A Hybrid Semiconductor Electrode for Wavelength‐Controlled Switching of the Photocurrent Direction

Abstract

The development of molecular and nanoscale assemblies that are capable of performing logic-gate functions has attracted significant interest aimed at novel approaches to information storage and processing.[1] Among other strategies, research has focused on novel types of photoelectrochemical devices, as their output can be controlled by selective stimulation with light; photons are considered the most efficient agent for driving the communication between chemical logic gates.[2] Of particular interest are photoelectrodes that exhibit wavelength-dependent switching of the photocurrent direction, as these could be exploited for information processing controlled simply by photons of different energy. [3, 4] Observations of wavelength-dependent changes in photocurrent direction have been reported for several different systems, such as metal-chlorophyll-metal sandwich cells, [5] gold electrodes covered with helical peptides containing various chromophores, [6] polymer multilayers, [3] and a ruthenium complex linked to viologen and a palladium phthalocyanine derivative.[7] Bilayers or core-shell composites of organic polymers and TiO 2 , [8] as well as TiO 2 modified with Fe II complexes [4,9] or with a ruthenium cluster dye also show these effects.[10]Herein we report the fabrication and characterization of a novel photoelectrode that exhibits unusually sharp wavelength-controlled switching of photocurrent direction. The electrode is a hybrid assembly of two inorganic nanocrystalline semiconductors-nitrogen-modified TiO 2 (TiO 2 -N, an ntype semiconductor) and CuI (p-type)-deposited on conducting indium-tin oxide (ITO) glass. Figure 1 shows a crosssectional view of the electrode with CuI nanocrystals randomly distributed in the interpore space of a densely packed pressed layer of nanocrystalline TiO 2 -N. The atomic ratio of Ti/Cu as measured by energy-dispersive X-ray analysis was 2.0 AE 0.1.Figure 2 a shows photocurrent transients for different wavelengths under intermittent irradiation recorded at 0.18 V vs. NHE. Whereas cathodic photocurrents are observed at wavelengths up to 410 nm, the direction of the photocurrent changes sharply to anodic above 420 nm. The incident-photon-to-current efficiencies (IPCE) exhibit cathodic and anodic maxima at 400 nm and 430 nm, respectively (Figure 2 a, inset). The switching behavior was observed in the potential range from 0 to 0.25 V vs. NHE and the four-cycle repetition experiment (Figure 2 b) reveals excellent stability of the photocurrent response.

(Photo)electrochemical Methods for the Determination of the Band Edge Positions of TiO2‐Based Nanomaterials

“…In the latter approach, 2 Advances in Physical Chemistry transition metals [86][87][88] or main-group elements like carbon [35,89], nitrogen [31,[90][91][92][93][94][95][96][97], and sulfur [98,99] are introduced into the lattice of titania resulting in formation of intrabandgap donor and acceptor levels, allowing thus for visible light (λ > 400 nm) excitation. Apart from the fields of solar cells and photocatalysis, the visible light-responsive TiO 2 materials opened up a route for further developments including photoelectrochemistry-based sensors [100,101] and light-addressable photoelectrochemical optoelectronic devices [102][103][104][105][106].…”

Hybrid Semiconducting Materials: New Perspectives for Molecular‐Scale Information Processing

“…The opposite effect is observed in the case of cathodic polarization with potentials higher than the Fermi level of the p-type component (Figure 7.14c). Composite materials with reported photocurrent switching following the above mechanism include p-n bulk structures based on n-TiO 2 -N/p-CuI [129], n-BiVO 4 /p-Co 3 O 4 [130], n-BiVO 4 /p-CuO [130], n-TiO 2 /p-Se [131,132], and n-CdS/p-CdTe [133]. If the optical criterion fails, the selective photoexcitation of semiconducting components is no longer possible.…”

Wavelength-switchable photocurrent in a hybrid TiO2–Ag nanocluster photoelectrode

“…[1][2][3] To trigger the signal change or switching in nanodevices, different stimuli including light, pH value, and applied potential have been used to design various switchable systems. 4,7 To date, several switchable photocurrent systems including helical peptide monolayers modified with different chromophores 4 or the assemblies of polymer nanosheets, 10 TiO 2 photoelectrodes modified with the ruthenium dye or Fe II complexes, 7,11 and hybrid n-/p-type semiconductor photoelectrodes 12,13 have been reported. Amongst various stimuli, the photon is one of the most convenient because it can simply drive the communication between the generated charges and the modified electrodes.…”

“…The use of Ag NCs in photoelectrodes as photosensitizers has been reported. 12 In our case, the mesoporous TiO 2 layer was fabricated using a doctor-blade method and the Ag NCs were wetchemically loaded on the TiO 2 layer (Fig. 1 and 2.…”

“…1 and 2. 12,20 Based on the above analysis, the mechanism of the switching of the photocurrent direction is rationally depicted in Fig. 18 In order to verify whether Ag NCs can solely be used as photocatalysts, the Ag NCs loaded on the bulk Au electrode through the linkage of (3-mercaptopropyl)trimethoxysilane (MPTMS) were fabricated and they exhibited cathodic photocurrent as shown in Fig.…”