ja9b10109_si_001.pdf (5.54 MB)
Why Silicon Doping Accelerates Electron Polaron Diffusion in Hematite
journal contribution
posted on 2019-12-15, 21:29 authored by Zhaohui Zhou, Run Long, Oleg V. PrezhdoIt is common that dopants enhance the conductivity of
hematite
Fe2O3, a popular photoanode, but the origin
of the enhancement remains unclear. We establish the detailed mechanism
by performing ab initio molecular dynamics simulations on electron
polarons (EPs) in Fe2O3, obtained by an excess
electron (e@EP) and a substitutional Si doping (Si@EP). For the first
time, we observe EP hopping in both pristine and doped Fe2O3. We find that the neighboring Fe–Fe distance
is the main driving force for the EP hopping, which occurs by the
adiabatic charge transfer mechanism. The EP transport is determined
by interplay of probabilities to reach a favorable configuration and
to hop in that configuration. The hopping barrier decreases as the
Fe–Fe distance decreases; however, hops can take place at larger
Fe–Fe distances, because such configurations are easier to
achieve. Importantly, we demonstrate that the Si dopant speeds up
the EP transfer process by increasing the EP mobility. The origin
can be ascribed to the following three factors: longer Fe–O
bonds, smaller activation energies, and creation of low energy metastable
EP states, in Si@EP Fe2O3 compared to e@EP Fe2O3. Interestingly, the EP hopping is random in
e@EP Fe2O3, but quasi-random in Si@EP Fe2O3 with specific pathways promoting efficient EP
transfer. These new findings greatly enrich the understanding of charge
transport in Fe2O3 photoanodes.
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Keywords
barrier decreasesEP mobilitySilicon Doping Accelerates Electron Polaron DiffusionEP transfer processhematite Fe 2 O 3Fe 2 O 3 photoanodesSi dopant speedsEP transportelectron polaronscharge transportadiabatic charge transfer mechanismFe 2 O 3activation energiessubstitutional Si dopingdynamics simulationsenergy metastable EP statesab initioEP transfer
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