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Feb 20, 2014
Atomic-Scale Observation of Multiconformational Binding and Energy Level Alignment of Ruthenium-Based Photosensitizers on TiO2 Anatase

A joint experimental-computational study performed as a collaboration between our group and researchers from the Max Planck Institute for Solid State Research has been published in Nano Letters. Through a combination of electrospray ion beam deposition, high resolution scanning tunnelling microscopy (STM) and spectroscopy (STS) measurements and density-functional theory (DFT) calculations, the work provides an unprecedented view of the interface formed between titanium dioxide and the ruthenium-based "N3" dye molecule, considered the prototypical interface for dye-sensitized solar cells. The STM experiments observe the dye molecule binding to the surface in a wide variety of different geometries, and the STS shows that the specific geometry can have a large effect on the expected performance of the solar cell. The work suggests that optimization strategies based solely on the electrochemical properties of the dye should be replaced by a more comprehensive approach where the focus is on the engineering of the chromophore–semiconductor interface at the atomic scale.

June 13, 2013
Study on the photophysics of diamondoids published in Nature Communications

Nature Communications published a study on the photophysics of diamondoids by Christopher Patrick and Feliciano Giustino. Diamondoids are the nanoscale relatives of diamond; molecules whose chemical bonding is the same as found in diamond, silicon and germanium, but with nanometre-scale diameters. These molecules are being considered for a diverse range of applications, including organic electronics, quantum computing, nanolubrication and drug delivery. However theoretical attempts to understand the diamondoids, particularly their optical properties, have met with some difficulty in the past. In their paper, Patrick and Giustino show that it is essential to include the quantum motion of the carbon nuclei into the theoretical description. Indeed, even at zero temperature, the "quantum fuzziness" of the nuclei introduces large qualitative and quantitative changes in the behaviour of diamondoids under illumination. The work demonstrates the importance of systematically incorporating the quantum mechanics of nuclei into the first-principles modelling of nanomaterials.

January 28, 2013
EU announces funding for FET Flagship initiative Graphene

The European Commission has chosen Graphene as one of Europe’s FET flagships. The Flagship Programme is part of EU's Future and Emerging Technologies (FET) initiative, and each Flagship Project will run for ten years, receiving funding of up to € 1 bn. Our group will be contributing to the Graphene Flagship project in the area of the computational modelling of photovoltaic materials and devices based on graphene.

December 11, 2012
Computational study on ZnO/P3HT solar cells makes the cover of Advanced Functional Materials

Hybrid organic-inorganic solar cells based on ZnO and P3HT have been the subject of significant interest over the past few years owing to their potential for low-cost and scalable solar energy technology. Despite the tremendous progress that has been made in this area, device efficiencies are still below 2%, in part due to low open-circuit voltages.

Keian Noori and Feliciano Giustino have performed the largest first-principles calculation on the ZnO/P3HT interface to date in order to shed light on the mechanisms determining the photovoltage in these systems.

According to the calculations the ideal open-circuit voltage of this interface, i.e., the maximum voltage that can be achieved in the absence of defects, is significantly higher than previous estimates. This finding makes ZnO/P3HT blends attractive for nanostructured photovoltaics.

This study suggests that there is substantial room for improvement in ZnO/P3HT-based solar cells and calls for a renewed effort to tailor this interface at the nanoscale. The article is available for free download from the Advanced Functional Materials website.

November 15, 2012
Feliciano Giustino receives Research Leadership Award from the Leverhulme Trust

Feliciano Giustino has received a Leverhulme Research Leadership Award to explore how biomimetic solar cells turn light into electricity at the atomic scale. The Leverhulme Trust awards only a handful of Research Leadership grants once every few years, and Universities are only allowed to nominate one candidate across all disciplines. Feliciano will use the grant from the Leverhulme Trust, worth approximately £900'000, to model biomimetic photovoltaic devices as part of a project nicknamed ELYSIA, after the photosynthetic sea slug elysia chlorotica.

More details on this award can be found on the official press release by the University or on the Materials Department and Wolfson College websites.

September 10, 2012
Quantitative Analysis of Valence Photoemission Spectra and Quasiparticle Excitations at Chromophore-Semiconductor Interfaces

We have performed the first calculation of the quasiparticle energy-level alignment at a complex interface found in biomimetic solar cells. In our paper published in Physical Review Letters we develop a theory of quasiparticle energy-level alignments of molecules adsorbed on oxide surfaces and apply it to the interface formed between the N3 dye molecule and anatase titanium dioxide, the prototype interface found in dye-sensitized solar cells. Comparison of theoretical and experimental data allows an unprecedented understanding of the valence photoemission spectrum of this important interface. The calculations, which encompass a number of sophisticated techniques, were carried out using the high-performance-computing facilities of the MML and the Oxford Supercomputing Centre.

April 24, 2012
GW quasiparticle bandgaps of anatase TiO2
starting from DFT + U

The anatase polymorph of titanium dioxide is the phase most commonly found in the nanostructured films employed in a wide variety of technologies. As such it is desirable to obtain an accurate understanding of this material, particularly with regard to its excited state properties. The GW approximation has proven to be highly successful in calculating the quasiparticle properties of many materials, and yields a bandgap of anatase TiO2 of around 3.7 eV. However, in an article published in the Journal of Physics: Condensed Matter we show that including an additional Hubbard U correction on the titanium 3d orbitals closes the gap to 3.3 eV, bringing it closer to the value of 3.2 eV measured in optical experiments. Our work calls for detailed photoemission experiments to establish whether DFT + U represents a better starting point with respect to DFT for computing the GW quasiparticle energies of TiO2. The paper has been included in the IOPselect collection of articles chosen for their "novelty, significance and potential impact on future research".

