Photoinduced Charge Generation Research Articles

Regulation of organic solar cells performance through external electric field: From charge transfer mechanisms to photovoltaic properties

In organic solar cells (OSCs), comprehending the charge transfer mechanism at D/A interfaces is crucial for photoinduced charge generation and enhancing power conversion efficiency (PCE). The charge transfer mechanism and photovoltaic performance of the parallel stacking interface configuration of the PTQ10 polymer donor and T2EH non-fullerene acceptor (NFA) are systematically studied at the microscopic scale. The analysis of the electron-hole distribution of the PTQ10/T2EH excited states revealed the presence of multiple charge excitation modes and charge transfer pathways. Using Marcus theory, we examine the charge separation rate (KCS) of PTQ10/T2EH under external electric field (Fext) modulation, and it is clarified that reorganization energy (λ) is the main factor that affects the KCS. Our results show that Fext has a positive impact on the photovoltaic properties of PTQ10/T2EH thin films, as evidenced by the modulation of the open circuit voltage (VOC), voltage loss (VLOSS) and fill factor (FF). Overall, this study provides valuable theoretical insights for Fext to accelerate the charge separation process and enhance photovoltaic efficiency.

Photoinduced charge generation of nanostructured carbon derived from human hair biowaste for performance enhancement in polyvinylidene fluoride based triboelectric nanogenerator

Carbon nanostructures derived from human hair biowaste are incorporated into polyvinylidene fluoride (PVDF) polymer to enhance the energy conversion performance of a triboelectric nanogenerator (TENG). The PVDF filled with activated carbon nanomaterial from human hair (AC-HH) exhibits improved surface charge density and photoinduced charge generation. These remarkable properties are attributed to the presence of graphene-like nanostructures in AC-HH, contributing to the augmented performance of PVDF@AC-HH TENG. The correlation of surface morphologies, surface charge potential, charge capacitance properties, and TENG electrical output of the PVDF composites at various AC-HH loading is studied and discussed. Applications of the PVDF@AC-HH TENG as a power source for micro/nanoelectronics and a movement sensor for detecting finger gestures are also demonstrated. The photoresponse property of the fabricated TENG is demonstrated and analyzed in-depth. The analysis indicates that the photoinduced charge carriers originate from the conductive reduced graphene oxide (rGO), contributing to the enhanced surface charge density of the PVDF composite film. This research introduces a novel approach to enhancing TENG performance through the utilization of carbon nanostructures derived from human biowaste. The findings of this work are crucial for the development of innovative energy-harvesting technology with multifunctionality, including power generation, motion detection, and photoresponse capabilities.

Photocatalytic degradation of tetracycline antibiotics by RGO-CdTe composite with enhanced apparent quantum efficiency

RGO-CdTe composite was synthesized using a straightforward, easy-to-realize, one-pot solvothermal technique. The synthesized composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller method (BET), Raman spectra, UV-Vis absorption, and photoluminescence measurement. The RGO-CdTe composite exhibited 83.6% photocatalytic degradation efficiency for the aqueous tetracycline (TC) antibiotic solution and the apparent quantum yield (AQY) for the same was as high as 22.29% which is 2.63 times higher than that of CdTe. The scavenger investigation demonstrated that although hole acts as the leading active species, despite that, superoxide and hydroxyl radicals have also played crucial roles. The initial pH-dependent photocatalytic performance was measured. The zeta potential of the composite at different pH values was evaluated to establish the photocatalytic performance of the RGO-CdTe towards TC degradation at different pH. The recycling experiment depicts that only a 10% degradation performance declines after 5 times recycle use of the RGO-CdTe photocatalyst. An efficient photocurrent generation in RGO-CdTe thin film device has also been observed. Our study establishes as-synthesized composite of RGO-CdTe as a highly potential, and stable photocatalyst for the degradation of antibiotics from the polluted aqueous environment with a very good photoinduced charge generation efficiency in its solid phase.

