Tunable Optoelectronic Properties Research Articles

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.

2D Multifunctional Phototransistor Based on MoTe2/Graphene/SnS0.25Se0.75 Heterostructure with High Photogain and Reconfigurable Polarized Detection

Abstract2D van der Waals (vdWs) heterojunctions exhibit facile fabrication process and tunable optoelectronic properties. However, suppressing interfacial charge traps and multifunctional photoresponse remain significant challenges. Here, the study designs a 2D multifunctional phototransistor based on ambipolar MoTe2/graphene (Gr)/p‐type SnS0.25Se0.75 double vdWs vertical heterostructure via alloy engineering. The middle Gr interlayer is pivotal in reducing interfacial charge traps, facilitating vertical photocarrier transportation, and enhancing light absorption coefficient. Under photogating effect, the trapped electrons in SnS0.25Se0.75 promote the photogating effect, resulting in the maximum photogain of 8084 and specific detectivity (D*) of 8.2 × 1012 Jones. Under photoconductive effect, a high responsivity (R) of 36.9 A W−1 and D* of 7.17 × 1011 Jones are achieved. Under photovoltaic effect, the devices exhibit a remarkable R of 501 mA W−1, D* of 1.4 × 1011 Jones. Notably, a self‐driven photocurrent polarized ratio of 8 under 635 nm is achieved because of the anisotropic nature of SnS0.25Se0.75 and the effective double built‐in electric fields. By varying the gate voltage, the polarization ratio can be modulated from 1 to 2.5, enabling reconfigurable polarized‐sensitive detection. Above all, the designed heterojunction with multifunctional and reconfigurable polarization detection.

Toward Ultrathin: Advances in Solution-Processed Organic Semiconductor Transistors.

In recent years, organic semiconductor (OSC) ultrathin films and their solution-processed organic field-effect transistors (OFETs) have garnered attention for their high flexibility, light weight, solution processability, and tunable optoelectronic properties. These features make them promising candidates for next-generation optoelectronic applications. An ultrathin film typically refers to a film thickness of less than 10 nm, i.e., several molecular layers, which poses challenges for OSC materials and solution-processed methods. In this paper, first we introduce the carrier-transport regulation mechanism under ultrathin limits. Second, we summarize various solution-processed techniques for OSC ultrathin films and elucidate advances in their OFETs performance, such as enhanced or maintained mobilities, improved switching ratios, reduced threshold voltages, and minimized contact resistance. The relationship between the ultrathin-film thickness, microstructure of various OSCs (small molecules and polymers), and device performance is discussed. Third, we explore the recent application of OSC ultrathin-film-based OFETs, such as gas sensors, biosensors, photodetectors, and ferroelectric OFETs (Fe-OFETs). Finally, the conclusion is drawn, and the challenges and prospects of ultrathin OSC transistors are presented. Nowadays, research on ultrathin films is still in its early stages; further experience in precise film deposition control is crucial to advancing research and broadening the scope of applications for OSC ultrathin devices.

Minimizing Efficiency Roll-Off in Organic Emitters via Enhancing Radiative Process and Reducing Binding Energy: A Theory Insight.

Organic solid-state lasers have received increasing attention due to their great potential for realizing organic continuous-wave or electrically driven lasers. Moreover, they exhibit significant promise for optoelectronic devices due to their chemically tunable optoelectronic properties and cost-effective self-assembly traits. Recently, a great progress has been made in organic solid-state lasers via spatially separated charge injection and lasing. However, making directly electrically driven organic semiconductor lasers is very challenging. It is difficult because of a number of excitonic losses caused by the spin-forbidden nature as well as serious efficiency roll-off at a high current density. Here, a multifunction gain material, functioning both as a thermally activated delayed fluorescence (TADF) emitter with exceptional optical gain and as a source of phosphorescence, was theoretically investigated. The new molecule we designed exhibits a reduction of triplet accumulation through an effective exciton radiative process (5-fold boost in figure of merit) and significantly decreased exciton binding energy (dipole moment from 5.77 to 14.03 D), which benefit amplified spontaneous emission and lasing emission. Our work provides theoretical insights into organic solid-state lasers and may contribute to the development of new and efficient laser-gaining molecules.

How the Spacer Influences the Stability of 2D Perovskites?

Two-dimensionallead halide perovskites (2D HPs) represent as an emerging class of materials given their tunable optoelectronic properties and long-term stability in perovskite solar cells. However, the ever-growing field of optoelectronic devices using 2D HPs requires fundamental understanding of the influence of the spacer on the physiochemical properties and stability of perovskites as well as establish which cation properties are closely related to suppress the halogen ion mobility. This study focuses on investigating the influence of organic spacers with intrinsic properties (e.g., rigidity and flexibility, special groups) and variations of material dimensions on the stability of halogen ions and inorganic frameworks in 2D HPs. It is found that the perovskite structure composed of rigidity molecules owns better stability of halogen ion and inorganic framework than that of flexible molecules. The stability of ions exhibits a negative correlation with the dimensions of perovskite. More importantly, a simple descriptor for measuring the stability of halogen ions in 2D HPs is constructed. By causal discovery algorithms with more physical and chemical significance, the Kappa shape index, number of rotatable bonds, and aromatic carbocycles in organic spacers are identified as causal and important features for the stability of halogen ions in 2D HPs.

