In the present report, preparation of various types of semiconductor through-hole membranes will be presented. For example, the preparation of ideally ordered TiO2 through-hole membranes by the combination process of two-layer anodization and pretexturing of Ti was described. The obtained TiO2 through-hole membranes with controlled geometrical structures will be applied to various types of energy conversion devices.

1. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed., 50, 2904 (2011).

2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995).

3. T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015).

4. T. Yanagishita, A. Kato, T. Kondo, and H. Masuda, Jpn. J. Appl. Phys., 56, 035202 (2017).

5. T. Yanagishita, H. Inada, T. Kondo, N. T. Nguyen, P. Schmuki, and H. Masuda, J. Electrochem. Soc., 165, E763 (2018).
Tunable Efficiency of Nanocomposites for Optoelectronic Applications
Authors: Kumar Avesh , Kumar Ravindra Pratap , Taneja Ajay
Published: May 2020

Metal oxide semiconductor photocatalyst is frequently used to oxidize organic and inorganic compounds in air and water due to its strong oxidation power, non-toxicity, low cost and others. One can achieve significant improvement of photocatalytic activity and photovoltaic efficiency in solar region by modification of metal oxide semiconductor surface with doping of noble metals (Au). Au nanoparticles are commonly used nanomaterials for improving the sensing performance of surface plasmon resonance (SPR) sensors. SPR exhibit strong absorption corresponding to excitation wavelength regions. Consequently, a large electric field due to SPR is excited on the surface of the nanoparticles. The SPR sensitivity is closely related to the excited electric field. Therefore larger the electric field has more sensitive of SPR sensors to the change of its surrounding medium. This can help in increased stability and trapping capability of plasmonic nanoparticles that will boost the development of numerous applications in science and technology. The inclusion of Au nanoparticles in metal oxide semiconductors shows very interesting optical responses including nonlinear effects linked to absorption by SPR. The generated high energetic electrons in the plasmonic nanoparticles may migrate to the adjacent oxide semiconductor if their energies are larger than the barrier at the interface between the metal and semiconductor. The energy of some electrons are not large enough surmount to barrier, they may also be injected into the semiconductor through the tunneling effect. This can generate electron-hole pair, which can increase laser technology, organic pollutants, solar cell, sensor, environmental purification and photo catalytic utilizations.
Arylphthalimidoporphyrins: New Approaches to Imaging pH and Temperature Simultaneously with Oxygen
Authors: Rao Allu Srinivasa , Troxler Thomas , Vinogradov Sergei
Published: May 2020

We will discuss a family of recently developed tetraarylphalimidoporphyrins (TAPIP) and diarylphalimidoporphyrins (DAPIP), which possess unique photophysical properties and suggest new approaches to the design of superior biological sensors for pH and temperature in addition to their already established ability as sensors for oxygen. The synthesis of TAPIP has already been developed by our group previously. Here we present a synthetic route to asymmetric diarylphthalimidoporphyrins (DAPIP) based on [2+2] condensation of the corresponding dipyrromethanes, followed by oxidative aromatization. We report the properties of free-base (H2), Zn(II), Pt(II) and Pd(II) DAPIP's, including their two-photon absorption (2PA) spectra. Using a combination of phosphorescent Pt complexes of TAPIP and DAPIP we are designing a phosphorescent sensor for pH and oxygen, termed pHOx, which operates by measuring ratios of phosphorescence lifetimes. Unlike all existing optical pH sensors, measurements by pHOx are not affected by optical heterogeneities of the medium and provide unbiased pH readings in vivo simultaneously with pO2. At the same time, Pd complexes of TAPIP have been shown to emit both phosphorescence and thermally activated E-type delayed fluorescence, providing a functional element for optical sensing of temperature. However, to make the temperature readings unobstructed by optical heterogeneities of biological tissue, a PdTAPIP-based probe is supplemented by another probe system, based on H2DAPIP, which emits prompt fluorescence at the same wavelengths and can serve as a correction standard for unbiased temperature measurements.
Understanding Charge-Transport in Metal−Organic Frameworks: Impact of the Framework-Topology and Electronic Structure on the Redox Hopping
Authors: Deria Pravas , Maindan Karan , Li Xinlin
Published: May 2020

Metal−organic frameworks (MOFs) are an emerging class of high surface area molecular compositions for electro- and photoelectrochemical energy conversion and storage. For these, work producing charges need to be delivered to catalytic centers and/or externally appended electrodes. Understanding and improving the charge-transport processes within the redox-active MOFs are important. Here, we discuss some key parameters that controls the redox-hopping process in a series of hydrolytically robust topologically different Zr(IV)-MOFs made of tetrakis(4-carboxyphenyl)porphyrinato iron(III), TCPP(FeIII). Topological variation offers fixed but different center-to-center (Fe-Fe) distances to define the hopping rate. Furthermore, we also discuss how axial coordination at the Fe-center can alter its spin-state to impact the TCPP(FeIII/II) -centered reorganization energy of this self-exchange process. Interestingly, the ability to attain a complete hexa-coordinated TCPP(Fe) through two-axial coordination is also determined by the pore diameter –i.e. the space available to accommodate two ligand-molecules. The improved hopping rate possibly be enough to drive electrochemical transformations, but the real question to address would be –how slow it is for photoelectrochemical processes?
Computational Modeling of Boron Subphthalocyanines and Subnaphthalocyanines to Justify Their Development and to Predict and Confirm Their Electrochemical and Physical Properties
Authors: Bender Timothy P , Holst Devon
Published: May 2020

For some time, our group has been focused on the molecular design, synthesis and application of derivatives of boron subphthalocyanines (BsubPcs) and subnaphthalocyanines (BsubNcs), which are macrocyclic molecules with a chelated central boron atom. Our focal point has been and continues to be equally balanced between the basic and applied chemistry of BsubPcs/BsubNcs and their application as light absorbing and electronic conducting materials in organic photovoltaics (OPVs)/organic solar cells. Electrochemical properties being critical to this application. For OPVs, we selected a preferred approach to the development of BsubPcs/BsubNcs whereby their molecular design and their synthesis is justified through a development cycle which includes data accumulation of their basic physical chemistry properties, their immediate integration into OPVs and their stability evaluation when applied into OPVs/organic solar cells. Based on data acquisition, we then cycle back to consider alternative molecular designs of BsubPcs/BsubNcs. Recently we have re-Integrated into this cycle our computational modeling methodology which is used to screen potential BsubPcs/BsubNcs for their application in OPVs/organic solar cells and other organic electronic devices.

For this presentation I will begin by outlining how we have re-adopted our past computational model to help develop these materials. I will start by showing how we calibrate several levels of computational modeling relative to firm experimental data. I will highlight how a low level and high level computational model can be calibrated and the difference between them. I will then move onto several examples of how we have developed BsubPcs/BsubNcs for application in OPVs and other organic electronic devices utilizing this method.

An example I will show is that we have recently identified a pathway to BsubPcs whereby all carbons are bio-sourced. In order to justify their synthesis with the desired OPV application, I will highlight how the computational model justified the time and resource commitment to their synthesis and development. I will also show how the computational calibration model did accurately predict their relevant properties, the prediction being a level of justification for their development.

I will outline several other BsubPc/BsubNc macrocycle structures that where either justified by the computational model to be developed or where not justified. I will also highlight to the community progress in avoiding bay-position halogenation of the BsubNc macrocycles during their formation.

Additional co-authors/investigators will be identified during this presentation.

Figure 1