Carrier Recombination Research Articles

Superior degradation of tetracycline hydrochloride, rhodamine B, and methyl orange by platinum-modified Bi4Ti3O12/Ti3C2Tx photocatalyst: Synthesis, Catalytic performance, and Mechanism

Photocatalytic degradation of organic compounds and antibiotics in water by solar energy represents a promising approach for addressing environmental problems. The precious metal particles of platinum were connected through a facile ultraviolet light deposition technique based on Bi4Ti3O12 that was in situ hybridized with Ti3C2Tx. The potential development process was elucidated by investigating the breakdown of TC-HCl. The prepared Pt/Bi4Ti3O12/Ti3C2Tx material achieved complete removal of pollutants under light conditions, including tetracycline hydrochloride (10min), rhodamine B (30min), and methyl orange (10min), which benefited from the mutual enhancement between Ti3C2Tx and Bi4Ti3O12. Additionally, the increased specific surface area of Pt/Bi4Ti3O12/Ti3C2Tx may provide additional pathways for electron insertion/extraction. The platinum (Pt) rapidly absorbs photogenerated electrons, which facilitates photoinduced charge transfer and effectively suppresses carrier recombination. These collective effects significantly enhance catalytic activity and reduce photo-corrosion. This study paves the way for the development of photocatalytic materials based on Bi4Ti3O12/Ti3C2Tx, incorporating metal loads to enhance sunlight absorption capacity and antibiotic degradation capability.

Insight into gain and transient response characteristics of AlGaN/GaN hetero-junction based UV photodetectors: Case study on the role of incident light intensity

Gain and response speed are two key performance parameters for high sensitivity photodetectors (PDs). However, the effect of incident light intensity on gain and transient response properties of AlGaN/GaN hetero-junction based PDs are still not fully understood. Here, we design and fabricate an AlGaN/GaN hetero-junction based ultraviolet (UV) PD with interdigitated electrodes formed by a conductive two-dimensional electron gas (2DEG) channel, which exhibits a low dark current of 2.92 × 10−11 A and a high responsivity of 3060 A/W at 10 V bias. The high-gain AlGaN/GaN 2DEG PD has a similar working mechanism to those of traditional phototransistors, but its device architecture is evidently simplified. By investigating the variation of gain and transient response characteristics of the 2DEG PD as a function of incident UV light intensity, it has been concluded that the gain of the PD in a low-light intensity region is dominated by hole accumulation-induced electron escape from the 2DEG, while in a high-light intensity region, the gain is dominated by photoconductivity effect and limited by carrier recombination. This study provides guidance for future practical applications of AlGaN/GaN-based PDs in complex UV illumination environments.

2D/2D Bi2MoO6/g-C3N4 direct Z-scheme Van der Waals heterojunction photocatalyst for boosting nitrogen fixation

Although photocatalytic nitrogen fixation is an efficient and environmentally-friendly technology for ammonia synthesis, it still faces challenges such as high recombination of photo-generated carriers and a lack of active sites for the reaction of catalysts. Constructing direct Z-scheme heterojunctions is considered an effective strategy to enhance carrier separation efficiency of catalysts. However, it still encounters the challenge of lacking surface active reaction sites. The 2D Z-scheme Van der Waals heterojunction has the same charge transfer mechanism of direct Z-scheme heterojunctions, ensuring high carrier efficiency and retaining strong redox ability. Additionally, its layered structure provides a large number of reactive sites. In this study, theoretical calculation simulation was employed to predict the properties of Bi2MoO6 (BMO) and g-C3N4 (CN), and to simulate the dynamic behavior of photogenerated carriers. A 2D/2D CN-BMO direct Z-scheme Van der Waals heterojunction was constructed. Remarkably, this heterojunction demonstrated significantly enhanced photocatalytic ammonium generation capabilities. This study provides valuable insights for the development of advanced heterojunction photocatalysts.