A Low‐Dimensional Donor‐Acceptor Perovskite for High‐Performance X‐Ray Detection

AbstractPerovskite materials hold significant promise for X‐ray detection due to their high X‐ray attenuation coefficient, efficient charge mobility, and tunable compositions and optoelectronic properties. Nonetheless, extracting the charges deep inside the thick semiconductors remains a challenge. Here, the 1D cytidine lead bromide perovskite (CytPbBr3) with a regularly arranged Donor (D)–Acceptor (A) heterojunction structure is reported. The organic interlayer contributes to the conduction band, while the inorganic framework constructs the valance band. Such a D–A heterojunction structure offers two separate channels for electrons and holes transport, suppressing the charge recombination rates with improved charge collection efficiency, and thus yields a high device sensitivity of 1.2 × 106 µC Gyair−1 cm−2 with a low noise equivalent dose (NED) of 44.6 pGyair.

Boron interaction with double-walled carbon nanotubes across temperature ranges

Boron-adsorbing carbon nanotubes receive considerable attention in materials science due to their unique properties and potential applications. In particular, boron-adsorbing double-walled carbon nanotubes (DWNTs) exhibit a wide range of tunable electronic and optoelectronic properties. This study explores the influence of boron atoms on metallic (5,5@10,10) and semiconducting (8,0@17,0) DWNTs. We examine alterations in partial charge depending on the quantity of boron atoms adsorbed and affixed to the DWNT surface across temperatures from 300 K to 900 K. The results show that in both DWNTs, with the increase of energy corresponding to the temperature, the adsorption index of boron atoms (adsorbed to the first layer of DWNT) and the positive partial charge increase. Specifically, the maximum partial charge of DWNT(8,0)@(17,0) and DWNT(5,5)@(10,10) is 1.94e and 1.30e (at 300 K), 4.87e and 3.66e (at 600 K), 6.97e and 6.16e (at 900 K). Increasing boron concentration leads to heightened positive partial charge of DWNTs. This, in turn, affects the conductivity of the nanotube.

Stoichiometry modulated tunable optoelectronic properties of Nb-doped WS2 synthesized by chemical vapor deposition method.

Significant progress has been made in the field of two-dimensional WS2, yet the precise control of the doping process to achieve desired properties and the interpretation of complex physical phenomena in these novel materials necessitate thorough research. In this study, Nb-doped WS2 is synthesized using chemical vapor deposition technology, leading to triangular flakes with a side length of 12-20μm. The X-ray photoelectron spectroscopy analysis indicates that the NbW substitution defect functions as an electron acceptor. The interlayer and transverse forces of the Nb-doped WS2 flake approach 1 nN and 150 pN, respectively. As the doping concentration increases, the valence band maximum energy of Nb-doped WS2 ranges from 4.06eV to 4.3eV. Furthermore, the performance of the photodetector is discussed.

Advanced Dual-Input Artificial Optical Synapse for Recognition and Generative Neural Network

Perovskite materials have emerged as leading candidates for optical synaptic devices due to their superior photosensitivity and tunable optoelectronic properties. However, the practical application of perovskite-based optoelectronic synaptic transistors has been hindered by issues of poor stability and high toxicity. This study developed an artificial synaptic thin film transistor (TFT) based on a Cs2AgBiBr6/InOx bilayer. The device demonstrated synaptic behavior under optoelectronic hybrid stimulation (largest wavelength ~520nm), such as excitatory postsynaptic current (EPSC), inhibitory postsynaptic current (IPSC), paired-pulse facilitation (PPF), spike-timing-dependent plasticity (STDP), short-term memory (STM) and long-term memory (LTM). Notably, the “light writing and voltage erasing” characteristics of these devices could be utilized to construct a convolutional neural network (CNN) classifier for the CIFAR-10 dataset, demonstrating noise tolerance close to the human eye. The loss in recognition accuracy was within 1% when Gaussian white noise and salt pepper noise were added. Furthermore, these devices exhibited great potential in Generative Adversarial Networks (CycleGAN), with the generated image quality achieving levels of 0.637 and 0.715 in Improved Perceptual Image Processing System (IPIPS) and Structural Similarity Index (SSIM) evaluation metrics for the zebra dataset, indicating good image quality. This study indicates that our Cs2AgBiBr6-based artificial optical synaptic thin-film transistors (TFTs) are promising for sensing and in-memory computing applications.

