Ultrafast carrier dynamics in BiVO₄ thin film photoanode material: interplay between free carriers, trapped carriers and low-frequency lattice vibrations

Abstract

We explore ultrafast carrier dynamics and interactions of photoexcited carriers with lattice vibrational modes in BiVO4 photoanode material using time-resolved terahertz spectroscopy and first-principles phonon spectrum calculations. We find that photoexcited holes form bound polaron states by introducing lattice distortion that changes phonon spectrum and suppresses the Ag phonon mode associated with opposite motion of Bi and VO4 molecular units. At excitation fluence higher than 1 mJ cm−2 (or 2 × 1015 cm−2 per pulse), lattice distortion due to self-localized holes alters the lattice symmetry and vibrational spectrum, resulting in bleaching of THz absorption by Ag phonons. Concurrently, we observe a short lived population of free carriers which exhibit Drude conductivity with mobility on the order of 200 cm2 V−1 s−1, orders of magnitude higher than typical carrier mobility in BiVO4. The anomalously high carrier mobilities are explained in the framework of a Mott transition. This demonstration of enhanced transport suggests how engineering BiVO4 photoanodes to take advantage of free carrier transport under high excitation conditions may in the future significantly enhance performance of photoelectrochemical devices

Balancing Light Absorption and Charge Transport in Vertical SnS2 Nanoflake Photoanodes with Stepped Layers and Large Intrinsic Mobility

“…[69,70] The sample was placed behind a 1.5 mm aperture in the center of an ≈3 mm to 400 nm beam spot to www.advancedsciencenews.com ensure uniform excitation of the studied portion. The vertical nanoflakes on quartz were excited by ≈100 fs duration, 400 nm pulses from a regeneratively amplified 1 kHz repetition rate Ti:sapphire laser at normal incidence as described in the previous reports.…”

“…[43][44][45][46][47][48] CSSgrown SnS 2 vertical nanoflakes were optically excited with 400 nm laser pulses with 100 fs duration and with 28 µJ cm −2 fluence, and transient photoconductivity (Figure 5a) was measured using a terahertz probe in the 0.25-1.70 THz frequency range, which corresponds to 1-7 meV energy range. [43][44][45][46][47][48] CSSgrown SnS 2 vertical nanoflakes were optically excited with 400 nm laser pulses with 100 fs duration and with 28 µJ cm −2 fluence, and transient photoconductivity (Figure 5a) was measured using a terahertz probe in the 0.25-1.70 THz frequency range, which corresponds to 1-7 meV energy range.…”

Atomic Layer Deposition of Space‐Efficient SnO2 Underlayers for BiVO4 Host–Guest Architectures for Photoassisted Water Splitting

“…Bismuth vanadate has for the past decade been studied as a photoanode for photoelectrochemical (PEC) water splitting, with continuous performance gains over time . The monoclinic scheelite phase (m‐BiVO 4 ) is the highest efficiency allotrope, with a conduction band edge near 0 V vs. the reversible hydrogen electrode (RHE).…”

Atomic Layer Deposition of Space‐Efficient SnO2 Underlayers for BiVO4 Host–Guest Architectures for Photoassisted Water Splitting

“…Bismuth vanadate has for the past decade been studied asa photoanode for photoelectrochemical (PEC) water splitting, [1] with continuous performance gains over time. [2][3][4][5][6][7][8][9][10][11] The monoclinic scheelite phase( m-BiVO 4 )i st he higheste fficiency allotrope, with ac onduction band edge near 0Vvs. the reversible hydrogen electrode (RHE).…”