Combined first-principles statistical mechanics approach to sulfur structure in organic cathode hosts for polymer based lithium–sulfur (Li–S) batteries

Polymer-based batteries that utilize organic electrode materials are considered viable candidates to overcome the common drawbacks of lithium–sulfur (Li–S) batteries. A promising cathode can be developed using a conductive, flexible, and free-standing polymer, poly(4-thiophen-3-yl)benzenethiol) (PTBT), as the sulfur host material. By a vulcanization process, sulfur is embedded into this polymer. Here, we present a combination of electronic structure theory and statistical mechanics to characterize the structure of the initial state of the charged cathode on an atomic level. We perform a stability analysis of differently sulfurized TBT dimers as the basic polymer unit calculated within density-functional theory (DFT) and combine this with a statistical binding model for the binding probability distributions of the vulcanization process. From this, we deduce sulfur chain length (“rank”) distributions and calculate the average sulfur rank depending on the sulfur concentration and temperature. This multi-scale approach allows us to bridge the gap between the local description of the covalent bonding process and the derivation of the macroscopic properties of the cathode. Our calculations show that the main reaction of the vulcanization process leads to high-probability states of sulfur chains cross-linking TBT units belonging to different polymer backbones, with a dominant rank around n = 5. In contrast, the connection of adjacent TBT units of the same polymer backbone by a sulfur chain is the side reaction. These results are experimentally supported by Raman spectroscopy

Proton Radiation Hardness of Perovskite Tandem Photovoltaics.

Monolithic [Cs0.05(MA0. 17FA0. 83)0.95]Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon.F.L. acknowledges financial support from the Alexander von Humboldt Foundation via the Feodor Lynen program and thanks Prof. Sir R. Friend for supporting his Fellowship at the Cavendish Laboratory. This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement number 756962). M.J, A.A.A., E.K., and S.A. acknowledge financial support from the German Federal Ministry of Education and Research (BMBF) via program “Materialforschung für die Energiewende” (grant no. 03SF0540), by the German Federal Ministry for Economic Affairs and Energy (BMWi) through the ‘PersiST’ project (Grant No. 0324037C). T.B. C.A.K. and R.S. acknowledge funding by BMWi through the speedCIGS (grant no. 0324095E) and EFFCIS project (grant no. 0324076D). D.K. and M.C. acknowledge financial support from the Dutch Ministry of Economic Affairs, via The Top-consortia Knowledge and Innovation (TKI) Program ‘‘Photovoltaic modules based on a p-i-n stack, manufactured on a roll-to-roll line featuring high efficiency, stability and strong market perspective’’ (PVPRESS) (TEUE118010) and “Bridging the voltage gap” (BRIGHT) (1721101). K. F. acknowledges the George and Lilian Schiff Fund, the Engineering and Physical Sciences Research Council (EPSRC), the Winton Sustainability Fellowship, and the Cambridge Trust for funding. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). The authors acknowledge the EPSRC for funding (EP/R023980/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 841265. A.R.B. acknowledges funding from a Winton Studentship, Oppenheimer Studentship, and funding from the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Centre in Photovoltaics (CDT-PV). K.G. acknowledges the Polish Ministry of Science and Higher Education within the Mobilnosc Plus program (Grant No. 1603/MOB/V/2017/0)

In situ monitoring of the etching of thin silicon oxide films in diluted NH4F by IR ellipsometry

Infrared spectroscopic ellipsometry (IRSE) was applied to monitor the etching process of electrochemically formed silicon oxides (11.5 and 3.8 nm thick films) in diluted NH4F solution. The optical properties of the amorphous silicon oxide film and the time dependent thicknesses of the oxide films during the etching process were deduced from quantitative evaluations of IRSE spectra. Keywords: IR reflection spectroscopy, Ellipsometry, In situ monitoring, Silicon oxid

Electronic Structure of Methoxy-, Bromo-, and Nitrobenzene Grafted onto Si(111)