Engineering the photo-induced charge generation between TiO2 and FeS2 heterojunction for enhanced photocatalytic wastewater purification

Wastewater treatment using photocatalytic processes is an eco-friendly approach to tackle the scarcity of drinkable water. In this study, a heterojunction of TiO2 and FeS2 nanostructures was synthesized via a one-pot polyol method, and their activity was investigated in eliminating crystal violet as a dye pollutant. The difference in the thermodynamic stability of iron and titanium oxides in polyol solution containing thiourea led to the formation of TiO2 nanorods and sulfurization of iron in the form of FeS2 nanospheres. Incorporating TiO2 nanorods with FeS2 chalcogenide nanostructures narrowed the band gap energy (from 3.05 to 2.6 eV) and enhanced the photo-induced charge carriers’ separation by forming an internal electric field. Compared to TiO2 nanorods, the synthesized heterojunction photocatalyst using 0.5 ml TBOT (FST-0.5) exhibited the best activity and increased crystal violet degradation from 55% to 89%. The optimization and modeling of the interaction between operating parameters were performed by response surface methodology based on central composite design. The statistically significant quadratic polynomial model was best for fitting the experimental data. Regarding this model, adjusting the catalyst weight, pollutant concentration, and solution pH at an optimum amount of 0.015 g, 4 ppm, and 9 causes the highest photocatalytic degradation, around 94%. The kinetics studies also revealed that photocatalytic degradation follows first-order kinetics with an apparent rate constant of 0.0184 min−1. The contribution of active species was determined by free-radical capture experiment. Herein, photo-holes had the main contribution (38.3%), and the rest accounted for hydroxide radicals (26.6%), superoxide anions (11.7%), and electrons (23.4%).

Ultrasmall Ag nanoparticles on photoactive metal-organic framework boosting aerobic cross-dehydrogenative coupling under visible light

The application of heterogeneous photocatalyst to conduct organic transformation is attractive in sustainable chemistry. Metal-organic frameworks (MOFs) are crystalline materials with diverse structures and rich components, which exhibit great potential to achieve heterogeneous photocatalysis. Herein, we report the synthesis of new photocatalysts of MOF-based nanocomposites to achieve cross-dehydrogenation coupling (CDC). A series of nanocomposites of Ag/MOF were prepared by simple photoreduction method. The resulting nanocomposites exhibit efficient and recyclable photocatalytic performance for CDC reactions under visible light. Experiments show that the photocatalytic activity of the MOF was promoted significantly upon the decoration of ultrasmall Ag nanoparticles (NPs), where the particle size and loading amount of Ag NPs play an important role to improve the photocatalytic performance. Ultrasmall Ag NPs not only boost the photoinduced charge generation by Schottky junction in the nanocomposite, but also promote the reaction by direct interaction with amine substrate. Reactive oxygen species (ROS) of singlet oxygen and superoxide radical were simultaneously generated from molecular oxygen in the photocatalytic reaction, owing to the photoinduced energy and electron transfer of the MOF. The study presents a rare example of photocatalytic CDC using MOF-based nanocomposite, providing more insights into the synergy effect of MOFs and metal nanoparticles for organic transformation.

Light control of droplets on photo-induced charged surfaces.

The manipulation of droplets plays a vital role in fundamental research and practical applications, from chemical reactions to bioanalysis. As an intriguing and active format, light control of droplets, typically induced by photochemistry, photomechanics, light-induced Marangoni effects or light-induced electric fields, enables remote and contactless control with remarkable spatial and temporal accuracy. However, current light control of droplets suffers from poor performance and limited reliability. Here we develop a new superamphiphobic material that integrates the dual merits of light and electric field by rationally preparing liquid metal particles/poly(vinylidene fluoride-trifluoroethylene) polymer composites with photo-induced charge generation capability in real time, enabling light control of droplets on the basis of photo-induced dielectrophoretic force. We demonstrate that this photo-induced charged surface (PICS) imparts a new paradigm for controllable droplet motion, including high average velocity (∼35.9mm s-1), unlimited distance, multimode motions (e.g. forward, backward and rotation) and single-to-multiple droplet manipulation, which are otherwise unachievable in conventional strategies. We further extend light control of droplets to robotic and bio-applications, including transporting a solid cargo in a closed tube, crossing a tiny tunnel, avoiding obstacles, sensing the changing environment via naked-eye color shift, preparing hydrogel beads, transporting living cells and reliable biosensing. Our PICS not only provides insight into the development of new smart interface materials and microfluidics, but also brings new possibilities for chemical and biomedical applications.

The beauty of being complex: Prussian blue analogues as selective catalysts and photocatalysts in the degradation of ciprofloxacin

We investigate the performance of four Prussian blue analogues (PBAs) as catalysts for the selective degradation of ciprofloxacin in water, under both dark and illumination conditions. We show that no light is actually needed to induce a selective degradation of the molecular target, while light irradiation spurs the process, without, however, resulting in the commonly reported photolysis-supported breaking down. We present a systematic characterization of the PBAs aiming at interpreting the catalytic outcomes in the light of a classic coordination chemistry analysis, empowered by the most recent findings in literature. We show that varying the transition metal binding the N atom of the cyanide bridge is key to promote photoinduced charge generation and transfer, which effectively disrupts the molecular target. The analysis of the materials before and after the irradiation with solar simulated light results in a change of the lattice parameters, indicating the possibility of a light-induced spin cross-over.

