Efficient Charge Transport Research Articles

Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility.

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41±0.206cm2V-1s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Continuous Growth of Crystalline InGaZnO on InLaO by Spray Pyrolysis for High‐Performance Thin‐Film Transistors with Excellent Stability

AbstractInGaZnO (IGZO) based thin film transistors (TFTs) are successfully employed in commercial displays due to their excellent electrical properties but next‐generation displaybackplanes demand higher mobility. A heterojunction structure crystalline oxides can offer superior mobility and stability. Herein, the continuous growth of IGZO is reported on the crystalline InLaO (ILO) layer by spray pyrolysis, which closely resembles the crystalline structure of grown ILO layer. The crystalline structure of the IGZO is confirmed by grazing incidence X‐ray diffraction and high‐resolution transmission electron microscopy. The bilayer IGZO/ILO TFT exhibits remarkable electrical performance, including a high saturation mobility of 55.0 cm2 V−1 s−1, low subthreshold swing of 110 mV dec−1, and high ION/OFF ratio of ≈109 with excellent stability under positive bias temperature stress with In addition, the inverter and ring oscillator based on the IGZO/ILO TFTs demonstrate a high voltage gain of 120 and a low propagation delay of 16.8 ns, respectively. The remarkable performance of bilayer IGZO/ILO TFT by spray pyrolysis is attributed to the In2O3‐like crystalline IGZO grown on ILO film. This leads to reduced lattice mismatch, resulting in minimizing grain boundaries and defects that can hinder electron transport at the interface. The matched crystal structure leads to efficient charge transport at the IGZO and ILO heterojunction, resulting in remarkable TFT performance.

Recent Advancements in Enhancing Interfacial Charge Transport for Perovskite Solar Cells

Finding the most suitable pathways to improve the interfacial charge transportation in lead halide perovskite solar cells is a highly desirable research area to enhance device performance and enable commercialization. The complexities of interfacial charge dynamics, encompassing separation, diffusion, and collection processes, pivot on the thoughtful selection of interlayers and their inherent properties. Challenges arise from nonideal interfaces characterized by mismatched energy levels and defects that hinder efficient charge transport. To address these concerns, implementing tailored interfacial engineering strategies, including interlayer modification, band alignments, and passivation techniques, can help mitigate unwanted nonradiative recombination. This review aims to elucidate the impact of trap states on suppressing charge transport in the device, along with subsequent passivation techniques designed to enhance interfacial charge transport. Following that, a comprehensive overview is presented, highlighting recent advancements in interface engineering techniques that improve interfacial properties between the electron transport layer/perovskite and perovskite/hole transport layer. Significantly, the impact of using buffer and dipole layers as interlayers on overall device performance and stability is investigated.

TuningHole Transport Properties and Perovskite Crystallization via Pyridine-Based Molecules for Quasi-2D Perovskite Solar Cells.

Quasi-2D perovskites show great potential as photovoltaic devices with superior stability, but the power conversion efficiency (PCE) is limited by poor carrier transport. Here, it is simultaneously affected the hole transport layer (HTL) and the perovskite layer by incorporating pyridine-based materials into poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) to address the key problem above in 2D perovskites. With this approach, the enhanced optoelectronic performance of the novel PEDOT:PSS is due to electron transfer between the additives and PEDOT or PSS, as well as a dissociation between PEDOT and PSS based on experimental and theoretical studies, which facilitates the charge extraction and transfer. Concurrently, in-situ X-ray scattering studies reveal that the introduction of pyridine-based molecules alters the transformation process of the perovskite intermediate phase, which leads to a preferred orientation and ordered distribution caused by the Pb─N chemical bridge, achieving efficient charge transport. As a result, the pyridine-treated devices achieve an increased short-circuit current density (Jsc) and PCE of over 17%.

Axially Chiral Organic Semiconductors for Visible-Blind UV-Selective Circularly Polarized Light Detection.

