Harvesting energy from sunlight is a major challenge for sustainable development. Devices able to convert the energy of light into other forms of energy such as electricity (photovoltaic, PV) or chemical compounds (photocatalysis, water splitting, CO2 photoreduction…) play a key role for that objective since they represent a real opportunity to produce electricity, chemicals, hydrogen fuels… at low environmental and economical costs. Generally these systems involve a semiconductor (SC) for the light absorption and for the conduction of the photogenerated charge carriers. Although the working principle of the photocatalytic and the photovoltaic devices can be complicated and different from one system to another, some fundamental steps are common to all of them such as the light absorption or the exciton dissociation. These steps are governed by fundamental properties (bandgap, exciton binding energies, dielectric constant…) of the SC. Frequently, DFT calculations are performed to characterize only the bandgap of a newly synthesized semiconductor. The objective of the lecture is to present, on several examples, how DFT can be used to compute other relevant properties in a reliable way. The lecture will be divided into three parts. In the first one, a pedagogic presentation of the working principle of these photocatalytic devices will be done where the role and the importance of the SC properties will be highlighted. The methodology to compute dielectric constants, effective masses and exciton binding energies by DFT will be presented.1–3 In the second section, the methodology presented will be applied to the BiCuOS semiconductor to determine its capacity as photovoltaic material.4 In the third section, the ability of C3N4 to photo-split water will be investigated within a similar approach. In addition to a better characterization of semiconductors, these calculations highlight the challenges that must be addressed by the community of theoretical chemists to model with reliability photovoltaic and photocatalytic devices. References: (1) Le Bahers, T.; Rérat, M.; Sautet, P. J. Phys. Chem. C 2014, 118, 5997. (2) Melissen, S. T. A. G.; Labat, F.; Sautet, P.; Le Bahers, T. Phys. Chem. Chem. Phys. 2015, 17, 2199. (3) Kandiel, T. A.; Anjum, D. H.; Sautet, P.; Le Bahers, T.; Takanabe, K. J. Mater. Chem. A 2015, 3 (16), 8896. (4) Le Bahers, T.; Haller, S.; Le Mercier, T.; Barboux, P. J. Phys. Chem. C 2015, 119 (31), 17585.

Semiconductors used in photovoltaic and photocatalytic devices: Insight from DFT based calculations

251st National Meeting (2016)

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