Functional hybrid interfaces between organic molecules and semiconductors are central to many proposed integrated platforms for photocatalysis. Here, we demonstrate a general, empirical parameter-free approach for computing and understanding frontier orbital energies � or redox levels � of a broad class of covalently-bonded organic-semiconductor surfaces, comparing in many cases to measured spectroscopy. We develop this framework in the context of specific density functional theory (DFT) and many-body perturbation theory calculations, within the GW approximation, of exemplar hybrid interfaces, including aromatic molecules covalently attached to functionalized Si (111) and GaP(110), where scanning tunneling spectroscopy measurements are available. Through detailed calculations accounting for structural and binding energetics of mixed-monolayers consisting of both covalently-attached aromatic adsorbates and hydrogen, chlorine, methyl, and other passivating groups, we quantify the impact of coverage, nonlocal polarization, and interface dipole effects on the alignment of the thiophene frontier orbital energies with the silicon band edges. For adsorbate frontier orbital energies, we observe significant corrections to standard DFT (~1 eV), including large nonlocal electrostatic polarization effects (~1.6 eV). Importantly, both results can be rationalized from knowledge of the electronic structure of the isolated adsorbate and substrate systems. Si and GaP band edge energies are predicted to vary by more than 2.5 eV, while molecular orbital energy stay similar for the different functional groups studied, suggesting the prospect of tuning orbital energy alignment (and potentially charge transfer kinetics) for a variety of adsorbates over a wide range for photoelectrochemistry applications.

Theory of organic adsorbate frontier orbital energies on functionalized light-absorbing semiconductor surfaces

246th National Meeting (2013)

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