Functional Materials in Clean Energy Engineering
Title: Functional Materials in Clean Energy Engineering
SNIC Project: SNIC 2014/1-240
Project Type: SNAC Medium
Principal Investigator: Clas Persson <clas.persson@mse.kth.se>
Affiliation: KTH Royal Institute of Technology
Duration: 2014-08-01 – 2015-08-01
Classification: 10304 10302 21001
Homepage: http://www.met.kth.se/~cpersson
Keywords:

Abstract

This application for NSC-Triolith resources considers a continuation of last research year’s allocation, SNIC 001/11-128. The project concerns theoretical studies of structural, electronic, and optical properties of chalcopyrite semiconductors (eg, Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 alloys) and transition metal-oxides (eg, WO3, HgO2, TiO2, SnO2, and ZnO) used in thin-film photovoltaics ("solar cells") and light-emitting technologies (eg, Cu(x)SbY(y) and Cu(x)BiY(y) with Y = S or Se). We have also started to investigate novel Cu-based solar cell materials with high optical activities. We believe that several breakthroughs have been made the last five years, however, there are still many interesting phenomena in these semiconductors, especially how one can modify the optical response of the materials by doping or native defects. Modifying and controlling the band-gap physics of the materials are of greatest importance to design new functional device structures. This can be achieved by alloying, doping, lattice mismatching, charge localization. TiO2, SnO2, and ZnO are transparent insulators which can be doped to show efficient n-type electronic character. Therefore, these metal oxides have been used as a window material in various optoelectronic semiconductor devices. Today, the research on these materials is focused on the optical response in nanostructures and in highly doped materials. The main issue is to modify the materials in order to achieve the desired optical and electronic property for designing more efficient high-power light-emitting devices. The present project will analyze the optical response at surface structures of TiO2, SnO2, and ZnO. These surface models help to understand the nanostructured devices, and also help to understand the interface physics when conducting polymers are attached to the metal-oxide surface in polymer-based solar cells. Effects due to surface relaxation or surface reconstruction can be utilized in low-scale devices. We will also study how doping and native defects (like vacancies) affects the optical response in the bulk materials as well as at the surfaces/interfaces. We use primarily the VASP 5.3 package. The scientific methods and algorithms are based on the Kohn-Sham method within the density-functional theory (DFT), but we will also use approaches that go beyond the DFT, like the GW method and the Bethe-Salpeter equation.