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. The last year, we have also have had focus on iron, iron-oxides, and high-κ oxides; the aim is to support experimentalist within metallurgy. 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 Cu/Ag-based solar cell materials (collaboration with Uppsala Univ) as well as to non-traditional semiconductor alloys. Surprisingly, little attention has been paid to understand these unconventional type of materials and alloy structures that are based on traditional semiconductors. In order to develop inorganic photovoltaics based on ultrathin photon-absorbing film the material shall exhibit optimized band-gap energy as well as having a very high absorption coefficient, especially for photons energies in the lower spectrum. We therefore suggest to tailor-make the materials to form direct gap multi-valley band edges. That can typically be achieved by considering alloys with heavy elements that have relatively localized sp-like orbitals or by structural disordering. With such tailored materials, we demonstrate that it is possible to reach a theoretical maximum efficiency as high about 25% for film thicknesses of about 50-100 nm. We will also 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 van der Waals systems, 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).