Fluorescent organic light-emitting diodes (OLEDs) still face major obstacles to combining high efficiency with solution processability and energy-sustainable operation. In this work, a tetra-carboxyphenyl porphyrin–nitrogen carbon dots (TCPP-NCDots) derivative is introduced as a solution-processable electron transport layer (ETL) in OLEDs based on a green–yellow emissive polymer. The structural, optical, and electronic properties of the TCPP-NCDots ETL are comprehensively characterised by ultraviolet–visible absorption spectroscopy, steady-state photoluminescence, Fourier-transform infrared spectroscopy, atomic force microscopy, and cyclic voltammetry. These studies reveal a synergistic effect of porphyrin functionalisation on the carbon dots, which improves electron injection and transport toward the emissive layer. At an optimum concentration of 1 mg mL−1, the TCPP-NCDots ETL yields a 21.6% enhancement in external quantum efficiency compared with the reference device without an ETL, while simultaneously suppressing efficiency roll-off. The optimised devices also maintain stable operation under ambient conditions, highlighting TCPP-NCDots as a promising, sustainable ETL platform for next-generation fluorescent OLEDs.

ABSTRACT Metal halide perovskite field‐effect transistors (PeFETs) have rapidly gained recognition as leading candidates for next‐generation electronic and optoelectronic technologies, owing to their exceptional optoelectronic properties, facile solution processability, and notable mechanical flexibility. Nevertheless, the practical deployment of high‐performance PeFETs is significantly impeded by persistent challenges, including ion migration, hysteresis effects, and environmental instability, which collectively hinder their widespread adoption. This review offers a thorough and up‐to‐date overview of recent progress in the field of PeFETs, with particular emphasis on advances in material engineering, device architecture optimization, and innovative processing techniques designed to enhance device performance. The discussion encompasses the fundamental physics governing charge transport in perovskite semiconductors, with a focus on the influence of defect chemistry, interface engineering, and stability considerations. Special attention is devoted to a comparative analysis of tin‐based and lead‐based PeFETs, elucidating their respective charge transport mechanisms, benefits, and limitations. The review concludes by identifying the principal challenges and outlining future research directions that are essential for realizing the full potential of perovskite transistors in delivering high‐speed, flexible, and cost‐effective electronic devices.

Tantalum disulfide (1T-TaS₂) is a quasi-two-dimensional transition metal dichalcogenide (TMD) that exhibits a series of charge density wave (CDW) transitions upon cooling and heating. These collective electronic phases can be tuned or disrupted by external stimuli such as pressure, electric fields, or illumination, leading to metastable or hidden metallic states. In nanoscale crystals of 1T-TaS₂, rapid cooling suppresses the insulating commensurate CDW (CCDW) phase and stabilizes a metastable metallic state, known as the super-cooled nearly commensurate CDW (SC-NCCDW) phase. However, the atomic-scale structure and microscopic origin of this state remain elusive. Here, we combine electrical transport measurements with structural characterization to elucidate the nature of the SC-NCCDW phase in 1T-TaS₂ nanocrystals. Temperature-dependent X-ray diffraction reveals that, under gradual cooling, the NCCDW-to-CCDW transition is accompanied by lattice-volume expansion. In contrast, this anomaly is strongly suppressed upon rapid cooling, correlating with the stabilization of the SC-NCCDW state. Complementary high-resolution transmission electron microscopy (HR-TEM) shows that rapid cooling produces a mixed-phase configuration containing structural motifs of both NCCDW and CCDW phases, indicating that the SC-NCCDW represents an intermediate structural configuration frozen by kinetic constraints. These findings provide, to our knowledge, the first direct structural evidence of the SC-NCCDW state and offer a mechanistic understanding of cooling-rate-controlled metastability in layered correlated compounds such as 1T-TaS₂.