Feb 10, 2012
Structural and Electronic Properties of Semiconductor-Sensitized Solar-Cell Interfaces

The solid-state semiconductor-sensitized solar cell is an evolution of the concepts of dye-sensitized solar cells and hybrid nanocrystal/polymer solar cells. During the past two years semiconductor-sensitized cells based on mesoporous TiO2 and quantum dots of stibnite (Sb2S3) have been fabricated, and cell efficiencies above 5% have been demonstrated. In an article published in Advanced Functional Materials, we report an atomistic investigation of semiconductor-sensitized TiO2 surfaces. By virtually screening several potential semiconductor sensitizers we have found that TiO2 films sensitized with antimonselite (Sb2Se3) may lead to higher power conversion efficiencies than those reported for the TiO2/stibnite system. The work constitutes the first step in the direction of engineering semiconductor-sensitized solar cells using rational design at the nanoscale. It has been selected to appear on the back cover of the issue and was one of the most-read AFM papers of December 2011.

August 31, 2011
Core-level shifts and dye supramolecular assembly at the TiO2/N3 interface

Among low-cost alternatives to silicon photovoltaics, dye-sensitized solar cells based on mesoporous TiO2 films sensitized with the dye Ru(dcbpyH2)2(NCS)2 (N3 dye) have gained prominence due to their high energy conversion efficiencies. In dye-sensitized cells the photocurrent is generated via ultrafast electron transfer from the photoexcited dye sensitizer to the semiconductor, and the atomistic nature of the semiconductor/dye interface plays an important role in the cell performance. In this work we investigated a variety of atomistic models of the TiO2/N3 interface, and performed a systematic comparison between measured and calculated O1s core-level spectra. Our analysis suggests that systematic hydrogen-bonding between dyes occurs on the TiO2 surface, leading to the supramolecular assembly of the N3 dyes.

May 25, 2011
CECAM/Psi-k Workshop on Challenges and Solutions in GW Calculations for Complex Systems

On June 7-10 the CECAM Headquarters in Lausanne will host the first workshop dedicated to methodological advances in GW quasiparticle calculations. The workshop is organized by Feliciano Giustino, Angel Rubio, and Paolo Umari and includes participants from 13 Countries and 26 speakers from around the World. Details on this event can be found at the workshop webpage.

December 20, 2010
Paper on electron-phonon renormalization of diamond band structure makes PRL Editors' Suggestion

Today Physical Review Letters published our work on the effect of the electron-phonon interaction on the band gap of diamond as an Editors' Suggestion. Within DFT/LDA the direct band gap of diamond is calculated to be 5.7 eV, significantly smaller than the measured band gap of 7.1 eV. If we include electron-electron many-body interactions using GW quasiparticle corrections, then the direct band gap becomes 7.7 eV. In this work we show that in order to explain the measurements we need to also take into account electron-phonon interactions, which introduce an additional correction of 0.6 eV. This finding is quite extraordinary because it is typically assumed that electron-phonon effects in semiconductor band structures are of the order of 10-50 meV. A detailed review of this topic can be found in the Review of Modern Physics article by Manuel Cardona and Mike Thewalt. The combined effects of electron-electron and electron-phonon interactions lead to a calculated band gap of 7.1 eV, in excellent agreement with experiment.

October 12, 2010
EPW technical paper and code release

The technical paper about EPW has been published in Computer Physics Communication. The code can now be download at http://epw.org.uk. We also launched a user forum to discuss how to run the code and keep up to date on code development. Thanks to Jesse Noffsinger@UC Berkeley for the huge effort put into this project, and to the Quantum-ESPRESSO and wannier90 teams for their help and support.

September 8, 2010
Harry Fisher wins Armourers & Brasiers award

Harry Fisher is the winner of 2010 Armourers & Brasiers Company Prize for the best Materials Science Part II Thesis. During his Part II project Harry investigated the magnetic phase diagram of iron pnictide superconductors. The prize will be presented on October 7th 2010.

July 15, 2010
Possible superconductivity in p-doped graphane

By using density-functional theory calculations we found that hydrogenated graphene, known as graphane, may become superconducting at the exceptionally high temperature of 90K when p-doped. If experimentally realized, superconducting graphane would be competitive with high-temperature copper oxide superconductors and pave the way to an entire new research front on nanoscale high-temperature superconductors based on carbon.

Our work has been selected as PRL Editors’ suggestion.

August 3, 2009
Feliciano Giustino awarded ERC Starting Grant

Feliciano Giustino has been awarded a European Research Council Starting Grant for the project "ALIGN - Ab-initio computational modelling of photovoltaic interfaces". In the words of Prof. F. Kafatos, President of the ERC, "the ERC Starting Grant funding scheme aims to fast-track the career development of the very best research talent from across the globe".

April 23, 2008
Work on cuprates gets news coverage from physworld.com

The following is taken from physworld.com