Exciton Separation Research Articles

Enhanced photocatalytic H2 production independent of exciton dissociation in crystalline carbon nitride

The role of exciton dissociation in charge separation dominated by in-plane crystallinity has been rarely addressed, although it is the decisive step of polymeric carbon nitride (CN) photocatalysis. Here, taking ten kinds of crystalline carbon nitride (CCN) as examples, the relationship between exciton dissociation, carrier mobility, conductivity, charge separation and photocatalytic activity under different in-plane crystallinity has been investigated. Although the in-plane crystallinity dominates charge separation and photocatalytic activity, it does not significantly reduce excitons binding energy (EBE) or improve exciton dissociation efficiency (EDE), only decreasing by 1.5 meV and increasing by 2.3 %, respectively. It is the greatly improved carrier mobility and conductivity that are more responsible for the increased charge separation and photocatalytic activity than the slight change in EDE. To our knowledge, this is the first reported case of overall water splitting in CCN of poly(heptazine imide) structure, resulting from the optimized in-plane crystallinity.

To improve device performance of self-driven heterojunction photodetectors by inserting a thin layer of silver nanoparticles into the electron-transporting layer

Lead selenide colloidal quantum dots (CQDs) are widely used in infrared photodetectors due to their size-dependent bandgap tunability, facile solution-processing techniques and low cost. Heterojunctions (HJs) are usually used to construct device to facilitate the separation of excitons and the transportation of photogenerated carriers. Based on the solution-processed HJ photodetector ITO/ZnO/PbSe/Ag, in which PbSe CQDs layer acts as the active layer and ZnO nanoparticles (NPs) layer as the electron-transporting layer, a greatly enhanced-performance was obtained after inserting 10 nm Ag NPs layer within the ZnO NPs layer close to the HJ ZnO/PbSe interface. By optimizing the concentration of Ag NPs solutions and the location of Ag NPs thin layer in ZnO film, the maximum responsivity of the self-driven HJ photodetector ITO/ZnO(50 nm):Ag-NPs(10 nm):ZnO(50 nm)/PbSe(300 nm)/Ag reaches to 6.25 mA/W with a specific detectivity D* of 5.17 ×1011 Jones under 8.5 μW/cm² 1550 nm illumination at zero bias. Further, the underlain physical mechanisms for the enhanced-performance were discussed in details. In this way, it provides a very efficient method for enhanced-performance self-driven HJ photodetectors by inserting a thin layer of metal NPs into the electron-transporting layer close to the heterojunction interface.

Probing the energy levels of organic bulk heterojunctions by varying the donor content

The performance of organic solar cells is strongly governed by the properties of the photovoltaic active layer. In particular, the energetics at the donor (D)–acceptor (A) interface dictate the properties of charge transfer (CT) states and limit the open-circuit voltage. More generally, energetic landscapes in thin films are affected by intermolecular, e.g., van der Waals, dipole, and quadrupole, interactions that vary with D:A mixing ratio and impact energy levels of free charges (ionization energy, electron affinity) and excitons (singlet, CT states). Disentangling how different intermolecular interactions impact energy levels and support or hinder free charge generation is still a major challenge. In this work, we investigate interface energetics of bulk heterojunctions via sensitive external quantum efficiency measurements and by varying the D:A mixing ratios of ZnPc or its fluorinated derivatives and C60. With increasing donor fluorination, the energetic offset between FxZnPc and C60 reduces. Moving from large to low offset systems, we find qualitatively different trends in device performances with D:C60 mixing ratios. We rationalize the performance trends via changes in the energy levels that govern exciton separation and voltage losses. We do so by carefully analyzing shifts and broadening sEQE spectra on a linear and logarithmic scale. Linking this analysis with molecular properties and device performance, we comment on the impact of charge–quadrupole interactions for CT dissociation and free charge generation in our D:C60 blends. With this, our work (1) demonstrates how relatively accessible characterization techniques can be used to probe energy levels and (2) addresses ongoing discussions on future molecular design and optimal D–A pairing for efficient CT formation and dissociation.