Technologies that detect circularly polarized light (CPL), particularly in the UV region, have significant potential for various applications, including bioimaging and optical communication. However, a major challenge in directly sensing CPL arises from the conflicting requirements of planar structures for efficient charge transport and distorted structures for effective interaction with CPL. Here, a novel design of an axially chiral n-type organic semiconductor is presented to surmount the challenge, in which a binaphthyl group results in a high dissymmetry factor at the molecular level, while maintaining excellent electron-transporting characteristics through the naphthalene diimide group. Experimental and computational methods reveal different stacking behaviors in homochiral and heterochiral assemblies, yielding different structures: Nanowires and nanoparticles, respectively. Especially, the homochiral assemblies exhibit effective π-π stacking between naphthalene diimides despite axial chirality. Thus, phototransistors fabricated using enantiomers exhibit a high maximum electron mobility of 0.22 cm2 V-1 s-1 and a detectivity of 3.9 ×1012 Jones, alongside the CPL distinguishing ability with a dissymmetry factor of responsivity of 0.05. Furthermore, the material possesses a wide bandgap, contributing to its excellent visible-blind UV-selective detection. These findings highlight the new strategy for compact CPL detectors, coupled with the demonstration of less-explored n-type and UV region phototransistors.

Impact of Electrostatic Interaction on Vertical Morphology and Energy Loss in Efficient Pseudo-Planar Heterojunction Organic Solar Cells.

Although a suitable vertical phase separation (VPS) morphology is essential for improving charge transport efficiency, reducing charge recombination, and ultimately boosting the efficiency of organic solar cells (OSCs), there is a lack of theoretical guidance on how to achieve the ideal morphology. Herein, a relationship between the molecular structure and the VPS morphology of pseudo-planar heterojunction (PPHJ) OSCs is established by using molecular surface electrostatic potential (ESP) as a bridge. The morphological evolution mechanism is revealed by studying four binary systems with vary electrostatic potential difference (∆ESP) between donors (Ds) and acceptors (As). The findings manifest that as ∆ESP increases, the active layer is more likely to form a well-mixed phase, while a smaller ∆ESP favors VPS morphology. Interestingly, it is also observed that a larger ∆ESP leads to enhanced miscibility between Ds and As, resulting in higher non-radiative energy losses (ΔE3). Based on these discoveries, a ternary PPHJ device is meticulously designed with an appropriate ∆ESP to obtain better VPS morphology and lower ΔE3, and an impressive efficiency of 19.09% is achieved. This work demonstrates that by optimizing the ΔESP, not only the formation of VPS morphology can be controlled, but also energy losses can be reduced, paving the way to further boost OSC performance.

Polymer donors based on alkyloxime‐substituted thiophene and 6‐undecylthiopheno[3,2‐b]thiophene for efficient organic solar cells

AbstractTwo new copolymers (named PTO‐BO and PTO‐HD) with alkyloxime‐substituted thiophene (TO) as acceptor unit and 6‐undecylthiopheno[3,2‐b]thiophene spacer as π‐bridge were synthesized and applied in organic solar cells (OSCs) as electron donors. PTO‐HD with 2‐hexyldecyl side chains on TO moiety possesses more suitable phase separation, more efficient exciton dissociation and charge transportation, and less charge recombination than PTO‐BO with 2‐butyloctyloxime‐substituted thiophene in OSCs with Y6 as the acceptor. As a result, the OSCs based on PTO‐HD:Y6 achieved an optimal power conversion efficiency (PCE) of 13.89% with a Voc of 0.799 V, a Jsc of 22.74 mA cm−2, and a FF of 67.67% without additives, which is higher than that (12.29%) of PTO‐BO:Y6 OSCs.

