Switching between Limiting Charge Extraction Regimes in an Illuminated Semiconductor-Metal-Organic Framework Junction

Area of Science:

• Materials Science
• Electrochemistry
• Photovoltaics

Background:

• Surface modification enhances photoelectrode performance by improving charge separation and transfer.
• Carrier transport within surface layers is often overlooked despite its impact on efficiency.

Purpose of the Study:

• To investigate the role of carrier transport within surface layers of modified photoelectrodes.
• To analyze limitations imposed by electron transport in a model metal-organic framework (MOF) coated photocathode.

Main Methods:

• Fabrication of p-Si/GaP photocathodes coated with a redox-active Zn-naphthalene diimide bis-pyrazolate (NDI) MOF layer.
• Experimental photoelectrochemical measurements under varying illumination intensities and electrolyte conditions.

Main Results:

• Electron transport limitations within the MOF surface layer were identified as a critical factor affecting photocurrent.
• A transport-limited regime emerges at higher illumination intensities, influenced by the semiconductor and electrolyte.
• Cation-coupled photoelectron hopping in the MOF layer allows visualization of transport dynamics.

Conclusions:

• Electron transport in surface layers is a significant, often neglected, factor in photoelectrode performance.
• Understanding and optimizing this transport is essential for designing efficient surface-modified photoelectrodes.
• The findings are relevant for various surface-modified systems, including those with thick cocatalysts or polymer coatings.