Electron-hole Research Articles

Polymeric Charge-Transporting Materials for Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) hold exceptional promise as next-generation photovoltaic technology, where both perovskite absorbers and charge-transporting materials (CTMs) play critical roles in cell performance. In recent years, polymeric CTMs have played an important role in developing efficient, stable, and large-area inverted PSCs due to their unique properties of high conductivity, tunable structures, and mechanical flexibility. This review provides a comprehensive overview of polymeric CTMs used in inverted PSCs, encompassing polymeric hole transport materials (HTMs) and electron transport materials (ETMs). the relationship between their molecular structures, modification strategies are systematically summarized and analyzed for adjusting energy levels, and improving charge extraction, enabling a deep understanding of these widely used materials. The review also explores effective strategies for designing even more efficient polymeric CTMs. Finally, an outlook is proposed on the exciting research of novel polymeric CTMs, paving the way for their commercialized applications in PSCs.

Surface Plasmon Polariton Photoluminescence Enhancement of Single InP Nanowires with InAsP Quantum Wells

A significant (up to 4 times) photoluminescence enhancement of single InP/InAsP/InP nanowires transferred onto a silicon oxide‐covered silver layer on silicon substrate with a metal surface roughness level of less than 1 nm and a dielectric thickness of 5 nm has been demonstrated. This phenomenon is explained by the interaction of electron–hole pairs in the semiconductor with surface plasmon polaritons. The photoluminescence kinetics and results of modeling confirm the indicated enhancement mechanism.

Visible light sensitive BiVO4–TiO2 nanocomposites for photocatalytic dye degradation

Abstract The hydrothermal approach was used to prepare visible light active BiVO4–TiO2 nanosheet composites in varying molar ratios. The photoluminescence (PL) spectrum, X-ray photoelectron spectroscopy (XPS), UV-Visible Diffuse Reflectance Spectroscopy (DRS), Transmission electroscopy (TEM), Brunauer-Emmett-Teller (BET) and field emission scanning electron microscopy (FESEM), were used to analyze the photocatalysts and composites. Photocatalytic activity of BiVO4–TiO2 composites was investigated by decolorizing methylene blue. Out of four different molar ratio BiVO4–TiO2 composites with a molar ratio of 3:1 BiVO4 TiO2 composite showed enhanced photocatalytic activity which is further proved by photoluminescence investigation of coumarin and Scavenger test. The DRS of BiVO4 TiO2 composite showed red shift in optical absorption. The enhanced photocatalytic activity is due to minimizing electron hole recombination by making composite with TiO2.

Improved hole injection for AlGaN-based DUV LEDs with graded-composition multiple quantum barrier insertion layers

The primary impediments to achieving high external quantum efficiency (EQE) and light output power (LOP) in AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) are inadequate hole injection efficiency and pronounced electron leakage. The significant polarization-induced positive charges, originating from the discontinuity in the Al composition between the last quantum barrier (LQB) and electron-blocking layer (EBL), attract electrons, consume holes, and reflect holes back into the p-type region, leading to severe electron leakage and low hole injection efficiency. In this paper, we introduce a graded-composition multiple quantum barrier (GQB) structure at the LQB/EBL interface. We adjust the Al composition in the insertion layer to alter the electrical polarity of the polarization-induced sheet charges, thereby modifying the electric field distribution in the EBL, LQB, and inserted GQB structure. Consequently, holes acquire boosted energy during their migration towards the active region. In addition, we enhance the hole injection and electron confinement ability via reducing the effective valence band barrier height and increasing the effective conduction band barrier height, thus diminishing the possibility of electron leakage from the active region into the p-type region. Therefore, the GQB structure proposed in this study provides a promising approach to improving the optical and electrical performance of DUV LEDs.

