Monitoring Photo-excitation and Electron-Hole Separation in Photovoltaic Materials

Efficiency of photovoltaic phenomena is governed not only by optical transition but also by separation of excited electrons and holes. However, these two events are in a tradeoff relation. For example, increasing optical transition rate by confining carriers in a quantum dot sacrifices carrier mobility and thus lowers electron-hole separation rate. For optimizing an efficiency of photovoltaic phenomena, theoretical analysis which can simultaneously treat photo-excitation and electron- hole separation are needed, while a conventional theory can merely treat these two events individually. In this presentation, I will introduce an approach of using the time- dependent density functional theory (TDDFT) for treating real- time propagation of electrons [1] under illumination of light which is mimicked by an alternating electric field. Then, photo- induced electron-hole creation and subsequent separation in polar crystallographic direction of 3C-SiC [2] will be demonstrated. In this simulation, the numerical stability was checked by the energy conservation rule [3] throughout the TDDFT simulation. \\[4pt] [1] O. Sugino and Y. Miyamoto, PRB{\bf 59}, 2579 (1999); PRB {\bf 66}, 89901(E) (2002).\\[0pt] [2] Y. Miyamoto, {\it submitted}.\\[0pt] [3] Y. Miyamoto and H. Zhang, PRB{\bf 77}, 165123 (2008).