We report the first incorporation of diverse lacunary polyoxometalate (POM) nanocluster materials as efficient interface modifiers in perovskite solar cells (PSCs). Devices utilizing POM-modified SnO2 electron transport layers demonstrated marked improvements in open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF), achieving power conversion efficiencies exceeding 21.6%. Transient photovoltage and photocurrent analyses revealed that the B1-type based device exhibited the longest carrier lifetime and most rapid charge extraction rate, indicating optimized charge transport and suppressed recombination losses. Stability assessments under ambient conditions confirmed that B1-type POM-modified devices retained higher efficiency over time with reduced hysteresis compared to control devices. Work function measurements indicated POM-induced energy level alignment shifts, facilitating efficient charge transport. Morphological and structural analyses via scanning electron microscopy and X-ray diffraction confirmed that POMs using tungsten (W) addenda (i.e., B1–W and B2–W) promoted superior perovskite crystallization, yielding larger grain sizes and enhanced crystallinity. These findings establish the potential for lacunary POMs to serve as effective interface modifiers for advancing the efficiency and durability of perovskite-based optoelectronic devices.

Work investigates the doping of molybdenum oxide (MoOx) with tungsten (W). The successful incorporation of W into the MoOx lattice was confirmed through X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS). Structural and optical analysis revealed the presence of oxygen vacancies within the W-MoOx film, which are known to facilitate resistive switching (RS) in memristive devices. Based on this, a flexible memristor with the structure PET/ITO/W-MoOx/polymethyl methacrylate (PMMA)/Al was fabricated. PMMA was strategically introduced between the W-MoOx layer and the aluminum electrode to modulate interfacial properties that influence RS behavior. The W-MoOx/PMMA-based memristor exhibited good resistive switching characteristics, with a memory window of approximately 12 and a retention time exceeding 2 × 104 s, demonstrating a non-volatile memory behavior. In the high-resistance state (HRS), the conduction mechanism under higher applied voltages follows a space-charge-limited current (SCLC) model, indicating that the RS process is primarily governed by charge trapping and de-trapping at the interface. Overall, the consistent and robust switching performance of the W-MoOx/PMMA heterostructure underlines its potential as a reliable functional layer for next-generation resistive random-access memory (ReRAM) devices.

Bulk heterojunction (BHJ) organic solar cells (OSCs) represent a promising technology due to their cost-effectiveness, lightweight design and potential for flexible manufacturing. However, achieving a high power conversion efficiency (PCE) and long-term stability necessitates optimizing the interfacial layers. Zinc oxide (ZnO), commonly used as an electron extraction layer (EEL) in inverted OSCs, suffers from surface defects that hinder device performance. Furthermore, the active control of its optoelectronic properties is highly desirable as the interfacial electron transport and extraction, exciton dissociation and non-radiative recombination are crucial for optimum solar cell operation. In this regard, this study investigates the sulfur doping of ZnO as a facile method to effectively increase ZnO conductivity, improve the interfacial electron transfer and, overall, enhance solar cell performance. ZnO films were sulfur-treated under various annealing temperatures, with the optimal condition found at 250 °C. Devices incorporating sulfur-doped ZnO (S-ZnO) exhibited a significant PCE improvement from 2.11% for the device with the pristine ZnO to 3.14% for the OSC based on the S-ZnO annealed at 250 °C, attributed to an enhanced short-circuit current density (Jsc) and fill factor (FF). Optical and structural analyses revealed that the sulfur treatment led to a small enhancement of the ZnO film crystallite size and an increased n-type transport capability. Additionally, the sulfurization of ZnO enhanced its electron extraction efficiency, exciton dissociation at the ZnO/photoactive layer interface and exciton/charge generation rate without altering the film morphology. These findings highlight the potential of sulfur doping as an easily implemented, straightforward approach to improving the performance of inverted OSCs.

