(668e) Experimental and Modeling Analysis of the Role of Insulating Layers on the Performance of Metal-Insulator-Semiconductor Photoelectrocatalysts for Solar Water Splitting

Solar water splitting is a promising avenue for sustainable hydrogen production.Most attractive materials for these applications contain semiconductor light absorbers combined with metal electrocatalysts. Techno-economic analysis has demonstrated that optimal performance requires semiconductors with a band gap 1-2 eV.Among attractive semiconductors, Si has been widely used since it has a band gap of 1.1 eV and is earth abundant.Unfortunately, Si and most semiconductor materials within this band gap range are chemically unstable under relevant reaction conditions.To address this issue, metal-insulator-semiconductor (MIS) materials have been investigated where the metal serves as the electrocatalyst (EC), and the insulator is introduced to protect the semiconductor (SC) light absorber from the harsh reactive environment.

We used numerical methods to iteratively solve the Poisson’s and charge carrier continuity equations to determine the potential and charge carrier concentration profiles across the illuminated MIS interface.^1-2Using the Butler−Volmer equation to model the rate of reaction on the catalyst, we have shown that the thickness of the insulating layer has a strong impact on the modeled system parameters.We have also fabricated experimental model systems using atomic layer deposition (ALD) to deposit variable layers of HfO₂ insulating layer on Si.Electrochemical testing was performed using a three-electrode setup and OER activity was measured under 1-sun-illumination under basic conditions.

Our studies indicate that by tuning the insulator layer thickness, the photovoltage in MIS systems can be optimized.Our finite-element-model showed that the improvement in photovoltage of a MIS system is due to the insulating layer-induced modification in the flux of charge carriers from the semiconductor to the metal.³Consequently, introducing the insulating layer minimizes parasitic losses by tuning the transfer of charge carriers.These insights provide general strategies to analyze MIS systems and optimize the design to approach fundamental performance limits.

1.Quinn, J.,Hemmerling,J.,Linic, S.,ACS Catal.(2018)

2.Quinn, J.,Hemmerling,J.,Linic,S.,ACS Energy Lett.(2019)

3.Hemmerling,J.,Quinn,J.,Linic,S.,Adv.Energy Mat.(2020)