Multifunctional and High‐Performance FAPBI3 Quantum Dots/Graphene UV Photodetectors by the Modulation of Photoconductivity

AbstractLow‐dimensional devices with different photoconductive effects attract much attention in optoelectronics. In this work, negative photoconductivity (NPC) monolayer graphene photodetectors are fabricated by chemical vapor deposition (CVD), and a positive photoconductivity (PPC) photodetector is realized by decorating perovskite FAPbI3 quantum dots prepared by a simple and cost‐effective non‐polar solvent synthesis method on a graphene surface. The graphene‐based photodetector exhibits an NPC characteristic, which is attributed to the absorption and desorption of water molecules on the graphene surface. The responsivity of the photodetector with an NPC characteristic is −0.86 A W−1 under intense ultraviolet light irradiation, and the detectivity is −2.45 × 109 Jones. The FAPbI3 quantum dots/graphene photodetector with a PPC feature has a responsivity of 8.03 A W−1 and a detectivity of 1.89 × 1010 Jones under the irradiation of ultraviolet light of 365 nm and 55.3 mW cm−2 intensity. Due to the intense light absorption of perovskite combined with the extremely high mobility of graphene, photodetectors have high exciton separation and photocurrents when the devices are irradiated by ultraviolet light. Individual photodetectors are successfully created with NPC and PPC effects; the critical analysis for the different photoconductive mechanisms is provided, which will benefit the development of future multifunctional systems.

Built in electric-field active 2D β-BN/ZIS coated water-fed photoelectrode for methane conversion into hydrogen gas and VAPs through non-oxidative coupling

The photocatalytic conversion of methane into value added products with an add on power generation offers new sustainable solution for the GHG and commercial methane reforming. In present study photo-electrochemical conversion of CH4 gas into H2 gas and other value-added products like C2H6, C3H8, and C4H10 gas under ambient conditions through non-oxidative coupling of CH3* radicals at chain termination were investigated. Interfaces between two photocenters hinder the charge mobility therefore, built-in electric field induced VDW heterojunction of 2D/2D β-BiNbO4/ZnIn2S4 is constructed to enhance the spatial separation of excitons. Additionally, to remove the bubble diffusion challenge of gas to liquid phase 2D β-BiNbO4/ZnIn2S4 coated PES Air-photoanode is adopted. It presented gas phase photocatalysis redox reaction of alkylation and significant hydrogen generation. Presence of porous morphology and polar group in PES increased the ECSA and performance of photoanode by reducing the Rs, Rct and accumulation layer impedances. Electrochemical analysis also proven the potency of VDW 2D β-BN/ZIS for substantial hydrogen generation. 14.2% light-to-hydrogen efficiency with 61% selectivity was observed which is much higher than most of the reported LTH efficiency of photo fuel cell. The light-to fuel (LTF) efficiency is more than 17.3% and 49.7 mW/m2 of power production providing an opportunity to oxidise the methane under the ambient environment into energy-rich derivatives along with electricity generation.

Polarization Reorientation of Carbon Nitride Induced by a Local Bridge Donor for Boosting Photocatalytic H2 Evolution Integrated with Selective Amine Oxidation

Polymeric carbon nitride (PCN) has attracted much attention in the field of photocatalysis, but the use of PCN is often confined to internal structures with highly symmetrical heptazine units bridged by N atoms. Accurate tuning of the positions of heteronuclear atoms is a meaningful strategy but remains a big challenge. Herein, a catalyst with P═N bonds accurately embedded among the heptazine units was prepared using a straightforward polymerization method. According to density functional theory simulation and experimental data, the embedded P═N chains act as donor units that cause a profound redistribution of the symmetric electron cloud density of heptazine, which significantly promotes local charge polarization and leads to a strong built-in electric field. The consequence is enhanced exciton dissociation, charge separation, and surface activation. In the photocatalytic oxidation of benzylamine over the optimized PCN under visible light irradiation without the use of a solvent and co-catalyst, the hydrogen production rate is 388 μmol·g–1·h–1 and the selectivity to N-benzylidenebenzylamine is >99%. In this paper, we propose a tractable strategy to precisely tune the position of heteroatoms, providing an efficient catalyst for hydrogen production together with the simultaneous generation of value-added imines.

Intrinsic Control of Interlayer Exciton Generation in Van der Waals Materials via Janus Layers

We demonstrate the possibility of engineering the optical properties of transition metal dichalcogenide heterobilayers when one of the constitutive layers has a Janus structure. We investigate different MoS2@Janus layer combinations using first-principles methods including excitons and exciton-phonon coupling. The direction of the intrinsic electric field from the Janus layer modifies the electronic band alignments and, consequently, the energy separation between dark interlayer exciton states and bright in-plane excitons. We find that in-plane lattice vibrations strongly couple the two states, so that exciton-phonon scattering may be a viable generation mechanism for interlayer excitons upon light absorption. In particular, in the case of MoS2@WSSe, the energy separation of the low-lying interlayer exciton from the in-plane exciton is resonant with the transverse optical phonon modes (40 meV). We thus identify this heterobilayer as a prime candidate for efficient generation of charge-separated electron-hole pairs.

