Organic/inorganic semiconductor heterojunctions are being explored in hybrid solar cells that take advantage of unique properties of both material systems. A key question concerns the mechanism of charge separation across the localized/delocalized semiconductor interface. Here we probe photoinduced charge transfer at a model interface between copper phthalocyanine (CuPc) and gallium arsenide (GaAs) by tracking the electric field on the femtosecond time scale using timeresolved second harmonic generation. For above bandgap excitation of GaAs, we resolve distinction channels of charge separation on 10 2 fs time scales: charge carrier separation in GaAs due to the delocalized space charge field and hole injection from photoexcited GaAs to localized CuPc molecular orbitals. At sufficiently high excitation density (>10 17 /cm 3 ), charge separation by the space charge field leads to band flattening, which accelerates resonant hole transfer from GaAs to CuPc. We discuss implications of these findings to the design of organic/inorganic hybrid solar cells.

The electronic correlation strength is a basic quantity that characterizes the physical properties of materials such as transition metal oxides. Determining correlation strengths requires both precise definitions and a careful comparison between experiment and theory. In this paper, we define the correlation strength via the magnitude of the electron self-energy near the Fermi level. For the case of LaNiO 3 , we obtain both the experimental and theoretical mass enhancements m /m by considering high resolution angle-resolved photoemission spectroscopy (ARPES) measurements and density functional + dynamical mean field theory (DFT + DMFT) calculations. We use valence-band photoemission data to constrain the free parameters in the theory and demonstrate a quantitative agreement between the experiment and theory when both the realistic crystal structure and strong electronic correlations are taken into account. In addition, by considering DFT + DMFT calculations on epitaxially strained LaNiO 3 , we find a strain-induced evolution of m /m in qualitative agreement with trends derived from optics experiments. These results provide a benchmark for the accuracy of the DFT + DMFT theoretical approach, and can serve as a test case when considering other complex materials. By establishing the level of accuracy of the theory, this work also will enable better quantitative predictions when engineering new emergent properties in nickelate heterostructures.