Bandgap engineering of ZnX (X = O, S, Se, Te) QDs/Graphene nanocomposites: Towards the designing of a highly efficient light-harvesting device

Increasing the power conversion efficiency (PCE) of photovoltaic devices (PVDs) is a topic of fundamental importance not only for academia but also for industry. In this study, we systematically investigated the electronic structure of ZnX (X = O, S, Se, and Te) quantum dots (QDs)/Graphene (G) nanohybrid systems by employing the density functional method. To understand the key issues, associated with photoinduced charge generation, generated charge separation, charge transfer process, recombination probability, and variations of PCE, we have considered different combinations of hybrid nanostructures composed with ZnX QD and G. The tuning of the electronic properties of hybrid systems has been done as a function of the size of ZnX QD's, chalcogenides, and hydrogen coverage percentage on G to design a highly efficient hybrid solar cell. We have also explored the photovoltaic efficiency of ZnX/ZnX’ (X/X' = O, S, Se, and Te) core/shell QDs/G to investigate the effect of core/shell QDs in composite nanomaterials. Bandgaps of ZnX QDs/G nanocomposites are very low (0.028eV–0.158 eV) which implies the probability of recombination of photo-induced separated charges at the heterojunction region is very high. After passivation with hydrogen atoms partially on the G, this unsavory circumstance is overcome. We have performed the bandgap and band alignment engineering of ZnX QDs/G hybrid nanostructures by varying the size of QD's and H-coverage percentage on G to form a type-II material which is very important to reduce the recombination rate and ultimately increase the PCE of the hybrid solar cells. Considering hydrogenated graphene (HG)-ZnX QDs nanocomposites we were achieving high PCE values (up to 30.25%), which implies our explored materials efficiency is exceptionally good and competitive with recently explored tandem/hybrid/latest perovskite solar cells.

Synergistic Effect of Au Interband Transition on Graphene Oxide/ZnO Heterostructure: Experimental Analysis with FDTD Simulation.

We furnish a comprehensive study on light-induced carrier generation due to the synergistic contribution of Au interband transition and graphene oxide (GO)/ZnO heterostructure. Plasmonic gold nanoparticles (Au_nps) are incorporated as a substructure sandwiched between GO and ZnO, assisting in additional photo-induced charge carrier generation. GO is prepared by a single-step plasma-enhanced chemical vapor deposition process. The GO/ZnO heterostructure having an active working area of 0.25 cm2 is created to unleash the pyroelectric property of ZnO, and subsequently, Au_np is introduced at the interface of GO/ZnO. Here, the interband transition of Au_np and its capability for charge carrier generation combined with the excitonic charge carrier generation of the highly crystalline non-centrosymmetric hexagonal wurtzite ZnO enhances the photoresponse. Furthermore, the interaction of Au_np with ZnO and its spatial electric field intensity distribution is demonstrated by finite difference time domain simulation which indicate toward an efficient carrier generation at the interface of Au_np and ZnO. The fabricated heterostructure has an active working wavelength in the UV-A region with the highest responsivity at 375 nm of the electromagnetic spectrum. The ultrafast response time (∼29 μs) of the device is due to the pyro-phototronic effect of the GO/ZnO heterostructure enhanced by the interband transition of Au. In the comparative study of the Au_np-enriched GO/ZnO heterostructure device with a GO/ZnO device, the former shows better performance. Both the devices work in the self-powered mode as well as the photoconductive mode, but with a higher on–off current ratio in the photoconductive mode. Hence, this work helps in properly understanding photo-induced charge generation in a Au interband transition enriched GO/ZnO heterostructure.

One-Pot Dual Catalysis of a Photoactive Coordination Polymer and Palladium Acetate for the Highly Efficient Cross-Coupling Reaction via Interfacial Electron Transfer.