Design of MnO2/g-C3N4 heterojunction composite photocatalysts for augmented charge separation and photocatalytic degradation performance with superior antibacterial activity

The development of advanced photocatalysts is critical for addressing environmental pollution and enhancing water purification processes. Our study has effectively developed a novel MnO2/g-C3N4 (MGC) heterojunction composite photocatalyst exhibiting superior photo-degradation under visible-light (VL) conditions and also established antibacterial activities. Comprehensive characterization was acquired using XRD, FT-IR, FE-SEM with EDX-associated mapping images, TEM, UV–Vis DRS and PL investigations, indicating the successful formation of well-dispersed MnO2 nanoparticles (NPs) over the g-C3N4 catalyst. The MGC composite heterojunction photocatalyst demonstrated increased photocatalytic degradation activity of 77.2 % in aqueous crystal violet (CV) under VL within 120 min, significantly outperforming pure g-C3N4 and MnO2 by 3.02 and 2.37 times, respectively. The MGC composite demonstrates remarkable stability and reusability, retaining 73.7 % of its efficiency after five consecutive cycles. Additionally, the as-synthesised composite endows potent antibacterial action against various pathogenic bacteria including K. pneumonia, S. aureus, E. coli and B. cereus. The active species analysis indicates that the composite photocatalyst facilitates charge transfer, while effectively preventing the recombination of photo-produced carriers via an effective Z-scheme mechanism, and the synergistic things among MnO2 and g-C3N4 are accredited to the boosted photocatalytic and antibacterial activities. This research describes a photocatalytic approach for efficiently eliminating various contaminants from water bodies, which has significant implications for the future development of photocatalytic technology for wastewater handling.

Lattice energy transfer from homo-crystalline substitution for enhanced piezo-photocatalytic CO2 conversion

The rapid recombination of carriers and large activation energy of CO2 compromise the efficiency of CO2 photoreduction. Herein, SrTiO3 (STO) with different molar ratios of La3+ and Al3+ double-site homo-crystalline substitution is prepared by a ball-milling molten salt method. The concentration of Ti3+ and excess oxygen vacancies decrease to improve the catalytic activity. Meanwhile, the double sites act as electron transfer platforms for easy electron transfer from the bulk phase to the surface to foster CO2 photoreduction. Not only that, the energy transfer due to doping-induced lattice distortion can potentially enhance the photocatalytic activity. A piezoelectrically polarized electric field is introduced to further expedite charge transport. As a result, the activity of La, Al-STO piezo-photocatalytic CO2 reduction is improved to 39.17 µmol g-1h−1, which is more than seven times better than that of the pure STO. Furthermore, CO2 adsorbs spontaneously on the catalysts because the thermodynamic energy barrier decreases due to the piezoelectric force, which is verified by density-functional theory calculation. This study reveals the great potential of double-site homo-crystalline substitution of STO pertaining to the charge transport kinetics and thermodynamics of the catalytic reaction in the piezo-photocatalytic CO2 process.

SnS2-supported MAPbI3 composites for effective photocatalytic hydrogen evolution

Metal halide perovskites have demonstrated encouraging photocatalytic potential due to their favorable photoelectric properties. However, severe carrier recombination greatly affects their catalytic performance. Here, we introduced cocatalyst SnS2 to synthesize novel SnS2/MAPbI3 composites via the electrostatic coupling method, which presented excellent hydrogen production performance. The hydrogen production rate of 5 % SnS2/MAPbI3 (5 wt% SnS2/MAPbI3) reached 445.96 μmol·g−1·h−1, about 325-fold increase compared to pure MAPbI3 (1.37 μmol·g−1·h−1). The 16 h cycle stability test proved its stability and effectiveness. Detailed experimental characterizations and analysis indicate that the cocatalyst SnS2 reduces the surface overpotential and facilitates electron transport and efficiently separates photogenerated charge carriers. This work provides new insights into effective photocatalysts based on MAPbI3.

CsF Improved Buried Interface for Efficient and Stable Inverted All-inorganic CsPbI2.85Br0.15 Perovskite Solar Cells

All-inorganic CsPbIxBr3-x is frequently used as the top cells in tandem devices due to its tunable bandgap, making it highly promising for future development. However, CsPbIxBr3-x films typically contain numerous defects at the interfaces and grain boundaries, significantly hindering carrier transport and thus reducing the device performance. Interface modification is commonly employed to passivate defects and enhance carrier transport at the interfaces. In this work, CsF was used to modify the buried interface between the perovskite film and self-assembled monolayers (SAMs). The interaction between fluoride ions (F⁻) and uncoordinated Pb2⁺ contributed to reduce defect density, enhance crystallization quality, and suppress non-radiative carrier recombination at buried interface. Consequently, the efficiency of inverted CsPbI2.85Br0.25 PSCs with CsF improved from 16.15% to 18.24%, compared to the control device. Moreover, the unencapsulated CsF-modified device retained 89% of its initial efficiency after storing for 600 h in ambient air with room-temperature and relative humidity (RH) of 20%. This demonstrates that CsF modification significantly enhances both the performance and stability of CsPbI2.85Br0.15 perovskite solar cells.

Preparation and investigation of physicochemical properties of g-C3N4/LaCoO3 heterostructure for photocatalytic dye degradation

Photocatalytic decomposition of pollutant is the most optimal approach for the wastewater remediation. Nevertheless, the development of a catalyst that is both cost-effective and extraordinarily active remains a substantial challenge. The g-C3N4/LaCoO3 heterostructure were prepared by different weight percentages of g-C3N4 (15, 30, 45, 60, and 75 wt%). The g-C3N4 and LaCoO3 were exhibits hexagonal and rhombohedral crystal structure respectively. The g-C3N4/LaCoO3 heterostructure exhibits tiny particles were anchored over the coarse like structure. The g-C3N4/LaCoO3 heterostructure promote visible light harvest and inhibit charge carrier recombination than the bare LaCoO3 and g-C3N4 and which helps to enhance the organic pollutant elimination performances. The g-C3N4/LaCoO3 heterojunction exhibits superior methylene blue degradation when compared to bare LaCoO3 and g-C3N4. Furthermore, the composite of LaCoO3/g-C3N4–60 wt% exhibits higher photocatalytic activity and exceptional stability were observed under visible light irradiation.

Highly efficient narrow bandgap Cu(In,Ga)Se2 solar cells with enhanced open circuit voltage for tandem application

Although an ideal bandgap matching with 0.96 eV and 1.62 eV for a double-junction tandem is hard to realize practically, among all mature photovoltaic systems, Cu(In,Ga)Se2 (CIGSe) can provide the closest bandgap of 1.00 eV for the bottom sub-cell by adjusting its composition. However, pure CuInSe2 (CISe) solar cell suffers strong interfacial carrier recombination. We hereby present approaches to introduce appropriate Ga gradients in both the back and front parts of absorber while maintaining the absorption spectrum close to CISe. With an appropriate front Ga gradient, the open circuit voltage can be enhanced by ~30 mV. With a pre-deposited CIGSe layer and a high copper excess deposition during absorber growth, the Ga diffusion can be well suppressed and a wide U-shaped Ga grading with a minimum bandgap of 1.01 eV has been created. Our optimized narrow-bandgap CIGSe solar cell has achieved a certified record PCE of 20.26%, with a record-low open circuit voltage deficit of 368 mV and a record-high contribution of 10% absolute efficiency to a four-terminal tandem. This work demonstrates the potential of controlling gallium diffusion to improve the performance of narrow bandgap CIGSe solar cells for tandem applications.

Numerical analysis and optimization of photovoltaic performance of Sb2Se3 based photocathode

Antimony selenide (Sb2Se3) based heterojunction photocathodes have recently received an increased attention, largely due to their outstanding performances for hydrogen production through photoelectrochemistry (PEC) water splitting. The PEC water splitting process encompasses both physical and electrochemical processes. The physical process is capable of generating a photo-voltage, which can drive the photo-generated electrons transport to the electrode/electrolyte interface through the p-n junction. However, unlike traditional photovoltaic device, the protective layer and co-catalyst will also affect the electrical performance of device, resulting in a decrease in PEC performances and stability. How to optimize the electrical properties of the photoelectrode is a concern. In this work, devoted to Sb2Se3/TiO2 photocathode structures, the photovoltaic performances of a photocathode were modeled and analyzed from three aspects: p-n junction, back contact, and transition layer between TiO2 and co-catalyst, using the SCAPS-1D software and a realistic set of material parameters. Based on reported optimization strategy, tthe interface electrical characteristics of photocathode were studied by adjusting energy band, donor/acceptor density, defect density, electron affinity, and other parameters. A low-cost and easy to implement optimization strategy was proposed, which used Cd1-xZnxS as the buffer layer between p-n junctions, W-doped TiO2 as the transition between TiO2/co-catalyst, and Sn-doped Sb2Se3 as the back surface layer to suppress the carrier recombination. The optimized photocathode can theoretically obtain photoelectric conversion efficiency of 17.01%–17.14% and a maximum Jsc of 38.79 mA/cm2, exhibiting the potential to obtain a large photocurrent in the photoelectrochemical water splitting process.

Atomic Zn-N4 Site-Regulated Donor-Acceptor Catalyst for Boosting Photocatalytic Bactericidal Activity.

Reactive oxygen species (ROS)-mediated photocatalytic antibacterial materials are emerging as promising alternatives for the antibiotic-free therapy of drug-resistant bacterial infections. However, the overall efficiency of photocatalytic sterilization is restricted by the rapid recombination of the charge carriers. Herein, we design an in-plane π-conjugated donor-acceptor (D-A) system (g-C3N4-Zn-NC), comprising graphitic carbon nitride (g-C3N4) as the donor and Zn single-atom anchored nitrogen-doped carbon (Zn-NC) as the acceptor. Experimental and theoretical results reveal that the introduction of Zn-NC induces the formation of an intermediate band in g-C3N4-Zn-NC, extending the spectral absorption range and facilitating charge carrier transfer and separation. Additionally, the synergistic effects of the dual sites, the N═C-N sites of the g-C3N4 "donor" and the atomic Zn-N4 sites of the Zn-NC "acceptor", boost ROS production. Consequently, the biocompatible g-C3N4-Zn-NC effectively kills methicillin-resistant Staphylococcus aureus (MRSA) under visible-light irradiation and promotes the healing of MRSA-infected wounds on mouse skin.

Improving the efficiency of polymer solar cells based on chitosan@PVA@rGO composites via gamma-irradiated treatment of rGO nanoparticles

Polymer solar cells (PSCs) are growing as attractive contenders for renewable energy technologies given their low cost, adaptability, and environmental sustainability, rendering them valuable in combating climate change. Interestingly, this work investigates the augmentation of photon absorption and overall efficiency in low-cost, effective active layers (ALs) via gamma irradiation treatment, thereby raising the number of active absorption sites. For the first time, novel Chitosan@PVA@rGO (CPG) composite sheets were created as AL materials and treated to varied dosages of in-situ gamma irradiation (0, 10, 20, 30, and 40 KGy) to optimize their microstructural and physicochemical characteristics. The processed ALs were subjected to comprehensive tests, which included J–V variable evaluation as well as evaluations of microstructure, porosity, morphology, contact angle, optical characteristics, and electrochemical impedance spectroscopy (EIS). The findings reveal that the composites' surface properties got better gradually as gamma irradiation dosages grew; peak performance was reached at 30 KGy (75.9 % apparent porosity and roughness parameter Ra = 6.22 μm). Extended gamma irradiation resulted in increased DSSC efficiency, which reached 6.85 % after 10 KGy and 7.63 % after 20 KGy. High-energy gamma photons boosted mobility and decreased resistive limits by reducing carrier recombination and facilitating charge carrier movement inside CPG compounds. This increased the longevity and charge transfer efficiency of the solar cell. After 30 KGy alteration, the CPG AL's optimized efficiency of 8.78 % and Jsc of 20.23 mA/cm2 indicate a 44.3 % improvement in efficacy over the pristine material. The insertion of oxygen-enriched free radicals into the CPG structure is responsible for the improvement in photovoltaic efficiency because it creates continuous pathways for fast electron transport. This work provides an innovative perspective on the use of heteroatom-doped ALs in PSCs by highlighting the benefits of co-doping and regulated heteroatom species.

Enhancing the Photocatalytic Performance of CsPbBr3 Nanocrystals through Ferrocene-Assisted Exciton Dissociation and Halide Vacancies.

Excited-state interactions at the interfaces of nanocrystals play a crucial role in determining photocatalytic efficiency. CsPbBr3 nanocrystals (CPB NCs), celebrated for their exceptional photophysical properties, have been explored for organic photocatalysis. However, their intrinsic limitations, such as charge carrier recombination and stability issues, hinder their full potential. Strategies to enhance exciton dissociation, such as complexing CPB NCs with charge-shuttling molecules, have shown promise but remain underexplored for fully realizing their potential in improving the photocatalytic performance. We coupled ferrocene carboxylic acid (FcA) with CPB to extract the photogenerated holes, leveraging them to oxidize (1,2-dibromoethyl)benzene to phenacyl bromide. Optimization using pristine CPB NCs achieved a production rate of 5 μmol gcat-1 h-1, which increased to 13.1 μmol gcat-1 h-1 upon FcA incorporation, marking a 2.5-fold enhancement. Mechanistic investigations revealed the simultaneous involvement of electrons and holes, with oxygen acting as a reactant contributing to the oxygenated product. Halide vacancies were identified as critical adsorption sites for the substrate, with post-synthetic treatments enhancing these vacancies, resulting in over a 2-fold increase in the reaction rate. This work not only establishes an effective approach for phenacyl bromide synthesis but also highlights the potential of leveraging dissociated charge carriers to enhance photocatalysis using CPB NCs.

Amorphous Bi-BiOx - inducted directional charges transfer in stalactite-like carbon nitride heterojunction for effective photocatalytic H2O2 production

Photocatalytic technology provides a clean and sustainable method for producing hydrogen peroxide (H2O2), while, the yield is significantly hindered by the rapid recombination of charge carrier and the low oxygen reduction activity of catalyst. Herein, the Bi-BiOx/CN heterojunction was successfully constructed by homogeneously loaded amorphous Bi-BiOx species on stalactite-like CN just via one-step pyrolysis with the pre-coordination confinement strategy. In the Bi-BiOx/CN heterojunction, the Bi-BiOx species acted as electron storage layer and induced electrons directional migrate from CN to Bi-BiOx species, which promoted the carrier separation. Meanwhile, the three-dimensional stalactite structure of CN not only increased the active sites and gas shuttle pores, but also shorten the electrons and holes diffuse distance from the bulk phase to the surface. As expected, the H2O2 generation rate of optimal Bi-BiOx/CN-10 reached 6036 μM/g/h, which is 1.86 times higher than that of CN. The experimental results proved that ·O2– plays an important role in H2O2 production, and the direct 2e- ORR reaction and the indirect 2e- ORR reaction coexist. This work validates the potential of Bi-BiOx species as an alternative to noble metals for heterojunction construction, and provides a feasible path for regulating efficient directional transfer of charge transfer.

Charge-separated 3D/2D layered heterojunction of NiNb2O6/E-gC3N4 as an efficient photocatalyst for photo-reduction of Cr6+ and photo-oxidation of dyes under visible and sunlight

The major challenge in photocatalysis for environmental remediation is rapid recombination of charge carriers. Recently, the construction of 3D/2D heterojunction is regarded as a viable strategy to overcome this drawback. Towards this objective, 3D NiNb2O6 − 2D E-gC3N4 type-II heterojunction, hitherto not reported, was constructed as a dual catalyst for photo-reduction of Cr6+ to Cr3+ and photo-oxidation of methylene blue (MB), malachite green (MG) and crystal violet (CV) under visible light. After optimizing the parameters, the photocatalytic activity was studied under direct sunlight. Among the prepared catalysts, NG-20 composite (NiNb2O6 −80 % & E-gC3N4 −20 %) exhibits excellent photocatalytic activity in removing 97 % of Cr (VI) under 120 min and degrading 97.4 %, 96.1 % and 98 % of MB, MG and CV respectively in 20 min under direct sunlight. For instance, the rate constant of NG-20 was found to be 4.2 and 5.8 times higher than NiNb2O6 & E-gCN respectively for MB degradation. The superior photocatalytic activity can be attributed to the enhanced charge carrier separation of electron-hole pair due to the construction of 3D/2D heterojunction. Superoxide (0O2−) and hydroxyl (0OH) radicals are the dominant reactive oxygen species (ROS) and a plausible mechanism for photocatalysis is proposed.

Doping-free Janus homojunction solar cell with efficiency exceeding 23%

Photovoltaic solar cell is one of the main renewable energy sources, and its power conversion efficiency (PCE) is improved by employing doping or heterojunction to reduce the photogenerated carrier recombination. Here, we propose a straightforward strategy for constructing high-PCE homojunction solar cells, where intrinsic driving forces can simultaneously enhance the efficiency of carrier separation and transport. Thanks to the intrinsic dipole of Janus structure, doping-free Janus homojunction has naturally not only a type-II band alignment to promote the photoexciton dissociation, but also a reduced effective bandgap to enhance light absorption. More importantly, the interfacial dipole can facilitate the separation of carriers into different layers, thereby promoting carrier separation; and the intrinsic dipole across the Janus structure can drive photoinduced electron and hole transfer to opposite layers, enhancing carrier transport. We illustrate the concept in titanium-based Janus monolayer homojunction, where the theoretically observed PCE reaches 23.22% of TiSSe homojunction. In contrast to the previous cell architectures that require complex processing procedures and often result in defects, the doping-free homojunction configuration promises both high PCE and significantly lower manufacturing costs. Our work opens an avenue to design low-cost, high-efficiency solar cells.

Effects of High-Temperature Treatments in Inert Atmosphere on 4H-SiC Substrates and Epitaxial Layers

Silicon carbide is a wide-bandgap semiconductor useful in a new class of power devices in the emerging area of high-temperature and high-voltage electronics. The diffusion of SiC devices is strictly related to the growth of high-quality substrates and epitaxial layers involving high-temperature treatment processing. In this work, we studied the thermal stability of substrates of 4H-SiC in an inert atmosphere in the range 1600–2000 °C. Micro-Raman spectroscopy characterization revealed that the thermal treatments induced inhomogeneity in the wafer surface related to a graphitization process starting from 1650 °C. It was also found that the graphitization influences the epitaxial layer successively grown on the wafer substrate, and in particular, by time-resolved photoluminescence spectroscopy it was found that graphitization-induced defectiveness is responsible for the reduction of the carrier recombination lifetime.