AbstractHalide organic–inorganic perovskites (HOIPs) are a promising class of materials for neuromorphic computing and processing systems demonstrating a variety of resistive switching (RS) mechanisms. HOIPs have been used as active layers in two‐ and three‐terminal synaptic devices reporting high performance in metrics of speed and energy consumption. Nevertheless, halide perovskites suffer from poor ambient stability and reproducibility. In this work, a highly robust double memristor based on two active layers forming a stacking heterojunction is demonstrated. In particular, the functional layer consists of a molybdenum oxide‐molybdenum sulfide compound (MoO3‐MoS2) and a quadruple cation perovskite (RbCsMAFA) deposited on top showing favorable band alignment for the specific application. The double memristor based on the MoO3‐MoS2/RbCsMAFA heterojunction exhibits impressive and stable resistive switching behavior with endurance of 100 cycles, high retention of 2 × 104 s, high environmental stability maintaining its memristive behavior for 1 month, and excellent artificial synaptic functions. The robust device also exhibits good thermal stability maintaining the memristive characteristics at 85 °C, as well as good photonic memristive behavior with an improved ON/OFF ratio under constant illumination. Here it is proven that the proposed double memristor is a promising candidate for artificial synapses and neuromorphic computing systems.

Transition metal oxides (TMOs) are a promising class of materials for neuromorphic computing and processing systems demonstrating a variety of resistive switching (RS) mechanisms. However, little is known about the correlation between its stoichiometry and RS. This study is focused on the development and characterization of amorphous molybdenum oxide memristors with different stoichiometry. Fully-stoichiometric (MoO3) and hydrogenated sub-stoichiometric (H-MoO3 − x) amorphous molybdenum oxide thin films were developed via a hot-wire chemical vapor deposition system. Both, stoichiometric and hydrogenated sub-stoichiometric molybdenum oxide devices showed good resistive switching behavior. However, the fully-stoichiometric memristor exhibited better RS properties with endurance of 250 cycles, ON/OFF ratio 103 and high retention of almost 3·104 s, compared with the poor RS behavior of the device based on the H-MoO3 − x film. This impressive memristive behavior could be attributed to the excess of oxygen vacancies in the case of fully-stoichiometric memristor in respect to the sub-stoichiometric H-MoO3 − x which play crucial role in the conductive behavior of the device. The high reproducibility observed in MoO3-based memristor highlights their potential for practical applications and scalability. Additionally, the outstanding features of the MoO3 memristor demonstrated through its long-term potentiation (LTP), long-term depression (LTD), and spike-timing dependent plasticity (STDP) indicate that the fully stoichiometric molybdenum oxide memristor has significant potential for simulating biological synapses, opening doors to a new era in neuromorphic computing applications.

Charge injection and transport interlayers based on artificial green carbon materials are imperative for a sustainable future of many classes of optoelectronic devices, including organic light-emitting diodes (OLEDs). Especially, porphyrin derivatives can act as efficient energy and charge funnels mimicking their successful photosynthetic function. Here, we report on the application of a novel green carbon material, in particular, a zinc porphyrin derivative bearing an amidine functional group (referred to as ZnP-amidine), as an electron transport material in fluorescent OLEDs based on a green-yellow co-polymer emitter. ZnP-amidine is processed from environmental friendly solvents without any annealing requirements thus being suitable for low-cost sustainable optoelectronics. It is applies as an ultra-thin interlayer between the aluminum cathode and the emissive layer to enable efficient electron transport and stable performance. This work paves the path towards low-cost green carbon materials inspired by natural processes for organic optoelectronics.

Although organic light-emitting diodes (OLEDs) are considered a mature technology, further enhancements in their efficiency are of paramount importance for advancing their incorporation in high-quality displays and flexible, wearable, electronic devices. In this regard, we propose an innovative approach, focusing on strategic modifications to the hole transport layer (HTL) through the integration of core-shell nanoparticles. Silver nanoparticles (Ag-NPs) encapsulated in a tungsten polyoxometalate compound (POM) are embedded within the prototype poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) (PEDOT:PSS) to form the modified HTL. Our work reveals the pivotal plasmonic role of Ag-NPs in enhancing OLED device performance based on commercially available conjugated polymers. Comprehensive analyses, including UV-Vis absorption spectroscopy, atomic force microscopy, photoluminescence spectroscopy, and electrical measurements, confirm the influence of the POM encapsulated Ag-NPs on improving the device efficiency. This is attributed to the synergistic influence of enhanced hole injection and conductivity and beneficial optical effects (i.e. the Localized Surface Plasmon Resonance (LSPR) and, likely, light scattering of the POM-Ag NPs in the core-shell configuration, depending on their diameter), contributing to enhanced carrier balance and exciton recombination rate. Comparison with POM gold NPs (POM-Au NPs) highlights the distinct advantages of POM-Ag NPs. Our work reveals the potential of this innovative approach to contribute to the evolution of high-performance OLEDs, ensuring a visually compelling and efficient future.

