Photoinduced Hole Transfer Research Articles

In2O3/boron doped g-C3N4 heterojunction catalysts with remarkably enhanced visible-light photocatalytic efficiencies

Novel In2O3/boron doped graphite-like carbon nitride (In2O3/g-C3N4B) heterojunction catalysts were successfully fabricated via a facile water-bath combined with calcination method. The resulting 5% In2O3/g-C3N4B catalyst with a proper In2O3 and B content exhibits excellent visible-light photocatalytic activities. Its conversion ratio for tetracycline hydrochloride (TH) and nitric oxide (NO) is 2.0, 1.9 times higher than that of In2O3, g-C3N4, g-C3N4B, g-C3N4B-R (reference sample), respectively. And its CH4 evolution rate is 9.0, 3.6, 2.2, 2.5 times higher than that of In2O3, g-C3N4, g-C3N4B, g-C3N4B-R, respectively. The remarkably enhanced photocatalytic properties are mainly attributed to the result that an appropriate boron and In2O3 modified the g-C3N4 promoted the efficient separation and transfer of photoinduced electrons and holes from the heterojunction interface by the band alignment between In2O3 and g-C3N4B. The probable mechanism on the activity enhancement was also discussed. Moreover, 5% In2O3/g-C3N4B shows good activity stability as evidenced by three recycling reactions. This work offers some useful insights to design and fabricate other highly efficient and stable g-C3N4-based heterojunction multifunctional materials for energy conversion and environmental restoration applications in the near future.

Electronic Properties of the Graphdiyne/CH3NH3PbI3 Interface: A First‐Principles Study

Graphdiyne (GDY), when used as the surface modifier, significantly influences the optoelectronic properties of the perovskite solar cells. To explore such impact for novel high‐performance solar cells, herein, the interfacial interactions and electronic properties of the GDY/CH3NH3PbI3 heterostructures are investigated using density‐functional first‐principles calculations with empirical dispersion corrections. Three interfacial configurations formed by van der Waals interactions are created in nondestructive contact. The calculated charge density differences indicate that the built‐in electric field inside GDY/CH3NH3PbI3 could accelerate the transfer and separation of photoinduced electrons and holes. The enhanced absorption intensity in the visible region of the heterostructures demonstrates the enhancement mechanism of photocatalytic performance. As an effective encapsulation layer, GDY can improve the hole‐transport efficiency and, thus, the device performance.

In Situ Construction of a Two-Dimensional Heterojunction by Stacking Bismuth Trioxide Nanoplates with Reduced Graphene Oxide for Enhanced Water Oxidation Performance.

In this study, a two-dimensional heterojunction consisting of bismuth trioxide nanoplates and layered reduced graphene oxide was synthesized using a facile In Situ growth route. A series of characterization tests indicated that the reduction of graphene oxide played a key role as an electron collector for enhancing photoinduced charge carrier separation efficiency. Thus, the as-prepared reduced graphene oxide/bismuth trioxide composite exhibited enhanced photocatalytic water oxidation, which was higher than that of pristine bismuth trioxide under simulated solar light irradiation. Furthermore, the photoelectrochemical properties of the prepared hybrid system were investigated to understand the transfer of photoinduced electrons and holes between layered reduced graphene oxide and bismuth trioxide nanoplates. Thus, this strategy provided an efficient approach for the fabrication of graphene composites containing hierarchical ternary oxides for photocatalysis.

Photoinduced Carrier Dynamics at the Interface of Pentacene and Molybdenum Disulfide.

Understanding of photoinduced interfacial carrier dynamics in organic-transition metal dichalcogenides heterostructures is very important for the enhancement of their potential photoelectronic conversion efficiencies. In this work we have used density functional theory (DFT) calculations and DFT-based fewest-switches surface-hopping dynamics simulations to explore the photoinduced hole transfer and subsequent nonadiabatic electron-hole recombination dynamics taking place at the interface of pentacene and MoS2 in pentacene@MoS2. Upon photoexcitation the electronic transition mainly occurs on the MoS2 monolayer, which corresponds to moving an electron to the MoS2 conduction band. As a result, a hole is left in the valence band. This hole state is energetically lower than certain occupied states of the pentacene molecule; thus, the interfacial hole transfer from MoS2 to pentacene is favorable in energy. In terms of nonadiabatic dynamics simulations, the hole transfer time to the HOMO-1 state of the pentacene is estimated to be about 600 fs; however, the following hole relaxation process from HOMO-1 to HOMO takes much longer time of ca. 15 ps due to the large energy gap between HOMO-1 and HOMO. Moreover, our results also show that the subsequent radiationless recombination process between the hole transferred to the pentacene molecule and the remaining electron on the MoS2 CBM needs about 10.2 ns. The computational results shed important mechanistic insights on the interfacial carrier dynamics of mixed-dimensional pentacene@MoS2. These insights could help to design excellent interfaces for organic-TMDs heterostructures.

