n-Type Molybdenum Diselenide-Based Photoelectrochemical Cells: Evidence for Fermi Level Pinning and Comparison of the Efficiency for Conversion of Light to Electricity with Various Solvent/Halogen/Halide Combinations

摘要

Interfacial energetics for n-type MoSe2 (E(g) = 1.4 eV, direct) and photoelectrochemical conversion of light to electrical energy in the presence of X(n)(-)/X(-) (X = Cl, Br, I) have been characterized in CH3CN electrolyte solution. Data for MoSe2 in H2O/I3(-)/I(-) are included for comparison, along with a comparison of MoSe2-based cells with MoS2- (E(g) = 1.7 eV, direct) based cells. Cyclic voltammetry for a set of reversible (at Pt electrodes) redox couples whose formal potential, E(o), spans a range -0.8 to +1.5 V vs. SCE has been employed to establish the interface energetics of MoSe2. For the redox couples having E(o) more negative than approximately -0.1 V. vs. SCE, we find reversible electrochemistry in the dark at n-type MoSe2. When E (o) is somewhat positive of -0.1 V vs. SCE we find that oxidation of the reduced form of the redox couple can be effected in an uphill sense be irradiation of the n-type MoSe2 with = or > E(g) light; the anodic current peak is at a more negative potential than at Pt for such situations. The extent to which the photoanodic current peak is more negative than at Pt is a measure of the output photovoltage for a given couple. For E(o) more positive than approximately +0.7 V vs. SCE it would appear that this output photovoltage is constant at approximately 0.4 V. For a redox couple such as biferrocene (E(o)(BF(+)/BF = +0.3 V vs. SCE) we find a photoanodic current onset at approximately -0.2 V vs. SCE; a redox couple with E = 1.5 V vs. SCE shows an output photovoltage of 0.43 V under the same conditions.