We report herein an exploration of the straightforward one-pot dual-catalysis strategy, i.e., direct combination of a photoactive coordination polymer (CP) with another metal catalyst, for carrying out the desirable photoinduced organic transformation. The strategy overcomes the necessity of the presynthesis of the metal/CP composite that has been demonstrated to be invalid in our case. A new two-dimensional CP showing the desirable properties of wide-range visible-light absorption and efficient photoinduced charge generation was synthesized via a solvothermal reaction. The synthesized CP was successfully applied to the photocatalytic C-C cross-coupling reaction via the one-pot dual-catalysis method, in combination with the simple and ligand-free palladium salt of Pd(OAc)2 as a metal catalyst. The reaction features a short reaction time, mild reaction conditions, good recyclability, and a high yield of Heck products from a broad variety of substrates. A comparative experiment showed the presynthesized Pd/CP composite was invalid for the reaction, demonstrating the significance of the one-pot dual-catalysis strategy. Mechanistic studies suggest the one-pot reaction depends on the synergy between the photocatalysis of a synthesized CP to generate reactive aryl radicals and Pd catalysis to generate target products, in which the interfacial electron transfer has been demonstrated to be vital for producing the transient and catalytically active Pd(0) species near the surface of the CP. The study shows the direct combination of a CP photocatalyst and a metal catalyst is a highly feasible method for the photochemical reaction and enhances the prospects of application of photoactive CPs.

Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts.

The conversion and storage of solar energy to chemical energy via artificial photosynthesis holds significant potential for optimizing the energy situation and mitigating the global warming effect. Photocatalytic water splitting utilizing particulate semiconductors offers great potential for the production of renewable hydrogen, while this cross-road among biology, chemistry, and physics features a topic with fascinating interdisciplinary challenges. Progress in photocatalytic water splitting has been achieved in recent years, ranging from fundamental scientific research to pioneering scalable practical applications. In this review, we focus mainly on the recent advancements in terms of the development of new light-absorption materials, insights and strategies for photogenerated charge separation, and studies towards surface catalytic reactions and mechanisms. In particular, we emphasize several efficient charge separation strategies such as surface-phase junction, spatial charge separation between facets, and polarity-induced charge separation, and also discuss their unique properties including ferroelectric and photo-Dember effects on spatial charge separation. By integrating time- and space-resolved characterization techniques, critical issues in photocatalytic water splitting including photoinduced charge generation, separation and transfer, and catalytic reactions are analyzed and reviewed. In addition, photocatalysts with state-of-art efficiencies in the laboratory stage and pioneering scalable solar water splitting systems for hydrogen production using particulate photocatalysts are presented. Finally, some perspectives and outlooks on the future development of photocatalytic water splitting using particulate photocatalysts are proposed.

Mechanochemical Construction 2D/2D Covalent Organic Nanosheets Heterojunctions Based on Substoichiometric Covalent Organic Frameworks.

Combining different semiconductor materials to construct heterojunctions is a promising method to achieve efficient photocatalysis; however, it is still a challenge to accurately construct heterojunctions through molecular regulation. In this work, we take advantage of the remaining aldehyde groups in a substoichiometric covalent organic framework (denoted as PTO-COF) to achieve precise construction of covalently linked 2D/2D covalent organic nanosheets (CONs) heterojunctions through mechanochemical methods. The ultrathin structure of CONs endowed them with superior photoinduced charge generation and separation. Additionally, the energy bands of two CONs materials in heterojunctions were precisely coupled in a Z-scheme by the well-designed covalent linkages, which lead to a 190% enhancement of photocatalytic degradation efficiency for PTO/TpMa CONs heterojunctions as compared with pure COFs. This work provides new insights for design and synthesis of innovative 2D organic heterojunction photocatalysts.

Construction of NiO and Ti3+ self-doped TNTs thin film as a high quantum yield p-n type heterojunction via a novel photoelectrodeposition-assisted anodization method

Recently, p-n type heterojunctions have been considered promising photocatalysts for application in energy conversion and storage systems. Therefore, in this study, the photoelectrodeposition-assisted anodization method has been proposed as a novel procedure to construct a p-n type heterojunction hybrid consisting of NiO nanoparticles (with different dosages) and 1D TiO2 nanotube arrays (NiO/TNTs) for wastewater purification. The results revealed that using the photoelectrodeposition-assisted anodization method not only led to the introduction of Ni2+ and Ti 3+ into TiO2 anatase lattice, but also significantly enlarged TNTs’ dimension. Furthermore, incorporating TNTs with NiO had a significant impact on its optical properties, in which doping 4 wt% of Ni2+ (NiO-TNTs (4%)) reduced the band gap energy from 3 to 1.6 eV. Also, by coupling an optimum dosage of NiO, the photocurrent density and photoconversion efficiency of TNTs were remarkably boosted from 0.17 to 0.58 mA.cm−2 and from 0.11% to 0.34%, respectively. Due to the promotion in optical properties and photo-induced charge generation, NiO-TNTs (4%) indicated much better photocatalytic activity than the pure sample. As compared with TNTs, the 2,4-dichlorophenol degradation percentage by NiO-TNTs (4%) increased from 75% to 100% under UV and from 49% to 71% under visible light irradiation. Moreover, the kinetics study confirmed that all photocatalytic reactions followed zero-order kinetics. Based on scavenging reactive species tests, holes (h+) had the main portion (with 43%) in 2,4-dichlorophenol degradation by NiO-TNTs (4%). The rest of the degradation pathways were proceeded with e-, •OH, and •O2– species by accounting for 27%, 21% and 9%, respectively.

