Extended systems: solids, surfaces, liquids. Applications (e.g photovoltaics)

STM image of an AgPd alloy surface

STM image of silicene on Ag at the Fermi level

Bright exciton in the TiO₂ anatase bulk

Dye molecule on a TiO₂ cluster

example of confined exciton in an anatase [010] nanowire

example of a delocalized exciton in an anatase [010] nanowire

rutile [001] nanowires of increasing size

• Van der Waals stacked hybrid solid materials show interesting electrical, mechanical and optical properties distinctly different from their starting parent layers. From extensive first principle calculations we identify i) a novel approach to control the dipole at the h-BN/G interface by properly sandwiching or sliding layers of h-BN and graphene, ii) a way to inject carriers in graphene upon UV excitations of the Frenkel-like excitons of the h-BN layer(s).

• GW-self-energy quasiparticle calculations. The interaction between electrons can be determined to great accuracy using Many Body Perturbation Theory, and in particular the "GW" approximation, which calculates the excitations of a system of electrons with much greater accuracy than mean-field techniques like Density Functional Theory.

• Electron/hole lifetimes of metal and insulators

• Description of the electronic structure of III-V and II-VI semiconductors, including structural-phase transitions under pressure.

• Photoemission at vecinal surfaces and from solids (in collaboration with the experimental group of E. Ortega). Subtle effects in the Fermi surface and electronic structure of metals, such as those due to spin-orbit coupling in heavy elements, can be understood using ab-initio tools.

• Electronic, dielectric and optical properties of organic molecular solids (e.g. pentacene and picene) and transition metal dichalcogenides (e.g. MoS₂ and MoSe₂).

• Electronic properties of monolayer, bilayer and multilayer silicene on Ag and other metal slabs.

MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS VOLUME 1370
Computational Semiconductor Materials Science
Symposium held Spring 2011, April 25–29, San Francisco, California, U.S.A.
Eds: S-H. Wei, A. Rubio, H. Guo, L. Liu. CAMBRIDGE UNIVERSITY PRESS

The search for new photovoltaic materials and devices is one of the most active subject in the field of green energy. Developments in the field relies on the joint knowledges coming from physics, organic and inorganic chemistry, electrochemical engineering. The theoretical-computational study can result quite useful to explain and predict behaviours of complex, mesoscopic systems, by giving a deep understanding of basic mechanisms as optical excitations and interfacial charge transfer.
In this framework, we aim at using the state-of-the-art theoretical methods in studying excited states of extended systems, in the analysis of hybrid dye-sensitized solar cells, for instance in the traditional configuration Ru-dye on TiO2 but also other molecules, and substrates as ZnO.
At present, 3 people are involved in this project, and the main investigation subjects are:

• Hybrid organic-oxide solar cells (Graetzel cells)

  • DFT structural and electronic properties of interfaces and nanostructures
  • TDDFT and MBPT description of optical properties and charge transfer behaviour
  • TDDFT investigation of dyes for PV applications: Ru-dyes, indolines, metal-free dyes
  • Optical and electronic properties of TiO₂ crystals, surfaces and nanostructures
  • Optical and electronic properties of ZnO crystals, surfaces and nanostructures

• Collaborations

  • Prof. Stefano Ossicini, Università di Modena e Reggio Emilia, Italy
  • Dr. Ivan Marri, Università di Modena e Reggio Emilia, Italy
  • Prof. Luciano Colombo, SLACS and Università di Cagliari, Italy http://www.slacs.it/
  • Dr. Alessandro Mattoni, CNR, Cagliari, Italy http://www.slacs.it/
  • Dr. Maurizia Palummo, Università di Roma Tor Vergata and ETSF, Italy
  • Dr. Giovanni Cantele, CNR-Università di Napoli Federico II, Italy
  • Prof. Maria-Carmen Asensio, SOLEIL-Synchrotron, France

Results of our research have been presented at:

Hybrid and Organic Photovoltaics Conference HOPV 2010, Assisi (PG), Italy, 23-27 May 2010
Young researchers meeting YRM 2010, University of Jyväskylä, Finland, 31 May-4 June 2010

We use the codes:
Quantum-ESPRESSO and VASP for DFT calculations
YAMBO for MBPT calculations
OCTOPUS for TDDFT calculations

Some reference material:
Photovoltaics and nanotechnology: from innovation to industry. The European Photovoltaics Clusters. Corporate author(s): European Commission, Directorate-General for Research and Innovation. 2011