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Antimony sulfide (Sb2S3) and selenide (Sb2Se3) have emerged as promising earth-abundant alternatives among thin-film photovoltaic compounds. A distinguishing feature of these materials is their anisotropic crystal structures, which are composed of quasi-one-dimensional (1D) [Sb4X6]n ribbons. The interaction between ribbons has been reported to be van der Waals (vdW) in nature and Sb2X3 are thus commonly classified in the literature as 1D semiconductors. However, based on first-principles calculations, here we show that inter-ribbon interactions are present in Sb2X3 beyond the vdW regime. The origin of the anisotropic structures is related to the stereochemical activity of the Sb 5s lone pair according to electronic structure analysis. The impacts of structural anisotropy on the electronic, dielectric and optical properties relevant to solar cells are further examined, including the presence of higher dimensional Fermi surfaces for charge carrier transport. Our study provides guidelines for optimising the performance of Sb2X3-based photovoltaics via device structuring based on the underlying crystal anisotropy.

We report a material screening study for phase transitions of multication hybrid halide perovskite films. Two hundred sixty-six films processed with flash infrared annealing were optically and structurally characterized. This data was compiled into a database to use as a reliable guide for fundamental studies of halide perovskites. We determine the optimum conditions for the formation of the mixed-cations halide perovskite active phase. We subjected the films to different stress conditions (light, temperature, humidity) resulting in five compositions that were thermodynamically stable. From these, the photoinduced phase instability process of the hybrid perovskite films was explored. These intrinsic stability tests showed that the correct multication combination plays a fundamental role in the crystal growth and thermodynamic stability of the films.

One of the key properties of lead-halide perovskites employed in solar cells is the defect tolerance of the materials, in particular regarding intrinsic point defects, which mainly form shallow traps. Considering that high luminescence yields and photovoltaic performance are obtained by simple solution processing from commercial chemicals, it is commonly anticipated that the defect tolerance-at least to a considerable degree-extends to grain boundaries and extrinsic defects, i.e. impurities, as well. However, the effect of impurities has hardly been investigated. Here, we intentionally introduce small quantities of bismuth (10 ppm to 2%) in solution to be incorporated in the perovskite films based on mixed cation mixed anion compositions. We observe that Bi impurities in the %-regime reduce charge carrier collection efficiency and, more importantly, that the open-circuit voltage decreases systematically with impurity concentration even in the ppm regime. This strong defect intolerance against Bi impurities comes along with reduced electroluminescence yields and charge carrier lifetimes obtained from transient photoluminescence experiments. Calculations based on molecular dynamics and density functional theory predict delocalized (≈0.16 eV) and localized deep (≈0.51 eV) trap states dependent on the structural arrangement of the surrounding atoms. Structural characterization supports the idea of Bi being present as a homogeneously spread point defect, which substitutes the Pb2+ by Bi3+ as seen from XPS and a reduction of the lattice parameter in XRD. Sensitive measurements of the photocurrent (by FTPS) and surface photovoltage (SPV) confirm the presence of tail states. Photoelectron spectroscopy measurements show evidence of a deep state. These results are consistent with the common idea of shallow traps being responsible for the reduced charge collection efficiency and the decreased fill factor, and deeper traps causing a substantial reduction of the open-circuit voltage. As Bi is only one potential impurity in the precursor salts used in perovskite solar cell fabrication, our findings open-up a research direction focusing on identifying and eliminating impurities that act as recombination centers-a topic that has so far not been fully considered in device optimization studies. Fil: Yavari, M.. École Polytechnique Fédérale de Lausanne; Suiza Fil: Ebadi, Firouzeh. École Polytechnique Fédérale de Lausanne; Suiza Fil: Meloni, Simone. Università di Roma; Italia Fil: Wang, Zishuai. École Polytechnique Fédérale de Lausanne; Suiza Fil: Yang, Terry Chien-Jen. École Polytechnique Fédérale de Lausanne; Suiza Fil: Sun, Shijing. Massachusetts Institute Of Technology; Estados Unidos Fil: Schwartz, Heidi. University Of Cologne; Alemania Fil: Wang, Zaiwei. École Polytechnique Fédérale de Lausanne; Suiza Fil: Niesen, Bjoern. École Polytechnique Fédérale de Lausanne; Suiza Fil: Durantini, Javier Esteban. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentina Fil: Rieder, Philipp. Julius Maximilian University Of Würzburg; Alemania Fil: Tvingstedt, Kristofer. Julius Maximilian University Of Würzburg; Alemania Fil: Buonassisi, Tonio. Massachusetts Institute Of Technology; Estados Unidos Fil: Choy, Wallace C.H.. The University Of Hong Kong; Hong Kong Fil: Filippetti, Alessio. Università Di Cagliari; Italia Fil: Dittrich, Thomas. Helmholtz Center Berlin For Materials And Energy; Alemania Fil: Olthof, Selina. University Of Cologne; Alemania Fil: Correa Baena, Juan Pablo. Massachusetts Institute Of Technology; Estados Unidos Fil: Tress, Wolfgang. École Polytechnique Fédérale de Lausanne; Suiza

ZnO is one of the most widely studied semiconductors due to its direct wide band gap and high exciton binding energy. Due to its ease of synthesis, robustness and low cost, ZnO has been applied in a wide range of devices, including nanogenerators, solar cells, and photodetectors. In this work, ZnO nanorods were synthesized in a single step using an aqueous method at temperatures below 100 °C. The nanorods were annealed in oxygen and nitrogen and a p-type polymer poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) was spray coated onto the top of ZnO nanorods to form a p–n junction. The I–V characteristics of the device showed that the annealing atmosphere had a significant effect on the rectification ratio of the device. Further analysis using Mott–Schottky, photoluminescence, and X-ray photoelectron spectroscopy (XPS) indicated that oxygen vacancy concentration correlated well with the free electron density in ZnO as well as the rectification ratio of the p–n junction devices. Devices made with ZnO nanorods annealed in nitrogen had a better rectification ratio than oxygen, representing a simple method to improve p–n junction diode behaviour through tuning the defect properties of the nanorods via controlled annealing.

Photoactive sulfide materials typically under-perform with respect to their theoretical maximum photovoltaic efficiency compared to other light absorbing solids. In an effort to reveal the underlying cause of this situation, we investigate several potential back contact metals for photovoltaic devices using the principles of band alignment; principles that have repeatedly shown to be of key importance in this field. Specifically, the sulfides SnS, CuInS2 and Cu2ZnSnS4 are studied in contact with the metals Mo, Sn, Ti, W and Zr and their common terminations. We also consider the stability with respect to interfacial chemical degradation and show that almost all systems used to date are likely to form interstitial two-dimensional metal disulfides at the heterojunction interface. The likely effects of these disulfide secondary phases are explored and the optimal configurations for each photoactive sulfide presented.

A convenient method of introducing pentafluorobenzene (PFB) as a single end-group in polythiophene derivatives is reported via in situ quenching of the polymerization. We demonstrate that the PFB-group is a particularly useful end-group due to its ability to undergo fast nucleophilic aromatic substitutions. Using this molecular handle, we are able to quantitatively tether a variety of common nucleophiles to the polythiophene backbone. The mild conditions required for the reaction allows sensitive functional moieties, such as biotin or a cross-linkable trimethoxysilane, to be introduced as end-groups. The high yield enabled the formation of a diblock rod-coil polymer from equimolar reactants under transition metal-free conditions at room temperature. We further demonstrate that water soluble polythiophenes end-capped with PFB can be prepared via the hydrolysis of an ester precursor, and that such polymers are amenable to functionalization under aqueous conditions.

With the aim of producing materials with enhanced optical and photocatalytic properties, titanate nanotubes (TNTs) modified by cobalt doping (Co-TNT) and by Na+ -> Co ion-exchange (TNT/Co) were successfully prepared by a hydrothermal method. The influence of the doping level and of the cobalt position in the TNT crystalline structure was studied. Although no perceptible influence of the cobalt ion position on the morphology of the prepared titanate nanotubes was observed, the optical behaviour of the cobalt modified samples is clearly dependent on the cobalt ions either substituting the Ti4+ ions in the TiO 6 octahedra building blocks of the TNT structure (doped samples) or replacing the Na+ ions between the TiO6 interlayers (ion-exchange samples). The catalytic ability of these materials on pollutant photodegradation was investigated. First, the evaluation of hydroxyl radical formation using the terephthalic acid as a probe was performed. Afterwards, phenol, naphthol yellow S and brilliant green were used as model pollutants. Anticipating real world situations, photocatalytic experiments were performed using solutions combining these pollutants. The results show that the Co modified TNT materials (Co-TNT and TNT/Co) are good catalysts, the photocatalytic performance being dependent on the Co/Ti ratio and on the structural metal location. The Co(1%)-TNT doped sample was the best photocatalyst for all the degradation processes studied., The authors thank Fundação para a Ciência e Tecnologia (FCT) for financial support under the projects PTDC/CTM-NAN/113021/2009, UID/MULTI/00612/2013, UID/CTM/04540/2013, UID/FIS/04650/2013 and SFRH/BD/101220/2014. XPS analyses were performed at CEMUP– Centro de Materiais da Universidade do Porto.

International audience; We address the question of charge delocalization in amorphous and crystalline fullerene solids by performing state of the art calculations encompassing force-field molecular dynamics, microelectrostatic and quantum-chemical methods. The solution of a tight-binding model built from spatially (down to atomistic scale) and time (down to fs) resolved calculations yields the density of electronic states for the charge carriers and their energy-dependent intermolecular delocalization. Both pristine C-60 and the soluble PC61BM/PC71BM acceptors may sustain high-energy states that spread over a few tens of molecules irrespective of morphology, yet electrostatic disorder (mostly dipolar and static in nature) makes the thermally available electron states collapse to hardly more than one molecule in PC61BM/PC71BM, while it has a much more limited impact in the case of the bare C-60. Implications of these results for charge transport and exciton dissociation at donor-fullerene interfaces are discussed.

Controllable chemical doping of graphene has already proven very useful for electronic applications, but when turning to optical and photonic applications, the additional requirement of having both a high transparency and a low surface roughness has, to our knowledge, not yet been fulfilled by any chemical dopant system reported so far. In this work, a new method that meets for the first time this optical-quality requirement while also providing efficient, controllable doping is presented. The method relies on F4-TCNQ dissolved in methyl ethyl ketone (MEK) yielding a uniform deposition after spin coating because of an extraordinary charge transfer interaction between the F4-TCNQ and MEK molecules. The formed F4-TCNQ/MEK layer exhibits a very high surface quality and optical transparency over the visible-infrared wavelength range between 550 and 1900 nm. By varying the dopant concentration of F4-TCNQ from 2.5 to 40 mg ml(-1) MEK, the doping effect can be controlled between Delta n - + 5.73 x 10(12) cm(-2) and + 1.09 x 10(13) cm(-2) for initially strongly p-type hydrogen- intercalated graphene grown on 6H-silicon-carbide substrates, and between Delta n = + 5.56 x 10(12) cm(-2) and + 1.04 x 10(13) cm(-2) for initially weakly p-type graphene transferred on silicon samples. This is the first time that truly optical-quality chemical doping of graphene is demonstrated, and the obtained doping values exceed those reported before for F4-TCNQ-based graphene doping by as much as 50%. This work was supported by ERC-FP7/2007-2013 grant 336940, EU-FET GRAPHENICS (grant agreement no. 618086), EU-FP7 Graphene Flagship (grant agreement no. 604391), the Polish National Science Centre UMO-2013/09/N/ST5/02481, BELSPO-IAP, VUB-OZR and Methusalem.

The growth and characterisation of a non-planar phthalocyanine (vanadyl phthalocyanine, VOPc) on a complete monolayer (ML) of a planar phthalocyanine (Iron(II) phthalocyanine, FePc) on an Au(111) surface, has been investigated using ultra-high vacuum (UHV) scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). The surface mesh of the initial FePc monolayer has been determined and shown to correspond to an incommensurate overlayer, not commensurate as previously reported. Ordered islands of VOPc, with (1 × 1) epitaxy, grow on the FePc layer at submonolayer coverages. The individual VOPc molecules occupy sites directly atop the underlying FePc molecules, indicating that significant intermolecular bonding must occur. It is proposed that this interaction implies that the V[double bond, length as m-dash]O points down into the surface, allowing a Fe-O bond to form. The detailed appearance of the STM images of the VOPc molecules is consistent with previous studies in other VOPc growth studies in which this molecular orientation has been proposed.

Open Access Article. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence., A roll-to-roll compatible, high throughput process is reported for the production of highly conductive, transparent planar electrode comprising an interwoven network of silver nanowires and single walled carbon nanotubes imbedded into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The planar electrode has a sheet resistance of between 4 and 7 Ω □−1 and a transmission of >86% between 800 and 400 nm with a figure of merit of between 344 and 400 Ω−1. The nanocomposite electrode is highly flexible and retains a low sheet resistance after bending at a radius of 5 mm for up to 500 times without loss. Organic photovoltaic devices containing the planar nanocomposite electrodes had efficiencies of ∼90% of control devices that used indium tin oxide as the transparent conducting electrode.

Poly(fluorene) conjugated polyelectrolyte (CPE)-di-ureasil organic-inorganic composites have been prepared using a versatile sol-gel processing method, which enables selective localisation of the CPE within the di-ureasil matrix. Introduction of the CPE during the sol-gel reaction leads to a homogeneous distribution of the CPE throughout the di-ureasil, whereas a post-synthesis solvent permeation route leads to the formation of a confined layer of the CPE at the di-ureasil surface. The CPE and the di-ureasil both function as photoactive components, contributing directly to, and enhancing the optical properties of their composite material. The bright blue photoluminescence exhibited by CPE-di-ureasils is reminiscent of the parent CPE; however the distinct contribution of the di-ureasil to the steady-state emission profile is also apparent. This is accompanied by a dramatic increase in the photoluminescence quantum yield to >50%, which is a direct consequence of the synergy between the two components. Picosecond time-correlated single photon counting measurements reveal that the di-ureasil effectively isolates the CPE chains, leading to emissive trap sites which have a high radiative probability. Moreover, intimate mixing of the CPE and the di-ureasil, coupled with their strong spectral overlap, results in efficient excitation energy transfer from the di-ureasil to these emissive traps. Given the simple, solution-based fabrication method and the structural tunability of the two components, this approach presents an efficient route to highly desirable CPE-hybrid materials whose optoelectronic properties may be enhanced and tailored for a targeted application.

peer-reviewed This article describes a complete study of the evolution of composition (from binary to quaternary) and shape (0D-1D) during the synthesis of CZTS nanocrystals. Aliquot studies were used to track the nucleation and growth in the early stages. Distinctive stages are evident in the reaction due to the progressive incorporation of tin and zinc into the primary copper sulfide particles as a result of their differing precursor reactivity. In addition, reaction windows for shape control were devised by tuning the amine concentration, thereby allowing the formation of a diverse range of shape morphologies including nanorods and ellipsoids, as well as atypical tadpole-shaped and P-shaped nanocrystals. Polytypic nanocrystals with wurtzite and zinc blende domains were also achieved by changing the type of metal precursors used initially in the reaction. ACCEPTED peer-reviewed

Charge transport in organic devices depends strongly on the molecular order and morphology of the organic semiconductor thin films. In the design of new organic semiconductors, the selection of the appropriate core plays a key role in the molecular packing and charge transport characteristics of the organic device. Four derivatives of carbazole that mainly differ in the extension of the pi-conjugated core, including indolo[3,2-b] carbazole and triindole derivatives, exhibited hole mobilities ranging from 10(-5) to 10(-2) cm(2) V-1 s(-1) as active layers in organic thin-film transistors (OTFTs). X-ray analyses of the single crystals and evaporated thin films gave insights into the molecular packing of the compounds that justified their OTFTs characteristics.

Halide perovskites have attracted attention for light-to-electricity conversion in solar cells due to their favorable optoelectronic properties. In particular, the replacement of the A cation by an isovalent molecule has proven highly successful. We explore the substitution of the X anion, producing polyanion perovskites based on hexafluorophosphate and tetrafluoroborate. Starting from CsPbI3, the effect of partial and complete substitution is investigated using relativistic electronic structure calculations. BF4− results in a larger perturbation to the electronic structure than PF6−; however, both localise the band edge states, and the end member compounds are predicted to be wide band gap dielectrics.

A new hybrid organic/inorganic composite consisting of poly(3-thiophene methyl acetate) (PT3MA), poly(vinylidene fluoride) (PVDF) and manganese-doped zinc silicate (Zn2SiO4:Mn) has been synthesized and applied for the fabrication of an optical device. Recrystallized PVDF was used as a host matrix for the PT3MA polymer and Zn2SiO4:Mn inorganic compound. The active layer was deposited on an indium-tin-oxide (ITO)-coated glass substrate by the drop casting technique. A spin-coating method was also used for morphological comparison purposes. The synthesized material as well as the device (aluminium electrodes/PVDF-PT3MA-Zn2SiO4:Mn/ITO/glass) was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), dark current-voltage (I-V) characteristic curves, absorbance and photoluminescence (PL) spectroscopy. The results show spherical-and irregular-shaped microparticles both dispersed on and within the PVDF matrix, which correspond to PT3MA and Zn2SiO4:Mn, respectively. The hybrid composite shows strong luminescence at approximate to 525 nm superimposed by a broadband between 600 and 800 nm, originating from the Zn2SiO4:Mn radiative transitions and from the recombination of photogenerated carriers at PT3MA. At room temperature, the device presented semiconductor behaviour typically observed for photodetectors and a DC electrical conductivity of approximate to 0.37 mu S cm(-1).

Optimum reaction conditions for the quantitative preparation of the highly reactive 3,4-di(methylene) tetrahydrothiophene-1,1-dioxide are described. The method involves the zinc-induced 1,4-debromination of 3,4-bis(bromomethyl)-2,5-dihydrothiophene-1,1-dioxide in acetone solvent either by using conventional heating, microwave or ultrasonic irradiation. The [4+2] cycloaddition reaction of 3,4-di(methylene) tetrahydrothiophene-1,1-dioxide with dienophiles such as DMAD and C-60 led to the efficient and clean formation of the corresponding Diels-Alder cycloadducts. Specifically for [60]fullerene, the short-chain C-60 monoadduct was formed in a short reaction time and in high overall yield (56%). In contrast, the iodine-induced 1,4-debromination using KI in toluene, in the presence of 18-crown-6 as a phase transfer catalyst, failed to give the corresponding [4+2] C-60 monoadduct at room temperature or in refluxing toluene and a low product yield (13%) was only obtained at a temperature of 45-50 degrees C. Rsc Advances