Anomalous Photoinduced Hole Transport in Type I Core/Mesoporous-Shell Nanocrystals for Efficient Photocatalytic H2 Evolution.

Controlling the carrier dynamics in a semiconductor nanoparticulate photocatalyst is the key to developing catalytic activity. Generally, type I band alignment is unsuitable for photocatalysts because the photoinduced carriers accumulate in the narrow bandgap semiconductor. To avoid the termination of reactions and/or photocorrosion of materials caused by carrier accumulation, it is common to employ type II band alignment for photoenergy conversion systems instead of type I. However, CdS/ZnS core/mesoporous-shell heterostructures show superior photocatalytic activity despite having type I band alignment that is generally unfavorable for photocatalytic reactions. Transient absorption spectroscopy and time-resolved microwave conductivity revealed efficient photoinduced hole transfer from the CdS phase to the ZnS phase. The defect-mediated hole transfer from the CdS to the ZnS phase resulted in long-lived charge separation (>2.4 ms) leading to high photocatalytic performance. This study provides insight into defect-mediated carrier transfer in nanoparticulate photocatalysts, which could be used as a guideline for the design of highly active and stable nanoparticulate photocatalysts.

Nonadiabatic Dynamics Simulations Reveal Distinct Effects of the Thickness of PTB7 on Interfacial Electron and Hole Transfer Dynamics in PTB7@MoS2 Heterostructures.

Mixed-dimensional hybrid heterostructures have attracted a lot of experimental attention because they can provide an ideal charge-separated interface for optoelectronic and photonic applications. In this Letter, we have employed first-principles DFT calculations and nonadiabatic dynamics simulations to explore photoinduced interfacial electron and hole transfer processes in two PTB7- nL@MoS2 models ( n = 1 and 5). The interfacial electron transfer is found to be ultrafast and completes within ca. 10 fs in both PTB7-1L@MoS2 and PTB7-5L@MoS2 models, which demonstrates that the electron transfer is not sensitive to the thickness of the PTB7 polymer. Differently, the interfacial hole transfer is sensitive to the thickness of the PTB7 polymer. The transfer time is estimated to be ca. 70 ps in PTB7-1L@MoS2, while it is significantly accelerated to ca. 1 ps in PTB7-5L@MoS2. Finally, we have found that the electron transfer is mainly controlled by adiabatic electron evolution, whereas in the hole transfer, nonadiabatic hoppings play a dominant role. These findings are useful for the design of excellent charge-separated interfaces of mixed-dimensional TMD-based heterojunctions for a variety of optoelectronic applications.

Decorating BODIPY with electron-rich unit THDTAP: An ICT-based fluorometric sensor toward peroxide, acid, and electrochemical stimuli

A new type of BODIPY dye, compound 2 which possesses donor-acceptor (D-A) type structure, is synthesized by decorating electron-rich THDTAP unit onto the meso-position of BODIPY. The THDTAP has two chemically active sites (S and N atoms) that are utilized to manipulate the optoelectronic properties. By stepwise oxidation of two S-atoms on THDTAP moiety with m-CPBA, the 2 was converted to 3, trans-4, syn-4, 5, and 6. This transformation results in large influence on optoelectronic properties. The theoretical calculations reveal that the LUMOs of 2–6 are all located on BODIPY core, whereas their HOMOs show the different distributions. The 2 and 3 show the intramolecular charge-transfer (ICT) transition as proved by TD-DFT calculations, red-shifts of absorption and emission bands, and solvatochromism. The ICT process is inhibited in trans-4, syn-4, 5, and 6 due to the high oxidation states of S-atoms on THDTAP moieties. As a result, these four compounds display characteristic fluorescence of BODIPY. The femtosecond transient absorption (fs-TA) spectroscopic study reveals that 2 shows photoinduced hole-transfer (PHT) process in dichloromethane (DCM) solution. Upon acidification and neutralization of N-atom on THDTAP moiety, the ICT/PHT process of 2 in DCM is reversibly manipulated to result in fluorescence ON/OFF of BODIPY core. Moreover, the fluorescence of BODIPY core on 2 can be switched on through electrochemical oxidation of N-atom on THDTAP moiety. The compound 2 is thus a promising fluorometric sensor toward peroxide, acid, and electrochemical stimuli.