A computational analysis to enhance performance of CIGS solar cells using back surface field and ZnSe buffer layer approach

Abstract This study aims to enhance CIGS solar cell efficiency while minimizing environmental impact by replacing the toxic CdS buffer layer with a ZnSe buffer layer. The CIGS chalcogenide semiconductor is a promising solar cell absorber material but has faced challenges related to defect-free manufacturing, misaligned buffer layers, and device configuration. Cuprous oxide (Cu2O) and zinc selenide (ZnSe), an inexpensive, eco-friendly, and widely available material, are suggested as a back surface field layer and buffer layer to enhance device performance. This paper proposes a new cadmium-free structure (Al/ZnO: Al/ZnO/ZnSe/CIGS/Cu2O/Ni) to enhance the efficiency of CIGS heterojunction solar cells by reducing charge carrier recombination losses. We utilized SCAPS-1D to simulate photovoltaic (PV) performance and examined the impacts of electron affinity, absorber thickness, interface defect density, operating temperature, radiative recombination coefficient, Mott-Schottky analysis, parasitic resistance, and quantum efficiency on photovoltaic characteristics. Optimization and choosing a suitable buffer and passivation layer gives the device efficiency of 31.13%, followed by VOC (0.92 V), JSC (40.40 mA/cm2), and FF (83.34 %) for the proposed structure. The radiative recombination coefficient found to be 10-13 cm3/s and the parasitic resistance of the solar cell are in good agreement for fabricating high-efficiency solar cells. These findings suggest that CIGS-based heterojunction solar cells represent a cutting-edge method for achieving high-efficiency solar cells that outperform earlier designs.

Ordered Vacancy Compound Formation at the Interface of Cu(In,Ga)Se2 Absorber with Sputtered In2S3‐Based Buffers: An Atomic‐Scale Perspective

The design of a Cd‐free and wider‐bandgap buffer layer is stringent for future Cu(In,Ga)Se2 (CIGSe) thin‐film solar cell applications. For that, an In2S3 buffer layer alloyed with a limited amount of O (well below 25 mol%) has been proposed as a pertinent alternative solution to CdS or Zn(O,S) buffers. However, the chemical stability of the In2S3/CIGSe heterointerface when O is added is not completely clear. Therefore, in this work, the buffer/absorber interface for a series of sputter‐deposited In2S3 buffers with and without O is investigated. It is found that the solar cell with the highest open‐circuit voltage is obtained for the O‐free In2S3 buffer sputtered at 220 °C. This improved open‐circuit voltage could be explained by the presence of a 20 nm‐thick ordered vacancy compound (OVC) at the absorber surface. A much thinner OVC layer (5 nm) or even the absence of this layer is found for the cell with In2(O0.25S0.75)3 buffer layer where O is inserted. The volume fraction of the OVC layer is directly linked with the magnitude of Cu diffusion from the CIGSe surface into the In2(OxS1−x)3 buffer layer. The O addition strongly reduces the Cu diffusion inside the buffer layer up to complete suppression for very high O contents in the buffer. Finally, it is discussed that the presence of the OVC layer may lower the valence band maximum, thereby forming a hole barrier, suppressing charge carrier recombination at the In2(OxS1−x)3/CIGSe interface, which could result in an increased open‐circuit voltage.

Oxygen vacancy enriched and Cu single-atom contained covalent organic frameworks: A competitive photocatalyst to promote hydrogen evolution under visible light

Single-atom loaded covalent organic frameworks (COFs) have been rapidly developed in the field of photocatalytic hydrogen production in recent years. Despite the insufficient active sites has been introduced, the high recombination rate of photogenerated carriers has hindered the progress of catalyst development. In this work, a novel approach is proposed to construct oxygen vacancies (OVs) on single atom Cu contained COF-TpPa, acting as an electron collector to facilitate the transfer and utilization of electrons. The Cu-OV-TpPa can provide a remarkable H2 production rate of 2.77 mmol g−1 h−1 under visible light, which is 2.6 times of Cu-P-TpPa (a H2 production rate of 1.02 mmol g−1 h−1). It achieves a high apparent quantum efficiency (AQE) of 20 % at 420 nm with no noble metal cocatalyst. A thorough analysis of carrier lifetime, recombination rate, electric conductivity and charge density reveals that the synergistic effect between OVs and single-atom Cu significantly enhances photogenerated carrier separation efficiency and reduces activation energy. This study presents a new strategy to design COF-based photocatalysts towards a competitive H2 production under visible light.