Charge Carrier Generation Research Articles

As-cast organic solar cells with 19.44% efficiency enabled by introducing functional fullerene derivative to facilitate charge carrier generation and transport

As-cast organic solar cells with 19.44% efficiency enabled by introducing functional fullerene derivative to facilitate charge carrier generation and transport

Regulation of Exciton Effects in Functionalized Conjugated Polymers by B-N Lewis Pairs for Visible-Light Photocatalysis.

Strong excitonic effects are common in organic conjugated polymer semiconductors, severely hindering the generation of free charge carriers for conducting photocatalysis. Therefore, exploring new channels to modulate exciton dissociation in polymers is far-reaching in facilitating photocatalysis. A series of B-N Lewis pair functionalized conjugated polymers have been developed to minimize exciton effects by modulating charge transfer pathways. Theoretical studies have shown that introducing B-N Lewis pairs can dramatically increase the distance of charge transfer (D index) and the amount of electron transfer and reduce the Coulomb attraction energy (EC), which contributes to breaking the equilibrium of the coexistence of excitons and charge carriers. Further experimental results show that the singlet excitons are efficiently dissociated into more free-charge carriers under photoexcitation to participate in surface reactions. The optimized polymer PyPBM shows an exponential increase in photocatalytic hydrogen and hydrogen peroxide production performance by visible light illumination.

Titanium Dioxide: A Versatile Earth‐Abundant Optical Material for Photovoltaics

AbstractTitanium dioxide (TiO2) has long been receiving attention as a promising material for enhancing the performance of photovoltaic devices due to its tunable optoelectronic properties. This paper reviews the utilization of TiO2 in recent photovoltaic applications, focusing primarily on its role as an optical material. The fundamental properties of TiO2 are reviewed, such as its wide bandgap and unique property of tunable refractive index. Furthermore, various strategies are discussed to harness the fundamental properties of TiO2 to improve light absorption and charge carrier generation within various photovoltaic devices. Overall, the pivotal role of TiO2 as an Earth‐abundant and non‐critical optical material is highlighted for future advances in the power conversion efficiency and viability of photovoltaic technologies, paving the way for future research and developments aimed at achieving sustainable and cost‐effective solar energy conversion.

Bi2Te3/Carbon Nanotube Hybrid Nanomaterials as Catalysts for Thermoelectric Hydrogen Peroxide Generation.

Harnessing waste heat from environmental or industrial sources presents a promising approach to eco-friendly and sustainable chemical synthesis. In this study, we introduce a thermoelectrocatalytic (TECatal) system capable of utilizing even small amounts of heat for hydrogen peroxide (H2O2) production. We developed a nanohybrid structure, combining carbon nanotubes (CNTs) and Bi2Te3 nanoflakes (Bi2Te3/CNTs), through a one-pot synthesis method. Bi2Te3, as a thermoelectric (TE) material, generates charge carriers under a temperature gradient via the Seebeck effect, enabling them to participate in surface redox reactions. However, the rapid recombination of these charge carriers greatly limits the TECatal activity. In the Bi2Te3/CNTs nanohybrid system, the introduction of CNTs substantially enhances the efficiency of H2O2 production, as the strong bonding between CNTs and Bi2Te3, along with the excellent conductivity of CNTs, facilitates charge carrier separation and transport, as confirmed by TE electrochemical tests. This study underscores the significant potential of thermoelectric nanomaterials for converting waste heat into green chemical synthesis.

Sensitive Self-Driven Single-Component Organic Photodetector Based on Vapor-Deposited Small Molecules.

Typically, organic solar cells (OSCs) and photodetectors (OPDs) comprise an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high-performance devices but has several drawbacks for upscaling and stability. This study presents a fully vacuum-deposited single-component OPD, employing the neat oligothiophene derivative DCV2-5T in the photoactive layer. Free charge carriers are generated with an internal quantum efficiency of 20 % at zero bias. By optimizing the device structure, a very low dark current of 3.4 · 10-11Acm-2 at -0.1V is achieved, comparable to the dark current of state-of-the-art bulk heterojunction OPDs. This optimization results in specific detectivities of 1· 1013Jones (based on noise measurements), accompanied by a fast photoresponse (f-3dB = 200kHz) and a broad linear dynamic range (>150dB). Ultrafast transient absorption spectroscopy unveils that charge carriers are already formed at very short time scales (<1ps). The surprisingly efficient bulk charge generation mechanism is attributed to a strong electronic coupling of the molecular exciton and charge transfer states. This work demonstrates the very high performance of single-component OPDs and proves that this novel device design is a successful strategy for highly efficient, morphological stable and easily manufacturable devices.

