(594c) Nanoscopic Control of the Interfaces to Optimize Metal-Insulator-Semiconductor Systems for Solar Water Splitting

Harnessing sunlight to split water is a promising route to produce sustainable hydrogen fuel for applications in the chemical industry and energy sector. An attractive system for high efficiency photoelectrochemical water splitting consists of two semiconductors connected in series and each coupled to a metal electrocatalyst. An efficiency analysis of these dual semiconductor systems demonstrates that the optimal band gap for the bottom absorber is between 1-1.4 eV [1]. Silicon has an optimal band gap of 1.1 eV, but it is chemically unstable in relevant water splitting conditions [2]. To overcome these stability concerns, metal-insulator-semiconductor (MIS) systems have emerged as a promising strategy. In MIS photocatalysts, the metal layer serves as the catalyst and the insulator serves as a protective layer. Besides improving stability, these MIS systems can be engineered to maximize the light absorption and the generated photovoltage. Previous research has shown that the insulator layer thickness is an important parameter that can be tuned to optimize the photovoltage [3,4]. The objective of this work is to further elucidate the mechanism by which the nanoscopic control of the insulator thickness enhances the performance of MIS photoelectrocatalysts and develop design principles to achieve even higher efficiencies. We will demonstrate our results by using an Ir/HfO_2­/n-Si MIS system and by comparing the experimental results to a theoretical model. This approach is general to other insulators and provides insights to identify favorable insulator material properties and further optimize the photovoltage in these MIS systems for water splitting applications.

References

1. Seitz, L.C., Chen, Z., Forman, A.J., Pinaud, B.A., Benck, J.D., Jaramillo, T.F. ChemSusChem 7, 1372, (2014).
2. Hu, S., Lewis, N.S., Ager, J.W., Yang, J., McKone, J.R., Strandwitz, N.C. Phys. Chem. C 119, 24201, (2015).
3. Quinn, J.P., Hemmerling, J.R., Linic, S. ACS Catal. 8, 8545, (2018).
4. Digdaya, I.A., Trzesniewski, B.J., Adhyaksa, G.W., Garnett, E.C., Smith, W.A., Phys. Chem C 122, 5462, (2018).