Negative Shifts in the Flatband Potential by Adsorption of Iodide Ions on Surface-Alkylated and Pt Nanodotted n-Si(111) Electrodes for Improvement of Solar Cell Characteristics

Abstract

The flatband potential (UFB) and solar cell characteristics for surface-alkylated and Pt nanodotted n-Si(111) electrodes have been studied in normalI3−∕normalI− redox electrolytes using various alkyls as the surface-terminating group. It is found that the UFB for the surface-methylated and Pt nanodotted n-Si(111) electrodes shifts toward the negative with increasing I− concentration in the electrolyte, in parallel to the equilibrium redox potential Ueq(I3−∕I−) , and thus the open-circuit photovoltage Voc remains nearly constant among various normalI3−∕normalI− redox electrolytes with different Ueq(I3−∕I−) . The constant Voc is observed only for the normalI3−∕normalI− redox couples with varied I− concentrations and not for other redox couples, indicating that it is not caused by the Fermi level pinning via a surface state. The UFB shift with the I− concentration is explained in terms of the I− adsorption in the form of a Si–I⋯normalI− complex at surface Si–I bonds, which are formed at nonmodified (naked) Si sites. The n-Si electrodes modified with long-chain alkyls show similar negative shifts in the UFB by iodine adsorption. The UFB measurements in the dark and under illumination have also shown that the Pt nanodots act as an efficient catalyst (gate) for interfacial electron transfer.

Open circuit potential shifts of activated carbon in aqueous solutions during chemical and adsorption interactions

“…As seen from the data, different positive and negative potential shifts occurred. Directions and magnitudes of potential shifts obtained for the substances and brands of carbons studied are shown in Tables 3 and 4 6 ] on AR-3A (269 mV and 252 mV, respectively). Thus, it was shown that interaction between inorganic salts and activated carbons did not lead to adsorption of either cations or anions, since the total amounts of iron, chromium, and sulfur was unchanged after the contact of the salt solutions with carbons.…”

Activated Carbon Open Circuit Potential Shifts in Aqueous Solutions

“…Directions and magnitudes of potential shifts obtained for the substances and brands of carbons studied are shown in Tables 3 and 4. As seen in these tables, K 2 Cr 2 O 7 , ZnSO 4 , and K 3 [Fe(CN) 6 ] gave only positive potential shifts, whose magnitudes depended on the oxidation state of the activated carbon; the greatest positive shifts occurred with K 2 Cr 2 O 7 and K 3 [Fe(CN) 6 ] on AR-3A (269 mV and 252 mV, respectively). The interaction between inorganic substances K 4 [Fe(CN) 6 ], K 3 [Fe(CN) 6 ], and K 2 Cr 2 O 7 and activated carbons SKT-6A and AKU was studied in more detail.…”

“…The following inorganic salts and organic compounds were studied: Na 2 SO 4 , Na 2 SO 3 , CuSO 4 , ZnSO 4 , NaNO 3 , NaNO 2 , K 2 Cr 2 O 7 , K 4 [Fe(CN) 6 Table 1. Potentials of activated carbon were measured in time against the silver/silver chloride reference electrode.…”

“…4 Fe 3+ (aq) + 3 Fe(CN) 6 4-(aq) → Fe 4 Likewise, for the hexacyanoferrate(III) ion, a solution of FeSO 4 was used to produce a blue iron(II) hexacyanoferrate(III) precipitate:…”

“…3 Fe 2+ (aq) + 2 Fe(CN) 6 3-(aq) → Fe 3 [Fe(CN) 6 ] 2 (s) [2] Each solution of the hexacyanoferrates was tested by adding several drops of both ferrous and ferric ion solutions.…”