Halogen-doped tin dioxide (SnO 2 ) is examined for its photocatalytic activity and further applications apart from the photovoltaic devices. While SnO 2 has been extensively examined in energy devices, not so much attention has been paid to its investigation as a photocatalyst. Preliminary studies on photocatalytic properties suggest that Br:SnO 2 shows a small improvement in hydrogen production in the first 14 h, whereas, in general, the presence of any halogen reduces the reactivity of SnO 2 . By incorporating this result with the observed increase in conductance, it can be suggested that the doping of Cl and Br serves as an effective method for enhancing the electron-transport properties of SnO 2 layers.

Molecular aggregation is a powerful tool for tuning advanced materials' photophysical and electronic properties. Here we present a novel potential for the aqueous-solvated aggregated state of boron dipyrromethene (BODIPY) to facilitate phototransformations otherwise achievable only under harsh chemical conditions. We show that the photoinduced symmetry-breaking charge separation state can itself initiate catalyst-free redox chemistry, leading to selective α-C(sp3)-H bond activation/Csp3-Csp3 coupling on the BODIPY backbone. The photoproduction progress was tracked by monitoring the evolution of the strong Stokes-shifted near-infrared emission, resulting from selective self-assembly of the terminal heterodimeric photoproduct into well-ordered J-aggregates, as revealed by X-ray structural analysis. These findings provide a facile and green route to further explore the promising frontier of packing-triggered selective photoconversions via supramolecular engineering.

The engineering of tin halide perovskites has led to the development of p-type transistors with field-effect mobilities of over 70 cm2 V-1 s-1. However, due to their background hole doping, these perovskites are not suitable for n-type transistors. Ambipolar lead halide perovskites are potential candidates, but their defective nature limits electron mobilities to around 3-4 cm2 V-1 s-1, which makes the development of all-perovskite logic circuits challenging. Here we report formamidinium lead iodide perovskite n-type transistors with field-effect mobilities of up to 33 cm2 V-1 s-1 measured in continuous bias mode. This is achieved through strain relaxation of the perovskite lattice using a methylammonium chloride additive, followed by suppression of undercoordinated lead through tetramethylammonium fluoride multidentate anchoring. Our approach stabilizes the alpha phase, balances strain and improves surface morphology, crystallinity and orientation. It also enables low-defect perovskite-dielectric interfaces. We use the transistors to fabricate unipolar inverters and eleven-stage ring oscillators. The use of additives in the fabrication of solution-processed n-type perovskite transistors alleviates lattice strain and suppresses undercoordinated lead, boosting the charge transport properties of the devices and making them suitable for use in complementary circuit applications.

Charge injection and transport interlayers play a crucial role in many classes of optoelectronics, including organic and perovskite ones. Here, we demonstrate the beneficial role of carbon nanodots, both pristine and nitrogen-functionalized, as electron transport materials in organic light emitting diodes (OLEDs) and organic solar cells (OSCs). Pristine (referred to as C-dots) and nitrogen-functionalized (referred to as NC-dots) carbon dots are systematically studied regarding their properties by using cyclic voltammetry, Fourier-transform infrared (FTIR) and UV–Vis absorption spectroscopy in order to reveal their energetic alignment and possible interaction with the organic semiconductor’s emissive layer. Atomic force microscopy unravels the ultra-thin nature of the interlayers. They are next applied as interlayers between an Al metal cathode and a conventional green-yellow copolymer—in particular, (poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1′,3}-thiadiazole)], F8BT)—used as an emissive layer in fluorescent OLEDs. Electrical measurements indicate that both the C-dot- and NC-dot-based OLED devices present significant improvements in their current and luminescent characteristics, mainly due to a decrease in electron injection barrier. Both C-dots and NC-dots are also used as cathode interfacial layers in OSCs with an inverted architecture. An increase of nearly 10% in power conversion efficiency (PCE) for the devices using the C-dots and NC-dots compared to the reference one is achieved. The application of low-cost solution-processed materials in OLEDs and OSCs may contribute to their wide implementation in large-area applications.

