Interfacial Charge Separation Research Articles

Enhanced charge transfer through defect and doping synergistic engineering for efficient hydrogen production

Simultaneous modification of catalysts by surface defects and atomic doping strategies can effectively inhibit the recombination of photogenerated carriers. In this study, the surface state of MoS2 was adjusted through the synergistic effects of sulfur defects and the doping of oxygen atoms, successfully constructing a type II heterojunction with hydrogen-substituted graphdiyne (H-GDY) for efficient photocatalytic hydrogen generation. The results showed that the H-GDY/O-MoS2-x exhibits the best hydrogen production performance (2272.97 μmol/g/h), which is about 25 times that of MoS2. And the synergistic effect of sulfur defects and oxygen doping engineering can modulate the energy band structure and increase the interfacial potential difference between H-GDY and O-MoS2-x, which enhances the driving force of electron transfer and improves the interfacial charge transfer and separation efficiency. This work shows that the synergistic effect of defect and doping engineering can effectively improve the photocatalytic performance and provides a new idea for the preparation of sulfide-based photocatalysts.

Core-shell nanorods film of p-CuZnS/n-TiO2 with boosting interfacial charge separation for sensitive photoelectrochemical photodetector

Copper zinc sulphide (CZS) due to high conductivity, fast photoresponse and good stability has attracted rising attention in optoelectronic field. Constructing heterojunctions with rational energy bands alignment can accelerate carrier separation to improve the performance of CZS-based photoelectric device. Herein, p-CZS/n-TiO2 core-shell nanorods heterojunction film was successfully fabricated for the first time. CZS nanoparticles (NPs) were directly loaded on the surface of TiO2 nanorods (NRs) through a simple chemical bath deposition. Photoelectrochemical (PEC) photodetector based on CZS/TiO2 composite film was designed and interfacial charge kinetics has also been investigated. The CZS/TiO2 PEC device exhibits fast response speed of 95/56 ms, high responsivity of 7.1 mA W-1 and detectivity of 5.6 × 1012 Jones at a bias voltage of 1 V. The light on/off ratio of self-powered CZS/TiO2 PEC device achieves 5.6 × 103, nearly 30.4 times higher than bare CZS PEC device. Furthermore, the photodetection performance of the CZS/TiO2 PEC device can be effectively regulated by light power density and environment conditions, promoting its adaptability in multifarious practical applications. The findings suggest that CZS/TiO2 heterostructure film devices have great potential for high-performance and energy-efficient PEC photodetectors.

Atomically dispersed Fe boosting elimination performance of g-C3N4 towards refractory sulfonic azo compounds via catalyst-contaminant interaction

Herein, an oxygen-doped porous g-C3N4 photocatalyst modified with atomically dispersed Fe (Fe1/OPCN) is successfully prepared and exhibits significant superiority in removing refractory sulfonic azo contaminants from water via catalyst-contaminant interaction. The elimination performance of Fe1/OPCN towards acid red 9, acid red 13 and amaranth containing similar azonaphthalene structure and increasing sulfonic acid groups increases gradually. The amaranth degradation rate of Fe1/OPCN is 17.7 and 6.1 times as that of homogeneous Fenton and OPCN, respectively. In addition, Fe1/OPCN also has more outstanding removal activities towards other contaminants with sulfonic acid and azo groups alone. The considerable enhancement for removing sulfonic azo contaminants of Fe1/OPCN is mainly ascribed to the following aspects: (1) The modified Fe could enhance the adsorption towards sulfonic azo compounds to accelerate the mass transfer, act as e- acceptor to promote interfacial charge separation, and trigger the self-Fenton reaction to convert in-situ generated H2O2 into •OH. (2) Fe(Ⅲ) could coordinate with —N=N— to form d-π conjugation, which could attract e- transfer to attack —N=N— bond. Meanwhile, the inhibited charge recombination could release more free h+ to oxidize sulfonic acid groups into SO4-•. (3) Under the cooperation of abundant multiple active species (•O2-, h+, e-, •OH, SO4-•) formed during the degradation reaction, sulfonic azo compounds could be completely mineralized into harmless small molecules (CO2, H2O, etc.) by means of —N=N— cleavage, hydroxyl substitution, and aromatic ring opening. This work offers a novel approach for effectively eliminating refractory sulfonic azo compounds from wastewater.