Functionalized polythiophene for corrosion inhibition and photovoltaic application

AbstractConjugated polymers are encouraging substitute for creating clean and renewable energy for photoinduced charge generation and transport media in polymer solar cells (PSCs). Successful synthesis of a new solution processable n‐type polythiophene based π‐conjugated polymer (P3HT‐CN) is done where polythiophene units are substituted by cyano groups through post functionalization approach of synthesized P3HT which is cheap, stable, easily prepared, and inert against ambient conditions and is expected to be a competitive candidate for the acceptor material in non fullerene acceptors (NFAs) PSCs against fullerene derivative and used as the highly efficient active layer in the bulk heterojunction (BHJ) which increase the donor‐acceptor interfacial area through controlling the phase separation indicating device structure ITO/PEDOT:PSS/P3HT:P3HT‐CN/Al. Photovoltaic measurement of this PSCs device based on P3HT:P3HT‐CN demonstrate the PCE of 0.008% with an increased short circuit current density (Jsc) of 0.11 mA cm−2. The thermal, optical, and electrochemical properties are examined in detail showing high thermal stability, absorbance in the visible part of the solar spectrum, higher charge carrier mobility, and also mixed type corrosion inhibitive behavior with 90 and 78% inhibitor efficiency for P3HT and P3HT‐CN, respectively, built this class of material as smart which can be used for many other applications.

Single particle dual plasmonic effect for efficient organic solar cells

Incorporating localized surface plasmon resonance (LSPR) into organic solar cells (OSCs) is a popular method for improving the power conversion efficiency (PCE) by introducing better light absorption. In this work, we designed a one-pot synthesis of Ag@SiO2@AuNPs dual plasmons and observed an immense increase in light absorption over a wide range of wavelengths. Ag@SiO2 plays the main role in enhancing light absorption near the ultraviolet band. The silica shell can also further enhance the LSP resonance effect and prevent recombination on the surface of AgNPs. The AuNPs on the Ag@SiO2 shell exhibited strong broad visible-light absorption due to LSP resonance and decreased light reflectance. By utilizing Ag@SiO2@AuNPs, we could enhance the light absorption and photoinduced charge generation, thereby increasing the device PCE to 8.57% and Jsc to 17.67 mA cm−2, which can be attributed to the enhanced optical properties. Meanwhile, devices without LSPR nanoparticles and Ag@SiO2 LSPR only showed PCEs of 7.36% and 8.18%, respectively.

Critical role of H-aggregation for high-efficiency photoinduced charge generation in pristine pentamethine cyanine salts.

The mechanism of photoinduced symmetry-breaking charge separation in solid cyanine salts at the base of organic photovoltaic and optoelectronic devices is still debated. Here, we employ femtosecond transient absorption spectroscopy (TAS) to monitor the charge transfer processes occurring in thin films of pristine pentamethine cyanine (Cy5). Oxidized dye species are observed in Cy5-hexafluorophosphate salts upon photoexcitation, resulting from electron transfer from monomer excited states to H-aggregates. The charge separation proceeds with a quantum yield of 86%, providing the first direct proof of high efficiency intrinsic charge generation in organic salt semiconductors. The impact of the size of weakly coordinating anions on charge separation and transport is studied using TAS alongside electroabsorption spectroscopy and time-of-flight techniques. The degree of H-aggregation decreases with increasing anion size, resulting in reduced charge transfer. However, there is little change in carrier mobility, as despite the interchromophore distance increasing, the decrease in energetic disorder helps to alleviate the trapping of charges by H-aggregates.