Synthesis of TiO2-ZnO n-n Heterojunction with Excellent Visible Light-Driven Photodegradation of Tetracycline

Zinc oxide-based photocatalysts with non-toxicity and low cost are promising candidates for the degradation of tetracycline. Despite the great success achieved in constructing n-n-type ZnO-based heterojunctions for the degradation of tetracycline under full-spectrum conditions, it is still challenging to realize rapid and efficient degradation of tetracycline under visible light using n-n-type ZnO-based heterojunctions, as they are constrained by the quick recombination of electron–hole pairs in ZnO. Here, we report highly efficient and stable n-n-type ZnO-TiO2 heterojunctions under visible light conditions, with a degradation efficiency reaching 97% at 1 h under visible light, which is 1.2 times higher than that of pure zinc oxide, enabled by constructing an n-n-type heterojunction between ZnO and TiO2 to form a built-in electric field. The photocatalytic degradation mechanism of n-n TiO2-ZnO to tetracycline is also proposed in detail. The demonstration of efficient and stable heterojunction-type ZnO photocatalysts under visible light is an important step toward commercialization and opens up new opportunities beyond conventional ZnO technologies, such as composite ZnO catalysts.

Biomimetic Dual‐Driven Heterojunction Nanomotors for Targeted Catalytic Immunotherapy of Glioblastoma

AbstractThe existence of the blood–brain barrier (BBB) and the characteristics of the immunosuppressive microenvironment in glioblastoma (GBM) present significant challenges for targeted GBM therapy. To address this, a biomimetic hybrid cell membrane‐modified dual‐driven heterojunction nanomotor (HM@MnO2‐AuNR‐SiO2) is proposed for targeted GBM treatment. These nanomotors are designed to bypass the BBB and target glioma regions by mimicking the surface characteristics of GBM and macrophage membranes. More importantly, the MnO2‐AuNR‐SiO2 heterojunction structure enables dual‐driven propulsion through near‐infrared‐II (NIR‐II) light and oxygen bubbles, allowing effective treatment at deep tumor sites. Meanwhile, the plasmonic AuNR‐MnO2 heterostructure facilitates the separation of electron–hole pairs and generates reactive oxygen species (ROS), inducing immunogenic tumor cell death under NIR‐II laser irradiation. Furthermore, MnO2 in the tumor microenvironment reacts to release Mn2+ ions, activating the cGAS‐STING pathway and enhancing antitumor immunity. In vitro and in vivo experiments demonstrate that these dual‐driven biomimetic nanomotors achieve active targeting and deep tumor infiltration, promoting M1 macrophage polarization, dendritic cell maturation, and effector T‐cell activation, thereby enhancing GBM catalysis and immunotherapy through ROS production and STING pathway activation.

Impact of PEDOT:PSS/Ti3C2Tx composite hole transport layer on the performance of perovskite light emitting diodes

The two-dimensional transition metal carbide MXenes, often designated by Ti3C2Tx, have garnered significant interest on account of their distinctive optoelectronic characteristics. In this paper, PEDOT:PSS/Ti3C2Tx composite hole transport layer (HTLs) was prepared by adding the MXenes material Ti3C2Tx into PEDOT:PSS, and quasi-two-dimensional perovskite light-emitting diodes (PeLEDs) were fabricated and investigated. While the addition concentration of Ti3C2Tx was 0.25 mg/mL, the optimal device shows the maximum luminance of 6250 cd/m2, and the current efficiency of 6.17 cd/A, which is 133 % and 112 % higher than the reference device without Ti3C2Tx, respectively. It is indicated that the additive incorporation of Ti3C2Tx in PEDOT:PSS can improve the efficiency of hole injection and conductivity of hole transport layer, and passivate the defects of perovskite film, thus enhancing the optoelectronic performance of PeLEDs. The findings of this study indicate that the PEDOT:PSS/Ti3C2Tx composite HTLs has considerable potential for application in PeLEDs.

Synergistic effect of FeOOH cocatalyst and Al2O3 passivation layer on BiVO4 photoanode for enhanced photoelectrochemical water oxidation

