Large-scale GW -BSE calculations with N3 scaling: Excitonic effects in dye-sensitized solar cells

Excitonic effects due to electron-hole coupling play a fundamental role in renormalizing energy levels in dye sensitized and organic solar cells determining the driving force for electron extraction. We show that first-principles calculations based on many-body perturbation theory within the GW -BSE approach provide a quantitative picture of interfacial excited state energetics in organic dye-sensitized TiO 2 , delivering a general rule for evaluating relevant energy levels. To perform GW -BSE calculations in such large systems we introduce a scheme based on maximally localized Wannier’ s functions. With this method the overall scaling of GW -BSE calculations is reduced from O(N 4 ) to O(N 3 ).