Regulation of Exciton Effects in Functionalized Conjugated Polymers by B‐N Lewis Pairs for Visible‐Light Photocatalysis

Strong excitonic effects are common in organic conjugated polymer semiconductors, severely hindering the generation of free charge carriers for conducting photocatalysis. Therefore, exploring new channels to modulate exciton dissociation in polymers is far‐reaching in facilitating photocatalysis. A series of B‐N Lewis pair functionalized conjugated polymers have been developed to minimize exciton effects by modulating charge transfer pathways. Theoretical studies have shown that introducing B‐N Lewis pairs can dramatically increase the distance of charge transfer (D index) and the amount of electron transfer and reduce the Coulomb attraction energy (EC), which contributes to breaking the equilibrium of the coexistence of excitons and charge carriers. Further experimental results show that the singlet excitons are efficiently dissociated into more free‐charge carriers under photoexcitation to participate in surface reactions. The optimized polymer PyPBM shows an exponential increase in photocatalytic hydrogen and hydrogen peroxide production performance by visible light illumination.

The Effect оf Laser Radiation оn Functional Properties of MOS Structures

The electrophysical properties of instrument MOSFET structures (capacitor, field-effect transistor with an isolated gate and an induced channel, CMOS integrated circuit) when exposed to unmodulated laser radiation are studied. Static and dynamic characteristics were measured. The theoretical study was carried out using the developed SPICE models and numerical experiments. An expression is obtained for the volt-ampere characteristic of a field-effect transistor operating in a mode with constant optical illumination. It is shown that the characteristics of the structures are determined by the generation and recombination of nonequilibrium charge carriers, the field effect, the photovoltaic effect in p—n junctions, the photo-Dember effect and tunneling of charge carriers through a gate dielectric. The results of the work are of interest from the point of view of creating high-speed transistors and integrated circuits of a new type.

ZnO@NiO core-shell heterojunction photoanode modified with NiOOH co-catalyst for high-performance self-powered photoelectrochemical-type UV photodetector

ZnO, a promising photoanode material, faces significant challenges in achieving high-efficient photoelectrochemical (PEC) type UV photodetectors due to inadequate charge separation and sluggish surface reaction kinetics. Constructing heterojunction nanostructures by coupling of p-NiO to n-ZnO nanowire arrays with well-aligned energy band positions presents a feasible strategy for enhancing PEC-type photodetector performance. Herein, we demonstrate that the designed ZnO@NiO core–shell nanowire arrays form a spatial charge transfer channel, facilitating efficient generation and extraction of charge carriers. The exceptional catalytic properties of NiOOH, derived from the transformation of NiO in an aqueous alkaline environment, serve as a potent co-catalyst, effectively accelerating the kinetics of the surface oxygen evolution reaction. Benefiting from the synergistic effect of the heterojunction and cocatalyst, the optimized photoanode achieves a high responsivity of 438.36 mA/W, a large detectivity of 4.85 × 1012 Jones, and rapid response time of 150.05/150.26 ms, while simultaneously exhibiting long-time PEC stability. This work highlights the critical role of nanostructure design in developing high-performance self-powered UV photodetectors.

Photocatalytic Seawater Splitting by Earth-Abundant Catalysts: Metal-Semiconductor Metamaterials Made of Plasmonic Magnesium Diboride and Transitional Metal Dichalcogenides.

