Photoinduced Charge Transfer Research Articles

All-Atom Photoinduced Charge Transfer Dynamics in Condensed Phase via Multistate Nonlinear-Response Instantaneous Marcus Theory.

Photoinduced charge transfer (CT) in the condensed phase is an essential component in solar energy conversion, but it is challenging to simulate such a process on the all-atom level. The traditional Marcus theory has been utilized for obtaining CT rate constants between pairs of electronic states but cannot account for the nonequilibrium effects due to the initial nuclear preparation. The recently proposed instantaneous Marcus theory (IMT) and its nonlinear-response formulation allow for incorporating the nonequilibrium nuclear relaxation to electronic transition between two states after the photoexcitation from the equilibrium ground state and provide the time-dependent rate coefficient. In this work, we extend the nonlinear-response IMT method for treating photoinduced CT among general multiple electronic states and demonstrate it in the organic photovoltaic carotenoid-porphyrin-fullerene triad dissolved in explicit tetrahydrofuran solvent. All-atom molecular dynamics simulations were employed to obtain the time correlation functions of energy gaps, which were used to generate the IMT-required time-dependent averages and variances of the relevant energy gaps. Our calculations show that the multistate IMT could capture the significant nonequilibrium effects due to the initial nuclear state preparation, and this is corroborated by the substantial differences between the population dynamics predicted by the multistate IMT and the Marcus theory, where the Marcus theory underestimates the population transfer. The population dynamics by multistate IMT is also shown to have a better agreement with the all-atom nonadiabatic mapping dynamics than the Marcus theory does. Because the multistate nonlinear-response IMT is straightforward and cost-effective in implementation and accounts for the nonequilibrium nuclear effects, we believe this method offers a practical strategy for studying charge transfer dynamics in complex condensed-phase systems.

Two-dimensional tellurium nanosheet: A novel sensitive and stable surface-enhanced Raman scattering substrate

Two-dimensional (2D) materials with merits such as low cost, high chemical inertness and tunable electronic structure have become favorable candidates for next generation of surface-enhanced Raman scattering (SERS) platforms. However, the SERS sensitivity of 2D materials still needs to be improved and the large-scale synthesis methods should be developed to meet the requirements of practical applications. In this work, we explored performances of a brand-new SERS substrate made of 2D Te nanosheets (NSs), which exhibited thickness-dependent SERS properties, with thinner nanosheets yielding stronger SERS intensity. Under optimized conditions, the limits of detection (LODs) reached the order of 10−9 M combining with SERS enhancement factors (EFs) as high as 105 for copper phthalocyanine (CuPc) and methylene blue (MB). This impressive SERS performance could be attributed to the strong interaction and photoinduced charge transfer (PICT) processes between 2D Te NSs and molecules. Benefiting from the appropriate positions of valence band (VB) and conduction band (CB), the 2D Te NSs showed significant Raman enhancement for various molecules. Furthermore, the 2D Te NSs exhibited good air-stability for up to ∼2 months. These outstanding performances establish 2D Te NSs as a favorable SERS detection material with enormous potential in practical applications.

Construction of composite SERS substrate based on black phosphorus/mesoporous ZIF-67 and its selective monitoring of food additives

Semiconductor-based surface-enhanced Raman scattering (SERS) dependent on chemical mechanism has shown favorable selective enhancement and recognition capabilities. However, the limited Raman enhancement capability of conventional semiconductor-based still remains a great challenge in the effective monitoring of trace molecules in a practical complex environment. In this context, a novel two-dimensional composite semiconductor substrate was developed by in-situ growing reticular ZIF-67 mesoporous film upon black phosphorus (BP) nanosheets. An attractive synergistic chemical enhancement was triggered attributed to the efficient continued charge transfer process in the BP/ZIF-67 system. Particularly, a selective SERS enhancement of food additive molecules with different orbital structures was found owing to the coupling degree of intrinsic molecular resonance and photo-induced charge transfer. A sensitive detection of lycopene in beverage samples with a high recovery rate was finally realized by the BP/ZIF-67 composite substrate, which exhibited great potential in practical molecular selective recognition.

Photophysics of a Monoannulated Indigo: Intra- and Intermolecular Charge Transfer.