Modulating surface-state-induced band bending for efficient charge transport and photoelectrochemical hydrogen production over bismuth vanadate photoanode

Modulating surface-state-induced band bending for efficient charge transport and photoelectrochemical hydrogen production over bismuth vanadate photoanode

Influence of N-type electron acceptors in perovskite absorbers for stabilized perovskite absorbers for high-performance perovskite solar cells

In this study, the impact of n-type organic electron acceptors incorporated in perovskite absorbers via antisolvent-assisted crystallization process is investigated on optical, electrical, and photovoltaic properties of perovskite solar cells (PSCs). The study examines the effect of three representative electron acceptors, including fullerene derivative (PC61BM), non-fullerene acceptor (ITIC), and fluorinated non-fullerene acceptor (ITIC-4F). The findings demonstrate that the inclusion of these electron acceptors stabilizes perovskite absorbers due to strong interaction between the organic acceptors and [PbI6]4- octahedra, leading to the successful passivation of defective antisites. Furthermore, ITIC-4F plays a crucial role in the tailored electronic structure of the perovskite absorber surface, facilitating efficient charge transport and suppressing carrier recombination in the device. The synergetic effect of defect passivation and electrical doping achieved by ITIC-4F resulted in an efficiency improvement of 17.31 % of MAPbI3-based PSCs under 1-Sun illumination, exceeding that of the pristine device (15.62 %) under the same conditions. The device passivated with ITIC-4F also delivered an efficiency of 20.00 % under dim-light irradiation conditions for indoor photovoltaic applications. The results highlight the potential of n-type organic semiconducting molecules as effective additives in the antisolvent-assisted crystallization of perovskite absorbers, offering valuable insights into the design of organic semiconducting additives for improving the film quality of perovskite absorbers and achieving high-performance PSCs. The findings provide a foundation for future research aimed at enhancing the optoelectronic properties and photovoltaic performance of PSCs.

Maximizing the Potential of Electrically Conductive MOFs.

ConspectusElectrically conductive metal-organic frameworks (EC-MOFs) have emerged as a compelling class of materials, drawing increasing attention due to their unique properties facilitating charge transport within porous structures. The synergy between electrical conductivity and porosity has opened a wide range of applications, including electrocatalysis, energy storage, chemiresistive sensing, and electronic devices that have been underexplored for their insulating counterparts. Despite these promising prospects, a prevalent challenge arises from the predominant adoption of two-dimensional (2D) structures by most EC-MOFs. These 2D frameworks often show modest surface areas and short interlayer distances, hindering molecular accessibility, which deviates from the inherent characteristics of conventional MOFs. Furthermore, the quest for efficient charge transport imposes design constraints, leading to a restricted selection of functional building blocks. Additionally, there is a lack of established functionalization methods within EC-MOFs, limiting their functional diversity. Thus, these challenges have impeded EC-MOFs from reaching their full potential.In this Account, we summarize and discuss our group's efforts aimed at enhancing molecular accessibility and deploying the functional diversity of EC-MOFs. Our focus on enhancing molecular accessibility involves several strategies. First, we employed macrocyclic ligands with intrinsic pockets as the building blocks for EC-MOFs. The integrated intrinsic pockets in the frameworks supplement surface areas and additional pores to enhance molecular accessibility. The resulting macrocyclic ligand-based EC-MOFs exhibit exceptionally high surface areas and confer advantages in electrochemical performances. Second, our efforts extend to addressing the structural limitations, frequently associated with EC-MOFs' 2D structures. Through the pillar insertion strategy, we transformed a 2D EC-MOF platform into a three-dimensional (3D) structure, thereby achieving higher porosity and enhanced molecular accessibility. In pursuing functional diversity, we have delved into molecular-level tuning of EC-MOF building blocks. We demonstrated that electron-rich alkyne-based pockets in the macrocyclic ligands can host transition metals and alkali ions, enabling ion selectivity and showcasing diverse use of EC-MOFs. We utilized a postsynthetic approach to further functionalize metal nodes on the molecular level within an EC-MOF framework, introducing a proton-conducting pathway while preserving its electrical conductivity.We aspire for this Account to provide practical insights and strategies to surmount structural and functional diversity limitations in the realm of EC-MOFs. By integrating enhanced molecular accessibility and diverse functionality, our endeavor to propel the utility of these materials will inspire further rational development for future EC-MOFs and unlock their full potential.