Tin dioxide (SnO2) is one of the most used materials for sensing applications operating at high temperatures. Commonly, “undoped SnO2” is made by precursors containing elements that can have a deleterious impact on the operation of SnO2 sensors. Here, we employ experimental and theoretical methods to investigate the structural properties and electronic structure of the rutile bulk and surface SnO2, focusing on unintentional doping due to precursors. Unintentional doping from precursors as well as intrinsic doping can play an important role not only on the performance of gas sensors, but also on the properties of SnO2 as a whole. The theoretical calculations were performed using density functional theory (DFT) with hybrid functionals. With DFT we examine the changes in the electronic properties of SnO2 due to intrinsic and unintentional defects and we then discuss how these changes affect the response of a SnO2-based gas sensor. From an experimental point of view, we synthesized low-cost SnO2 thin films via sol–gel and spin-coating processes. To further enhance the performance of SnO2, we coated the surface with a small amount of platinum (Pt). The crystalline structure of the films was analyzed using x-ray diffraction (XRD) and scanning electron microscopy (SEM), while for the determination of the elements contained in the sample, X-ray photoelectron spectroscopy (XPS) measurements were performed. Furthermore, we investigated the effect of temperature on the band structure of SnO2 in air, in a vacuum and in nitrogen and hydrogen chemical environments. To optimize the response, we used current–voltage characterization in varying environments. The aim is to associate the response of SnO2 to various environments with the changes in the band structure of the material in order to gain a better understanding of the response mechanism of metal oxides in different pressure and temperature environments. We found that the resistance of the semiconductor decreases with temperature, while it increases with increasing pressure. Furthermore, the activation energy is highly affected by the environment to which the thin film is exposed, which means that the thin film could respond with lower energy when exposed to an environment different from the air.

The increasing demand for efficient sensing devices with facile low-cost fabrication has attracted a lot of scientific research effort in the recent years. In particular, the scientific community aims to develop new candidate materials suitable for energy-related devices, such as sensors and photovoltaics or clean energy applications such as hydrogen production. One of the most prominent methods to improve materials functionality and performance is doping key device component(s). This paper aims to examine in detail, both from a theoretical and an experimental point of view, the effect of halogen doping on the properties of tin dioxide (SnO2) and provide a deeper understanding on the atomic scale mechanisms with respect to their potential applications in sensors. Density Functional Theory (DFT) calculations are used to examine the defect processes, the electronic structure and the thermodynamical properties of halogen-doped SnO2. Calculations show that halogen doping reduces the oxide bandgap by creating gap states which agree well with our experimental data. The crystallinity and morphology of the samples is also altered. The synergy of these effects results in a significant improvement of the gas-sensing response. This work demonstrates for the first time a complete theoretical and experimental characterization of halogen-doped SnO2 and investigates the possible responsible mechanisms. Our results illustrate that halogen doping is a low-cost method that significantly enhances the room temperature response of SnO2.