In the present work, the photoinduced charge-transfer (CT) behavior of 7-phenyl-6H-pyrido[1,2-a:3,4-b']diindole-6,13(12H)-dione (HCB) as a function of solvent polarity is reported by UV-vis absorption, steady-state and time-resolved fluorescence, and quantum chemical calculations. Calculated excited state energies of HCB at the B3PW91/6-31+G* level in vacuo and in solvents fulfill the energy requirements for singlet fission, which is the most promising path for the generation of highly efficient solar cells. The calculated potential energy curve for the compound reveals that the keto form is the predominant form in the ground state. Large bathochromic shifts in fluorescence with decreasing trends of quantum yield and lifetime indicate the occurrence of intramolecular CT from the indole bicycle to the indolinone moiety of HCB in highly polar solvents. The observed quenching of HCB fluorescence in different solvents without altering the spectral shape upon addition of a donor, triethylamine, is attributed to intermolecular CT, and it was examined in terms of the Stern-Volmer kinetics. The thermodynamics of photoinduced CT processes in HCB was analyzed using the measured photophysical data and cyclic voltammetric redox potentials via the Rehm-Weller equation. Analyses with the semiclassical Marcus theory suggest that both the CT processes fall under the Marcus normal region.

Harnessing interfacial π–d conjugation in covalently linked COFs with amine-Zn0.4Cd0.6S strengthens photoinduced charge transfer for photocatalysis

This study focuses on the effective enhancement of photocatalytic activity by strategically combining inorganic and organic semiconductors in a heterojunction. The challenge lies in seamlessly integrating these disparate components. In this research, we successfully fabricated inorganic–organic bridged heterojunctions between COF (Covalent Organic Framework) and metal sulfides, linked by stable covalent bonds. This approach led to efficient photocatalytic hydrogen (H2) evolution from water (H2O), marking a significant milestone. Comparing the performance of our ZCS-COF hybrids to the individual constituents, i.e., pure TpPa-1-COF and amine-Zn0.4Cd0.6S (ZCS), we observed a remarkable improvement in photocatalytic efficiency under visible light irradiation. Particularly noteworthy is the ZCS-COF-20 hybrid, which exhibited an impressive photocatalytic H2 production rate of 11.3 mmol g-1h−1. This rate is tenfold higher than that of the pristine TpPa-1-COF. This enhancement can be attributed to the interfacial π-d conjugation effects within the heterojunction. These effects facilitate the transfer of electrons from the metal sulfide to COFs via covalent bonds, ensuring efficient charge separation and transfer. Consequently, the resulting hybrid exhibits exceptional photocatalytic activity and stability.

Incorporation of the 99TcO4- Anion within the Ag24(C≡CtBu)204+ Cluster Unveiling the Unique Shell-to-Core Charge Transfer.

We present the first example of an 99TcO4- anion entrapped within the cavity of a silver cluster, revealing an unprecedented photoinduced charge transfer phenomenon. [Ag24(C≡CtBu)20(99TcO4)]·(BF4)3 (denoted as 99TcO4-@Ag24) was successfully synthesized and structurally characterized. Single-crystal X-ray diffraction and Raman spectroscopy reveal that the tetrahedral structure of the 99TcO4- anion sustains significant symmetry breaking with weakened Tc-O bond strength under confinement within the Ag24(C≡CtBu)204+ cluster. Notably, 99TcO4-@Ag24 exhibits a broadband electronic absorption spectrum in the visible region, which was absent for the other 99TcO4--containing compounds. Density functional theory calculations elucidate that host-guest electrostatic interactions result in an electron polarization effect between the 99TcO4- anion core and the Ag24 cationic shell. The emergence of an absorption band in 99TcO4-@Ag24 is rationalized by intermolecular charge transfer from the Ag24 electronic states to the lowest unoccupied molecular orbitals of 99TcO4- instead of the intramolecular electron transition observed in other 99TcO4--containing compounds.

