Published July 30, 2020 | Supplemental Material
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Surface Passivation and Positive Band-Edge Shift of p-Si(111) Surfaces Functionalized with Mixed Methyl/Trifluoromethylphenylacetylene Overlayers

Abstract

Chemical functionalization of semiconductor surfaces can provide high-efficiency photoelectrochemical devices through molecular-level control of the energetics, surface dipole, surface electronic defects, and chemical reactivity at semiconductor/electrolyte junctions. We describe the covalent functionalization by nucleophilic addition chemistry of p-Si(111) surfaces to produce mixed overlayers of trifluoromethylphenylacetylene (TFMPA) and methyl moieties. Functionalization of Cl-terminated Si(111) surfaces with TFMPA moieties introduced a positive surface molecular dipole that in contact with CH₃CN or Hg produced a positive band-edge shift of the semiconductor relative to junctions with CH₃-Si(111) surfaces. Methylation of the Cl/TFMPA surfaces using methylmagnesium chloride resulted in the degradation of the TFMPA moieties, whereas methylation using methylzinc chloride allowed controlled production of mixed TFMPA/methyl-terminated surfaces and permitted reversal of the order of the functionalization steps so that nucleophilic addition of TFMPA could be accomplished after methylation of Cl–Si(111) surfaces. Mixed TFMPA/methyl functionalization resulted in a Si(111) surface with surface recombination velocities of 2 × 10² cm s⁻¹ that exhibited an ∼150 mV positive band-edge shift relative to CH₃–Si(111) surfaces.

Additional Information

© 2020 American Chemical Society. Received: March 9, 2020; Revised: June 29, 2020; Published: June 30, 2020. M.C. acknowledges support from the Ford Foundation under the Postdoctoral Scholar Fellowship program. B.S.B. and M.C. acknowledge support from the National Science Foundation CCI Solar Fuels Program under grant no. CHE-1305124. N.S.L. and M.C. acknowledges support from the National Science Foundation under grant no. CHE-1808599. Instrumentation support was provided by the Molecular Materials Resource Center of the Beckman Institute at the California Institute of Technology. The authors declare no competing financial interest.

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