Ultrabroadband Imaging Based on Wafer-Scale Tellurene.

High-resolution imaging is at the heart of the revolutionary breakthroughs of intelligent technologies, and it is established as an important approach toward high-sensitivity information extraction/storage. However, due to the incompatibility between non-silicon optoelectronic materials and traditional integrated circuits as well as the lack of competent photosensitive semiconductors in the infrared region, the development of ultrabroadband imaging is severely impeded. Herein, the monolithic integration of wafer-scale tellurene photoelectric functional units by exploiting room-temperature pulsed-laser deposition is realized. Taking advantage of the surface plasmon polaritons of tellurene, which results in the thermal perturbation promoted exciton separation, in situ formation of out-of-plane homojunction and negative expansion promoted carrier transport, as well as the band bending promoted electron-hole pair separation enabled by the unique interconnected nanostrip morphology, the tellurene photodetectors demonstrate wide-spectrum photoresponse from 370.6 to 2240nm and unprecedented photosensitivity with the optimized responsivity, external quantum efficiency and detectivity of 2.7×107 AW-1 , 8.2×109 % and 4.5 × 1015 Jones. An ultrabroadband imager is demonstrated and high-resolution photoelectric imaging is realized. The proof-of-concept wafer-scale tellurene-based ultrabroadband photoelectric imaging system depicts a fascinating paradigm for the development of an advanced 2D imaging platform toward next-generation intelligent equipment.

Triplet Separation after the Fastest Intramolecular Singlet Fission in the Smallest Chromophore.

Singlet fission is of key importance in harvesting solar energy in solar cells, as it generates a pair of triplet excitons on the incidence of a photon. This phenomenon is not yet widely employed in the organic photovoltaics industry mostly because of the rarity of singlet fission chromophores. Pyrazino[2,3-g]quinoxaline-1,4,6,9-tetraoxide was recently designed as the smallest intramolecular singlet fission chromophore, and it undergoes the fastest singlet fission with a 16 fs time scale. The subsequent separation of the generated triplet-pair is of likewise importance as their efficient generation. Through quantum chemistry calculations and quantum dynamics simulations, we show that the triplet-pair separates to residing on two chromophores with an ∼80% probability on each collision between a chromophore with the triplet-pair and a ground state chromophore. Avoided crossing, instead of conical intersection, is involved in the efficient exciton separation.

Exciton Manipulation for Enhancing Photoelectrochemical Hydrogen Evolution Reaction in Wrinkled 2D Heterostructures.

2D materials' junctions have demonstrated capabilities as metal-free alternatives for the hydrogen evolution reaction (HER). To date, the HER has been limited to heterojunctions of different compositions or band structures. Here, the potential of local strain modulation based on wrinkled 2D heterostructures is demonstrated, whichhelpsto realize photoelectrocatalytically active junctions. By forming regions of high and low tensile strain in wrinkled WS2 monolayers, local modification of their band structure and internal electric field due to piezoelectricity is realized in the lateral direction. This structure produces efficient electron-hole pair generation due to light trapping and exciton funneling toward the crest of the WS2 wrinkles and enhances exciton separation. Additionally, the formation of wrinkles induces an air gap in-between the 2D layer and substrate, which reduces the interfacial scattering effect and consequently improves the charge-carrier mobility. A detailed study of the strain-dependence of the photocatalytic HER process demonstratesa 2-fold decrease in the Tafel slope and a 30-fold enhancement in exchange current density. Finally, optimization of the light absorption through functionalization with quantum dots produces unprecedented photoelectrocatalytic performance and provides a route toward the scalable formation of strain-modulated WS2 nanojunctions for future green energy generation.

