Title:	Atomistic Modeling of Unconventional Alloys for Solar-Energy Applications
DNr:	SNIC 2018/3-370
Project Type:	SNIC Medium Compute
Principal Investigator:	Clas Persson <claspe@kth.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2018-08-01 – 2019-08-01
Classification:	10304 10302 21001
Homepage:	http://www.met.kth.se/~cpersson
Keywords:

Abstract

Our team searches for the optimized materials’ functionalities for solar energy technologies, like next generation solar cells, solar-fuel conversion, light-emitting diodes. Our research also covers energy related research on power battery, smart windows, and ultrathin film optoelectronics. We model, compute, 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 various unconventional alloys and their defects. Special focus is paid to ZnO-X and ZnTe-X (with X = SiC, AlN, GaN, InN, GaP, and GaO). Surprisingly, little attention has been paid to understand these unconventional type of alloy structures that are based on traditional semiconductors. 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. These result indicates 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 will continue the on-going research by also include 2D-like layered structures. Here, our team has expertise in van der Waals interaction in the DFT (i.e., vdW-DF) and dispersion forces (Casimir and Casimir-Polder). For 2D-like materials, charge carrier transport is expected to occur mainly along the plane. Whenever orbital hybridization is strong in few-to-several layer systems or with the intercalated molecule, we will also study interlayer charge transport. We explore these alloys and their defects using state-of-the-art methods 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. When needed, exciton contribution will be included using the Bethe-Salpeter approach. Electronic transport in materials and prototype device will be analyzed by combine atomistic DFT, non-equilibrium Green’s function (NEGF), and quantum transport simulator (incl. inelastic scattering and correlation effects).