Tuning p-Si(111) Photovoltage via Molecule|Semiconductor Electronic Coupling

Area of Science:

• Materials Science
• Surface Chemistry
• Electrochemistry

Background:

• Photoelectrochemical (PEC) device efficiency is fundamentally limited by semiconductor junction energetics and band alignment.
• Controlling these properties through molecular functionalization offers a promising strategy for improving solar fuel generation.

Purpose of the Study:

• To investigate the structure-function relationship between chemically functionalized p-type silicon (pSi(111)) surfaces and their photoelectrochemical performance.
• To elucidate the interplay of chemical structure, electronic coupling, and interfacial dipoles in molecularly modified semiconductor junctions.

Main Methods:

• Covalent attachment of various aryl surface modifiers (phenyl, nitrophenyl, anthracene, nitroanthracene) to pSi(111) surfaces.
• Electrochemical characterization using methyl viologen as a redox mediator to determine band edge shifts and barrier heights.
• Photoelectrochemical measurements to assess solar fuel performance (V_oc).
• Density Functional Theory (DFT) calculations to analyze the electronic structure of the functionalized interfaces.

Main Results:

• High-fidelity pSi(111) surfaces with low defect densities (< 50 cm/s) were achieved.
• Systematic shifts in band edges (up to 0.99 V barrier height) and high photoelectrochemical performance (V_oc up to 0.43 V vs MV²⁺) were observed, correlating with interfacial dipoles.
• Functionalization was extended to hydrogen evolution reaction (HER) conditions, demonstrating tunable V_oc in a pSi(111)-R|TiO₂|Pt architecture.
• DFT calculations revealed hybridization between molecule-based electronic states and silicon band edges, indicating electronic coupling and the formation of induced density of interfacial states (IDIS).

Conclusions:

• Molecular functionalization provides precise control over semiconductor energetics and band alignment for PEC devices.
• The chemical structure of surface modifiers dictates interfacial dipole formation and electronic coupling, significantly impacting performance.
• The findings highlight the critical interplay between interfacial chemistry, electronic structure, and device efficiency, paving the way for rational design of advanced solar fuel systems.