Aqueous synthesis of core/shell/shell CdSe/CdS/ZnS quantum dots for photocatalytic hydrogen generation

A novel water-soluble core/shell/shell CdSe/CdS/ZnS quantum dot (QD) is prepared and employed as photocatalysts in the water splitting for hydrogen production. The combination of CdSe with CdS shell and ZnS shell effectively enhances the light harvest ability of the photocatalyst in the visible region, facilitates the separation and transfer of photoinduced electrons and holes and inhibits the recombination of photogenerated electron–hole pairs. The results of photocatalytic hydrogen production show that the amount of hydrogen produced by CdSe/CdS/ZnS QDs increases significantly within 7 h compared with CdSe QDs and CdSe/CdS QDs. In addition, the excellent recyclability of the photocatalyst makes it more promising for practical application.

Morphology-Dependent Hole Transfer under Negligible HOMO Difference in Non-Fullerene Acceptor-Based Ternary Polymer Solar Cells.

In the field of organic solar cells, it has been generally accepted until recently that a difference in band energies of at least 0.3 eV between the highest occupied molecular orbital (HOMO) level of the donor and the HOMO of the acceptor is required to provide adequate driving force for efficient photoinduced hole transfer due to the large binding energy of excitons in organic materials. In this work, we investigate polymeric donor:non-fullerene acceptor junctions in binary and ternary blend polymer solar cells, which exhibit efficient photoinduced hole transfer despite negligible HOMO offset and demonstrate that hole transfer in this system is dependent on morphology. The morphology of the organic blend was gradually tuned by controlling the amount of ITIC and PC70BM. High external quantum efficiency was achieved at long wavelengths, despite ITIC-to-PC70BM ratio of 1:9, which indicates efficient photoinduced hole transfer from ITIC to the donor despite an undesirable HOMO energy offset. Transient absorption spectra further confirm that hole transfer from ITIC to the donor becomes more efficient upon optimizing the morphology of the ternary blend compared to that of donor:ITIC binary blend.

Photoinduced hole transfer from tris(bipyridine)ruthenium dye to a high-valent iron-based water oxidation catalyst.

An efficient water oxidation system is a prerequisite for developing solar energy conversion devices. Using advanced time-resolved spectroscopy, we study the initial catalytic relevant electron transfer events in the light-driven water oxidation system utilizing [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a light harvester, persulfate as a sacrificial electron acceptor, and a high-valent iron clathrochelate complex as a catalyst. Upon irradiation by visible light, the excited state of the ruthenium dye is quenched by persulfate to afford a [Ru(bpy)3]3+/SO4˙- pair, showing a cage escape yield up to 75%. This is followed by the subsequent fast hole transfer from [Ru(bpy)3]3+ to the FeIV catalyst to give the long-lived FeV intermediate in aqueous solution. In the presence of excess photosensitizer, this process exhibits pseudo-first order kinetics with respect to the catalyst with a rate constant of 3.2(1) × 1010 s-1. Consequently, efficient hole scavenging activity of the high-valent iron complex is proposed to explain its high catalytic performance for water oxidation.

Surface hydroxylated hematite promotes photoinduced hole transfer for water oxidation

An extremely simple sonication method is reported to hydroxylate a hematite surface without affecting its bulk properties.

High lying energy of charge-transfer states and small energetic offsets enabled by fluorinated quinoxaline-based alternating polymer and alkyl-thienyl side-chain modified non-fullerene acceptor

Abstract Significant driving forces are the prerequisite to achieve fast and efficient charge separation in fullerene derivatives-based polymer solar cells to achieve high power conversion efficiency (PCE). However, the large driving forces both in photo-induced hole transfer (PHT) and in photo-induced electron transfer (PET) processes lead to significant energy losses, resulting in low open-circuit voltage in the devices. Recent studies indicate the driving forces in non-fullerene acceptors-based devices can be reduced to very low values but still with high PCE and low energy losses. Herein, we report a new donor:acceptor system with high lying energy of charge-transfer excitons (ECT) of 1.50 eV and very small driving forces (PHT of 0.28 eV and PET of 0.11 eV), in which a fluorinated quinoxaline-based alternating polymer (FTQ) and an alkyl-thienyl side-chain modified small molecule (ITIC-Th) are taken as the donor material and non-fullerene acceptor material, respectively. A high power conversion efficiency (PCE) of 8.19% with maximal external quantum efficiency of 71% are achieved successfully in FTQ:ITIC-Th-based device after appropriate thermal annealing treatment, indicating FTQ can be further applied as donor materials with other highly efficient NF-acceptors to achieve enhanced performances and low energy losses.

