The impact of boundary conditions on calculated photovoltages and photocurrents at photocatalytic interfaces
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Research Letter
The impact of boundary conditions on calculated photovoltages and photocurrents at photocatalytic interfaces Asif Iqbal and Kirk H. Bevan, Materials Engineering, McGill University, Montréal, H3A 2B2, Québec, Canada Address all correspondence to Asif Iqbal and Kirk H. Bevan at E-mail: [email protected]; [email protected] (Received 20 January 2018; accepted 6 March 2018)
Abstract This work presents an in-depth study of how the choice of boundary conditions can impact upon the calculated photovoltage and photocurrent in photoelectrochemical (PEC) devices. Utilizing a floating boundary condition for the electrostatic potential and pseudo-Schottky boundary conditions for the interfacial electron/hole currents, we show simultaneous calculation of photovoltage and photocurrent. We also explore the significance of capturing the photovoltage, with proper boundary conditions, to accurately replicate practical photocurrent along with the realistic band alignments. Finally, our results decouple the interfacial hole transfer from the recombination at the interface/space-charged region and suggest possible methods to engineer the mesoscopic transfer process at PEC electrodes.
Introduction The rising societal and environmental costs of fossil fuels have driven a resurgence of intense research into artificial photosynthesis.[1–5] Solar-driven water splitting using light-absorbing semiconducting electrodes can delineate a possible route toward solar-to-chemical fuel conversion.[6] Extensive ongoing research in this direction has outlined critical scientific problems that entail urgent resolution through combined theoretical and experimental efforts.[7–11] Nevertheless, inadequate understanding of the complex processes governing semiconductor photocatalysis significantly impedes progress toward cost competitive unassisted solar water splitting.[11] Thus, device models exploring the mesoscopic charge transfer processes driving photocatalysis at semiconductor–liquid (SL) junctions can deliver fundamental insights into these processes and may provide more efficient photoelectrochemical (PEC) device designs. The modeling of mesoscopic phenomena at SL junctions comprises a long-standing problem in modern photoelectrochemistry.[12–14] In recent years, however, the development of numerical techniques, which provide an enhanced understanding of the photocatalytic process at SL junctions, has gained a considerable amount of attention. This includes, but is not limited to the calculation of steady-state band diagrams,[15] transient analysis of PEC device behavior,[16] modeling of surface-state dynamics,[7] complete solution of combined driftdiffusion equations,[17] and the simulation of electrocatalystcoated photoelectrodes.[18] In general, mesoscopic charge transport in an SL junction can be self-consistently calculated by solving the coupled Poisson-continuity equations.[17] However, to capture the photocurrent (Jph) and the
photovoltage (Vph) (two of the most commonly measured quantities in typical PEC experiments),
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