Non-fused polymerized small-molecular acceptors containing thieno[3,4-c]pyrrole-4,6-dione core for all-polymer solar cells

The innovation of polymer acceptors through the polymerized small molecular acceptors (PSMAs) strategy has promoted the rapid development of all-polymer solar cells (all-PSCs) in recent years. However, the non-fused PSMAs have been rarely investigated compared with the fused-ring non-fullerene counterpart. In this work, we reported the synthesis of non-fused PSMAs with thieno[3,4-c]pyrrole-4,6-dione (TPD) core, exhibiting planar configuration, simplified synthesis, and near-infrared absorption. Two PSMAs with regiorandom or regioregular structures were prepared based on the TPD core, in which all-PSCs offered efficiencies of 4.00% for the regiorandom polymer and 10.99% for the regioregular polymer, respectively, which is among the highest performance for non-fused PSMAs. Further morphological and electrical characterizations unveiled that higher device performance of regioregular TPD-based PSMAs was due to the efficient exciton separation and charge transport with more ordered backbone packing in the solid state. This work demonstrates that the TPD unit is a promising building block for the construction of PSMA polymers, providing more selections for the design of high-performance all-PSCs.

A critical review on core/shell-based nanostructured photocatalysts for improved hydrogen generation

Photocatalytic water splitting into gaseous hydrogen and oxygen in the presence of semiconductor photocatalysts under a visible spectrum of solar irradiation is one of the most promising processes for plummeting energy demands and environmental pollution. Among the successful photocatalytic materials, the core/shell nanostructures show promising results owing to their fascinating morphology that protects the surface features of the core besides the effective separation of photo-excitons resulting in an enhanced rate of hydrogen production up to 162 mmol h−1g−1cat, which is a notable highest value reported in the literature. In this review, we have focused on the basic characteristics of the core-shell structure-based semiconductor photocatalytic systems and their efficient water-splitting reactions under light irradiation. Comprehensive detail on various synthesis methods of core-shell nanostructures, shell thickness-dependent properties, charge-transfer reaction mechanisms, and photocatalytic stability are highlighted in this review. Core-shell nanostructured materials have been extensively used as a photocatalyst, co-catalyst, and by coupling with supporting materials to improve the apparent quantum efficiency up to 45.6%. Besides, important photocatalytic properties that influence the redox reactions i.e., effective exciton separation, the effect of different light sources/wavelengths, surface charge modeling, photocatalytic active sites, and turnover frequency (TOF) have also been focused on and extensively described. Finally, the present and future prospects of the core-shell nanostructured photocatalysts for solar energy conversion into green hydrogen production have been expounded.

In-situ CdS nanowires on g-C3N4 nanosheet heterojunction construction in 3D-Optofluidic microreactor for the photocatalytic green hydrogen production

Herein, we reported a simple and cost-effective fabrication method to develop an effective corrugated serpentine OFMR (C-SOFMR) with advanced features, such as expansion/contraction and wavy microstructure. A laminar flow with no back mixing was observed in plain serpentine OFMR (P-SOFMR). While, stretching and folding of fluid along with back mixing was observed in C-SOFMR. Further, the CdS nanowires on g-C3N4 nanosheet (CN/CdS) heterojunction was synthesized in situ both P-SOFMR and C-SOFMR and utilized the device for the photocatalytic green hydrogen generation. The CN/CdS heterojunction endowed with narrow band gap energy (2.01 eV). The longer CdS nanowires (∼110 nm) benefit the electronic interface with CN in the CN/CdS heterojunction and lead to the spatial separation (reduced recombination) of excitons along the CdS axial direction. The charges generated were utilized efficiently for the HER reaction in both P-SOFMR and C-SOFMR at higher flow rates attributing to the rapid micro-mixing and mass transfer. The CN/CdS heterojunction showed the highest photocatalytic activity (6.38 μmol h−1 in C-SOFMR and 6.16 μmol h−1 in P-SOFMR at 1.0 mL min−1) due to its good optronic properties. This study is a path forward for the utilization of advanced optofluidic devices to produce green hydrogen directly from solar energy.

Alkyl Branching Sites on π-Spacers for Dipyran-Based High-Efficiency Organic Solar Cells

The configuration of A-π-D-π-A type is one effective way for nonfullerene acceptor (NFA) design to achieve excellent photovoltaic performance with reduced synthetic complexity. Additional side chain engineering either around the center or at the terminus of the D core has been widely adopted in the molecular optimization of A-D-A type NFAs. Herein, the branch alkyl and branched sites of the side chains on π-spacers of A-π-D-π-A type acceptors are carefully evaluated, where dipyran ladder-type core Ph-DTDPi is employed as the D core. All three dipyran-based acceptors have been fully characterized and distinct behaviors have been detected in solid UV–vis absorption spectra, molecular stacking orientation, and miscibility with the polymer donor accompany with the side chain alternation. The balanced crystallization characteristics and good miscibility endows the blend film of DTDPi-C2:PBDB-T with a uniform morphology containing even smaller nanoscopic structures with interweaved fibers and balls, which enlarges the donor–acceptor contact and facilitates efficient exciton diffusion and separation. Hence, Ph-DTDPi-C2-based devices achieved a high PCE of 12.4% with a high JSC of 21.88 mA/cm2 and significantly enhanced FF of 69.26%. In short, adjusting the alkyl branch point on the π bridge is an effective strategy for dipyran-based acceptor and future molecular design.