Broadband photodetector based on Co3O4/ZnO/Si double heterojunctions: A morphological and optoelectronic study

The growing demand for efficient and cost-effective optoelectronic devices has motivated extensive research into advanced photodetector architectures. This work realizes a robust platform for broadband photodetection via architectural engineering of Co3O4/ZnO/Si double heterojunctions using facile chemical spray pyrolysis. Comprehensive materials and device characterization provides fundamental insights into the role of tailored morphology, band alignment engineering, and defect landscape in dictating device behavior. Aligned ZnO nanorods and fine-grained Co3O4 layers enable efficient light harvesting and charge transport. A triple bandgap structure stemming from the synergistic combination of the two oxides facilitates broadband spectral response from 400 to 1000 nm. Based on the optical properties, triple energy bandgap ranges have been observed, ZnO exhibits an energy bandgap ranging from 2.35 eV to 3.15 eV, while Co3O4 shows energy bandgaps in the range of 1.85 eV–2.23 eV and 1.35 eV–1.5 eV. The responsivity measurements show that Co3O4/ZnO/Si double-heterojunction device has the highest responsivity over a wide range, with distinct peaks at 480 nm and 950 nm, reaching values of 3.5 A/W and 4.5 A/W, respectively. Analysis of electrical transport characteristics and energy band diagrams elucidates the photogenerated carrier dynamics and photocurrent generation governed by strategic heterointerfaces. These fundamental insights into nanoscale interface and architecture engineering lay the foundation for custom-designing high performance metal oxide heterojunction photodetectors through facile and scalable spray pyrolysis technique.

Achieving balanced properties in graphene/Cu composite with oriented bimodal grains: Strength, ductility, and conductivity

In the pursuit of advanced materials with multifunctional capabilities, graphene-based composites have gained substantial attention due to their exceptional mechanical, electrical properties, etc. In this paper, we present a straightforward method for fabricating graphene/Cu composites with an oriented bimodal structure through an in-situ synthesis process combined with hot rolling. Dendritic copper powder, mechanical exfoliation graphene and polyacrylonitrile were used as the raw materials. The graphene/Cu composite with oriented bimodal grains achieves a good balance between strength, ductility and electrical conductivity. Both the fine grains arising from the raised fine particles of dendritic copper powder and the graphene coated on the surface of fine grains facilitate the load transfer, resulting in improved strength of the composites. Furthermore, the formation of coarse grains during sintering and hot rolling deformation contributes to enhanced ductility. Simultaneously, the oriented structure of these coarse grains and graphene sheets establishes an efficient charge transport pathway, ensuring high electrical conductivity. The tensile yield strength of the oriented bimodal composite measures 315 MPa with 0.073 wt% carbon content, while its fracture elongation is 12.4%, and the electrical conductivity remains at 95.7% IACS. This study not only sheds light on the synergistic effects between graphene and copper in a bimodal composite system but also introduces a methodology for tailoring the microstructure to achieve a desired balance between mechanical strength, ductility, and electrical conductivity.

Quantum chemical study of symmetricalnon-fullerene acceptor chromophores for organic photovoltaics

