| 1. |
- Araujo, Rafael B., et al.
(author)
-
Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application
- 2017
-
In: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 5:9, s. 4430-4454
-
Journal article (peer-reviewed)abstract
- Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.
|
|
| 2. |
- Choi, Joong Il Jake, et al.
(author)
-
Atomic-scale view of stability and degradation of single-crystal MAPbBr(3) surfaces
- 2019
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:36, s. 20760-20766
-
Journal article (peer-reviewed)abstract
- While organic-inorganic hybrid perovskite solar cells are emerging as promising candidates for next-generation solar cells with fascinating power conversion efficiency, the instability of perovskites remains a significant bottleneck for their commercialization. An atomic scale understanding of the degradation of hybrid perovskites, however, is only in its beginning stages because of the difficulty in preparing well-defined surface conditions for characterization. Using atomic force microscopy at ultra-high vacuum and room temperature, we report the first direct observation of the degradation process of a cleaved methylammonium lead bromide, MAPbBr(3) (MA: CH3NH3+), single crystal. Upon in situ cleavage, atomic force microscopy images show large flat terraces with monolayer height steps, which correspond to the surface of cubic MAPbBr(3) with methylammonium ligand termination. While this surface can be prepared via the cleavage process and is energetically stable, we observe that after several weeks under dark and vacuum conditions it degrades and produces clusters surrounded by pits. Guided by density functional theory calculations, we propose a degradation pathway that initiates even at low humidity levels and leads to the formation of surface PbBr2 species. We finally identify the electronic structure of the MA-bromine-terminated flat surface and find that it is correlated with a strong field-induced degradation of the MAPbBr(3) only at positive sample bias voltages.
|
|
| 3. |
- Ebadi, Mahsa, et al.
(author)
-
Assessing structure and stability of polymer/lithium-metal interfaces from first-principles calculations
- 2019
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:14, s. 8394-8404
-
Journal article (peer-reviewed)abstract
- Solid polymer electrolytes (SPEs) are promising candidates for Li metal battery applications, but the interface between these two categories of materials has so far been studied only to a limited degree. A better understanding of interfacial phenomena, primarily polymer degradation, is essential for improving battery performance. The aim of this study is to get insights into atomistic surface interaction and the early stages of solid electrolyte interphase formation between ionically conductive SPE host polymers and the Li metal electrode. A range of SPE candidates are studied, representative of major host material classes: polyethers, polyalcohols, polyesters, polycarbonates, polyamines and polynitriles. Density functional theory (DFT) calculations are carried out to study the stability and the electronic structure of such polymer/Li interfaces. The adsorption energies indicated a stronger adhesion to Li metal of polymers with ester/carbonate and nitrile functional groups. Together with a higher charge redistribution, a higher reactivity of these polymers is predicted as compared to the other electrolyte hosts. Products such as alkoxides and CO are obtained from the degradation of ester- and carbonate-based polymers by AIMD simulations, in agreement with experimental studies. Analogous to low-molecular-weight organic carbonates, decomposition pathways through C-carbonyl-O-ethereal and C-ethereal-O-ethereal bond cleavage can be assumed, with carbonate-containing fragments being thermodynamically favorable.
|
|
| 4. |
- George, Zandra, 1985, et al.
(author)
-
Two-in-one : Cathode modification and improved solar cell blend stability through addition of modified fullerenes
- 2016
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:7, s. 2663-2669
-
Journal article (peer-reviewed)abstract
- The synthesis of dual purpose modified fullerenes with pyridine-as well as amine-functional groups is reported. Addition of these fullerenes to a polymer : fullerene bulk-heterojunction blend based on a thiophene-quinoxaline donor polymer is found to modify the active layer/cathode interface of inverted solar cells (glass/ITO/active layer/MoO3/Al). In particular the open-circuit voltage of devices is increased from 0.1 V to about 0.7 V, which results in a drastic rise in photovoltaic performance with a power conversion efficiency of up to 3%. At the same time, presence of the functionalised fullerene additives prevents the detrimental formation of micrometre-sized fullerene crystals upon annealing at 140 degrees C. As a result, the device performance is retained, which promises significantly increased thermal stability of the bulk-heterojunction blend nanostructure.
|
|
| 5. |
- Grob, Stefan, et al.