Improving the performance of the self-powered polymer-based UV/Vis photodetectors via carbon fibers

Both Polyvinylpyrrolidone (PVP) and matrix-polymer of carbon (C)-PVP fibers (Fs) composites were synthesized by using the electrospinning technique and deposited onto the p-Si wafers to obtain PVP Fs/p-Si and C-PVP Fs/p-Si devices. The ultraviolet/Visible (UV/Vis) photodetector performance of both devices was compared. Both devices gave self-powered mode and with increasing the visible light intensity, the photocurrents of both devices increased. Besides, it was observed that the optical performance of the device containing C was better than the PVP Fs/p-Si device in both visible and UV lights. This was attributed to the high absorption properties of carbon and the increase in conductivity in the PVP due to carbon fibers. Furthermore, it is thought that the electric field formed in the carbon-PVP interaction and C-PVP/p-Si interface improves the optical properties of the device by increasing the exciton separation efficiency. Under the self-powered mode, the C-PVP Fs/p-Si device exhibited a maximum detectivity and ON/OFF ratio of 5.60 × 1010 Jones and 53 764, respectively for UV light of 365 nm. Under 100 mW visible light, these values ​​were determined as 1.01 × 1010 Jones and 9739, respectively, at V = 0. In addition, from the obtained noise-equivalent power (NEP) values, it was concluded that weaker signals can be detected under UV light (6.94 × 10−14 w Hz−1/2, at −2 V) than visible light (3.32 × 10−13 w/Hz1/2, at −2 V) for C-PVP Fs/p-Si.

Amide Linkages in Pyrene-Based Covalent Organic Frameworks toward Efficient Photocatalytic Reduction of Uranyl

The bond linkages in covalent organic frameworks (COFs) partly determine its physical and chemical properties, thus affecting the photoreactive activity by influencing the generation of photoelectrons and the separation of excitons. Herein, pyrene-based amide COF 4,4',4″,4‴-(pyrene-1,3,6,8-tetrayl)tetrabenzaldehyde-3,8-diamino-6-phenylphenanthridine (TFPPy-DP) was synthesized by postsynthetic modification of imine COFs. Due to the introduction of oxygen atoms into the framework and the change in polarity, an increased number of photogenerated electrons and a wide band gap for amide COFs were found, hydrophilicity and dispersibility were prompted as well. Both imine and amide COF TFPPy-DP were applied in the photocatalytic reduction and removal of toxic U(VI) under visible light, the catalytic reduction equilibrium (91% removal percentage of 238 ppm U at pH 3) was achieved by imine COFs with 10 h of irradiation, while amide COFs only took 2 h of irradiation (82% removal percentage). The much faster photocatalytic reduction rate of U(VI) can be attributed to the fact that amide COF TFPPy-DP retained crystallinity and permanent porosity and exhibited lower electrochemical impedance and enhanced charge separation and accumulation. Further electronic excitation analysis based on time-dependent density functional theory calculations revealed that the intramolecular charge-transfer effect in amide TFPPy-DP enhanced its photocatalytic rate.

Theoretical study on the electronic properties of different types of the donor:acceptor complexes

Non-fullerene organic solar cells can be classified into four forms in line with the different types of donor (D) and acceptor (A) in the active layer: all-polymer (PD:PA), polymer D:small-molecule A (PD:MA), small-molecule D:polymer A (MD:PA), and all-small-molecule (MD:MA). On the basis of having studied the electronic properties of a large number of related monomer molecules and D:A complexes, this work constructed four groups of D:A molecular pairs as described above as examples to investigate their electronic properties with first-principles density functional theory. The results show that the absolute value of the average binding energy of the PD:PA complex D18:P(NDI2HD-T) is larger than others, indicating the structure is relatively more stable. In accordance of the Bader charge analysis, the intra-molecular charge transfer of small-molecule is greater than polymers. For these blends, the intermolecular charge transfer of the all-polymer pair D18:P(NDI2HD-T) is larger, revealing that the PD:PA pair may result in a stronger intermolecular dipole electric field, which is beneficial to facilitate the separation of excitons. In addition, the MD:MA pair DRTB-T:FDICTF-2Cl and the PD:MA complex D18:FDICTF-2Cl all exhibit a larger amount of intra-molecular charge transfer, which indicates that the small-molecule acceptors in D:A complexes are conducive to promoting intra-molecular charge transfer.