Electrochemical synthesis of donor-acceptor triazine based polymers with halochromic and electrochromic properties

Two triazine monomers substituted with aromatic α,β unsaturated ketones (chalcones) as connecting arms, holding triphenylamine or carbazole ending groups, were by the first time synthesized using commercial and inexpensive starting materials in just two steps. Triphenylamine and carbazole groups were strategically introduced in order to allow electrochemical polymerization and redox activity of the obtained films. The chalcone, together with the triphenylamine or carbazole outer groups, give rise to the formation of a donor-acceptor systems, allowing the generation of photoinduced intramolecular charge transfer (ICT) electronic transitions and providing basic sites for protonation. Because of the star-like chemical structure of the used triazine, electrochemical polymerization of these monomers conducted to the formation of hyperbranched structures. The polymeric materials exhibited not only electrochromic properties but also showed a halochromic behavior. Spectroelectrochemical studies of the films showed different colorations in the three redox states (neutral, semioxidized and fully oxidized). The color changes are fast and easily detected by the naked eye. Electrochemical parameters such as optical contrast, coloration efficiency, optical memory, and long-term stability for both films were obtained and compared. A quasi-solid window-type electrochromic device was assembled using the electrogenerated polymer with the best electrochromic performance and stability. Moreover, the triphenylamine based polymer showed reversible color changes upon acid-base vapor exposure cycles, demonstrating that this polymer can be used not only in electrochromic devices but also in acid vapor sensors.

Enhanced degradation of bisphenol AF (BPAF) by visible light irradiated zero valent iron activated persulfate system

In this study, we conducted a systematic study of bisphenol AF (BPAF) removal by visible light coupled zero valent iron activated persulfate (Vis/Fe0/PS) system. The results showed that in Fe0/PS system, the removal rate of BPAF increased by 46.4% with the addition of Vis. New mechanisms were proposed: that PS became excited under Vis irradiation, which favored its reaction with Fe2+ to produce more free radicals. Moreover, Fe3+ could form complex with mono-hydroxylated and mono-carboxylated intermediate of BPAF, and the photoinduced ligand-metal charge transfer (LMCT) process could effectively transfer the charge to the metal ion, accelerating the reduction of Fe3+ to Fe2+ to enhance the generation of free radicals. The generation of hydroxylation products of bisphenol AF in the Vis/Fe0/PS system was greatly increased compared to the Fe0/PS system. The Vis/Fe0/PS system had a great application prospect, as it reduced the economic cost of treating bisphenol AF by at least 49.5% compared to other methods. Moreover, 99.6% of bisphenol AF was degraded after 45 min of reaction under natural light. Findings of this study provides new insights into the synergistic role of Vis in Fe0/PS systems and may advance the practical application of Vis/Fe0/PS system in water and wastewater treatment.

Fabrication of p-n Heterostructured Photocatalysts with Triazine-Based Covalent Organic Framework and CuInS2 for High-Efficiency CO2 Reduction.

The application of covalent organic frameworks (COFs) for the photocatalytic reduction of CO2 is mostly limited by severe charge recombination and low sunlight utilization. Herein, a triazine-based COF with an electron-rich and large π-conjugated system (TCOF) was employed as a building block and integrated with CuInS2 (CIS) to construct a noble-metal-free and high-efficiency photocatalyst for CO2 reduction. The in situ growth of CIS nanosheets on TCOF creates a p-n heterojunction, named CIS@TCOF. Compared with TCOF, the CIS@TCOF heterostructure exhibits a dramatically boosted photocatalytic performance in the reduction of CO2. The produced HCOOH yield over 10 wt % CIS@TCOF can be up to 171.2 μmol g-1 h-1 under visible light irradiation with good reproducibility, which is about 3 times as high as that over TCOF. Further in-depth studies indicate that the introduction of CIS not only enhances the visible light utilization but also restrains the recombination of photogenerated electron-hole pairs efficiently and facilitates the photoinduced charge transfer via the p-n heterojunction system due to the unique structural and compositional features. This research shows the great potential of COFs as efficient photocatalytic carbon fixation materials and provides a versatile route to construct semiconductor-COF heterostructures for photocatalysis.

Synergistic photoinduced charge transfer resonance from porous ZIF-67 decorated violet phosphorus array for SERS immunoassay of SARS-CoV-2 spike protein

As a rapid, highly sensitive, and user-friendly technique, surface-enhanced Raman scattering (SERS) has an extraordinary appeal to home self-test of COVID-19 during the post pandemic era. However, most of the existing SERS substrates have been still criticized in stability, repeatability, and sample enrichment. To address these obstacles, a novel non-metallic SERS substrate with porous surfaces and array geometry was developed by in-situ growing ZIF-67 particles on two-dimensional violet phosphorus (VP) matrix. Chemical enhancement was prominently promoted by the synergistic photoinduced charge transfer resonance in the hybrid band structure of the ZIF-67@VP substrate, facilitating a noble metal-similar enhancement factor of 6.11 × 107. The biocompatible ZIF-67@VP porous array with attractive enhancement capability and high anchoring efficiency was further utilized to monitoring SARS-CoV-2 spike protein in practical saliva samples based on a sandwich immunostructure, achieving a limit of detection of 1.7 ng/mL assisted by black phosphorus nanosheets. This nonmetallic immunoassay strategy with exceptional sensitivity and specificity is predicted to extend the utilization of SERS obstacle in daily infectious disease screening.

