Trends in the open circuit voltage of semiconductor/liquid interfaces: studies of n-AlₓGa₁₋ₓAs/CH₃CN-Ferrocene^(+/0) and n-AlₓGa₁₋ₓAs/KOH-Se^(~/2~)(aq) Junctions

Abstract

Trends in open-circuit voltage (V_(oc)), short-circuit current density (J_(sc)), and energy conversion efficiency have been determined for the n-type AlₓGa₁₋ₓAs series of photoelectrodes (x = 0.0, 0.09, 0.16, 0.24, 0.31) in contact with CH₃CN-Ferrocene^(+/0) and KOH-Se^(~/2~)(aq) electrolytes. V_(oc) increased linearly with increases in bandgap energy (E_g) of the n-AlₓGa₁₋ₓAs alloy electrodes, with ΔV_(oc)/ΔE_g = 0.45 ± 0.04 V eV⁻¹ in CH₃CN and 0.41 ± 0.09 V eV⁻¹ in KOH-Se^(~/2~)(aq) at a light intensity sufficient to provide J_(sc) = 1.0 mA cm². J_(sc) values under solar-simulated illumination decreased monotonically with increasing bandgap energy. The relatively low value of ΔV_(oc)/ΔE_g implies decreases in optimal energy conversion efficiency as the mole fraction of A1 in the AlₓGa₁₋ₓAs alloy is increased. This is in contrast to the behavior of the GaAsₓP₁₋ₓ alloy series in the same electrolytes. The lower value of ΔV_(oc)/ΔE_g for n-AlₓGa₁₋ₓAs also indicates that predictions of the "common anion rule" in solid-state barriers do not apply to this family of III—V semiconductor/liquid junctions.

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