It is well reported that the fused ring acceptor modification can be an effective method for improving the optoelectronic and photovoltaic properties of organic materials. The addition of acceptor groups to a core can enhance its electron-withdrawing ability, resulting in improved charge transport and higher power conversion efficiencies in organic solar cells (OSCs). Thieno[3,2-b]thiophene, and diketopyrrolopyrrole are commonly used groups in OSCs due to their powerful electron-withdrawing capabilities and well-established synthetic protocols. Their incorporation into donor–acceptor systems has been shown to enhance the materials absorption spectra, increase the open-circuit voltage (VOC), and improve device performance. Following integrating several acceptor groups onto the recently synthesized core based on thieno[3,2-b]thiophene, and diketopyrrolopyrrole, we have created six novel electron donors (BDPTM1-BDPTM6) with interesting optoelectronic and photovoltaic properties. It is indeed common practice to use computational methods such as density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to investigate the optoelectronic and photovoltaic properties of newly created molecules. These methods allow researchers to obtain crucial parameters such as the HOMO and LUMO energies, energy gap (Egap), frontier molecular orbital alignment, density of states, molecular electrostatic potential, absorption maxima (λmax), excitation energy (Eex), binding energy and transition density matrix…… Among all the designed compounds, BDPTM3 exhibited the lowest energy bandgap (1.63 eV) with bathochromic shift of 921.610 nm in Dichloro-methane and 852.242 nm in gaseous phase. BDPTM2 displayed the highest dipole moment (µtot) at 7.557 eV, BDPTM5, and BDPTM6 demonstrated consistent linear polarizability〈α〉 at 191.612 × 10−22 esu and 196.2823 × 10−22 esu respectively. Notably, BDPTM6 calculated the highest frst hyperpolarizability βtot at 583.849 × 10–30. Based on the results obtained from the theoretical investigation of the optoelectronic and photovoltaic properties of the developed molecules, it may be possible to recommend them as better candidates for use in organic solar cells (OSCs).

Tailoring Electronic Properties of Colloidal Quantum Dots for Efficient Optoelectronics

Colloidal quantum dots (CQDs) are nanocrystals synthesized in solution, boasting remarkable optical properties and notable electronic characteristics, such as size‐tunable bandgaps and high photoluminescence quantum yield. These features, coupled with solution processability, position CQDs as potential candidates for cost‐effective and high‐performance optoelectronic devices. However, several technological challenges hinder the full exploitation of CQDs in optoelectronics. Among these is the need for long insulating organic ligands in liquid‐phase synthesis, which restrict efficient charge injection and transport in quantum dot (QD) films. Furthermore, the high surface‐to‐volume ratios and core–shell structures prompt complexities in terms of doping and modifying electronic properties. The colloidal nature of quantum dots (QDs) also raises challenges regarding controlled deposition and patterning, which are critical for device fabrication. In this review, the imperative is outlined to tailor CQDs for optoelectronic applications, the limitations that obstruct the implementation of desired modifications are elaborated on, and the specific hurdles confronting electronic coupling, targeted doping, and precision patterning of CQDs are focused on. Additionally, herein, a summary of the solutions proposed to date is offered, insights are shared on the discussed topics, and areas warranting future investigation are highlighted.

Porous MnF2 with micro-nanostructures coated by a nitrogen doped carbon shell as an anode for enhanced lithium storage

MnF2, an intriguing anode material for lithium-ion batteries (LIBs), has garnered significant attention due to its high theoretical capacity. However, its commercial viability is impeded by issues such as volume expansion and poor conductivity. In this study, we present the development and fabrication of MnF2@NC microspheres with micro-nanostructured pores, comprising MnF2 nanoparticles encapsulated within a nitrogen-doped carbon shell. This was achieved through a combination of hydrothermal synthesis and fluorination techniques. The MnF2@NC composite exhibits a high level of porosity, effectively mitigating the significant volume expansion of MnF2 and facilitating efficient charge transport. Moreover, the incorporation of nitrogen-doped carbon shell enhances the overall structural and promotes electrical conductivity. Leveraging these inherent characteristics, the MnF2@NC electrode demonstrates exceptional electrical conductivity and superior long-term stability. The MnF2@NC electrode serves as an anode for LIBs, exhibiting a remarkable reversible capacity of 991.2 mAh/g at 0.1 A/g, exceptional cycle performance with a capacity retention of 872.2 mAh/g after 700 cycles at 1.0 A/g, and outstanding rate capability surpassing the reported outcomes of MnF2-based composite anodes. These results unequivocally demonstrate the suitability and potential applicability of MnF2@NC as high-capacity anodes for LIB.

