Photoinduced Charge Transfer Properties Research Articles

Photoinduced charge transfer in small-molecule organic solar cells dependent on external electric field

In this paper, MTDATA is selected as the electron donor and BPhen as the acceptor. The trianiline structure of the donor molecule provides a variety of charge transfer pathways for charge separation. Based on Marcus theory, the photoinduced charge transfer properties of non-fullerene acceptor organic solar cells (NFA-OSCs) in external electric field (Fext) were studied. By analyzing the changes of reorganization energy (λ), Gibbs free energy (ΔG), electron transfer integral (Vda) and charge transfer rate under the influence of Fext, it was found that Fext can effectively regulate the charge transfer. Moreover, the change of charge transfer rate under Fext is similar to Vda, indicating that Vda is the main factor affecting charge transfer rate. To a certain extent, this study provides theoretical support for improving the photoelectric performance of NFA-OSCs.

Study of photo-induced charge transfer properties in Cs3Bi2I9/BiFeO3/TiO2 film

Inorganic lead-free perovskite Cs3Bi2I9 has attracted extensive attention due to its enhanced stability and environmental friendliness. However, the photon-to-current conversion of Cs3Bi2I9 perovskites is not efficient, partly due to inefficient electron-hole separation. In this manuscript, BiFeO3 was deposited at the interface of Cs3Bi2I9/TiO2 as the interface modifier by sol–gel method, and the photocurrent and responsiveness of the Cs3Bi2I9/BiFeO3/TiO2 were significantly higher than those of the Cs3Bi2I9/TiO2 based device. Kelvin probe force microscope, photoelectrochemical impedance spectroscopy and in-situ surface photovoltage spectra demonstrated that a self-polarized electric field of BiFeO3 contributed to the separation of photogenerated charge carriers at the Cs3Bi2I9/TiO2 interface. By analyzing the surface photovoltage phase spectra via a vector model method, complicated surface photovoltage processes were identified, and a detailed relationship between photocurrent generation and transfer characteristic of the photogenerated charge carriers have been discussed.

Unraveling photo-induced charge transfer properties at 3D/2D perovskite interfaces via in-situ surface photovoltage spectroscopy

As a non-destructive and contactless characterization technique, the surface photovoltage (SPV) method based on a lock-in amplifier was applied to characterize charge transfer at the nanoscale of 3D/2D perovskite interface. The SPV response of the 3D/2D perovskite was found to be stronger than that of the 3D perovskite, suggesting improved separation and transfer of photo-induced electron-hole pairs by the 2D overlayer. The photovoltaic process can be presented as a vector diagram with the magnitude and the phase angles to unravel charge transfer direction. The magnitude of the overall photovoltaic vector increases with an anticlockwise rotation and confirms the hole transfer at 3D/2D perovskite interfaces. Moreover, light-chopping-frequency dependent measurements were performed to study photogenerated electron transfer kinetics at the 3D/2D interface. The frequency of peak SPV for 3D/2D MAPbI3 perovskite was higher than that of 3D MAPbI3 demonstrated a faster charge separation in 3D/2D interface. The results provide valuable information about the in-situ charge transfer properties of photogenerated charge carriers at the 3D/2D perovskite interfaces.

Sulfur Vacancies‐Triggered High SERS Activity of Molybdenum Disulfide for Ultrasensitive Detection of Trace Diclofenac

AbstractDue to the efficient photoinduced charge transfer properties of nonmetals, nonmetallic surface‐enhanced Raman scattering (SERS) substrates have been advanced rapidly these years. And among of these, molybdenum disulfide (MoS2) is perceived as one of the most representative nonmetallic SERS substrates due to its abundant active sites. However, its progress in SERS field is severely hindered because of the lower SERS activity. Herein, one type of vacancies‐triggered highly sensitive SERS substrate based on nanostructured MoS2 with sulfur vacancies (VS) is proposed. The VS‐MoS2 substrates are intended to promote the SERS performance through the VS density regulation. Intrinsically, moderate VS can change the bandgap structure of MoS2, thus promoting the separation of internal carriers and enhancing the interaction with target species. Externally, the presence of VS can bring abundant adsorption sites on MoS2 surface, which greatly improves its ability to enrich target molecules. Both internal and external properties make VS‐MoS2 a high SERS activity substrate. Moreover, with the antibiotic contaminant diclofenac as a model probe molecule, the VS‐MoS2 substrate can accurately perceive its nanomolar concentration level with an enhancement factor up to 5.85 × 103. This work demonstrates exciting potential for analysis in real water environments based on nonmetallic SERS applications.