Symbiotic coupling of ZnO nanoparticles and coumarin photosensitizer in soft polyurethane matrices for boosting visible-light photocatalytic performance

Photocatalysis provides a practical and efficient solution to eliminate harmful substances from the environment by using light energy to activate the catalysts, and the development of sustainable photocatalysts easily recoverable and highly efficient in visible light remains a significant challenge. To address this issue, herein we present a facile approach to immobilize silane-functionalized ZnO NPs in polyurethanes with coumarin chromophore, resulting in highly active recyclable and reusable hybrid materials as photocatalytic systems for the degradation of organic dyes. Characterization of ZnO NPs revealed that the attachment of silane units to nanoparticles' surface decreased band gap values (up to 2.83 eV) and reduced the rate of charge carrier recombination. The performed investigations showed that incorporation of ZnO NPs into macromolecular chains via quaternization near to coumarin units promoted efficient photoinduced charge transfer between semiconductor nanoparticles and photosensitizer molecules. The band gap energy for hybrid films ranged between 2.73 eV and 2.32 eV, and the best photodegradation results for malachite green (MG) under visible-light irradiation were attained after 17 min (k = 17.7 × 10−2 min−1). The photocatalytic mechanism was clarified using scavenger tests and the photocatalytic efficiency of the best performing sample was tested for the degradation of other dyes (brilliant blue R, sunset yellow, congo red, rhodamine B, s.o.) and for the removal of MG from binary dye mixtures. The stability and integrity evaluation after 7 catalysis cycles reveals that the photocatalytic potential is retained without substantial structural changes.

Symmetry-Breaking Charge Transfer in Metal-Organic Frameworks.

High quantum-yield charge carrier generation from the initially prepared excitons defines a key step in the light-harvesting and conversion scheme. Photoinduced charge transfer in molecular electron donor-acceptor assemblies is driven by a sizable ΔG0, which compromises the potential of the generated carriers. Reminiscent of the special pair at the reaction center of the natural light-harvesting complex, symmetry-breaking charge transfer (SBCT) within a pair of identical struts of metal-organic framework (MOF) will facilitate the efficient generation of long-lived charge carriers with maximized potentials without incorporating any foreign redox species. We report SBCT in pyrene-based zirconium metal-organic framework (MOF) NU-1000 that leads to efficient generation of radical ions in a polar solvent and bound CT states in a low-polar solvent. The probe unveils the role of the low-lying non-Franck-Condon excitonic states as intermediates in the formation of the SBCT state from the initially prepared Franck-Condon S1 states. Ultrafast and transient spectroscopy─probed over 200 fs-30 μs time scale─evinces a kSBCT = (110 ps)-1 in polar media (εs = 37.5) forming solvated radical ions with recombination rate kCR = (∼45 ns)-1. A slower rate with kSBCT = (203 ps)-1 was recorded in low-polar (εs = 7.0) solvent manifesting a bound [TBAPy•+ TBAPy•-] state with kCR ≈ (17 μs)-1. This discovery, along with other unique photophysical features relevant to light harvesting, should define a MOF-based platform for developing heterogeneous artificial photon energy conversion systems.

Silver Nanoparticles Embedded ZnO Foam and its Surface Photoinduced Charge Transfer Behaviors

AbstractZinc oxide (ZnO) has been widely acknowledged as a highly effective photocatalyst for the degradation of organic pollutants. In this study, we presented silver nanoparticles (AgNPs) embedded ZnO foam photocatalyst (Ag−ZnO) on glass substrates by the chemical bath in‐situ co‐deposition method. Our findings demonstrat that at low Ag‐loading content, metallic Ag0 NPs are embedded within the ZnO foam, while at high Ag‐loading content, they accumulates increasingly from inside to the surface of the foam. With the increase of AgNPs loading from 0.1 mM to 1.5 mM, the absorption of Ag−ZnO foams in the visible light region gradually enhances. The photocatalytic degradation efficiency of rhodamine B (RhB) is the highest in Ag−ZnO foams when the Ag loading concentration reaches 0.8 mM, suggesting an optimal content of Ag for enhanced performance. This trend is attributed to the photo‐induced charge transfer behavior of Ag−ZnO samples. The AgNPs embedded inside the ZnO foam enhance the separation of photo‐induced charges and prevent their recombination. As a result, Ag−ZnO(0.8 mM) foam with more photo‐induced holes participate in the photocatalytic reaction, leading to a remarkably high photocatalytic activity.