Metal-semiconductor metamaterials hold great promise for photocatalytic water splitting due to their excellent light harvesting in a broad spectral range as well as efficient charge carrier generation and transfer. In the majority of such metamaterials, semiconductors are used to initiate the water splitting reaction, while their metal counterparts are employed to improve light harvesting through plasmonic effects. Here, we describe for the first time an exceptional reversed case of metal-semiconductor photocatalysts in which metals are used to initiate the water splitting reaction and semiconductors are employed to improve light harvesting through the blackbody effect and serve as co-catalysts. The studied photoanodes are made of non-noble plasmonic MgB2 combined with transition metal dichalcogenides (TMDCs). The plasmonic resonances of the MgB2 component contribute to field confinement, plasmon-exciton coupling, and hot-electron transfer providing an enhancement of photoactivity in the entire solar spectrum capable of water splitting. The TMDC component provides impedance matching and enhances light absorption by the metal catalyst. We demonstrate seawater splitting with MgB2-TMDCs photoanodes attaining current densities of ~3 mA cm-2 at solar radiation. The overall efficiency of hydrogen production in seawater splitting by sunlight with the help of the studied photoanodes is 3 % at a bias voltage of Vbias=0.3 V.

Substance discrimination imaging derived from switchable soft and hard x‐ray sensing in direct x‐ray detector

AbstractSubstance discrimination beyond the shape feature is urgently desired for x‐ray imaging for enhancing target identification. With two x‐ray sources or stacked two detectors, the two‐energy‐channel x‐ray detection can discriminate substance density by normalizing the target thickness. Nevertheless, the artifacts, high radiation dose and difficulty in image alignment due to two sources or two detectors impede their widespread application. In this work, we report a single direct x‐ray detector with MAPbI3/MAPbBr3 heterojunction for switchable soft x‐ray (&lt;20 keV) and hard x‐ray (&gt;20 keV) detection under one x‐ray source. Systematic characterizations confirm soft and hard x‐ray deposit their energy in MAPbI3 and MAPbBr3 layer, respectively, while working voltages can control the collection of generated charge carriers in each layer for selective soft/hard x‐ray detection. The switching rate between soft and hard x‐ray detection mode reaches 100 Hz. Moreover, the detector possesses a moderate performance with ~50 nGy s−1 in limit‐of‐detection, ~8000 μC Gy−1 cm−2 in sensitivity and ~7 lp/mm in imaging resolution. By defining the attenuation coefficient ratio (𝜇L/𝜇H) as substance label, we effectively mitigate the influence of target thickness and successfully discriminate substances in the acquired x‐ray images.image

Submicron-scale Au-decorated TiO2 mesoporous spheres for enhanced photon harvesting in DSSCs through near-field enhancement, light scattering, and dye loading

Light harvesting materials are crucial for capturing the sunlight in a device such as a solar cell for better efficiency. In this study, we developed high surface area, submicron-sized TiO2 spheres (MTS) incorporated with anisotropic Au nanoparticles (Au_MTS) to create highly light-absorbing photoanodes for enhanced dye-sensitized solar cell (DSSC) efficiency. The high surface area of MTS (∼125 m2/g) allows for increased dye-loading, while their submicron size (150–300 nm) provides superior light-scattering capabilities for significantly enhancing the photoanode’s light absorption. Furthermore, incorporating of anisotropic Au nanoparticles enables broadband surface plasmon resonance (SPR) coupling, synergistically boosting photon harvesting in the Au_MTS photoanodes. The interconnected tiny TiO2 nanoparticle network in MTS supports charge carrier generation and transport, providing ample sites for dye adsorption and efficient electron pathways. Au_MTS with varying amounts of Au nanoparticles synthesized by a greener microwave-assisted synthesis method and DSSC devices were fabricated and compared with devices made from pristine MTS and P25 nanoparticles. The optimal Au_MTS device, containing ∼1.3 wt% Au nanoparticles, achieved a maximum power conversion efficiency (PCE) of ∼7.7%, representing improvements of ∼40% and ∼60% over pristine MTS (PCE of ∼5.2%) and P25 nanoparticles (PCE of ∼4.71%), respectively. Overall, this work demonstrates the effectiveness of plasmonic mesoporous photoanodes in enhancing DSSC performance through improved photo response, light scattering, and dye loading.

