Historically, the development of new materials for solar energy conversion devices has been largely empirical and somewhat unsuccessful. In this talk we will look at new computational approaches to coupling the important parameters for solar energy conversion including contacts and absorbers with the identification of new high performance materials. The discovery of new materials has been enabled by recent theoretical developments and the availability of massively parallel computers allowing for the prediction of a range of properties for real materials with quantitative accuracy and at reasonable computational cost. This allows searching large chemical spaces for new material solutions as well as finding ways to improve the performance of existing materials in a wide range of applications. We will extend this approach to the design of new semiconductor materials for photoelectrochemical water splitting to hydrogen and oxygen which in addition requires accurate prediction of the position of the semiconductor band edges relative to the water oxidation and reduction levels. We describe a theoretical/computational approach<i>that allows quantitative predictions ionization potentials (IPs) and electron affinities (EAs) of semiconductors and insulators and, in addition, provides a route to relate IPs and EAs directly to the electrochemically measured positions of the band edges in aqueous environment. Our computational approach employs a combination of the state-of-the-art GW method for the electronic structure of bulk systems, and density functional theory surface calculations resulting in accurate and surface orientation dependent IPs and EAs. The relation between IPs and EAs and electrochemical measurements we derive from the extensive comparison of calculated IPs and EAs with available experimental data, both from photoemission and electrochemical measurements. From this comparison we find that there is on average a nearly constant 0.5 eV difference between the semiconductor band edges, derived from IPs and EAs, and those measured electrochemically at the pH value corresponding to the point of zero charge (PZC). This 0.5 eV upshift of the band edges of semiconductors in aqueous environment relative to those in vacuum is a consequence of the interaction with water molecules at the interface. This result allows direct alignment of the semiconductor band edges with water redox potentials just on the basis of known IPs, EAs, and PZCs, eliminating explicit modeling of semiconductor/water interfaces, which are still challenging for computationally. In this way an efficient, reliable and relatively simple procedure can be constructed and used in searching for new water splitting materials.Acknowledgments:  This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, as part of an Energy Frontier Research Center under contract No. DE-AC36-08GO28308 to NREL. The use of high performance computing resources of the National Energy Research Scientific Computing Center and of NREL's Computational Science Center are gratefully acknowledged[1] V. Stevanovic, S. Lany, D. S. Ginley, W. Tumas, and A. Zunger, �Assessing Capability of Semiconductors to Split Water Using Ionization Potentials and Electron Affinities Only�, Phys. Chem. Chem. Phys.16, 3706 (2014) DOI:10.1039/c3cp54589j

Computational identification of materials for solar energy conversion including semiconductors for water splitting

248th National Meeting (2014)

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