Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

Abstract

Widespread application of solar water splitting for energy conversion is largely dependent on the progress in developing not only efficient, but also cheap and scalable photoelectrodes. Metal oxides, which can be deposited with scalable techniques and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). In this paper, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one of the most promising metal oxide photoelectrodes, as a method to overcome the carrier transport limitations. Timeresolved microwave and terahertz conductivity measurements reveal more than two-fold enhancement of the carrier lifetime for the hydrogen-treated BiVO4, without significantly affecting the carrier mobility. This is in contrast to the case of tungsten-doped BiVO4, although hydrogen is also shown to be a donor type dopant in BiVO4. The enhancement in carrier lifetime is found to be caused by significant reduction of trap-assisted recombination, either via passivation of deep trap states or reduction of trap state density, which can be related to vanadium anti-site on bismuth or vanadium interstitials according to density functional theory calculations. Overall, these findings provide further insights on the interplay between defect modulation and carrier transport in metal oxide photoelectrodes, which will benefit the development of low-cost, highly-efficient solar energy conversion devices.

Determination of the Intrinsic Defect at the Origin of Poor H2 Evolution Performance of the Monoclinic BiVO4 Photocatalyst Using Density Functional Theory

“…Benchmark tests with increased cutoff energy up to 500 eV or including or by Relative stability of the various explored intrinsic defective BiVO 4 structures with respect to the pristine one was investigated by computing the defect formation energies under the experimental conditions, following the method that has been successfully applied to investigate the thermodynamic stability of various defective materials used in photocatalysis or photoelectrochemitry, and was in line with the experimental observations. [32][33][34] Benchmark tests with increased cutoff energy up to 500 eV or including Bi 5d-electrons on Bi revealed minor impact on the formation energy.…”

Directly Photoexcited Oxides for Photoelectrochemical Water Splitting

“…Mullins et al synthesized nanostructured BiVO 4 by means of reactive ballistic deposition. [181] As ignificant improvement of charge-carrierl ifetimew as achieved withouta ffecting carrier mobilityu sing hydrogen treatment. Through seed-mediated solution growth, ordered arrays of pyramid-shaped BiVO 4 werea chieved.…”

“…[176] They found that, with al arger glancing incident angle,t he photoactivity varied, dependingo ns urfaces tructure and morphology. However,atrade-off has to be made betweenhigh carrier density,w hich reduces carrier transporti mpedance, and lower carrierd ensity for less bulk recombination.Amore efficient procedure is either to build a gradient of dopantc oncentration in the out-of-plane direction, that is, ad istributed n + -n homojunction, [181] or to fabricatea type II heterojunction (hindering one kind of charge,w hile allowinga nother) to assist charges eparation; [182] by applying these approaches, the performance hasb een greatly enhanced. [177] Another strategy for solving the charge-transport problemi s through applying appropriately designed doping methods.…”

Kohlenstoffnitridmaterialien für photochemische Zellen zur Wasserspaltung

“…4) Schnelle Reaktionskinetik an der CN-Elektrolyt-Grenzfläche und Langzeitstabilität: Bei den meisten der kürzlich berichteten Hochleistungs-PEC umfasst die beste Konfiguration häufig einen Halbleiter und OER-Cokatalysatoren (an der Photoanode). In diesem Fall ist sowohl die Nutzung eines Cokatalysators [116,154] zeitaufgelçste Fluoreszenzmessungen [116,161] und zeitaufgelçste Mikrowellenleitfähigkeit, [5] hilfreich sein, um tiefere Einblicke in die beteiligten photoelektrochemischen Prozesse zu gewinnen. Es gibt mehrere Faktoren, die beim Integrieren eines Cokatalysators auf einer CN-Schicht berücksichtigt werden sollten.…”