High-Performance Fullerene-Free Polymer Solar Cells Featuring Efficient Photocurrent Generation from Dual Pathways and Low Nonradiative Recombination Loss

Efficient charge generation is a prerequisite to achieve high power conversion efficiency (PCE) in organic/polymer solar cells (OSCs/PSCs), which involves photoinduced electron transfer and/or hole transfer between the donor/acceptor interface upon photoexcitation. A high yield of charge from both processes usually requires sufficient energy offset between the donor and acceptor for charge separation, fast transport, and extraction for charge collection, as well as significant absorption complementation to maximize photon harvest. Here we demonstrate highly efficient PSCs with efficient dual photocurrent generation pathways from a blend of a polymer donor and two narrow-bandgap nonfullerene acceptors, with an outstanding certified PCE of 13.0% (verified as 12.5%) in PSCs with single-junction device architecture. The devices from these material systems show nonradiative recombination loss of ∼0.22–0.24 V, one of the smallest values for OSCs achieved so far and comparable to those of solar cells based on mo...

Layered BiOBr/Ti3C2 MXene composite with improved visible-light photocatalytic activity

Layered BiOBr/Ti3C2 (BTC) composites were synthesized by first preparing Ti3C2 nanosheets through the liquid etching of Ti3AlC2 powder and then hybridizing with BiOBr via a facile reflux process. The morphology, crystal structure, light-harvesting capacity, chemical nature of atoms and visible-light photocatalytic degradation activity were systematically studied and discussed. It was found that the introduction of Ti3C2 nanosheets improved UV–Vis light absorption region of BiOBr. A contact interface was formed between BiOBr nanoplate and Ti3C2 nanosheet due to the similar layered structures, which could accelerate the efficient separation and transfer of photoinduced electrons and holes. Thus, the obtained BTC composites showed the higher visible-light photocatalytic activity for the degradation of RhB than pure BiOBr. The generated active species were determined by the active species capture experiment and ESR spectra, showing that ·O2− and ·OH played a crucial role in the photocatalytic degradation of RhB. The corresponding photocatalytic mechanism was proposed. This work may provide a new insight into the construction of earth-abundant MXene-based photocatalysts with high performance and low cost.

Solution‐Processed High‐Performance Hybrid Photodetectors Enhanced by Perovskite/MoS2 Bulk Heterojunction

AbstractA hybrid structure strategy, utilizing a perovskite/MoS2 bulk heterojunction (BHJ) as the photosensitizer and a reduced graphene oxide (rGO) layer as the conducting channel, is developed to realize high‐performance photodetectors. All the active layers are prepared by a simple and low‐cost solution process. The perovskite/MoS2 BHJ can significantly suppress the recombination of photogenerated carriers due to the selective electron trapping in the MoS2 nanoflakes, and thus the photoinduced hole transfer from perovskite to rGO is facilitated to largely increase the photocurrent. The hybrid photodetectors show excellent figures of merit, such as high responsivity of 1.08 × 104 A W−1, high detectivity of 4.28 × 1013 Jones, high external quantum efficiency of 2.0 × 106%, and fast photoresponse time less than 45 ms. The demonstration of flexible photodetectors on a flexible substrate finds potential applications in wearable and portable electronics. This work highlights the significance of a hybrid structure, combining an appropriate BHJ film with a graphene channel, as a general and effective way for achieving low‐cost and high‐performance photodetectors.

Efficient Charge Separation from F- Selective Etching and Doping of Anatase-TiO2{001} for Enhanced Photocatalytic Hydrogen Production.

TiO2 nanomaterials with coexposed {001} and {101} facets have aroused much interest owing to their outstanding photocatalytic performance. In this study, on the basis of its unique characteristics of photoinduced electron and hole transfer to different lattice planes, we synthesized F- selective etching and doping on {001} facets of anatase TiO2 nanosheets using TiO2 nanosheets with coexposed {001} and {101} facets as a precursor. Through a series of measurements, such as photoluminescence, transient photocurrent response, electrochemical impedance spectra, and Mott-Schottky measurements, it is proved that F- selective etching and doping on {001} facets of TiO2 can extremely accelerate the separation of photogenerated carriers by shortening the transfer pathway of holes and introducing Ti3+ and oxygen vacancies in {001} facets. Therefore, the as-obtained sample shows excellent photocatalytic properties under the visible-light irradiation; the highest rate of photocatalytic H2 evolution is up to 18270 μ mol h-1 g-1 and its quantum efficiency is up to 21.6% at λ = 420 nm. As an innovative exploration, this study provides a direct spatial charge separation strategy for developing highly efficient photocatalysts.

Mechanisms of Ultrafast Charge Separation in a PTB7/Monolayer MoS2 van der Waals Heterojunction.

