Doped, porous iron oxide films and their optical functions and anodic photocurrents for solar water splitting

Abstract

The fabrication and morphological, optical, and photoelectrochemical characterization of doped iron oxide films is presented. The complex index of refraction and absorption coefficient of polycrystalline films are determined through measurement and modeling of spectral transmission and reflection data using appropriate dispersion relations. Photoelectrochemical characterization for water photo-oxidation reveals that the conversion efficiencies of electrodes are strongly influenced by substrate temperature during their oblique-angle physical vapor deposition. These results are discussed in terms of the films’ morphological features and the known optoelectronic limitations of iron oxide films for application in solar water splitting devices.

Optical properties of iron oxide (α-Fe2O3) thin films deposited by the reactive evaporation of iron

“…In an earlier study, the refractive index was reported at a single spectral position [4]. It is worth mentioning that only in a few studies the obtained films were transparent, with transmittance exceeding 80% in the visible and near infrared ranges [3,4,10,12].…”

“…The dispersion relations were determined for ␣-Fe 2 O 3 thin films deposited by sputtering [5], sol-gel [6,7], and spray pyrolysis [9]. The optical properties of titanium-doped ␣-Fe 2 O 3 , deposited by pulsed laser deposition, were reported [12]. Moreover, the optical constants of ultrathin ␣-Fe 2 O 3 films were reported for films prepared by the oxidation of bulk iron [13].…”

“…Therefore, it has been investigated as a potential candidate for many optical applications, such as solar energy conversion, electrochromism, photocatalysis, interference filters, and photo-oxidation of water [1][2][3][4]. Hematite thin films have been prepared by a variety of techniques, including sputtering [2,5], sol-gel-deposition [6,7], spray pyrolysis [3,8,9], metalorganic deposition [10], electrodeposition [11], and pulsed laser deposition [12]. One of the simplest techniques for the preparation of ␣-Fe 2 O 3 thin films is reactive evaporation, which requires no more than evaporation of pure iron in an oxygen atmosphere [4].…”

Effect of Cr doping on the photoelectrochemical performance of hematite nanorod photoanodes

“…For example, the resistivity of a-Fe 2 O 3 was decreased by more than 3 orders of magnitude by 0.2% doping with Mg 2 + [32], which proved to be especially effective for the enhancement of PEC water splitting activity [33]. Ti-doped a-Fe 2 O 3 photoanodes have been produced using different methods by many groups [22][23][24], and Ti incorporation was reported to efficiently improve the charge transport properties and the overall PEC performance. Especially, in Li's study, the Ti-doped a-Fe 2 O 3 film prepared by a facile deposition-annealing process achieved a benchmark comparable photocurrent density of 2.80 mA cm À2 at 1.23 V vs RHE [23].…”

“…In the past decades, many metal ions such as Ti [22][23][24], Cu [25], Zn [26], Sn [27][28][29], Cr [3], Pt [30], and Ta [31] have been adopted as effective dopants to improve the PEC activity of a-Fe 2 O 3 electrodes for water splitting. It was suggested that doping could increase the solar energy conversion efficiency of a-Fe 2 O 3 photoanodes by improving the electronic conductivity and charge transport properties.…”