Atomistic Modeling of Unconventional Alloys for Solar-Energy Applications
Title: Atomistic Modeling of Unconventional Alloys for Solar-Energy Applications
DNr: SNIC 2015/1-261
Project Type: SNIC Medium Compute
Principal Investigator: Clas Persson <claspe@kth.se>
Affiliation: Kungliga Tekniska högskolan
Duration: 2015-08-01 – 2016-08-01
Classification: 10304 10302 21001
Homepage: http://www.met.kth.se/~cpersson
Keywords:

Abstract

Our research team searches for the optimized materials for solar-energy technologies, like next generation solar cells, solar-fuel conversion, light-emitting diodes. Our research also covers energy related research on CO2 storage, power battery, and smart windows. We model, calculate, and analyze materials and material structures in order to understand fundamental material physics, support experimentalists in their work, but also to explore new types of material structures. By modeling the material on atomistic and nanoscale, we study the electronic and optical properties, the stability of the materials, impact of defects or alloying, interfaces between materials. With this knowledge we can tailor make materials for an optimized performance of devices. In this project we compute and analyze alloys and defects in ZnO-X (X= GaN and InN). Surprisingly, however, little attention has been paid to understand these unconventional type of alloy structures. Our theoretical studies of ZnO-GaN and ZnO-InN reveal intriguing material properties. Incorporating 1-20% of X = GaN or InN in ZnO, the random (ZnO){1-y}X{y} alloys narrows the energy gap. However, although the incorporation implies broken crystalline symmetry and semi-local density-of-states structures of the valence- and conduction-band edges, the strong exciton peak of ZnO is not diminished. That is, the strong exciton absorption remains in the alloy. Moreover, the presence of InN-like nanoclusters enhances the effect on the electronic structure and significantly narrows the band gap, but it decreases the excitonic coupling. The result indicates that the exciton coupling in (ZnO){1-y}X{y} is correlated both to the band-edge states as well as the chemical X content and configuration. Hence, by properly growing and designing ZnO-X, the compound can be suitable for a variety of novel integrated nano-systems ranging from photocatalysis, solid-state lighting, photonics, bio-sensing, to nano-piezoelectricity applications. We want to carefully explore these alloys using sophisticated method for accurate calculations. The scientific methods and algorithms are based on the Kohn-Sham method within the density-functional theory (DFT), however in this project we employ the GGA and HSE exchange-correlation potentials as well as the post-DFT approach GW method which implies heavy calculations in terms of computational time and memory. The regular DFT is not enough to determine the material properties of our material with sufficiently accuracy, and our research team need a HPC resource for large scale jobs.