Surface Magnetism: Relativistic Effects at Semiconductor Interfaces and Solar Cells

Ab initio calculations of the electronic g-tensor of paramagnetic states at surfaces and solar cells are presented, whereby special emphasis is given onto the influence of relativistic effects. After discussing the numerical requirements for such calculations, we show that for silicon surfaces the g-tensor varies critically with the hydrogen coverage, and provides an exceptionally characteristic property. This holds also in the case of powder spectra where only the isotropic part g av is available from experiments. Extending our calculations onto microcrystalline 3C-SiC, our study explains why sol-gel grown undoped material can serve as an excellent acceptor material for an effective charge separation in organic solar cells: Due to an auto-doping mechanism by surface-induced states it fits excellently into the energy level scheme of this kind of solar cell and has the potential to replace the usually used rather expensive fullerenes.