Over 18.8% Efficiency of Layer‐By‐Layer Organic Photovoltaics Enabled by Ameliorating Exciton Utilization in Acceptor Layer

AbstractThe layer‐by‐layer (LbL) organic photovoltaics (OPVs) are constructed with wide‐bandgap donor PM1 and narrow‐bandgap acceptor L8‐BO. The exciton utilization near cathode is still challenging considering restricted diffusion distance of excitons and inability for transferring energy from L8‐BO to PM1. Herein, donor incorporation into acceptor layer (DIA) strategy is employed to improve exciton utilization near cathode. The efficiency of LbL OPVs can be improved from 18.02% to 18.81% by incorporating 10 wt% PM1 into L8‐BO layer, which is closely associated with efficient exciton separation into L8‐BO layer originated from more adequate donor/acceptor interface for faster charge transfer, as evidenced by magneto‐photocurrent and transient absorption results. The in situ test and morphological characterization clarify that molecular packing property can be improved benefited from prolonged aggregation and nucleation time of acceptor layer assisted by DIA strategy, contributing to more efficient charge transport and inhibited charge recombination in active layers. The thickness insensitive property of LbL OPVs can be also improved induced by DIA strategy, indicated by PCE retention value (82.2% vs. 74.0%) for PM1/L8‐BO:PM1 and PM1/L8‐BO OPVs when acceptor layer thickness increased to ≈180 nm. This work demonstrates the effectiveness of DIA strategy in improving efficiency and thickness tolerance of LbL OPVs.

Tailoring quantum transport efficiency in molecular junctions via doping of graphene electrodes

The efficiency of charge transport across a well-ordered molecular array is influenced not only by the molecular structure but also by the state of the electrode.

In situ monitoring drying process to disclose the correlation between the molecular weights of a polymer acceptor with a flexible spacer and the performance of all-polymer solar cells

All-PSCs with different Mn PYTS were examined. The morphology evolution was in situ monitored, revealing that extended drying time for high Mn PYTS leads to a more tightly packed structure, beneficial for more efficient charge transport and PCE.

Efficient charge separation and transportation using 1D iron-sulfide@titania heterojunctions as photoanodes for improved interface stability and photoelectrochemical activity to produce hydrogen

1D FeS–FeS2@TiO2 heterojunctions were developed to investigate the photoexcited charge separation and transportation to active sites for improved photocatalytic properties for the hydrogen production from water splitting.

Numerical study of charge transport layers in inverted ternary organic photovoltaic cells

This study investigates the crucial role of charge transport layers in enhancing the performance of inverted organic photovoltaic cells (OPVs) through advanced numerical simulations using OghmaNano software. OPVs offer distinct advantages, including lightweight, flexibility, and potential cost-effectiveness compared to traditional silicon-based counterparts, making them pivotal for sustainable energy solutions. We evaluate the efficiency of inverted (iOPVs) employing binary (PM6:L8-BO) and ternary (PM6:D18:L8-BO) active layers, utilizing electron transport layers (ETLs) including ZnO, TiO2, and SnO2, and hole transport layers (HTLs) such as MoO3, PEDOT, and WO3. Results highlight ZnO with a 15 nm-thick layer combined with MoO3 HTL achieving an impressive efficiency of 18.89% in ternary devices, demonstrating the effectiveness of organic materials and ternary blends. The study demonstrates that TiO2 or SnO2 ETLs can compete effectively with ZnO ETLs, particularly when used at thinner thicknesses, and offers alternative fabrication methods. It suggests that employing thin ETL layers (15 ± 2 nm) could significantly enhance the performance of iOPV devices. Simulations are crucial for optimizing iOPV device configurations with thin ETL layers, enabling rapid prototyping and cost-effective exploration of material combinations and device architectures. These layers play a critical role in balancing charge carrier generation and transport efficiency, collectively maximizing device performance. Overall, the study underscores the pivotal role of simulations and optimized layer thicknesses in advancing OPV technology by refining manufacturing processes and accelerating the adoption of OPVs for sustainable energy solutions.