(author)
-
Solvent vapor annealing on perylene-based organic solar cells
- 2015
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 3:30, s. 15700-15709
-
Journal article (peer-reviewed)abstract
- Diindenoperylene (DIP) and tetraphenyldibenzoperiflanthene (DBP) are two commonly used donor materials in organic solar cell devices. Despite their structural similarities, DIP films are crystalline, exhibiting good charge and exciton transport, whereas DBP films are amorphous and have lower carrier mobility and a short exciton diffusion length. However, DBP reveals a distinctly higher absorption due to the lying orientation of its transition dipole moments. In this paper, we investigate the influence of solvent vapor annealing (SVA) on the solar cell performance of both materials. In general, SVA induces a partial re-solubilization of the material leading to enhanced crystallinity of the treated layer. For DBP, extended annealing times result in a strong aggregation of the molecules, creating inhomogeneous layers unfavorable for solar cells. However, in DIP cells, SVA leads to an increase in fill factor (FF) and also a slight increase in short-circuit current density (JSC) due to interface roughening. The best results are obtained by combining solvent vapor annealed DIP layers with strongly absorbing DBP and C-70 on top. Through this device architecture, we obtain the same increase in FF in addition to a higher gain in J(SC), elevating the power conversion efficiency by a factor of 1.2 to more than 4%.
|
|
| 6. |
|
|
| 7. |
- Juarez-Perez, Emilio J., et al.
(author)
-
Photodecomposition and thermal decomposition in methylammonium halide lead perovskites and inferred design principles to increase photovoltaic device stability
- 2018
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 6:20, s. 9604-9612
-
Journal article (peer-reviewed)abstract
- Hybrid lead halide perovskites have emerged as promising active materials for photovoltaic cells. Although superb efficiencies have been achieved, it is widely recognized that long-term stability is a key challenge intimately determining the future development of perovskite-based photovoltaic technology. Herein, we present reversible and irreversible photodecomposition reactions of methylammonium lead iodide (MAPbI(3)). Simulated sunlight irradiation and temperature (40-80 degrees C) corresponding to solar cell working conditions lead to three degradation pathways: (1) CH3NH2 + HI (identified as the reversible path), (2) NH3 + CH3I (the irreversible or detrimental path), and (3) a reversible Pb(0) + I-2(g) photodecomposition reaction. If only the reversible reactions (1) and (3) take place and reaction (2) can be avoided, encapsulated MAPbI(3) can be regenerated during the off-illumination timeframe. Therefore, to further improve operational stability in hybrid perovskite solar cells, detailed understanding of how to mitigate photodegradation and thermal degradation processes is necessary. First, encapsulation of the device is necessary not only to avoid contact of the perovskite with ambient air, but also to prevent leakage of volatile products released from the perovskite. Second, careful selection of the organic cations in the compositional formula of the perovskite is necessary to avoid irreversible reactions. Third, selective contacts must be as chemically inert as possible toward the volatile released products. Finally, hybrid halide perovskite materials are speculated to undergo a dynamic formation and decomposition process; this can gradually decrease the crystalline grain size of the perovskite with time; therefore, efforts to deposit highly crystalline perovskites with large crystal sizes may fail to increase the long-term stability of photovoltaic devices.
|
|
| 8. |
- Wang, Yuming, et al.
(author)
-
Light-induced degradation of fullerenes in organic solar cells : a case study on TQ1:PC71BM
- 2018
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 6:25, s. 11884-11889
-
Journal article (peer-reviewed)abstract
- The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.
|
|
