Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

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Authors

Paradzah, Alexander Tapera
Diale, M. (Mmantsae Moche)
Maabong, Kelebogile
Kruger, T.P.J. (Tjaart)

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Elsevier

Abstract

Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.

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Keywords

Fluorine-doped tin oxide (FTO), Oxide thin films, Photoanodes, Water oxidation, Carrier dynamics, Optical properties, Photocurrent density, α-Fe2O3 electrodes, Photoelectrochemical (PEC) performance, Nanostructured hematite, Sol- gel method, Hematite, Ultrafast pump-probe spectroscopy, Under-layer materials, Stannic oxide (SnO2), Niobium oxide (Nb2O5), Silicon dioxide (SiO2)

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Citation

Paradzah, A.T., Diale, M., Maabong, K. & Kruger, T.P.J. 2018, 'Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy', Physica B : Consensed Matter, vol. 535, pp. 138-142.