Copper porphyrin modified BiOBr/Bi19S27Br3 for efficient CO2 photoreduction

The insufficient solar light response ability of the photocatalyst, rapid recombination of interface charges, and lack of active sites significantly inhibit the efficiency of photocatalytic CO2 reduction. Addressing these challenges simultaneously is a very challenging task. Herein, an interface engineering coupled surface polarization strategy is proposed to optimize the CO2 photoreduction performance. The copper tetracarboxyphenylporphyrin (CuTCPP) modified BiOBr/Bi19S27Br3 (BBS) heterostructure was developed. The built-in electric field formed between BiOBr and Bi19S27Br3 interfaces induces the effective interfacial charge separation, while the surface polarization of CuTCPP induces the transfer of electrons from the conduction band (CB) of BBS to the CB of CuTCPP. Benefiting from this unique configuration and abundant active sites in CuTCPP, greatly improved photocatalytic CO2 reduction performance can be realized. Without adding cocatalysts and sacrificial agents, the optimized CO generation performance of CuTCPP-BiOBr/Bi19S27Br3 (BBS-CT) is 3.5 times higher than that of BBS. This work provides valuable insights of interface engineering coupled surface polarization strategy for collaborative improve the photocatalytic CO2 reduction performance.

Lattice Match-Enabled Covalent Heterointerfaces with Built-in Electric Field for Efficient Hydrogen Peroxide Photosynthesis.

Crafting semiconducting heterojunctions represents an effective route to enhance photocatalysis by improving interfacial charge separation and transport. However, lattice mismatch (δ) between different semiconductors can significantly hinder charge dynamics. Here, meticulous lattice tailoring is reported to create a covalent heterointerface with a built-in electric field (BIEF), imparting markedly improved hydrogen peroxide (H2O2) photosynthesis. Specifically, an In2S3/CdS heterojunction with a coherent heterointerface, characterized by covalent In─S─Cd bridge and exceptionally low lattice mismatch of 0.27%, and a BIEF from In2S3 to CdS, is rationally designed. This heterojunction entails rapid charge separation and transfer, achieving an outstanding H2O2 production rate of 2.09 mmol g-1 h-1 without the need for scavengers and oxygen bubbling, and a high apparent quantum efficiency of 17.73% at 400 nm. Density functional theory (DFT) calculations further reveal that this Z-scheme heterojunction facilitates the adsorption of *O2 and the generation of *OOH intermediates during the 2e- oxygen reduction reaction, associated with a low Gibbs free energy. This study underscores the significance of fine-tuning interfacial lattices and integrating BIEF to accelerate photocatalysis. The simple yet robust strategy can be conveniently leveraged to enhance device performance in optoelectronics, electrocatalysis, photoelectrocatalysis, and sensing.

Heterojunction Organic Solar Cells with Efficient Charge Mobility and Separation Capabilities Studied by DFT.

The properties of the active layer materials play a decisive role in determining the power conversion efficiency of organic solar cells (OSCs). Chlorophyll and its derivatives are abundant and environmentally friendly functional organic molecular materials. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we have calculated the absorption spectra and their excited state properties based on optimized ground state structures. It was found that bacteriochlorin exhibits superior structural properties, a smaller energy gap and hole reorganization energy, redshifted absorption spectra, and higher hole mobility compared to the donor D18. This suggests that bacteriochlorin exhibits superior donor properties. Comparative studies between o-AT-2Cl and m-AT-2Cl showed that o-AT-2Cl had superior acceptor properties, implying that differences in substitution positions can influence the physicochemical properties of non-fullerene acceptors (NFAs). Subsequently, six bulk heterojunctions (BHJs) were constructed by combining three donors with nonfused ring electron acceptors, o-AT-2Cl and m-AT-2Cl. The bacteriochlorin-based BHJs performed well among them, with BChl3/o-AT-2Cl and BChl4/o-AT-2Cl having the largest interfacial charge separation rate. The results suggested that BHJs composed of bacteriochlorin and NFAs can improve OSCs' photovoltaic performance, providing a feasible scheme for designing efficient OSCs.

Interface Synergy of Exposed Oxygen Vacancy and Pd Lewis Acid Sites Enabling Superior Cooperative Photoredox Synthesis.

Photo-driven cross-coupling of o-arylenediamines and alcohols has emerged as an alternative for the synthesis of bio-active benzimidazoles. However, tackling the key problem related to efficient adsorption and activation of both coupling partners over photocatalysts towards activity enhancement remains a challenge. Here, we demonstrate an efficient interface synergy strategy by coupling exposed oxygen vacancies (VO) and Pd Lewis acid sites for benzimidazole and hydrogen (H2) coproduction over Pd-loaded TiO2 nanospheres with the highest photoredox activity compared to previous works so far. The results show that the introduction of VO optimizes the energy band structure and supplies coordinatively unsaturated sites for adsorbing and activating ethanol molecules, affording acetaldehyde active intermediates. Pd acts as a Lewis acid site, enhancing the adsorption of alkaline amine molecules via Lewis acid-base pair interactions and driving the condensation process. Furthermore, VO and Pd synergistically promote interfacial charge transfer and separation. This work offers new insightful guidance for the rational design of semiconductor-based photocatalysts with interface synergy at the molecular level towards the high-performance coproduction of renewable fuels and value-added feedstocks.

Modulating stacking mode and molecular polarization in CTF/molecule heterojunction for meliorating photocatalytic CO2 conversion with nearly 100% CO selectivity

Herein, two conjugated molecules, i.e., D-π-A TAPT and non-D-A TAPB, are finely designed to incorporate with covalent triazine framework (CTF) in A-A and A-B stacking mode via π-π interaction, respectively. The transient photocurrent response of the generated AA-CTF/TAPT Z-Scheme heterostructure is 1.14 × 10-7 A, significantly higher than that of the other two metal-free heterostructures (AA-CTF/TAPB and AB-CTF/TAPT). The promoted photocarrier transportation is attributed to strong polarization (dipole moment = 2.634 D) imposed by the D-π-A effect in TAPT that motivates the interfacial charge separation, and the coexisting charge transfer channel built by the ordered A-A stacking mode in AA-CTF that expedites the charge delivery. The photocatalytic CO2 conversion conducted by AA-CTF/TAPT gives the optimal CO conversion rate as 7.47 μmol·g−1·h−1, and with nearly 100 % product selectivity obtained, which is attributable to the lower energy barrier of CO desorption barrier (−1.07 eV) rather than that of CHO* formation (1.52 eV) for generating CH4.

Needle growth of Nb2O5 nanoparticles on BiOCl nanosheets to fabricate S-scheme heterojunction with oxygen vacancies for enhanced photooxidation of cyclohexane

The exploration of cost-efficient, environmentally friendly, and high-efficacy photocatalysts for the enhanced selective photooxidation of cyclohexane to KA oil (cyclohexanone (CHA-one) and cyclohexanol (CHA-ol)) is a pivotal challenge in the industrial realm. Herein, the present study focuses on the synthesis of needle-like S-scheme heterojunction photocatalysts with oxygen vacancies, which are achieved by the needle growth integration of nano-sized Nb2O5 particles onto the BiOCl nanosheets. Remarkably, the 40 % Nb2O5/BiOCl composites exhibited superior performance in the solvent-free photooxidation of cyclohexane at room-temperature and under atmospheric pressure. The production yield of KA oil was 180.3 μmol (CHA-one/CHA-ol molar ratio = 3.5), and exceptional selectivity towards KA oil, reaching up to 99.3 %. The enhanced photocatalytic efficiency in cyclohexane oxidation can be attributed to the unique S-scheme heterogeneous interfaces with specific nanoneedle morphology, which result in the enhanced photonic absorption, effective charge carrier separation, a high density of oxygen vacancies, and the exposure of the highly reactive (001) plane of BiOCl. The excellent interfacial charge separation and transfer pathways of S-scheme heterojunction are disclosed by the in-depth EPR analysis and DFT calculations. These insights highlight the significant potential of the needle-like Bi-based S-scheme heterojunction photocatalysts for the efficient photooxidation of saturated alkanes.

Constructing type II heterojunction of 2D/1D Pg-C3N4/Ag3VO4 nanocomposite with high interfacial charge separation for boosting photocatalytic CO2 reduction under solar energy

The well-designed, template-free synthesis of 2D protonated g-C3N4 nanosheets (Pg-C3N4) coupled with novel 1D Ag3VO4 nanorods has been investigated to construct 2D/1D interface heterostructures with strong electrostatic interactions between the positively charged 2D Pg-C3N4 nanosheets and the negatively charged 1D Ag3VO4 nanorods. The coupling of Pg-C3N4 and Ag3VO4 with desirable characteristics resulted in a 2D/1D interface heterojunction with a type II charge carrier transfer mechanism, effectively maintaining and utilizing charge carriers. The 2D/1D Pg-C3N4/Ag3VO4 exhibited remarkable photocatalytic performance for CO2 conversion with H2O, resulting in maximum CH4 and dimethyl ether (DME) production of 352.3 and 130.9 µmol/g-cat, respectively. A quantum yield of 0.23 % for CH4 generation was achieved over the 2D/1D Pg-C3N4/Ag3VO4, which was 2.9 and 1.4 times higher than that of the Pg-C3N4 and Ag3VO4 samples, respectively. The improvement in photocatalytic performance primarily stems from the effective interaction between Pg-C3N4 and ternary Ag3VO4, leading to enhanced transfer and separation of photoinduced charge carriers through the creation of a type II heterojunction. The findings of this study are useful in designing template-free heterojunctions for photocatalytic CO2 conversion and other solar energy applications.

Improved UV Photoresponse Performance of ZnO Nanowire Array Photodetector via Effective Pt Nanoparticle Coupling.

Ultraviolet (UV) photodetectors (PDs) based on nanowire (NW) hold significant promise for applications in fire detection, optical communication, and environmental monitoring. As optoelectronic devices evolve towards lower dimensionality, multifunctionality, and integrability, multicolor PDs have become a research hotspot in optics and electronic information. This study investigates the enhancement of detection capability in a light-trapping ZnO NW array through modification with Pt nanoparticles (NPs) via magnetron sputtering and hydrothermal synthesis. The optimized PD exhibits superior performance, achieving a responsivity of 12.49 A/W, detectivity of 4.07 × 1012 Jones, and external quantum efficiency (EQE) of 4.19 × 103%, respectively. In addition, the Pt NPs/ZnO NW/ZnO PD maintains spectral selectivity in the UV region. These findings show the pivotal role of Pt NPs in enhancing photodetection performance through their strong light absorption and scattering properties. This improvement is associated with localized surface plasmon resonance induced by the Pt NPs, leading to enhanced incident light and interfacial charge separation for the specialized configurations of the nanodevice. Utilizing metal NPs for device modification represents a breakthrough that positively affects the preparation of high-performance ZnO-based UV PDs.

Identifying Root Origin of Insulating Polymer Mediated Solar Water Oxidation.

Rational construction of high-efficiency photoelectrodes with optimized carrier migration to the ideal active sites, is crucial for enhancing solar water oxidation. However, complexity in precisely modulating interface configuration and directional charge transfer pathways retards the design of robust and stable artificial photosystems. Herein, a straightforward yet effective strategy is developed for compact encapsulation of metal oxides (MOs) with an ultrathin non-conjugated polymer layer to modulate interfacial charge migration and separation. By periodically coating highly ordered TiO2 nanoarrays with oppositely charged polyelectrolyte of poly(dimethyl diallyl ammonium chloride) (PDDA), MOs/polymer composite photoanodes are readily fabricated under ambient conditions. It is verified that electrons photogenerated from the MOs substrate can be efficiently extracted by the ultrathin solid insulating PDDA layer, significantly boosting the carrier transport kinetics and enhancing charge separation of MOs, and thus triggering a remarkable enhancement in the solar water oxidation performance. The origins of the unexpected electron-withdrawing capability of such non-conjugated insulating polymer are unambiguously uncovered, and the scenario occurring at the interface of hybrid photoelectrodes is elucidated. The work would reinforce the fundamental understanding on the origins of generic charge transport capability of insulating polymer and benefit potential wide-spread utilization of insulating polymers as co-catalysts for solar energy conversion.