The properties of Si 111 surfaces grafted with benzene derivatives were investigated using ultraviolet photoemission spectroscopy UPS and X ray photoelectron spectroscopy XPS . The investigated materials were nitro , bromo , and methoxybenzene layers C6H4 X, with X NO2, Br, O CH3 deposited from diazonium salt solutions in a potentiostatic electrochemical process. The UPS spectra of the valence band region are governed by the molecular orbital density of states of the adsorbates, which is modified from the isolated state in the gas phase due to molecule molecule and molecule substrate interaction. Depending on the adsorbate, clearly different emission features are observed. The analysis of XPS intensities clearly proves multilayer formation for bromo and nitrobenzene in agreement with the amount of charge transferred during the grafting process. Methoxybenzene forms only a sub monolayer coverage. The detailed analysis of binding energy shifts of the XPS emissions for determining the band bending and the secondary electron onset in UPS spectra for determining the work function allow one to discriminate between surface dipole layerss changing the electron affinitysand band bending, affecting only the work function. Thus, complete energy band diagrams of the grafted Si 111 surfaces can be constructed. It was found that silicon surface engineering can be accomplished by the electrochemical grafting process using nitrobenzene and bromobenzene siliconderived interface gap states are chemically passivated, and the adsorbate related surface dipole effects an increase of the electron affinit

Communication—large electron-hole diffusion lengths in methylammonium lead triiodide perovskite films prepared by an electrochemical-chemical approach

Methylammonium lead triiodide (CH3NH3PbI3) perovskite films were generated by chemical conversion of PbO2 layers electrodeposited over NiO hole selective contact, by simple immersion in CH3NH3I isopropanol solution under ambient conditions. 2.4 μm charge carrier diffusion lengths were measured by surface photovoltage, being these very similar to the size of the as formed perovskite crystals, showing that there are not deleterious encounters with defects or impurities. The electrochemical procedure used here demonstrates the capacity of this technique for the fabrication of perovskite films with large electron-hole diffusion lengths by solution based processes using only water and isopropanol.Fil: Macor, Lorena Paola. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Sigal, Agustín. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Dittrich, Thomas. Helmholtz-zentrum Berlin Fâür Materialien Und Energie G; AlemaniaFil: Rappich, Jörg. Helmholtz-zentrum Berlin F¨ur Materialien Und Energie; AlemaniaFil: Otero, Luis Alberto. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Gervaldo, Miguel Andres. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentin

The influence of the grain size on the properties of CH3NH3PbI3 thin films

Hybrid perovskites have already shown a huge success as an absorber in solar cells, resulting in the skyrocketing rise of power conversion efficiency to more than amp; 951; 22 . Recently, it has been established that the crystal quality is one of the most important parameters to obtain devices with high efficiencies. However, the influence of the crystal quality on the material properties is not fully understood. Here, the influence of the morphology on electronic properties of CH3NH3PbI3 thin films is investigated. Post annealing was used to vary the average grain size continuously from amp; 8776;150 to amp; 8776;1000 nm. Secondary grain growth is thermally activated with an activation energy of Ea 0.16 eV. The increase of the grain size leads to an enhancement of the photoluminescence and, hence, indicates an improvement of the material quality. According to surface photovoltage measurements, the charge carrier transport length exhibits a linear increase with increasing grain size. The charge carrier diffusion length is limited by grain boundaries. Moreover, an improved morphology leads to the drastic increase of power conversion efficiency of the device

Photoinduced charge separation in organic-inorganic hybrid system: C60-containing electropolymer / CdSe-quantum dots

A photoactive interface is formed between an electrochemical generated organic polymer film and CdSe quantum dots. The specifically designed and synthesized 3,4 ethylenedioxythiophene electroactive monomer, holding C60 buckminsterfullerene, allows the formation of thin films containing both, electron acceptor and hole transport moieties. The generation of photoinduced heterogeneous charge transfer in CdSe quantum dots-electropolymer system was characterized by time resolved and spectral dependent surface photovoltage. In films containing C60 moieties whose surface was modified with 5 nm CdSe quantum dots, the illumination generated photovoltage values around twenty times larger than those obtained without nanoparticles decoration. The results show that this organic-inorganic hybrid interface is a potential structure for the development of optoelectronic devices.Fil: Otero, Manuel. Helmholtz Center Berlin for Materials and Energy; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Dittrich, Thomas. Helmholtz Center Berlin for Materials and Energy; AlemaniaFil: Rappich, Jörg. Helmholtz Center Berlin for Materials and Energy; AlemaniaFil: Heredia, Daniel Alejandro. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fungo, Fernando Gabriel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Durantini, Edgardo Néstor. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Otero, Luis Alberto. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin