MNCL Highlights
Electronic structure of MAPbI3 and MAPbCl3: importance of band alignmentThe organic-inorganic Methylammonium Lead Iodide (MAPbI3) perovskite immediately caught the attention of the scientific community in the quest for efficient and cost-effective solar energy harvester materials. It combines, in fact, the high efficiency proper of classical semiconductor-based solar cells (Si and CIGS, for instance) - up to 25% - with the low-cost materials and fabrication processes proper of the organic solar cells.
To optimise the overall efficiency of a solar cell, however, solar absorbers must be combined with proper electrodes, in order to ensure an efficient separation and transport of the excited charges. Therefore, a detailed knowledge of the energetic level alignment between the organic-inorganic perovskite and its potential electrodes, and understanding how this can be tailored, is mandatory. |
In this paper we tackle exactly this problem, with an accurate joined diffraction-photoemission-computational approach to the relative band alignment among the canonical MAPbI3 perovskite, the Cl-containing perovskite (MAPbCl3), their lead halide precursors (PbI2 and PbCl2 respectively), together with a mixed MAPbI3 - MAPbCl3 perovskite phase.
Diffractograms showed immediately that the mixed phase is actually composed by crystals of the two pure MAPbI3 and MAPbCl3 perovskites. At the same time, through photoemission spectroscopy we could define precisely the frontier orbitals energy, together with their vacuum energy level. These are two fundamentals quantities to define wether the energy levels of a junction are properly aligned in order to efficiently dissociate the photo generated electron-hole pairs. In our case we found that a photo generated electron hole pair in MAPbI3 can just transfer holes in PbI2, while all the other charge transfer processes are inibite by the energy level alignment. |
Finally, our mixed MAPbI3 - MAPbCl3 perovskite phase showed that is possible to tune the energy level alignment through a proper choice of the substrate used to grow the samples.
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Electronic structure of MAPbI3 and MAPbCl3: importance of band alignment
2 Istituto Officina dei Materiali - CNR, Laboratorio TASC, I-34149 Trieste, Italy
4 Istituto di ricerca sull'inquinamento atmosferico - CNR, I-87036 Rende, Italy
5 Laboratorio computazionale per fotovoltaico ibrido/organico - CNR, I-06123 Perugia, Italy
6 CompuNet - IIT, I-16163 Genova, Italy
7University of Padua, I-35131 Padua, Italy
E-mail: marco.caputo@elettra.eu, andrea.goldoni@elettra.eu ; Tel: +39 0403758973
Sci Rep 9, 15159 (2019)
DOI: 0.1038/s41598-019-50108-0
Received 17 June 2019, Accepted 28 August 2019
First published online 22 October 2019
Metal decorated carbon nanotubes for electrocatalytic water splitting
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Multi-wall carbon nanotubes (CNTs) are grown by Chemical Vapour Deposition onto Si wafer, and then metals were thermally evaporated on them. Subsequent exposure to the air oxidised almost completely Co and Ni as shown by XPS. The CNTs diameter increased from 25 to 35 nm upon metal deposition as indicate by SEM images.
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Voltammograms show that, either in the Hydrogen and Oxygen Evolution Reactions, the metal functionalised CNTs have superior performances, in terms of over-potential reduction and current density, than either pristine CNTs and metal-functionalised graphite. |
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Metal decorated carbon nanotubes for electrocatalytic water splitting
b Laboratory for Solid State Physics, ETH Zurich, Zurich, 8093 Switzerland
c Department of Chemical and Pharmaceutical Sciences and INSTM UdR Trieste, University of Trieste, Via L. Giorgieri 1, 34127, Trieste, Italy
E-mail: luca.cozzarini@elettra.eu, andrea.goldoni@elettra.eu ;
International Journal of Hydrogen Energy 42, 30 (2017)
Received 23 December 2016, Accepted 13 June 2017
First published online 5 July 2017
Enhancing the sensitivity of chemiresistor gas sensors based on pristine carbon nanotubes to detect low-ppb ammonia concentrations in the environment
Crucial features in gas sensors for environmental monitoring are the sensitivity in the low ppb range and the ability to discriminate variations of a certain polluting gas from other interfering gases. Monitoring of ammonia concentrations in the environment is mandatory because, besides being a toxic molecule, NH3 is one of the main precursors of secondary fine particulate (PM10, PM2.5). In spite of this urgency, the detection of ammonia concentrations in urban areas with CGS has been so far widely overlooked, since the average levels are usually low, i.e. in the 20-30 ppb range and the CGSs are usually tested by exposure to ammonia in the ppm range.
SWCNTs can provide a high physical and chemical stability and a wide range of possible operational features, that make them a unique system for gas detection. Several CNT-based architectures have been proposed and ppt sensitivity of pristine CNTs to ammonia has been demonstrated in inert Ar atmosphere under UV irradiation. Though results so far reported are encouraging, the use of inert atmosphere represents a limitation for environmental monitoring. To overcome this limitation, the present study was carried out in the lab air environment, which is much closer to the final destination of the CNTs sensors. |
Among the several kind of gas sensors, chemiresistor gas sensors are the simplest to produce, being composed of a substrate, a sensitive element deposited on top, and the electrodes to contact the device to a readout circuit. By measuring the variation of the current (or resistance) induced by the presence of gas, the sensor response ΔR/R0 is obtained and after a sequence of exposure to different gas concentrations it is possible to draw the response curve. Finally the detection limit (DL), defined as the limit of detectable concentration, which corresponds to the minimum detectable signal above 5σ, can be estimated by considering the baseline R0, the noise σ, and the fit parameters of the response curve. For the present layers deposited on ceramic substrates a DL down to 3 ppb was estimated, well below the expected average ammonia concentration values in a urban area.  |
Further possibilities to improve the CNT-based gas sensor performances are expected from CNT-oxide hybrid systems, in particular from the blend of CNT with nanoparticle metal oxides such as TiO2, SnO2, WO3, indium-tin oxide (ITO). This is the case of the SWCNT-ITO sensing layers prepared at the MNC-lab on plastic substrates. Plastic substrates were chosen in view of possible device development with printable electronics methods.
These layers displayed a three-fold sensitivity increase with respect to pristine CNT for concentrations above 200 ppb. Moreover,the opposite resistance variation of SWCNT and functionalized ITO-SWCNT when exposed to water vapor (inset of Fig.2b) discloses the possibility to tailor the sensor selectivity with respect to the relevant interfering effects of humidity, expected in outdoor environmental monitoring. |
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Enhancing the sensitivity of chemiresistor gas sensors based on pristine carbon nanotubes to detect low-ppb ammonia concentrations in the environment
Federica Rigoni,ab Silvia Tognolini,ab Patrizia Borghetti,bc Giovanni Drera,ab Stefania Pagliara,ab Andrea Goldonid and Luigi Sangaletti*ab
a Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP), via dei Musei 41, Brescia, Italy
b Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore, via dei Musei 41, Brescia, Italy
c Centro de Física de Materiales (CSIC/UPV-EHU) – Materials Physics Center, Paseo Manuel de Lardizabal 5, E-20018 San Sebastián, Spain
d Elettra Sincrotrone Trieste S.C.p.A., s.s.14 Km. 163.5, Trieste, Italy
E-mail:
Analyst, 2013,138, 7392-7399
DOI: 10.1039/C3AN01209C
Received 19 Jun 2013, Accepted 03 Oct 2013
First published online 04 Oct 2013
Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography
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NIL process is a strong candidate for low cost high throughput technique for PEDOT:PSS nano structuration but with traditional NIL process results with limited aspect ratios were obtained (Max 0,86 AR for sub-100nm resolution). The process here presented was optimized with respect to relative humidity, applied pressure and temperature (RH, P, T). The control of environmental humidity was found to be crucial.
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High quality nanostructures were reproducibly obtained at high relative humidity values (RH >75%), with sub-100 nm resolution features attaining aspect ratios (AR) as high as ~6 at ~95% RH. The developed process of water-vapour-assisted NIL (WVA-NIL) strongly affects the electronic properties of PEDOT:PSS. By current-voltage measurements and ultraviolet photoemission spectroscopy we demonstrate that the process parameters p, T and RH are correlated with changes of PEDOT:PSS conductivity, work function and states of the valence band. In particular, an increase in the films conductivity by factors as high as 105 and a large decrease in the work function, up to 1.5 eV, upon WVA-NIL processing were observed. Moreover, it was found that workfunction shift can be reversed by a short oxygen plasma treatment, without altering significantly the layer's nano structure or conductivity. Employing the produced PEDOT:PSS nanostructured layers as anode buffer layer in P3HT:ICBA bulk heterojunction solar cells, a significant performance increase was obtained (60% relative increase of efficiency respect to a not patterned reference cell). |
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Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography
b University of Trieste, Piazzale Europa, I-34127 Trieste, Italia
c ThunderNIL srl, via Ugo Foscolo 8, 35131 Padova, Italy
d Sincrotrone Trieste SCpA, I-34149 Trieste, Italy
e Department of Chemistry, Addis Ababa University, P. O. Box: 1176, Addis Ababa, Ethiopia
E-mail: tormen@iom.cnr.it ;Tel: +39 0403758416
RSC Adv., 2014,4, 34014-34025
Received 21 May 2014, Accepted 23 Jul 2014
First published online 23 Jul 2014
Alkali Metal Doped Picene Layers: Insulating Phase in Multilayer Doped Compounds
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Theoretical studies on K3picene showed that the superconductivity could be driven by electron−phonon (intramolecular) coupling, as in the case of K3C60. On the other hand, recent DFT calculations showed that K3picene turns into a Mott−Hubbard insulator when its unit cell experiences an enlargement of 5%, like observed in C60 compounds. Therefore, a fundamental question has to be addressed: do correlation effects and crystal arrangements play a decisive role in doped picene electronic structure and superconductivity as in the case of C60 compounds? Figure 1 shows the K-doped picene multilayer valence bands at various doping stages, namely K0.5picene and K3picene. A new state (C) near the Fermi level appears as a consequence of the LUMO − LUMO +1 derived picene bands filled by 4s electrons of K, however this new state is peaked at 0.8 eV of binding energy, and there is no DOS at the Fermi level showing, therefore, an insulating phase for the system.There is a possibility that the metallic state should appear by competing with a phonon-driven (and correlation-assisted) ground state, leading to an insulator−metal transition as a function of temperature.  |
Figure 2 shows the valence band spectra close to the Fermi level of K3picene as a function of temperature, but is evident that the LUMO − LUMO+1 peak remains below the Fermi level, and there is not any DOS appearing at EF.Therefore, the system is insulating also at low temperature. To understand if the observed insulating behaviour is related to correlation effects, we analyze the picene monolayer where possible correlation effects should be screened by Ag substrate electrons. The evolution of the valence band for the pristine and K (Na) doped monolayers of picene is shown in figure3. The first observation is that in the pristine monolayer there is a Fermi level, and the HOMO-derived band is shifted from 3 to 2.7 eV in the undoped monolayer with respect to the multilayer. The presence of the Fermi level in the monolayer/substrate system is mainly due to the underlying Ag, but it is evident that the DOS near EF changes as the alkali metals are added to the monolayer, as shown in figure4. Both the shift of the HOMO in the undoped system and the metallic phase for the doped monolayer can be ascribed to the screening effect of the metallic substrate. This behavior could be explained in close analogy to fullerides assuming that the HOMO−LUMO gap and the insulating state, observed in photoemission adding electrons to the LUMO − LUMO+1 bands, may have a strong Coulomb contribution. However, it is worth noting that the UHV pristine films grown on Ag(111) have a peculiar adsorption geometry, which is different from the expectation based on crystal structure calculations and measurements for picene crystals. Due to strong correlation effects, small variations in the crystal structure (molecular arrangements) may be the reason for the observed insulating state in our doped picene multilayer. |
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Experimental Study of Pristine and Alkali Metal Doped Picene Layers: Confirmation of the Insulating Phase in Multilayer Doped Compounds
, C. Lal †