In situ N‐doped Bi3O4Br/(BiO)2CO3 ultrathin nanojunctions with matched energy band structure for nonselective photocatalysis pollutant removal

AbstractNovel N‐doped Bi3O4Br/(BiO)2CO3 ultrathin nanojunctions have been prepared. Alkalization dehalogenation was performed to form Bi3O4Br, surfactant was employed to control the ultrathin thickness, and few‐layers of C3N4 as a sacrificial agent were used to build the N‐doped (BiO)2CO3. The photocatalytic behavior of the achieved N‐doped Bi3O4Br/(BiO)2CO3 ultrathin nanojunctions was evaluated through the degradation of antibiotic agent ciprofloxacin, tetracycline hydrochloride, and endocrine disrupting chemical bisphenol A as well as typical dye rhodamine B under visible light irradiation. The matched energy band structure between Bi3O4Br and (BiO)2CO3 could endow the highly efficient interfacial charge separation, thus leading to excellent nonselective photocatalytic behavior. The structure design in this system will open new windows for the reasonable design of other photocatalysts.

Data-Driven Design of Electroactive Spacer Molecules to Tune Charge Carrier Dynamics in Layered Halide Perovskite Heterostructures.

Crafting rational heterojunctions with nanostructured materials is instrumental in fostering effective interfacial charge separation and transport for optoelectronics. Layered halide perovskites (LHPs) that form heterojunctions between organic spacer molecules and inorganic metal halide layers exhibit tunable photophysics owing to their customizable band alignment. However, controlling photogenerated carrier dynamics by strategically designing layered perovskite heterojunctions remains largely unexplored. We combine a data-driven approach with time-domain density functional theory (TD-DFT) and non-adiabatic molecular dynamics (NAMD) to screen and select electronically active spacer dications (A') that introduce a type-II heterojunction in the lead iodide-based Dion-Jacobson phase LHPs. The composition-structure-electronic property correlations reveal that the number of nitrogens in aromatic heterocycles is the key factor in designing electron-accepting spacers in these perovskites. The detailed atomistic simulations validate the design strategy further by modeling (A')PbI4 perovskites, which incorporate three different screened electroactive A' spacers. The computed excited charge carrier dynamics illustrate the phonon-mediated ultrafast interfacial electron transfer from the inorganic conduction band edge to the lower-lying unoccupied orbitals of spacers, exhibiting photoluminescence quenching in these (A')PbI4 perovskites. The spatially separated electrons and holes at the type-II heterojunction interface prolong the excited charge carrier lifetime, boosting the carrier transport and exciton dynamics. Our work illustrates a robust in silico approach for designing LHPs with exciting optoelectronic properties originating from their fine-tuned heterojunctions.

Piezoelectric assisted boosting photocatalytic hydrogen evolution over a finely prepared Pt/TiO2/g-C3N4 composite system using lactic acid as sacrificial agent

A one-step calcination method was employed to fabricate a new TiO2/g-C3N4(TCN) composite catalyst. The therein TiO2 nanoparticles with good dispersion were synthesized through a sol-gel method and followed by additional heat treatment. The ultra-thin and flat g-C3N4(CN) nanosheets were synthesized by calcining a mixture of urea and melamine. The obtained TCN exhibited significantly excellent performance, especially when 3 wt% Pt was added and lactic acid (HL) was used as a sacrificial agent, achieving a rate of 32.5 mmol/h/g. This improvement can be attributed to the uniform dispersion of nano TiO2 particles on g-C3N4, the flat ultra-thin layer structure of CN, and the constructed heterojunctions between two, which promote the separation of photogenerated electron-hole pairs. Measurements of PL and photocurrent response confirmed enhanced efficiency in interface charge separation and transfer. Additionally, it demonstrated lower internal resistance in EIS tests. Notably, owing to the piezoelectric properties of CN, when the reaction liquid was subjected to additional ultrasonic treatment, the hydrogen production rate further increased to 43.57 mmol/h/g and 2.9 mmol/h/g, respectively, in simulated sunlight and visible light response. The piezoelectric effect of CN induced by ultrasound regulated the bandgap width of the catalysts, broadening their response to visible light.