The surface electric conduction in amorphous and crystallized molybdenum oxide films was studied as a function of electronic structure by current–voltage and simultaneous spectroscopic ellipsometry measurements on structures of the kind Al/Molybdenum oxide (MoO x )/Al, at temperatures up to 400 °C and in ambient air. At room temperature, both amorphous and crystalline MoO x samples were found to be sub-stoichiometric in oxygen. The random distribution of oxygen vacancies and the imperfect atomic ordering induced the creation of an intermediate band (IB) located near the valence band and of individual electronic gap states. At temperatures below 300 °C, the conduction was found to exhibit ambipolar character in which electrons and holes participated, the former moving in the conduction band and the latter in the IB and though gap states. Above 300 °C, due to samples gradual oxidation and improvement of atomic ordering (samples crystallization), the density of states in the IB and the gap gradually decreased. The above in their turn resulted in the gradual suppression of the ambipolar character of the conduction, which at 400 °C was completely suppressed and became similar to that of ordinary n-type semiconductor. The above phenomena were found to be reversible, so as the semiconducting MoO x samples were returning to room temperature the ambipolarity of the conduction was gradually re-appearing giving rise to an unusual phenomenon of “metallic” temperature variation of electrical resistance when electrons were injected.

Two gallium porphyrins, a tetraphenyl GaCl porphyrin, termed as (TPP)GaCl, and an octaethylporphyrin GaCl porphyrin, termed as (OEP)GaCl, were synthesized to use as an electron cascade in ternary organic bulk heterojunction films. A perfect matching of both gallium porphyrins’ energy levels with that of poly(3-hexylthiophene-2,5-diyl) (P3HT) or poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) polymer donor and the 6,6-phenyl C71 butyric acid methyl ester (PCBM) fullerene acceptor, forming an efficient cascade system that could facilitate electron transfer between donor and acceptor, was demonstrated. Therefore, ternary organic solar cells (OSCs) using the two porphyrins in various concentrations were fabricated where a performance enhancement was obtained. In particular, (TPP)GaCl-based ternary OSCs of low concentration (1:0.05 vv%) exhibited a ~17% increase in the power conversion efficiency (PCE) compared with the binary device due to improved exciton dissociation, electron transport and reduced recombination. On the other hand, ternary OSCs with a high concentration of (TPP)GaCl (1:0.1 vv%) and (OEP)GaCl (1:0.05 and 1:0.1 vv%) showed the poorest efficiencies due to very rough nanomorphology and suppressed crystallinity of ternary films when the GaCl porphyrin was introduced to the blend, as revealed from X-ray diffraction (XRD) and atomic force microscopy (AFM). The best performing devices also exhibited improved photostability when exposed to sunlight illumination for a period of 8 h than the binary OSCs, attributed to the suppressed photodegradation of the ternary (TPP)GaCl 1:0.05-based photoactive film.

Halide perovskites are compelling candidates for the next generation of photovoltaic technologies owing to an unprecedented increase in power conversion efficiency and their low cost, facile fabrication and outstanding semiconductor properties.

Inverted perovskite solar cells (PSCs) have attracted increasing attention in recent years owing to their low-temperature fabrication proces s. However, they suffer from a limited number of electron transport materials available with [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) to be the most widely studied based on its appropriate energy levels and high electron mobility. The low relative permittivity and aggregation tendency upon illumination of PCBM, however, compromises the solar cell efficiency whereas its modest hydrophobicity negatively impacts on the device stability. Alternative electron transport materials with desired properties and appropriate degree of hydrophobicity are thus desirable for further developments in inverted PSCs. Herein, we synthesize a triethyleneglycol C-60 mono-adduct derivative (termed as EPF03) and test it as a novel electron transport material to replace PCBM in inverted PSCs based on a quadruple cation (RbCsMAFA) perovskite. We also compare this derivative with two novel fullerenes decorated with two (EPF01) or one dodecyl (EPF02) long side chains. The latter two fail to perform efficiently in inverted PSCs whereas the former enabled a power conversion efficiency of 18.43%, which represents a 9% improvement compared to the reference device using PCBM (17.21%). The enhanced performance mainly stems from improved electron extraction and reduced recombination enabled by the insertion of the large relative permittivity amongst other properties of EPF03. Furthermore, our results indicate that triethylene glycol side chains can also passivate perovskite trap states, suppress ion migration and enhance photostability and long-term stability of EPF03 based perovskite solar cells.