, and A. Goldoni *† † ST-INSTM Lab., Sincrotrone Trieste S.C.p.A., s.s. 14 km 163.5 in Area Science Park, 34149 Trieste, Italy
Department of Physics, Obafemi Awolowo University Ile-Ife, Nigeria Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur, India
2H-TPP on Ag: carbon de-hydrogenation and geometrical adaptation
We observe a selective carbon de-hydrogenation, the formation of new aryl-aryl bonds between phenyl groups and the macrocycle, as well as the rotation of the phenyl rings in a flat conformation. Experiments and theoretical calculations prove this chemical reaction. |
 In our recent investigations we have demonstrated that one monolayer of 2H-TPP, prepared by thermal desorption of the corresponding multilayer at 550 K on Ag(111), adsorbs with the macrocycle and the phenyl flat. This information has been directly addressed by means of X-ray absorption and photoemission experiments. |
Theoretical calculations suggest a possible molecular reaction and modification of porphyrins, in order to explain this adsorption conformation: the de-hydrogenation of eight carbon atoms in the remaining monolayer after the multilayer desorption, with the formation of four new aryl-aryl carbon bonds. While the reaction takes place also in the deposited monolayer annealed at 550 K, the initial presence of the multilayer favors a decrease of the aryl-aryl coupling barrier and the selection of a spiral conformation in the de-hydrogenated molecule. The chemical reaction produces a stable molecule that forms a patterned square lattice on Ag(111) and that can be further modified by the introduction of central metal atoms. |
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Supramolecular Engineering through Temperature-Induced Chemical Modification of 2H-Tetraphenylporphyrin on Ag(111): Flat Phenyl Conformation and Possible Dehydrogenation Reactions
1INSTM—Micro & Nano-Carbon Laboratory, Sincrotrone Trieste S.C.p.A. s.s.14 km. 163.5, 34149 Trieste (Italy), Fax: +(39) 040-3758565Empa, Swiss Federal Laboratiories for 2Materials Science and Technology nanotech@surfaces Laboratory, Ueberlandstrasse 129, 8600 Dübendorf (Switzerland)
3Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics, Università Cattolica del Sacro Cuore, Brescia (Italy)
4Istituto Officina dei Materiali-CNR, Lab. TASC, s.s. 14 km 163.5, 34149 Trieste (Italy)
*E-mail:
Chemistry - A European Journal vol 17, Issue 51, 14354, December 16, 2011
DOI: 10.1002/chem.201102268
Publication Date (Web): November 23, 2011
Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Metalation of tetraphenylporpyrin with Fe atoms and their conformational adaptation onto the Ag(111) surface.In-situ metalation of porphyrin is of great interest for the characterization of pure species in a controlled environment. We have followed the formation of pure 2H-tetraphenylporphyrin and Fe- tetraphenylporphyrin layers on Ag(111) single crystal. G. Di Santo et al., J. Phys. Chem. C 115, 4155 (2011) |
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In this experiment we characterized the electronic states and the molecules' geometrical adaptation during the formation of pure 2H-5,10,15,20-tetraphenylporphyrin (2H-TPP) and Fe- tetraphenylporphyrin (Fe-TPP) layers on Ag(111) single crystal. Core level absorption spectra indicate the flat conformation of the monolayer suggesting an adatom hopping instead of a surface mediated dopant diffusion for the metalation process. Photoemission points out that the interaction between Fe dz-states and Ag bands increases the monolayer metallic character already induced by the charge transfer from the substrate. The NEXAFS spectra, taken in s and p light polarization at N and C K-edges, put in evidence the flat configuration for the macrocycle and showed that the phenyl groups lie flat in the case of the monolayer while having nonflat orientation in the multilayer. |
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The multilayer Fe metalation favors a macrocycle N distortion, while in the monolayer, the conformation of the phenyl legs and the interaction with the substrate reduce the degrees of freedom of the macrocycle toward the already reached lowest energy situation. The influence of the Fe metallic center in the porphyrin core has only minor structural effects in the monolayer. Both core level and valence band photoemission results give evidence that the charge injection from the substrate is more likely confined to the first monolayer. The metallic state of the first layer evolves with Fe complexation because of d state hybridization with the s−p bands of the substrate. |
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Conformational Adaptation and Electronic Structure of 2H-Tetraphenylporphyrin on Ag(111) during Fe Metalation
J. Phys. Chem. C, 2011, 115 (10), 4155
Adsorption Geometry and Electron Transfer of Zn-tetraphenyl-porphyrin on different substrates