Engineering Surface Passivation and Hole Transport Layer on Hematite Photoanodes Enabling Robust Photoelectrocatalytic Water Oxidation.

Regulation of charge transport at the molecular level is essential to elucidating the kinetics of junction photoelectrodes across the heterointerface for photoelectrochemical (PEC) water oxidation. Herein, an integrated photoanode as the prototype was constructed by use of a 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin-cobalt molecule (CoTCPP) and ZnO on hematite (α-Fe2O3) photoanode. CoTCPP molecules serve as a typical hole transport layer (HTL), accelerating the transport of the photogenerated holes to oxygen evolution cocatalysts (OECs). Meanwhile, ZnO as the surface passivation layer (SPL) can passivate the interfacial state and reduce the level of electron leakage from hematite into the electrolyte. After the integration of OECs, the state-of-the-art α-Fe2O3/ZnO/CoTCPP/OECs photoanode exhibits a distinguished photocurrent density and excellent stability in comparison with pristine α-Fe2O3. The simultaneous incorporation of a ZnO and CoTCPP dual interlayer can effectively modulate the interfacial photoinduced charge transfer for PEC reaction. This work provides in-depth insights into interfacial charge transfer across junction electrodes and identifies the critical roles of solar PEC conversion.

Surface‐Enhanced Raman Scattering in BIC‐Driven Semiconductor Metasurfaces

AbstractSemiconductor‐based surface‐enhanced Raman spectroscopy (SERS) substrates, as a new frontier in the field of SERS, are hindered by their poor electromagnetic field confinement and weak light‐matter interaction. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, enable strong electromagnetic field enhancement and optical absorption engineering for a wide range of semiconductors. However, the engineering of semiconductor substrates into metasurfaces for improving SERS activity remains underexplored. Here, an improved SERS metasurface platform is developed that leverages the combination of titanium oxide (TiO2) and the emerging physical concept of optical bound states in the continuum (BICs) to boost the Raman emission. Moreover, fine‐tuning of BIC‐assisted resonant absorption offers a pathway for maximizing the photoinduced charge transfer effect (PICT) in SERS. High values of BIC‐assisted electric field enhancement (|E/E0|2 ≈103) are achieved, challenging the preconception of weak electromagnetic (EM) field enhancement on semiconductor SERS substrates. The BIC‐assisted TiO2 metasurface platform offers a new dimension in spectrally‐tunable SERS with earth‐abundant and bio‐compatible semiconductor materials, beyond the traditional plasmonic ones.

Efficient photocatalytic degradation of textile dye pollutants using thermally exfoliated graphitic carbon nitride (TE–g–C3N4)

Graphitic carbon nitride (g–C3N4), an organic photocatalyst was reported to have beneficial properties to be used in wastewater treatment applications. However, g–C3N4, in its bulk form was found to have poor photocatalytic degradation efficiency due to its inherent limitations such as poor specific surface area and fast electron–hole pair recombination rate. In this study, we have tuned the physiochemical properties of bulk g–C3N4 by direct thermal exfoliation (TE–g–C3N4) and examined their photocatalytic degradation efficiency against abundant textile dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB). The degradation efficiencies for MB, MO, and RhB dyes are 92 ± 0.18%, 93 ± 0.31%, and 95 ± 0.4% respectively in 60 min of UV light irradiation. The degradation efficiency increased with an increase in the exfoliation temperature. The prepared catalysts were characterized using FTIR, XRD, FE-SEM, EDAX, BET, and UV-DRS. In BET analysis, TE–g–C3N4 samples showed improved surface area (48.20 m2/g) when compared to the bulk g–C3N4 (5.03 m2/g). Further, the TE–g–C3N4 had 2.98 times higher adsorption efficiency than the bulk ones. The free radicals scavenging studies revealed that the superoxide radicals played an important role in the photodegradation for dyes, when compared to the hydroxyl radical (.OH) and the photo-induced holes (h+), Photoluminescence (PL) emission and electrochemical impedance spectroscopy (EIS) spectra of TE–g–C3N4 indicated a lowered electron–hole pairs’ recombination rate and an increased photo-induced charge transfer respectively. Further, the TE–g–C3N4 were found to have excellent stability for up to 5 cycles with only a minor decrease in the activity from 92% to 86.2%. These findings proved that TE–g–C3N4 was an excellent photocatalyst for the removal and degradation of textile dyes from wastewater.