BiVO4 is one of the most attractive photoanodes for water oxidation due to its 2.4 eV narrow band gap, suitable band edge position, good stability in aqueous solution, low cost and non-toxicity. However, due to some inherent disadvantages such as low carrier mobility, severe charge recombination and slow water oxidation kinetics, the actual BiVO4 photocurrent density is often lower than the theoretical value of 7.5 mA cm−2. In this paper, BiVO4 was modified by alkali-treated Al2O3 passivation layer and FeOOH, and the photocurrent density of BiVO4 reached an astonishing 3.8 mA cm−2 at 1.23 VRHE, and the ABPE (applied bias photon-to-current efficiency) was close to 1 %. The detailed structural characterization and electrochemical test show that Al2O3 prepared by ALD (atomic layer deposition) can play a role in passivation of BiVO4 surface state after alkali treatment, inhibit electron hole recombination on BiVO4 surface, and accelerate hole transfer. As a hole storage layer and catalyst layer, FeOOH promoted the interfacial hole transfer, increased the active sites at the electrode electrolyte interface, and significantly increased the water oxidation activity. This work provides a novel method to enhance the performance of water electrolysis by using ALD to assist passivation of bismuth vanadate photoanode surface states.

Charge Diffusion and Repulsion in Semiconductor Detectors

Semiconductor detectors for high-energy sensing (X/γ-rays) play a critical role in fields such as astronomy, particle physics, spectroscopy, medical imaging, and homeland security. The increasing need for precise detector characterization highlights the importance of developing advanced digital twins, which help optimize the design and performance of imaging systems. Current simulation frameworks primarily focus on modeling electron–hole pair dynamics within the semiconductor bulk after the photon absorption, leading to the current signals at the nearby electrodes. However, most simulations neglect charge diffusion and Coulomb repulsion, which spatially expand the charge cloud during propagation due to the high complexity they add to the physical models. Although these effects are relatively weak, their inclusion is essential for achieving a high-fidelity replication of real detector behavior. There are some existing methods that successfully incorporate these two phenomena with minimal computational cost, including those developed by Gatti in 1987 and by Benoit and Hamel in 2009. The present work evaluates these two approaches and proposes a novel Monte Carlo technique that offers higher accuracy in exchange for increased computational time. Our new method enables more realistic performance predictions while remaining within practical computational limits.

Numerical simulation of electrically pumped active vertical‐cavity surface‐emitting lasers diodes based on metal halide perovskite

AbstractMetal halide perovskites (MHP)‐based electrically pumped vertical‐cavity surface‐emitting lasers (EPVCSEL) are promising candidates in optoelectronics due to low‐carbon footprint solution processing method. However, significant challenges impede MHP‐EPVCSEL manufacturing: (1) Distributed Bragg Reflectors (DBRs) composed of typical electron transport layers (ETLs) and hole transport layers (HTLs) are not conductive enough. (2) Due to large mobility difference of typical ETLs and HTLs, carriers‐unbalanced injection leads to severe performance degradation. Herein, we propose a potential strategy to address such challenges using MAPbCl3 and CsSnCl3 as carrier transport layers with mobility 3 orders larger than typical ETLs and HTLs. Via transfer matrix method calculations, we find that the reflectance of DBRs composed of MAPbCl3 (130.5 nm)/CsSnCl3 (108 nm) is larger than 91% with 10 pairs of DBRs. Furthermore, the proposed EPVCSEL device simulation shows that MHP‐EPVCSEL has the potential to achieve room temperature continuous wave lasing with a threshold current density of ∼69 A cm−2 and output optical power ∼10−4 W. This work can provide a deep insight into the practical realization of MHP‐EPVCSEL.

Enhanced photocatalytic degradation of organic pollutants by randomly oriented 2D SnS2 nanostructures

Abstract In this study, we present a bottom-up solvothermal technique using tin tetrachloride pentahydrate (SnCl4.5H2O) and thioacetamide as precursors to synthesize SnS2 nanostructures. Different solvents including isopropyl alcohol, ethanol (EN), and ethylene glycol were used in the reaction to enhance the photodegradation efficiency of organic pollutants, Methylene Blue (MB), and Tetracycline (TC) in an aqueous medium under simulated solar light irradiation. The SnS2 nanostructures synthesized with these solvents were characterized using various structural, morphological, and optical techniques, including x-ray diffraction, RAMAN, field emission scanning electron microscope, x-ray photoelectron spectroscopy, UV–Vis, and Brunauer–Emmett–Teller analysis. The choice of solvent was found to significantly affect the structural, morphological, and optical properties of the SnS2 nanostructures. Notably, the sample synthesized with EN as the solvent displayed a unique morphology, enhanced light-harvesting ability, efficient charge carrier separation, and a larger specific surface area, all of which contributed to its superior photocatalytic activity. This sample achieved 99.9% degradation of MB and 95% degradation of TC within 20 and 40 min, respectively. The kinetic analysis revealed maximum rate constant (k) values of 0.15242 min−1 for MB and 0.060 95 min−1 for TC, as determined by the pseudo-first-order kinetic model. We also discuss the plausible mechanism involving visible light-induced electron–hole pairs that generate reactive species, leading to the mineralization of dyes into H2O, CO2, and other gaseous products. The synthesized SnS2 nanostructures demonstrate significant potential for enhanced photocatalytic activity in organic pollutant degradation, underscoring their promise in addressing water pollution challenges.