Advanced CuO-Ag2WO4-Ni nanophotocatalyst in the synthesis of some chromeno[4,3-b]chromenes as effective lung cancer drugs

A novel heterogeneous nanocomposite CuO-Ag2WO4-Ni embedded within a foam matrix has been biosynthesized from Cressa Cretica leaves extract and comprehensively characterized using various techniques, including FT-IR, XRD, EDX, FE-SEM, DRS, TEM, and BET. This innovative nanocomposite demonstrates exceptional photocatalytic efficiency in the synthesis of some chromeno[4,3-b]chromenes, which have shown promise as effective medications in lung cancer treatment. The photocatalytic reactions are facilitated under a green laser light using ethanol as solvent. Compared to individual components of CuO-Ag2WO4-Ni, the nanocomposite exhibited superior performance in terms of light absorption, surface tunability, charge carrier generation, and stability. Noteworthy advantages of this nanocomposite include high reusability and ease of separation from the reaction mixture, thereby ensuring strong reproducibility. The foam structure plays a pivotal role in enhancing photocatalytic activity due to its high surface area and distinctive morphology. Mechanistic studies indicate that the generated holes and electrons effectively drive selective oxidation and reduction reactions, providing a reliable method for synthesizing a range of chromenes. The CuO-Ag2WO4-Ni exhibited remarkable stability across multiple catalytic cycles, with minimal morphological degradation and low leaching of the catalytic species, ensuring long-term effectiveness and cost efficiency for industrial applications. At the final part of this study, the MTT experiment was planned to investigate cytotoxicity of CuO-Ag2WO4-Ni on A549 lung cancer cells. This study affirmed that the performed nanomaterial has effective toxicity agaings the selected cell line.

Patterned 3D-graphene for self-powered broadband photodetector

The remarkable ultra-wideband energy capabilities of zero-bandgap two-dimensional (2D) graphene have made it an outstanding material for photon absorption and charge carrier generation across a broad spectrum. However, atomically thick 2D-graphene only exhibits a light absorption efficiency of 2.3%, posing a challenge for graphene-based photodetectors to harness photon energy effectively. This study utilized plasma-enhanced chemical vapor deposition technology and a mask to create in situ patterned 3D-graphene/Si-based Schottky heterojunctions. The porous structure and natural nano-resonant cavities of the 3D-graphene enhanced the probability of light absorption, while the curved and sharp edges and corners of the patterned 3D-graphene concentrated the local electromagnetic field and induced localized surface plasmon resonance. Both theoretical and experimental analyses confirmed the improved light absorption mechanisms and charge transfer of photogenerated carriers under the built-in electric field. The photodetector based on the patterned 3D-graphene/Si Schottky structure exhibits excellent broadband response characteristics spanning from 380 to 1550 nm, with responsivity and specific detectivity of 68.47 A/W and 1.43 × 1012 Jones at a wavelength of 1550 nm. Furthermore, the photodetector demonstrated ultrafast microsecond-level response times (116/120 μs rise/fall times) along with exceptional stability and reliability. The potential applications of as-fabricated photodetector include logic devices such as “AND” and “OR” gates and information encryption. This research holds valuable scientific significance for the design of future optoelectronic devices and provides crucial insights and technical support for developing high-performance Si-based graphene detectors.

B-site engineering in rare earth ferrites: Composition and polymorphic control of electrical and photocatalytic functionalities