Mixed-dimensional van der Waals heterojunctions comprising polymer and two-dimensional (2D) semiconductors have many characteristics of an ideal charge separation interface for optoelectronic and photonic applications. However, the photoelectron dynamics at polymer-2D semiconductor heterojunction interfaces are currently not sufficiently understood to guide the optimization of devices for these applications. This Letter reports a systematic exploration of the time-dependent photophysical processes that occur upon photoexcitation of a type-II heterojunction between the polymer PTB7 and monolayer MoS2. In particular, photoinduced electron transfer from PTB7 to electronically hot states of MoS2 occurs in less than 250 fs. This process is followed by a 1-5 ps exciton diffusion-limited electron transfer from PTB7 to MoS2 and a sub-3 ps photoinduced hole transfer from MoS2 to PTB7. The equilibrium between excitons and polaron pairs in PTB7 determines the charge separation yield, whereas the 3-4 ns lifetime of photogenerated carriers is probably limited by MoS2 defects.

Synthesis of β-AgVO3 nanowires decorated with Ag2CrO4, with improved visible light photocatalytic performance

Silver chromate−silver vanadate (Ag2CrO4/β-AgVO3) heterojunction composites are synthesized through a facile precipitation process. The Ag2CrO4/β-AgVO3 hybrids obtained exhibit better photocatalytic activity in degradation of RhB than both pure Ag2CrO4 and β-AgVO3 under visible light irradiation. The 20 wt% Ag2CrO4/β-AgVO3 heterojunction possesses the best photocatalytic ability for degrading RhB: 24.4 times that of pristine β-AgVO3 nanowires and 3.2 times that of individual Ag2CrO4 particles. The phase of the nanocomposites was analyzed using x-ray diffraction as well as x-ray photoelectron spectroscopy. Their morphology was observed via scanning electron microscopy and transmission electron microscopy. The improvement in photocatalytic performance is chiefly ascribed to the synergies between Ag2CrO4/β-AgVO3 heterostructure, which can enhance the light absorbance ability and also accelerate the separation and transfer of photoinduced electrons and holes under visible light irradiation; this is also confirmed by UV–vis diffuse reflection spectrometry and fluorescence emission spectra.

Boosting visible light photoreactivity of photoactive metal-organic framework: Designed plasmonic Z-scheme Ag/AgCl@MIL-53-Fe

In this work, we report the efficient integration of plasmonic Ag/AgCl with a typical photoactive metal-organic framework (MOF, MIL-53-Fe) to boost the visible light photoreactivity of MOFs. The Ag/AgCl@MIL-53-Fe photocatalysts are rationally designed and successfully prepared by a facile one-pot solvothermal route, where the Ag/AgCl nanoparticles are firmly anchored on the surface of MIL-53-Fe microrods. The formed structure is in favor of the synergetic transfer of photoinduced electrons and holes in the Ag/AgCl@MIL-53-Fe by a Z-scheme mechanism, ensuring the long lifetime of charge carriers and yielding the enhanced photocatalytic activity. The photocatalytic experiments reveal that Ag/AgCl@MIL-53-Fe is highly efficient for organic pollutant degradation and Cr(VI) reduction under visible light irradiation. The photocatalytic reactivity of Ag/AgCl@MIL-53-Fe is about 21.4 times and 10.8 times higher than that of bare MIL-53-Fe for the degradation of RhB and reduction of aqueous Cr(VI), respectively. Our finding on photoredox of Ag/AgCl@MIL-53-Fe would bring new insight into the design and development of highly efficient MOF-based photocatalysts.

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It is a widespread concern to address the antibiotics in water with low-cost and eco-friendly photocatalysts that could efficiently harvest solar light. Herein, we designed an efficient photocatalyst by integrating the lamellar g-C3N4 into Znln2S4 microflowers through a one-step hydrothermal method. The as-synthesized g-C3N4/Znln2S4 heterojunction photocatalysts exhibited evidently enhancement on the photocatalytic activities for the degradation of tetracycline (100 mL, 20 mg/L) compared with pristine g-C3N4 and Znln2S4. Significantly, g-C3N4/Znln2S4 composite with loading 50 wt.% g-C3N4 showed the highest photocatalytic performance (almost 100% degradation within 120 min), which was around 40 and 22.8 times higher than that of g-C3N4 and Znln2S4, respectively. This enhanced photocatalytic activity of g-C3N4/Znln2S4 is mainly attributed to the formation of heterostructure that can efficiently promote the transfer of photoinduced electrons and holes between g-C3N4 and ZnIn2S4, restricting the recombination of electron-hole pairs. In addition, a possible mechanism was also proposed.