Development of new semiconductors for photovoltaic and photocatalysis is a challenge for the community working these fields. Generally quantum chemical calculations are used at the end of the experimental work to support experiments. Frequently, these calculations are performed to characterize only the bandgap. However, quantum chemical calculations (DFT in this case) can compute more properties such as dielectric constants (both electronic and vibrational), absorption spectrum, effective masses, exciton binding energies… in a reliable way that can be used to design semiconductors before synthesis. The objective of the lecture is to present, on several examples, how DFT can be used to compute other relevant properties. The methodology used to compute all the properties will be clearly detailed on a well-known semiconductor, CuInS2. This first part allows us to highlight the influence of the functional on these properties and the level of reliability of the methodology. Then, this methodology will be applied to characterize two semiconductors: BiCuOS and wurtzite CuGaS2 in order to understand their potentiality for photovoltaic and water splitting applications. In the case of BiCuOS, it appears that while all the intrinsic properties of the bulk are very good for photovoltaic application, the simulation of the p-n junction (using the semiconductor’s equations) reveals that this material has some drawbacks. Finally, the ability of C3N4 to photo-split water will be investigated within a similar approach. This last work will highlight the strength of the simple Wannier model to determine properties of exciton. It appears clearly that the exciton dissociation and charge carrier diffusion are the bottleneck for the use of C3N4 in water splitting device. In addition to provide physical and chemical insights on the use of specific materials for photovoltaic and photocatalytic application, this methodology can be seen as a toolbox for the design of new semiconductors.

Development of new semiconductors for water splitting and photovoltaic devices based on DFT computed properties

251st National Meeting (2016)

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