P25-inspired α/γ-Fe2O3 isoelement heterostructures for visible-light photocatalysis: Optimization of crystalline ratios and mechanism investigation

Heterojunction with same elements but different types of semiconductors is a special material which is convenient for fabrication and industrialization. In this work, a series of α/γ-Fe2O3 isoelement heterostructures with different crystal contents (γ-Fe2O3, 10 % α-Fe2O3/90 % γ-Fe2O3, 33 % α-Fe2O3/67 % γ-Fe2O3, 55 % α-Fe2O3/45 % γ-Fe2O3, 78 % α-Fe2O3/22 % γ-Fe2O3 and α-Fe2O3) were constructed by hydrothermal method combined with controlled partial annealing process. Physicochemical analyses including XRD, TEM, XPS, BET, UV-Vis, PL spectra and ESR analyses were applied to investigate the advantages of isoelement α/γ-Fe2O3 compared with the pure single-crystalline Fe2O3. Benefiting from the enlarged specific surface area and staggered band structure, the fabricated heterostructure with 78 wt% α-Fe2O3 content exhibited more efficient separation of charge carriers and thus superior photodegradation efficiency than pure Fe2O3 under visible-light irradiation. Different from TiO2-based P25 heterostructures, Fe2O3 system possesses narrower bandgap and cannot efficiently consumed the excited holes. As a result, the accumulated h+ would inhibit the further separation of excitons with photocatalysis proceeding and thus induce insufficient driving force for the increment of photocatalytic ability like P25. The results presented in this work would be conducive to the rational design of staggered heterostructures.

Ferroelectric nano-heterojunctions for piezoelectricity-enhanced photocatalysis

Nanoscale heterojunctions of high dielectric constant piezoelectrics and optoelectronic semiconductors are attractive for photocatalytic degradation of hazardous organic compounds. In this work, such a nano-heterojunction was prepared by mixing of surface-carboxylated ferroelectric BaTiO3 nanoparticles (BTO NPs) and protonated graphitic carbon nitride (g-C3N4). Due to strong electrostatic interactions, intimate contact between BTO NPs and g-C3N4 was achieved for efficient charge separation and transfer. Two piezoelectric BTO NPs were used to prepare the BaTiO3/g-C3N4 heterojunctions: as-received BTO (arBTO) and 950 °C-annealed BTO (anBTO) with larger ferroelectric domains. Under ultrasonication, the photocatalytic degradation rate of levofloxacin by anBTO/g-C3N4 heterojunctions were 0.0462 min−1, which were 9.2 times of arBTO and 3.6 times of those in the absence of ultrasonication. The underlying mechanism was attributed to the higher current density, the accelerated charge separation of photo-activated excitons, and the reduced charge recombination via a synergistic effect of heterostructures and the local piezo-potential generated by the ferroelectric BTO NPs. By combination of thermal annealing of arBTO to enlarge the ferroelectric domains and construction of heterostructures, a highly efficient photocatalyst could be obtained. This study provides us a simple yet effective method to achieve highly efficient photocatalysts using the piezoelectric effect of ferroelectric BTO NPs.

Improved Charge Separation in Poly(heptazine-triazine) Imides with Semi-coherent Interfaces for Photocatalytic Hydrogen Evolution.

The construction of heterojunctions is a promising manner to accelerate the separation and transfer of the charge carriers at the interface. Herein, a binary poly(heptazine-triazine) imides (PHI/PTI) with semi-coherent interfaces was fabricated via a facile two-step salt-melt synthetic process. The built-in electric fields at the semi-coherent interface endow prompt exciton splitting and charge carrier separation. Hence, the optimized PHI/PTI-based copolymer presents a high apparent quantum yield (AQY=64 %) for visible-light driven hydrogen production, by the aids of K2 HPO4 as charge transfer mediator. This study provides physical insights for the rational promotion of the photocatalytic performance from the viewpoint of interfacial engineering of photocatalytic junctions on crystalline carbon nitride based semiconductors.