Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance

Abstract

Spectra show both transient photocarriers and lattice heating.

The Spatial Collection Efficiency of Charge Carriers in Photovoltaic and Photoelectrochemical Cells

“…As discussed in Hayes et al 28 , the photogeneration yield of hematite changes considerably across the spectrum due to excitations that generate mobile charge carriers (LMCT bands) and excitations that do not (d-d transitions), depending on the wavelength. Considering the LMCT bands reported by Hayes et al 28 , the optimal spectral window for extracting the f(z) profile is between 356 and 396 nm, where LMCT transitions account for more than 93% of the total optical absorption.…”

“…For example, in transition metal oxides such as hematite (a-Fe 2 O 3 ) and copper vanadate (g-Cu 3 V 2 O 8 ), considered as potential photoelectrode candidates for PEC cells for solar water splitting, it has been reported that d-d transitions produce excited states that are site localized and hence cannot be harvested efficiently as useful photocurrent. [28][29][30][31] However, other transitions, such as ligand-to-metal charge transfer (LMCT) transitions, give rise to mobile charge carriers that contribute more effectively to the photocurrent. 28,31 Thus, different types of transitions yield different probabilities of the photogenerated charge carriers to contribute to the photocurrent, such that the effective charge carrier generation function, G, depends not only on the amount of light absorbed but also on the type of the electronic transition induced by the absorbed photons.…”

“…[28][29][30][31] However, other transitions, such as ligand-to-metal charge transfer (LMCT) transitions, give rise to mobile charge carriers that contribute more effectively to the photocurrent. 28,31 Thus, different types of transitions yield different probabilities of the photogenerated charge carriers to contribute to the photocurrent, such that the effective charge carrier generation function, G, depends not only on the amount of light absorbed but also on the type of the electronic transition induced by the absorbed photons. This leads to a wavelength-dependent charge carrier generation profile that can be written as:…”

“…28,29 Indeed, recent studies report wavelength-dependent charge carrier dynamics and transport properties in hematite, 28,31,40 suggesting that the charge carrier generation profile depends not only on the absorption profile, A(l,z), but also on the photogeneration yield, x(l), which accounts for the probability that absorbed photons of wavelength l give rise to mobile charge carriers (see Equation 5). Therefore, extracting the SCE profile out of the photocurrent action spectra requires prior information on x(l).…”

“…Considering the LMCT bands reported by Hayes et al 28 , the optimal spectral window for extracting the f(z) profile is between 356 and 396 nm, where LMCT transitions account for more than 93% of the total optical absorption. The SCE profiles were extracted from photocurrent action spectra within this spectral window, as indicated by the shaded region of Figure 3B, measured at different applied potentials.…”