Carbon quantum dots passivated CsPbBr3 film with improved water stability and photocurrent: Preparation, characterization and application

All-inorganic cesium lead perovskite quantum dots (PQDs) with excellent optical properties have obtained extensive study in the field of optoelectronics. However, the poor stability of CsPbBr3 in the atmosphere and water severely limits their practical application. In this work, carbon quantum dots (CQDs) were exploited as dopants to improve the aqueous stability and photo-induced charge transfer properties of CsPbBr3. A highly fluorescent and aqueous stable film, consisting of CQDs-CsPbBr3 embedded in polyvinylidene fluoride (PVDF) polymer, was obtained by a simple spin coating method. Experiment results showed that the fluorescence (FL) intensity of CQDs-CsPbBr3@PVDF film retained about 85% of its initial value after being soaked in water for 50 days, indicating the good water stability of CQDs doped CsPbBr3. Besides, the photocurrent of CsPbBr3 film increased from 0.1 μA to 0.9 μA after doping CQDs under light irradiation, which proved that the improved charge transfer of CsPbBr3 was beneficial from CQDs. The application of CQDs-CsPbBr3@PVDF film in down-converted light emitting diodes has also been checked. This work highlighted one application of CQDs for improving the performances of PQDs in the field of optoelectronics.

Photo-Induced Charge Transfer on Pt/Bi₂WO6 Composite Photocatalysts.

Pt/Bi₂WO6 composite photocatalysts were prepared by a facile photoreduction method. Pt nanoparticles with an average size of 5-8 nm were successfully deposited on the surface of Bi₂WO6 microspheres and the photocatalytic activity of Bi₂WO6 was greatly improved by Pt nanoparticles. The photo-induced charge transfer properties of samples were studied by means of surface photovoltage (SPV) and transient photovoltage (TPV) techniques, giving an insight into the intrinsic reasons of the improvement in photocatalytic activity. The SPV and TPV results revealed that the deposited Pt nanoparticles could trap photo-induced electrons and then largely enhance the separation efficiency of photo-induced charge carriers.

Carbon Dots–Implanted Graphitic Carbon Nitride Nanosheets for Photocatalysis: Simultaneously Manipulating Carrier Transport in Inter‐ and Intralayers

Carbon dots (CDs) present unique photoinduced charge transfer and reservoir properties, showing promising application potential in photocatalysis. The in situ preparation of CDs in a graphitic carbon nitride (g‐C3N4) matrix provides not only a new approach for electronic structure modulation and heterostructure construction but also an effective way to improve their photocatalytic performance. However, incorporating CDs into ultrathin g‐C3N4 remains a challenge. Moreover, simultaneously tuning their carrier transport in inter‐ and intralayers is difficult but significant for their application as efficient photocatalysts. Herein, an unprecedented Se‐chaperoned thermal polymerization method for the synthesis of zero‐dimensional CD‐implanted g‐C3N4 nanosheets (CCNS) is reported. The CCNS simultaneously facilitate carrier transport and suppress recombination because of the seamless bonding heterostructure of CDs within the in‐plane domains of the g‐C3N4 nanosheets. Accordingly, the photocatalytic rates of water splitting for H2 evolution and CO2 reduction are enhanced 3.1 and 4.1 times, respectively. In addition, the photocatalytic RhB degradation efficiency dramatically increases 18 times. This work presents a promising solution to solving the current worldwide energy shortage and environmental pollution issues.

Switchable organoplatinum metallacycles with high quantum yields and tunable fluorescence wavelengths

The preparation of fluorescent discrete supramolecular coordination complexes (SCCs) has attracted considerable attention within the fields of supramolecular chemistry, materials science, and biological sciences. However, many challenges remain. For instance, fluorescence quenching often occurs due to the heavy-atom effect arising from the Pt(II)-based building block in Pt-based SCCs. Moreover, relatively few methods exist for tuning of the emission wavelength of discrete SCCs. Thus, it is still challenging to construct discrete SCCs with high fluorescence quantum yields and tunable fluorescence wavelengths. Here we report nine organoplatinum fluorescent metallacycles that exhibit high fluorescence quantum yields and tunable fluorescence wavelengths through simple regulation of their photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) properties. Moreover, 3D fluorescent films and fluorescent inks for inkjet printing were fabricated using these metallacycles. This work provides a strategy to solve the fluorescence quenching problem arising from the heavy-atom effect of Pt(II), and offers an alternative approach to tune the emission wavelengths of discrete SCCs in the same solvent.

