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

Trends in open-circuit voltage (V(oc)), short-circuit current density (J(sc)), and energy conversion efficiency have been determined for the n-type Al(x)Ga1-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 (Eg) of the n-Al(x)Ga1-xAs alloy electrodes, with DELTA-V(oc)/DELTA-E(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 cm-2. J(sc) values under solar-simulated illumination decreased monotonically with increasing bandgap energy. The relatively low value of DELTA-V(oc)/DELTA-E(g) implies decreases in optimal energy conversion efficiency as the mole fraction of Al in the Al(x)Ga1-x(AS) alloy is increased. This is in contrast to the behavior of the n-GaAS(x)P1-x alloy series in the same electrolytes. The lower value of DELTA-V(oc)/DELTA-E(g) for n-Al(x)Ga1-x(AS) 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.