Design and application of hierarchical α-Fe2O3/In2O3 heterojunction photoanode for enhanced photoelectrochemical water oxidation

α-Fe2O3 attracted great attention as a promising photoanode candidate for photoelectrochemical (PEC) H2O spitting. In this paper, one dimensional (1D) α-Fe2O3 nanorods coupled 2D porous In2O3 nanosheet assemblies were designed to construct a S-scheme α-Fe2O3/In2O3 heterojunction photoanode. The unique porous In2O3 nanosheet assemblies are conductive to improve light-harvesting efficiency and provide more active sites. An internal electric field induced at the α-Fe2O3/In2O3 heterojunction interface could promote interfacial charge separation and transfer, enhancing redox kinetics. The as-obtained 2D/1D In2O3/α-Fe2O3 photoanode achieved a stable photocurrent density of 2.2 mA cm−2 at 1.23 V (vs. RHE). It is 6.3 times higher than that of the α-Fe2O3 component, and got a max applied bias photo-to-current efficiency (ABPE) of 0.28%, which is about 5.8 times that of bare α-Fe2O3 at 1.01 V. The work provides a promising strategy to construct high-performance S-scheme heterostructure photoanodes, featuring the role of surface and interface science in sustainable energy.

2D/2D Bi2WO6/C3N5 S-scheme heterojunction for highly selective production of CH4 by photocatalytic CO2 reduction under visible light

Photocatalytic CO2 reduction is a practical solution to the energy dilemma and environmental damage caused by greenhouse gases, and it is very important to explore high-efficiency photocatalysts. In this study, a novel Bi2WO6/C3N5 step(S)-scheme heterojunction was successfully constructed and applied for CO2 photoreduction. The 2D/2D structure showed excellent photocatalytic properties, with methane production reaching 1.976 μmol·g−1·h−1 and selectivity reaching 100 % under 5 hours of visible light irradiation. The result indicates that combining Bi2WO6 and C3N5 can promote interfacial charge separation and maintain the optimal reducing ability of photogenerated electrons. Based on experimental and theoretical calculations, we characterized the reaction mechanism and heterojunction formation mechanism. This study offers a novel approach to improve the selectivity and photocatalytic efficiency of CO2 reduction products.

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

Boosted charge separation in porphyrin-based MOFs/CdS photocatalyst via interfacial −N−Cd− bridge bond construction

The high interfacial charge transfer barrier has been a main thermodynamic obstacle for improving the catalytic efficiency of heterojunction materials. Optimizing the interfacial environment is an effective strategy to achieve high catalytic efficiency. Herein, the coordinate bond (−N−Cd−) is designed to connect the hafnium porphyrin−metal organic framework (HT) and CdS nanoparticles, which is systematically analyzed by the 1H NMR, FTIR, Raman and DRS, respectively. The optimized 15HT1.5 H/CdS6 composite featuring interfacial bridge bonds, exhibits an H2 production up to 11.9 mmol·g−1·h−1, which is 28.5, 52.8 and 7 times greater than pure CdS, HTH, and mechanically mixed sample without interfacial chemical bonds connected, respectively. Mechanistic study suggests that the coordination bonds between HT and CdS serve as the directional carrier transfer bridges, significantly improving interfacial charge separation and chemical stability. Moreover, the formed Z-scheme charge transfer mechanism also endows the composite with high redox ability. This strategic construction of interfacial chemical bonds within heterojunction provides an effective pathway for improving interfacial charge transfer in the heterojunction photocatalysts.

20.1 % Certified Efficiency of Planar Hole Transport Layer‐Free Carbon‐Based Perovskite Solar Cells by Spacer Cation Chain Length Engineering of 2D Perovskites

AbstractThe planar triple‐layer hole transport layer (HTL)‐free carbon‐based perovskite solar cells (C‐PSCs) have outstanding advantages of low cost and high stability, but are limited by low efficiency. The formation of a 3D/2D heterojunction has been widely proven to enhance device performance. However, the 2D perovskite possesses multiple critical properties associated with 3D perovskite, including defect passivation, energy level, and charge transport properties, all of which can impact device performance. It is challenging to find a powerful means to achieve comprehensive regulation and trade‐off of these key properties. Herein, we propose a chain‐length engineering of alkylammonium spacer cations to achieve this goal. The results show that the 2D perovskite formed by short‐chain alkylammonium cations primarily acts to passivate defects. With the increase in cation chain length, the 2D perovskite achieves a more matched energy level with 3D perovskite, enhancing the built‐in electric field and promoting charge separation. However, the further increase in chain length impedes the charge transport due to the insulativity of organic cations. Comprehensively, the 2D perovskite formed by tetradecylammonium cations achieves the optimal balance of defect passivation, interface charge separation, and charge transport. The planar HTL‐free C‐PSCs exhibit a new record efficiency of 20.40 % (certified 20.1 %).