Stabilization of Si Photoanodes in Aqueous Electrolytes through Surface Alkylation

Abstract

A two-step chlorination/alkylation method was used to introduce −C n H2 n +1 (n = 1−6) functionality onto single-crystal, (111)-oriented, n-type Si surfaces. H-terminated Si photoanodes were unstable under illumination in contact with an aqueous 0.35 M K4Fe(CN)6−0.05 M K3Fe(CN)6 electrolyte. Such electrodes displayed low open-circuit voltages and exhibited a pronounced time-dependent deterioration in their current density vs potential characteristics due to anodic oxidation. In contrast, Si surfaces functionalized with −CH3 and −C2H5 groups displayed significant improvements in stability while displaying excellent electrochemical properties when used as photoelectrodes in the aqueous Fe(CN)6 3-/4- electrolyte.

Control of the Stability, Electron-Transfer Kinetics, and pH-Dependent Energetics of Si/H2O Interfaces through Methyl Termination of Si(111) Surfaces

“…This behavior is in accord with the stability toward oxidation of alkyl-terminated Si(111) photoanodes under illumination. 25,26 The inhibition of oxidation enabled the measurement of interfacial electron-transfer processes that were in accord with the ideal model of electron transfer at the semiconductor/liquid interface. The current density for an electron-transfer process from the conduction band of an n-type semiconductor to an acceptor species, A, in solution, is given by …”

The role of surface passivation for efficient and photostable PbS quantum dot solar cells

“…Prior reports have recognized the deleterious effects of hydroxide species on the (photo)stability of other organic and inorganic PV technologies [29][30][31] , whereas alkyl-terminated ligands, such as oleic surfactants on QDs, can benefit the stability 32 . We tested the photostability of non-encapsulated QD solar cells soaked under simulated AM1.5G illumination in the N2-filled glove box, to eliminate additional degradation effects due to oxidation from the environment.…”

Preparation of air-stable, low recombination velocity Si(111) surfaces through alkyl termination

“…Crystalline Si has been functionalized previously at atmospheric pressure with organic layers through the use of alkyl Grignard and alkyl lithium reagents, 6 alkenes, [7][8][9] and phenyldiazonium salts, 10 while the reaction chemistry of porous Si has been developed yet further to include use of alkynes 11,12 and organohalides. 13 The electrochemical properties of some of these surfaces have been reported, 14,15 but to date there appears to be no information on the electrical properties of such systems. We report herein that crystalline Si functionalized through a twostep, wet-chemistry-based chlorination/alkylation procedure 6 has an extremely low surface recombination velocity.…”

“…The electrical properties of these alkylated surfaces in air correlate well with the improved electrochemical properties of these surfaces in contact with nonaqueous and aqueous electrolytes, and with the improved resistance to oxidation observed previously for such alkylated Si surfaces. 14,15 The long-term stability of the various alkylated surfaces in air is currently under investigation, as are other routes to surface functionalization that will be equally electrically passive yet allow further elaboration of the chemical and physical properties of overlayers on the Si surface.…”