N+/p+ GaN and n+/p+ Al0.10Ga0.90N tunnel junctions: a promising alternative for hole injection in deep ultraviolet light-emitting diodes

This research replaced the traditional hole source layers in a conventional LED with a tunnel junction. In conventional light-emitting diodes (LEDs) two hole injecting layers (p-GaN and p-AlxGa1-xN) have been used, in which holes have to surpass greater energy barriers that hindered holes injection. A heavily doped GaN tunnel junction (TJ) has been used as a replacement for conventionally used hole injection layers, which has reduced the energy barriers for holes and increased the electron confining ability of wells. As a result, the internal quantum efficiency (IQE) of the LED has increased from 52% to 72%. Instead of GaN TJ, Al0.10Ga0.90N – GaN hybrid tunnel junction (HTJ) has been introduced to lower the efficiency droop and raise the efficiency further to 81% simultaneously. Using TJ and HTJ, we have demonstrated that the conventional hole’s source layer can be replaced by TJs, which results in better hole injection because of reduced barrier height, increased electron confinement, greater electron–hole radiative recombination, and higher spontaneous emission intensity.

Y, Yb, and Gd tri-doping on B-site of Ba(Zr, Ce)O3-δ with improved proton conduction performance

Perovskite-type proton conducting electrolytes are garnering significant attention due to its key role in protonic ceramic electrochemical cells (PCEC) and its application in hydrogen sensors (HS) used for metal melt measurements. Developing high proton conduction perovskite materials with good chemical stability is always a worldwide research focus. In this paper, Y, Yb and Gd triple-doping on B-site of BaCeO3-BaZrO3 solid solution were carried out to investigate the effect of gadolinium doping on the performance of protonic conducting electrolytes. BaZr0.1Ce0.7(Y0.5Yb0.5)0.2-xGdxO3-δ (x = 0, 0.1, 0.15 and 0.2), which were also referred as BZCYYbGdx (x = 0, 10, 15 and 20), were synthesized by solid-state reaction at 1600 °C for 10 h. It is found that BZCYYbGd15 has the highest proton conductivity and proton transfer number among the four prepared materials. The proton mobility of BZCYYbGd15 is 4.06 × 10−6 cm2/(Vꞏs) at 800 °C, which increases with an increased temperature. Its proton transfer number is higher than 0.9 at 500 °C under the atmosphere of PH2O = 0.018 atm. A moderate doping of gadolinium increases the temperature threshold for proton conduction. Proton, oxygen vacancy, electron hole and total conductivity activation energies of BZCYYbGd15 under the wet atmosphere are found to be 0.74, 1.58, 1.41 and 0.92 eV, respectively. Furthermore, the chemical stability of pellets is improved after gadolinium doping. This study provides a reference value for future research on high proton conduction electrolytes.

Piezo-modulated interface field facilitating hydroxyl radical formation of SrTiO3/ZnO heterojunction for water purification