Structural Conjugation Tuning in Covalent Organic Frameworks Boosts Charge Transfer and Photocatalysis Performances.

Structural conjugation greatly affects the optical and electronic properties of the COF photocatalyst. Herein, we show that 2D hydrazone COFs with either π-extended biphenyl (BPh-COF) or acetylene (AC-COF) frameworks demonstrated distinct charge transfer and photocatalytic performances. The two COFs show good crystallinity and decent porosity as their frameworks are enforced by intra/interlayers hydrogen bonding. However, computational and experimental data reveal that AC-COF managed broader visible-light absorption and narrower optical bandgaps and performed efficient photoinduced charge separation and transfer in comparison with BPh-COF, meaning that the ethynyl skeleton with enhanced planarity better improves the π-conjugation of the whole structure. As a result, AC-COF exhibited an ideal bandgap for rapid oxidative coupling of amines under visible-light irradiation. Furthermore, taking advantage of its better charge transfer properties, AC-COF demonstrated considerable enhanced product conversion and notable functional tolerance for metallaphotocatalytic C-O cross-coupling of a wide range of both aryl bromides and chlorides with alcohols. More importantly, besides being recoverable, AC-COF showcased the previously inaccessible etherification of dihaloarene. This report shows a facile approach for manipulating the structure-activity relationship and paves the way for the development of a COF photocatalyst for solar-to-chemical energy conversion.

Generalized nonequilibrium Fermi's golden rule and its semiclassical approximations for electronic transitions between multiple states.

The nonequilibrium Fermi's golden rule (NE-FGR) approach is developed to simulate the electronic transitions between multiple excited states in complex condensed-phase systems described by the recently proposed multi-state harmonic (MSH) model Hamiltonian. The MSH models were constructed to faithfully capture the photoinduced charge transfer dynamics in a prototypical organic photovoltaic carotenoid-porphyrin-C60 molecular triad dissolved in tetrahydrofuran. A general expression of the fully quantum-mechanical NE-FGR rate coefficients for transitions between all pairs of states in the MSH model is obtained. Besides, the linearized semiclassical NE-FGR formula and a series of semiclassical approximations featuring Wigner and classical nuclear sampling choices and different dynamics during the quantum coherence period for the MSH model are derived. The current approach enables all the possible population transfer pathways between the excited states of the triad, in contrast to the previous applications that only addressed the donor-to-acceptor transition. Our simulations for two triad conformations serve as a demonstration for benchmarking different NE-FGR approximations and show that the difference between all levels of approximation is small for the current system, especially at room temperature. By comparing with nonadiabatic semiclassical dynamics, we observe similar timescales for the electronic population transfer predicted by NE-FGR. It is believed that the general formulation of NE-FGR for the MSH Hamiltonian enables a variety of applications in realistic systems.

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.

Exploring the mechanism of photoinduced charge transfer based on a dspirobifluorene- decorated donor under an external electric field

Charge separation and recombination dynamics of 3-(4-(9,9‘-spirobi[fluorene]-3-yl(phenyl)amino)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarboni-trile (SDPA-APDC) system with intervention of external electric field have been systematically explorated based on Marcus theory. Theoretical exploration on excited-state properties of SDPA-APDC system was presented with density functional theory and time-dependent density functional theory. Our results show the PCT reaction of SDPA-APDC system occurs in the inverted region judging from the result of |ΔG| >λ. Furthermore, the calculative KCS shows a evident variation with addition of different Fext strengths and the positive electric field behaves an accretion in KCS. Additionally, as meaningful parameter of the Marcus theory, electronic coupling and Gibbs free energy were affected by external electric field. Our results advise this strategy as a useful tool to evaluate the impact of external electric field on charge transfer process and conduct design of novel organic-based D/A interfaces.