Lignite-derived carbon quantum dot/TiO2 heterostructure nanocomposites: photoinduced charge transfer properties and enhanced visible light photocatalytic activity

A facile and green route to cleanly utilize lignite coal as a carbon source for preparing CQDs/TiO2 catalysts.

Polyoxometalate Photocatalysis for Liquid-Phase Selective Organic Functional Group Transformations

Polyoxometalates (POMs), which are anionic metal oxide clusters, have recently attracted considerable attention as photocatalysts because of their unique photoinduced charge-transfer properties, redox properties, acid–base properties, and reactivities. In this Review, we present a summary of recent developments in POM photocatalysis for organic synthesis. Various organic functional group transformations can be selectively induced by photoirradiation in the presence of catalytic amounts of suitably designed POMs. In particular, many liquid-phase functional group transformations based on the activation of substrates by decatungstate have been reported. However, decatungstate photocatalysis requires irradiation with UV light because of the large energy gaps between the O2–-based highest occupied molecular orbitals (HOMOs) and the W6+-based lowest unoccupied molecular orbitals (LUMOs) therein. Various strategies have been developed in efforts to utilize visible light, including hybridization with photosensiti...

Photoelectrochemical Performance for Water Oxidation Improved by Molecular Nickel Porphyrin-Integrated WO3 /TiO2 Photoanode.

A WO3 /TiO2 heterojunction photoanode was prepared by in situ growth of WO3 on a mesoporous TiO2 electrode. The photoinduced charge-transfer properties and chargeseparation improvement in this kind of type-II heterojunction were characterized by transient surface photovoltage spectra. By using sulfite oxidation as a hole scavenger, we demonstrated that 72 % of the photo-generated holes are reaching the surface of the photoanode, but the efficiency of hole injection (ηox ) into the electrolyte was only 48 %. For the first time, a NiII meso-tetra(4-carboxyphenyl)porphyrin (NiTCPP) was incorporated as a water oxidation catalyst into the WO3 /TiO2 heterojunction photoanode, which promoted the value of ηox to 81 %. The maximum applied bias photon-to-current efficiency for the WO3 /TiO2 /NiTCPP photoanode was determined to be 0.2 % at 1.01 V vs. the reversible hydrogen electrode (RHE), under which condition a Faradic efficiency of 89 % for water oxidation was achieved (averaged over 1 h of photolysis).

Study on the photoconductive properties of charge carriers in donor-acceptor copolymer P(EDOT-FL) and P(EDOT-FL):PCBM blend

The photoinduced charge transfer properties of low band gap donor-acceptor π-conjugated copolymer poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene)) labelled as P(EDOT-FL) has been investigated through solvatochromic and photoconductivity studies. The effect of strong acceptor, Phenyl-C61-butyric acid methyl ester (PCBM) on the photogeneration of free carriers is studied by comparing the fluorescence spectra and photoconductive properties of the polymer-PCBM blend [P(EDOT-FL):PCBM] films with the pristine polymer films. The positive solvatochromism exhibited by the P(EDOT-FL) revealed its photoinduced charge transfer nature of the absorption and emission bands. The blend films exhibited quenching of the fluorescence intensity and showed increased photoconductivity. Internal photocurrent efficiency and photoconductive sensitivity of the pristine P(EDOT-FL) films and P(EDOT-FL):PCBM blend films were calculated as a function of electric field, by measuring the photocurrent generated in the sample. Blend films exhibited higher internal photocurrent efficiency of 86% and photoconductive sensitivity of 5.44×10−7 SW−1cm at 70V/μm. The obtained photoconductive sensitivity at low electric field (<10V/μm) is sufficient for photorefractive applications.