Rare-earth perovskites possess structural features conducive to co-existence of interesting functionalities. This study establishes structural tunability of B-site tailored GdFeO3 and its implications. Isovalent introduction of In3+ at B-site by hybrid synthesis approach yielded GdInxFe1-xO3 (0.0 ≤ x ≤ 1.0) system. The synthesis-route adopted could enable stabilization of metastable C-type and hexagonal (H) polymorphs that eventually led to thermodynamically stable phases in H (hexagonal), O (orthorhombic) and biphasic (H + O) phases. Gradual evolution of phases with respect to temperature as well as composition were studied with XRD, HT-XRD and Raman spectroscopy. Density functional theory was employed to explain prevalence of wide biphasic-field and it was attributed to non-favourable energetics of Fe3+ at trigonal-bipyramidal site in H-polymorph. The system exhibits structure and composition-dependent electrical behaviour and tunable band gap. Detailed study highlighted a very low leakage current(I) and low dielectric loss in In3+-rich polymorphs(H). Typically, GdInO3 shows I of 4 × 10−9A/cm2, high dielectric constant (ε) of 106 with a stable loss of 0.009. The energy storage performance showed decrease in recoverable E-density (Wrec) and increase in energy storage efficiency with In3+-content. Optimum properties were observed for equimolar composition, GdIn0.5Fe0.5O3 (Wrec= 560 mJ/cm3; ɳ= 82 %). An intriguing observation is effect of structure on visible light-catalysed degradation of methylene blue with O-polymorphs showing excellent photodegradation (̴ 99 % dye/180 min) while H-polymorphs performing abysmally. This is explained based on band gaps, surface charges and plausible difference in generation of photo-induced charge carriers.

Efficient photocatalytic H2 evolution over CuCo2S4 decorated ZnIn2S4 with S-scheme charge separation way

The construction of an S-scheme heterojunction can facilitate the separation and utilization of photogenerated charges, as well as reserve the reducing power of electrons to induce proton reduction for H2 evolution. In this study, CuCo2S4 nanoparticles and ZnIn2S4 nanoflowers were both synthesized via a hydrothermal method, and then CuCo2S4 was employed to decorate ZnIn2S4 to form CuCo2S4/ZnIn2S4 heterojunction through a simple physical solvent evaporation strategy. The experiment result shows that the rate of photocatalytic H2 evolution (rH2) over 10 wt% CuCo2S4/ZnIn2S4 can reach up to 20421.3 μmol g−1 h−1, which is 4.0 times that of ZnIn2S4 (5062.5 μmol g−1 h−1) and 144.6 times that of CuCo2S4 (141.2 μmol g−1 h−1). The improved activity results from the establishment of an S-scheme charge transfer way between CuCo2S4 and ZnIn2S4, which facilitates efficient charge separation while preserving active e− and h+. Besides, the formation of the heterojunction broadens the range of light absorption, promotes charge carrier generation, reduces charge transfer impedance, and increases electrochemically active surface area, these together lead to faster H2 evolution kinetics. The present study demonstrates the potential of bimetallic sulfides as a promising catalyst for construction ZnIn2S4-based photocatalysts for efficient solar conversion.

Investigating the Local Bonding Structure of Amorphous Zinc Tin Oxide to Elucidate the Effect of Altering the Intercation Ratio.

In this paper, the local bonding structure in amorphous zinc tin oxide (a-ZTO) is probed using a combination of XANES and EXAFS techniques at the Zn and Sn K-edges to gain insight into charge carrier generation in the material. a-ZTO is prepared using two growth methods; spray pyrolysis and magnetron sputtering. It is seen that a-ZTO grown by magnetron sputtering shows no changes in the chemical environment as the cation ratio is varied; meanwhile, XANES analysis of spray pyrolysis grown samples shows alterations to spectra likely due to the effects caused by different precursors. Although a slight shift in Sn-O bond length is visible between magnetron sputtered and spray grown samples, no correlation could be discerned between bond length and variation in cation ratio. It is concluded that a-ZTO, while amorphous over longer ranges, is locally composed of ZnO and SnO2 "building blocks". An alteration in the cation ratio changes the hybridization at the conduction band minimum, resulting in the observed variation in the mobility, charge carrier concentration, and bandgap.

Well-designed V2AlC MAX supported g-C3N4/TiO2 Z-scheme heterojunction for photocatalytic CO2 reduction through bi-reforming to produce CO and CH4