Reduced titania nanorods and Ni–Mo–S catalysts for photoelectrocatalytic water treatment and hydrogen production coupled with desalination

This study presents a ternary hybrid solar desalination process coupled with photoelectrocatalytic water treatment and H2 production in a single device. The desalination of brackish water in the desalination cell is initiated via photoinduced charge generation with a thermochemically reduced TiO2 nanorod array photoanode. The chlorides transferred to the neighboring anolyte at ion-transport efficiency of ∼100% are photoelectrochemically transformed into reactive chlorine species responsible for the decomposition of urea into nitrate in the anolyte. Simultaneously, the H2 production with a Ni–Mo–S (Ni2S3/MoS2) composite catalyst grown onto porous Ni substrate is achieved at Faradaic efficiency of ∼90% in the catholyte concentrated with desalted Na+. Regardless of the operation condition, the H2 energy contributes to the reduction in the energy consumption for desalination by 25%–30%. The overall ternary hybrid process is understood systematically, and the physiochemical properties and electrochemical behavior of the Ni–Mo–S catalysts are examined.

Electromagnetic induction effect induced high-efficiency hot charge generation and transfer in Pd-tipped Au nanorods to boost plasmon-enhanced formic acid dehydrogenation

Improving the photo-induced hot charge utilization rate in granular catalysts with specific nanostructure is hindered by limited hot electron production and rapid recombination in plasmonic metal particles; therefore, promoting photo-induced hot charge generation and transfer during the plasmonic process is a vital approach for enhancing plasmonic catalytic performance. In this work, with the intention of constructing Pd-tipped Au nanorod heterostructures to achieve plasmon-enhanced formic acid dehydrogenation, the magnetic-field-derived electromagnetic induction effect is utilized to further boost the generation and transfer of plasmonic hot charges in Au nanorods. By exposing the plasmonic catalytic system to a rotating permanent magnet at 28 °C, formic acid dehydrogenation efficiency was improved by approximately 60%. The improvement rate in the same system can exceed 150% at 45 °C. This enhancement is attributed to the increase in plasmonic hot charges and the suppression of charge recombination based on the electromagnetic induction effect of plasmonic Au nanorods in a rotating magnetic field. This work provides a practical strategy for designing high-activity catalysts regulated via magnetic field for formic acid dehydrogenation. • The magnetic-field is utilized to further boost the plasmonic hot charge generation and transfer from Au nanorods to Pd. • The formic acid dehydrogenation efficiency were improved 60% and 150% at 28 °C and 45 °C in rotatingmagnetic field. • The increase in plasmonic hot charges and the suppression of charge recombination by the electromagnetic induction effect.

Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity.

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D3h -symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C54 N6 -COF) via Knoevenagel condensation with another D3h -symmetric monomer 2,4,6-tris(4'-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C2v -symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C52 N6 -COF). The octupolar conjugated characters of g-C54 N6 -COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C52 N6 -COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C54 N6 -COF enabled the two-half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 μmol h-1 g-1 and H2 evolution rate of 2518.9 μmol h-1 g-1 . Such values are among the highest of state-of-the-art COF photocatalysts.

Comprehensive and Comparative Analysis of Photoinduced Charge Generation, Recombination Kinetics, and Energy Losses in Fullerene and Nonfullerene Acceptor-Based Organic Solar Cells.

In this work, a unique comprehensive and comparative analysis of photoinduced charge generation, recombination kinetics, and energy losses has been carried out to study the effect of different fullerene-based acceptors (FBAs) and nonfullerene acceptors (NFAs) on the performance of organic solar cells (OSCs). For this, different FBAs, specifically ICBA, PC60BM, and PC70BM, and NFAs, namely, ITIC, IT-4F, and IEICO-4F, were employed independently along with a particular donor polymer, PBDB-T, to fabricate bulk heterojunction OSCs and their performances have been compared. This donor molecule is known to give similar power conversion efficiency (PCE) with FBAs and NFAs and hence is ideal for comparative studies. The origin of the higher PCE of NFA-based OSCs vs FBA-based OSCs is analyzed in terms of spectral coverage, charge generation, recombination, and energy loss. It is found that the energy loss (ΔEloss) is ∼0.8 to 1 eV for FBA-based OSCs, while it is 0.5-0.7 eV for NFA-based OSCs. Interestingly, for the PBDB-T:IEICO-4F-based system, energy losses due to charge generation (ΔECT) are ∼0 eV and therefore this system has minimum ΔEloss among all of the studied devices. Providing a systematic, comprehensive, and comparative outlook, our study may further be extended to new upcoming NFA systems and beyond the donor system used in this work.