Piezo-modulated interface engineering is an effective method for tuning the charge transfer process to enhance piezocatalytic dynamics. In this study, SrTiO3/ZnO heterojunctions were successfully synthesized via hydrothermal methods to degrade carbamazepine in water. The optimal SrTiO3/ZnO-5 % sample exhibited a remarkable 99.9 % degradation efficiency of carbamazepine within 60 min under ultrasonic vibration. The piezocatalytic reaction rate (k value = 0.0746 min−1) was 4.63 times and 10.97 times higher than that of pure SrTiO3 and pure ZnO, respectively. Reactive species scavenger tests, electron paramagnetic resonance techniques, and bands gap analysis revealed that the enhanced activity can be attributed to the construction of an interfacial electric field in SrTiO3/ZnO heterojunctions and the modification of an internal piezoelectric polarized field. This allowed charge redistribution and transport across the SrTiO3/ZnO heterojunction interface, and facilitated the generation of hydroxyl radicals (HO•) through simultaneous hole oxidation and electron reduction. This study provides a comprehensive mechanistic understanding about piezoelectric heterojunctions in the catalytic redox reactions, and offers valuable insights for designing more effective piezoelectric heterojunctions for the degradation of pharmaceutical organic pollutants.

Construction of BiVO4/g-C3N4/Ag3PO4 ternary heterojunction with double Z-scheme and its photocatalytic and bacteriostatic properties

A novel Bi-composite photocatalyst BiVO4/g-C3N4/Ag3PO4 with a double Z-scheme structure was prepared by hydrothermal method assisted by honeysuckle extract. When the mass fraction of Ag3PO4 in the composite is 10 %, the inactivation rates of E.coli and S. aureus were 6.9 and 4.6 log, respectively. The MIC results were 0.6 and 0.8 mg/ml, respectively. The capture experiment confirmed that h+ and O2− were the main active substances that catalyzed bacteriostasis. Double Z heterojunction reduces the photochemical corrosion of Ag3PO4, changes the transmission path of photogenerated electrons, and then promotes the separation of photogenerated electron holes, thus obtaining significant photocatalytic activity.

Hydroxylated SiO2-modified {0 0 1}-TiO2 nanosheets as a surface multifunctional photocatalyst for enhanced degradation of gaseous toluene

The relatively weak activity and serious deactivation of anatase TiO2 nanosheet catalysts with highly exposed {001} facets ({001}-TiO2) limits its wide application in photocatalytic degradation of gaseous pollutants. Herein, we propose a hybrid photocatalyst composed of {001}-TiO2 and SiO2 with numerous hydroxyl groups (denoted as {001}-TiO2/HO-SiO2). The catalyst showed excellent performance for gaseous toluene degradation under UV illumination, with 99.2 % removal efficiency and 204.7 μmol L−1 CO2 yield (about 85.9 % mineralization efficiency) within 120 min. It also demonstrated superior durability over five consecutive cycles of toluene photodegradation. The modification of HO–SiO2 on {001}-TiO2 facilitate the selective adsorption of toluene on the catalyst surface by H-bonding interaction, and make the major poisoning species, benzoic acid, easily desorb from the surface, reducing the catalyst inactivation. Most importantly, we found that the formed TiOSi bond promotes the separation of photogenerated electron–hole pairs, and provides abundant available electrons for the formation of reactive oxygen radicals and the left holes for the conversion of toluene to benzyl radicals or oxidation of H2O to hydroxyl radicals, which results in the improved activity. This study highlights the importance of the introduction of secondary components with special functions on TiO2, which is helpful for the design of photocatalysts with high performance and anti-deactivation ability for treatment of volatile organic compounds.

BCP Buffer Layer Enables Efficient and Stable Dopant-Free P3HT Perovskite Solar Cells.

Poly(3-hexylthiophene) (P3HT) has garnered significant attention as a novel hole transport material (HTM). Principally, its cost-effective synthesis, excellent hole conductivity, and stable film morphology make it one of the most promising HTMs for perovskite solar cells (PSCs). However, the efficiency of PSCs employing P3HT remains less than ideal, primarily due to the mismatch of energy levels and insufficient interface contact between P3HT and the perovskite film. In this work, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was inserted into the P3HT/perovskite interface for effectively alleviating the recombination loss. BCP could effectively anchor uncoordinated Pb2+ and establish π-π stacking interactions with P3HT. These interactions not only neutralize flaws to reduce energy depletion but also enhance the configuration of P3HT, aiding in carrier transfer. Consequently, the BCP-modified device achieved an efficiency of 19.27%, which is significantly superior to the control device (12%).