Construction of p-n heterojunction β-Bi2O3/BiVO4 nanocomposite with improved photoinduced charge transfer property and enhanced activity in degradation of ortho-dichlorobenzene

To achieve efficient conversion of solar to chemical energy in photocatalysis, development of visible-light-induced catalysts with high charge carrier mobility and superior activity is essential. In this work, a novel β-Bi2O3/BiVO4 nanocomposite with p-n heterojuction structure, which is assembled by interconnected quantum dots, has been successfully constructed through a facile approach. The structural and optical properties of the as-prepared materials were comparatively characterized. Steady-state and transient-state photoluminescence spectra demonstrate that the photo-induced charge carriers in β-Bi2O3/BiVO4 nanocomposite display higher separation and much longer lifetime than those in individual BiVO4 samples, which is attributed to the formation of efficient interfacial electric field between β-Bi2O3 and BiVO4. The photocatalytic performance of the samples was explored by the degradation of ortho-dichlorobenzene (o-DCB). Electron spin resonance examinations confirmed that much more superoxide radicals were generated in the system of β-Bi2O3/BiVO4 nanocomposite, which could be mainly responsible for the outstanding activity. In addition, the adsorption and oxidation of o-DCB over the as-prepared materials were studied by in situ FTIR spectroscopy to investigate the nature of surface intermediates formed on the catalysts. To clarify charge migration route, a detailed photocatalytic mechanism in terms of the energy band structures is proposed.

Substitution Effects on the Photoinduced Charge-Transfer Properties of Novel Perylene-3,4,9,10-tetracarboxylic Acid Derivatives.

We report here the synthesis and photophysical study of a series of electron donor–acceptor molecules, in which electron-donating 4-methoxyphenoxy groups are attached to the 1,7-bay positions of four different perylene tetracarboxylic acid derivatives, namely, perylene tetraesters 1, perylene monoimide diesters 2, perylene bisimides 3, and perylene monobenzimidazole monoimides 4. These perylene derivatives are used because of their increasing order of electron-accepting capability upon moving from 1 to 4. Two additional donor–acceptor molecules are synthesized by linking electron-donating 4-methoxyphenyl groups to the imide position of perylene monoimide diester 2 and perylene bisimide 3. The motivation for this study is to achieve a good control over the photoinduced charge-transfer (CT) process in perylene-based systems by altering the position of electron donors and tuning the electron deficiency of perylene core. A comprehensive study of the photophysical properties of these molecules has shown a highly systematic trend in the magnitude of CT as a function of increased electron deficiency of the perylene core and solvent polarity. Importantly, just by changing the attachment of electron-donating group from “bay” to “imide” position, we are able to block the CT process. This implies that the positioning of the electron donor at the perylene core strongly influences the kinetics of the photoinduced CT process. In these compounds, the CT process is characterized by the quenching of fluorescence and singlet excited-state lifetimes as compared to model compounds bearing non-electron-donating 4-tert-butylphenoxy groups. Transient absorption spectroscopy did not reveal spectra of CT states. This most likely implies that the CT state is not accumulated, because of the faster charge recombination.

Study on photo-induced charge transfer properties in CdS quantum-dot-sensitized mesoporous TiO2 photoelectrode

In this study, well-crystallized mesoporous anatase TiO2 spheres (TiO2-MS) were prepared via a simple sol–gel process followed by subsequent hydrothermal treatment and then used as photoelectrode for quantum-dot-sensitized solar cell (QDSC) application. The mesoporous structure exhibits efficient QD loading and good light-scattering properties for light harvesting. In the meantime, both surface photovoltage technique based on lock-in amplifier and transient photovoltage measurement reveal that the QDs-sensitized mesoporous TiO2 sphere photoelectrode is conducive to promote the separation of photo-induced charges and reduce the charge recombination owing to the efficient charge transfer. As a result, the QDSCs based on mesoporous TiO2 spheres photoelectrode shows a power conversion efficiency of 1.34 %, which is significantly higher than that derived from P25 nanoparticle electrode. The relation between the performance of QDSCs and their photovoltage characterization was also discussed.

Controllable Synthesis of Bi2Fe4O9Nanocrystal with High Active Facets and the Enhanced Visible Light Photoelectrochemical Property

Bi 2 Fe 4 O 9 nanocrystals with high active facets were controllably synthesized via a chemical co-precipitation process followed by a hydrothermal treatment at various microenvironment. The nanocrystals can be controlled preferentially to grow along (001) and show flat side facets of (110) and (10). The photoinduced charge-transfer property of Bi 2 Fe 4 O 9 was significantly improved. Such a high photo-to-current conversion efficiency is ascribed to the synergistic effect of energy band structure and the high reactivity of exposed (110) and (10) facets. The high surface energy at the interface of the Bi 2 Fe 4 O 9 efficiently reduced the recombination of photoinduced electron-hole pairs, and thus increasing the lifetime of charge carriers and enhancing the photo-to-current efficiency of the Bi 2 Fe 4 O 9 .