Well-designed V2AlC MAX supported g-C3N4/TiO2 Z-scheme heterojunction was synthesized and tested for photocatalytic CO2 reduction through bi-reforming under UV and visible light in batch and continuous photoreactors. Compared to V2AlC/g-C3N4, V2AlC/TiO2 produced 2.17 times more CO and 6.40 times more CH4, along with H2. The highest CO production of 14644 μmol g−1 h−1 was obtained over V2AlC-g-C3N4/TiO2 composite at a selectivity of 20.21 %. Similarly, CH4 and H2 production of 56567 and 1253 μmol g−1 h−1 was obtained, which were 11.11 and 169.9 folds higher for CH4 and 2.77 and 2.32 folds higher for H2 production compared to using g-C3N4/TiO2 and V2AlC/TiO2, respectively. The efficient generation and separation of charge carriers were achieved by the Z-scheme heterojunction of g-C3N4/TiO2 with V2AlC MAX cocatalysts, which led to a greatly increased photocatalytic activity. Using a continuous process, the production of CO was decreased by 1.12 folds, whereas the production of methane disappeared and the reaction pathway was the conversion of CO2 to CO. Using methanol with UV light resulted in higher production of protons and hydrogen, achieving the highest quantum efficiency. The stability study further confirmed the continuous evolution of CO, CH4, and H2 over four cycles.

Photoredox-promoted from full spectrum photo-driven co-production of dihydroxyacetone and hydrogen peroxide over OV-Bi2O2S/ZnIn2S4 with Bi-S-In bridges

Photocatalysis leveraging solar energy to generate charge carriers presented a potentially sustainable strategy for the co-production of dihydroxyacetone (DHA) and hydrogen peroxide (H2O2). The development of photocatalysts capable of broadband light absorption across the entire spectrum coupled with the presence of suitable active sites, was highly desirable. In this study, a novel Ov-Bi2O2S/ZnIn2S4 (Ov-BOS/ZIS) catalyst featuring Bi-S-In bridges was successfully synthesized. This catalyst exhibited oxygen vacancies (OV) and a high density of Bi and In sites within the Bi-S-In bridges, demonstrating exceptional activity and stability in photocatalytic systems. Experimental results revealed that photocatalytic co-production of H2O2 and DHA in one photoredox. Moreover, the tightly bonded heterointerfaces, characterized by unique Bi-S-In bridges, reduced the energy barriers for O2 activation and *OH coupling, thereby facilitating the generation of H2O2 and DHA. The incorporation of Bi-S-In bridges into the Ov-BOS/ZIS catalyst led to a high H2O2 production rate of 67.57 mmol•g−1•h−1.

Interplay between strain and charge in Cu(In,Ga)Se2 flexible photovoltaics

Flexible and lightweight Cu(In,Ga)Se2 (CIGS) thin-film solar cells are promising for versatile applications, but there is limited understanding of stress-induced changes. In this study, the charge carrier generation and trapping behavior under mechanical stress was investigated using flexible CIGS thin-film solar cells with various alkali treatments. Surface current at the CIGS surface decreased by convex bending, which occurs less with the incorporation of alkali metals. The formation energy of the carrier generating defects increased in convex bending environments clarifying the degradation of the surface current. Moreover, alkali-related defects had lower formation energy than the intrinsic acceptors, mitigating current degradation in mechanical stress condition. The altered defect energy levels were attributed to the deformation of the crystal structure under bending states. This study provides insights into the mitigating of strain-induced charge degradation for enhancing the performance and robustness of flexible CIGS photovoltaic devices.

Achieving Efficient Intrinsically Stretchable Organic Photovoltaics with a Conjugated and Elastomeric Dual‐Network Morphology

AbstractStretchable organic photovoltaics (OPVs) are pivotal for advancing conformable electronics, yet achieving both efficient and intrinsically stretchable OPVs remains a significant challenge. The main issue is maintaining electronic and mechanical properties under deformation. Here, a ternary blend system, PTzBI‐oF:PYIT:EVA is presented, incorporating ethylene‐vinyl acetate (EVA) to establish a conjugated and elastomeric dual‐network morphology. The elastomer network dissipates applied stress, preserving the crystalline packing of the conjugated network and enabling improved mechanical stability of charge carrier generation and transport. Specifically, with 15% EVA content, the ternary blend achieved a power conversion efficiency (PCE) of 15.28% in rigid devices and exhibited a crack onset strain of 17.23%. Notably, the stretchable OPVs retained over 80% of their initial PCE under 30% strain. These findings underscore the potential of conjugated and elastomeric dual‐network morphology in developing high‐performance stretchable electronics for various applications.