Design and performance exploration of Pb-free low-cost all-inorganic perovskite-inspired CuAgBi2I8 solar cells: theoretical approach

Abstract Organic–inorganic halide perovskites have demonstrated great potential for photovoltaic applications owing to their unprecedented optoelectronic properties and low manufacturing costs. However, the commercialization of this technology is hindered by its thermal instability and inherent toxicity. In this study, SCAPS-1D simulation software was used to study the performance of solar cell based on CuAgBi2I8, which is a novel inorganic non-toxic lead-free perovskite-inspired material. Different electron transport layers (TiO2, In2S3, ZnO, Zn0.75Mg0.25O,SnO2 and SrTiO3) and hole transport layers (CuI, PEDOT:PSS, CuSCN and Cu2O) were studied, our research indicated that SnO2 and NiO formed the optimal combination. Further analysis revealed that the optimal absorption layer thickness was 900 nm, the absorption layer doping concentration should be less than 1 × 1013 cm−3 and the defect density should be less than 1 × 1014 cm−3. The optimal thickness of SnO2 and NiO was 30 nm, the optimal doping concentration of SnO2 and NiO was 1 × 1020 cm−3, the defect density of absorber layer/SnO2 and absorber layer/NiO interfaces should be less than 1 × 1012 cm−3, C was the optimal back electrode material. Consequently, the optimal device configuration was identified as FTO/SnO2/CuAgBi2I8/NiO/C, the efficiency was improved from original 2.76% to 19.10% after above optimization. These results indicate that solar cell with CuAgBi2I8 as the absorber layer is a potential alternative to organic–inorganic lead halide perovskite solar cells.

Dual Electric Field Coupling with Tunable Schottky Barrier Synergistically Regulating Electronic Configuration in CoP@Ni‐CdS Heterojunction for Efficient Photocatalytic H2 Evolution

AbstractDesigning and exploiting visible‐light‐responsive materials that converts solar into chemical energy is promising in achieving green energy sustainability, but addressing low electron–hole separation efficiency and sluggish surface kinetic process remains formidable challenges. Herein, a novel CoP@Ni‐CdS Schottky junction composed of Ni‐doped CdS nanorods and quasi‐metallic CoP nanoparticles is constructed via a simple hydrothermal–calcination method. Experiments and theoretical calculations demonstrate that magnetic Ni‐doping not only induces a spin‐polarized electric field and enhances the built‐in interfacial electric field strength, but also rises the Schottky barrier height at the heterointerface, which synergistically accelerates the separation efficiency of photoinduced charges and modulates the electronic configuration of the active site to optimize the adsorption–desorption behaviors for H2O molecules and H* intermediates. Therefore, the designed CoP@Ni‐CdS catalyst exhibits an exceptional photocatalytic performance with H2 evolution rate of 42.14 mmol g−1 h−1 with the apparent quantum efficiencies of 16.8% at 420 nm, which is 14.14 and 2.21 times higher than that of pristine CdS and Ni‐CdS, respectively. This work provides in‐depth insights into fabricating dual electric fields, tuning the Schottky barrier and modulating the electronic configuration of active sites in Schottky heterojunction for ameliorative photocatalytic activity.

Core/Shell ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 Nanoparticles for the Photodecomposition of Brilliant Blue E-4BA

The synthesis and characterization of ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 core/shell nanoparticles (NPs) is reported. The NPs were used for photocatalytic degradation of brilliant blue E-4BA under UV and visible light irradiation, monitored by high-performance liquid chromatography and UV-vis absorption spectroscopy. The size of the NPs ranged from 10 to 30 nm for the core and an additional 3 nm for the TiO2 shell. Al2O3/TiO2 and Al1.9Co0.1O3/TiO2 showed superior degradation under UV and visible light compared to ZnO/TiO2 and SiO2/TiO2 with complete photodecomposition of 20 ppm dye in 20 min using a 10 mg/100 mL photocatalyst. The “Co-doped” Al1.9Co0.1O3/TiO2 NPs show the best performance under visible light irradiation, which is due to increased absorption in the visible range. DFT-calculated band structure calculations confirm the generation of additional electronic levels in the band gap of γ-Al2O3 through Co3+ ions. This indicates that Co-doping enhances the generation of electron–hole pairs after visible light irradiation.