Long-Range π-Conjugation in Phenothiazine-containing Donor-Acceptor Dyes for Application in Dye-Sensitized Solar Cells.

Four organic donor-π-bridge-acceptor dyes containing phenothiazine as a spacer and cyanoacrylic acid as an acceptor were synthesized and tested as sensitizers in dye-sensitized solar cells (DSCs). The influence of iodide- and cobalt-based redox electrolytes on the photovoltaic device performance was investigated. In these new dyes, systematic π-conjugation was extended by inserting one or two phenothiazine moieties and investigated within the context of the resulting photoinduced charge-transfer properties. A detailed investigation, including transient absorption spectroscopy and quantum chemical methods, provided important information on the role of extended π-conjugation on the photophysical properties and photovoltaic device performance. Overall, the results showed that the extension of π-conjugation by one phenothiazine unit resulted in the best device performance owing to reduced recombination rates, whereas extension by two phenothiazine units reduced dye adsorption on TiO2 probably owing to the increase in molecular size. The performance of the dyes in DSCs was found to be a complex interaction between dye structure and size.

Photoelectrochemical water splitting under visible light over anti-photocorrosive In2O3-coupling ZnO nanorod arrays photoanode

In2O3 quantum dots with a high crystallinity were deposited on the surface of ZnO nanorods through a chemistry bath method. The resulting In2O3-sensitizing ZnO nanorod arrays not only exhibited enhanced photoelectrochemical activity for water splitting under visible-light irradiation, but also possessed anti-photocorrosion property. The photo-induced charge-transfer property of In2O3 could be improved greatly by coupling with ZnO. This observation demonstrated that the heterojunction at the interface between In2O3 and ZnO could efficiently reduce the recombination of photo-induced electron–hole pairs and increase the lifetime of charge carriers and therefore enhance the photo-to-current efficiency of the In2O3–ZnO nanocrystalline arrays. It reveals that the heterojunction construction between two different semiconductors plays a very important role in determining the dynamic properties of their photogenerated charge carriers and their photo-to-current conversion efficiency.

Synthesis of g-C3N4/Ag3VO4 composites with enhanced photocatalytic activity under visible light irradiation

The g-C3N4/Ag3VO4 hybrid photocatalysts were developed to study the photocatalytic activity under visible light irradiation. The samples were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The photocatalytic activity of g-C3N4/Ag3VO4 composites for the photodegradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation was much higher than that of the pure g-C3N4 and Ag3VO4. The kinetics of the g-C3N4/Ag3VO4 composites were proposed to investigate the intervened effects of g-C3N4 to Ag3VO4 on the promotion of photocatalytic property. The photocurrents were measured to study the photoinduced charge-transfer properties of the g-C3N4/Ag3VO4 composites. The possible photocatalytic mechanism of the composites was proposed by implementing a series of radical trapping experiments to guide the further improvement of their photocatalytic activity. It is suggested that the outstanding photocatalytic activity of g-C3N4/Ag3VO4 composites was ascribed to the separation of the photoinduced electron–hole pairs with the integration of g-C3N4 and Ag3VO4 from analyses above.

Self-assembled BiVO4/Bi2WO6 microspheres: synthesis, photoinduced charge transfer properties and photocatalytic activities.

Three-dimensional (3D) BiVO4/Bi2WO6 composite microspheres with enhanced visible-light (λ > 420 nm) photodegradation activity of methylene blue (MB) were synthesized by a simple, one-pot, template-free solvothermal method. A mixture of ethylene glycol (EG) and H2O (volume ratio of EG-H2O was 1 : 1) was used as the solvent. To investigate the relationship between structure and photocatalytic performance, the as-synthesized samples were characterized by XRD, FESEM, HRTEM, UV-vis DRS, SPS and TPV. Structural characterizations indicated that the composite nanostructure mainly consisted of two single-crystal phases, which were BiVO4 and Bi2WO6. In addition, a possible growth mechanism of this microsphere composite and the separation process of photoinduced charge carriers in the heterojunction are discussed.