The importance of substrate and interfaces has been exploited in this experimental study on the interaction of one single layer of Zn-tetraphenyl-porphyrin with Ag(110) and Si(111). Photoemission, near-edge X-ray absorption, and resonant photoemission were used to investigate the bonding nature, the adsorption geometry as well as the dynamics of electron transfer between the molecules and the metal or semiconductor surfaces. ChemPhysChem, 11: 2248. |
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We report on the preparation of a conformationally controlled Zn-tetraphenyl-porphyrin (ZnTPP) single layer on two possible substrates, Ag(110) and Si(111).The ZnTPP molecule is characterized by four phenyl groups bonded to the macrocycle and a central Zn atom. As substrates we have chosen silver, normally used as contact in photovoltaic or transistor devices, and silicon, worldwide employed in semiconductor industry. The substrate can influence the thin film morphology, the distortion of the molecules and the electronic charge transfer as a consequence. The molecular orientation with respect to the substrate was monitored using angular dependent near edge x-ray absorption fine-structure spectroscopy (NEXAFS), while the electronic properties of the filled states were investigated using x-ray and ultraviolet photoemission (XPS and UPS). Depending on the substrate, the adsorption orientation is mainly mastered by the coupling of the phenyl legs or the macrocycle with the surface. The ResPES behavior indicates that for the phenyl rings the charge transfer into the substrate is less favorable than on the Ag(110) case and comparable to the multilayer case. Core level photoemission indicates that the molecule is interacting with the substrate using a macrocycle pyrrole ring, while the phenyl rings are rotated in such a way to minimize the interaction with the substrate. |
Substrate Influence for the Zn-tetraphenyl-porphyrin Adsorption Geometry and the Interface-Induced Electron Transfer
ChemPhysChem Volume 11, Issue 10, 2248, July 12, 2010
Article first published online: 10 JUN 2010
Structure and Molecule–Substrate Interaction in a Co-octaethyl Porphyrin Monolayer on the Ag(110) SurfaceThe structure and the morphology of a highly ordered ultrathin film of Co-OEP is described in detail by means of STM images and NEXAFS spectroscopy, while the molecular interaction with the substrate and the electronic structure of the film are studied by means of UPS, NEXAFS at the Co 2p threshold, and DFT calculations. J. Phys. Chem. C 2011, 115, 11560 |
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Ordered thin films of metallorganic magnetic molecules, e.g. metal porphyrins adsorbed on ferro- magnetic transition metal substrates, are potentially interesting in the fields of data storage and spintronics. Herein, we choose the octaethyl-porphyrins with the magnetic Co metal as the central atom, to investigate the possible realization of a long- range ordered 2D array of magnetic elements, by exploiting the self-organizing properties of porphyrins on Ag(110), a noncova- lently interactive and nonmagnetic substrate. The properties of this model system, which is prepared under highly controlled conditions and in ultra high vacuum, can be studied with the full capabilities of surface science techniques. In this work we present a combined experimental and theoretical study of the ultrathin film of Co-octaethylporphyrin (Co-OEP) molecules deposited on the Ag(110) surface. The morphological and electronic properties of this heterogeneous metallorganic interface were studied by means of scanning tunneling microscopy (STM), near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, ultraviolet photoemission spectroscopy (UPS), and density functional theory calculations (DFT). The long-range self-ordered single layer of Co-OEP was obtained by thermal desorption of the molecular multilayer. The single-layer molecules were arranged in a noncommensurate rectangular lattice aligned with the substrate high-symmetry directions.
The combination of experimental techniques and numerical simulations indicated that in this configuration each molecular macrocycle is tilted with respect to the metal surface of about 15°. The strong molecular interaction with the substrate leads to the electron transfer from the metal substrate to the molecule. The direct interaction with the substrate involves mostly the Co metal center, which modifies the valence state with respect to the free Co-OEP molecules due to the hybridization between Co states and Ag bands. |
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Structure and Molecule–Substrate Interaction in a Co-octaethyl Porphyrin Monolayer on the Ag(110) Surface
, Carla Castellarin-Cudia†, Patrizia Borghetti#, Giovanni Di Santo†, Luca Floreano‡, Alberto Verdini‡, Albano Cossaro‡, Ivana Vobornik‡, Emilia Annese‡, Federica Bondino‡, Stefano Fabris§, and Andrea Goldoni† Department of Physics and Astronomy, University of Tennessee Knoxville, 1408 Circle Drive, Knoxville, Tennessee 37996, United States - # Università Cattolica del Sacro Cuore, Dipartimento di Matematica e Fisica, via Musei 41, I-25121, Brescia, ItalyJ. Phys. Chem. C, 2011, 115 (23), 11560