Experimental Investigation of Si/SnOx Heterojunction for Its Tunable Optoelectronic Properties

Experimental Investigation of Si/SnOx Heterojunction for Its Tunable Optoelectronic Properties

Tuning optoelectronic properties of indandione-based D-A materials by malononitrile group acceptors: A DFT and TD-DFT approach.

Indandione-based materials are promising candidates for organic electronics, offering high electron mobility and tunable optoelectronic properties. In this study, we explore the optoelectronic and photovoltaic properties of indandione-based donor-acceptor (D-A) materials, specifically (R1) and (R2), by introducing malononitrile group acceptors into their molecular structure. These strong electron-withdrawing acceptors are designed to enhance charge transfer and overall material performance. The designed molecules (DM1-DM4) exhibit a low optical band gap of approximately 1.77eV, significantly lower than the reference materials (R1 and R2) at around 2.24eV in a solvent environment. Among the designed molecules, DM4 stands out with superior photovoltaic parameters, including a narrow optical band gap (1.77eV), higher electron affinity (3.49eV), an extended excited state lifetime (10.0ns) owing to its low electron and hole reorganization energies (λe ~ 0.13eV and λh ~ 0.24eV), and improved short-circuit current density (Jsc) of ~ 15.73mA/cm2. Notably, DM4 achieves a power conversion efficiency (PCE) of ~ 18.5%, making it an excellent candidate for device applications. A comprehensive computational investigation was carried out on indandione-based D-A materials with malononitrile group acceptors (DM1-DM4) using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, as implemented in Gaussian 16 software. We examined the electronic and optical properties of the proposed molecules through frontier molecular orbital (FMO) analysis, UV-Vis absorption spectra, density of states (DOS), exciton binding energy (Eb), and transition density matrix (TDM) analysis, utilizing GaussView 6.0 and Multiwfn 3.8 software. The photovoltaic parameters and power conversion efficiency (PCE) were evaluated using the Scharber and Alharbi models.

Tunable Electronic, Optoelectronic, and Photocatalytic Properties of MoS2 and GaS Monolayers in the MoS2/GaS Heterostructure

AbstractThe electronic structure calculations show that the GaS and MoS2 monolayer and MoS2/GaS hetero‐bilayer systems are semiconducting materials. It is also justified by the density of states. In the hetero‐bilayer system, the band gap is reduced. It causes an increase in the absorption, compared to their monolayers, of incident light in the visible region. This may be because of the charge transfer and the interlayer interaction between these monolayers in the heterostructure form. The calculated higher extinction coefficient causes the fast absorption of light, hence, the increased absorption coefficient. The heterostructure system makes the refractive index and reflection coefficient of GaS and MoS2 monolayers tuneable. The static reflection coefficient is in the following order GaS < MoS2/GaS < MoS2. It means that the MoS2/GaS heterostructure system can increase the static refractive index of GaS and decrease that of MoS2 monolayers simultaneously. The calculated band edge positions show that the MoS2 and GaS monolayers have excellent water oxidation and reduction capability, respectively. These predictions show that the proposed heterostructure may be a potential candidate for nanoelectronics and optoelectronics.

Encapsulation of linear carbon chains in single-walled carbon nanotubes: Towards 1D van der Waals heterostructures for high-efficiency excitonic solar cells

One-dimensional van der Waals heterostructures (1D vdW HTs) based on single-walled carbon nanotubes (SWCNTs) encapsulating linear carbon chains (LCCs) with tunable optoelectronic properties provide a fresh ground for efficient excitonic solar cells (XSCs) alternative to those based on 2D monolayer materials. As an effort to identify for the first time 1D vdW HTs for efficient XSCs application, we perform here a systematic theoretical investigation on the energetic and structural stability, optoelectronic and photovoltaic properties of 1D vdW HTs based on SWCNTs encapsulating 50 symmetrical LCCs of different lengths, and capped with different conjugated endgroups through comprehensive first-principles calculations. We showed the fundamental role of the length and the endgroups effects in modulating the optoelectronic properties of LCCs. Through exploration of the energetic stability of the 1D vdW HTs of LCCs@SWCNTs from the universal force field (UFF) including vdW interactions, we determined the optimal SWCNTs diameters for which the resulting 1D vdW HTs are stable. Then, the band alignment in the 50 stable 1D vdW HTs of LCCs@SWCNTs is examined. Intriguingly, stable LCCs@SWCNTs are identified as type-II 1D vdW HTs complying the prerequisite of XSCs with strong optical absorption in the UV–visible-NIR spectral regions, and power conversion efficiency (PCE) reaching well over 21 %. These findings unravel the enormous potential of the 1D vdW HTs in designing next-generation XSCs devices competitive with state-of-the-art solar cells.

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor.

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

High Thickness Tolerance in All-Polymer-Based Organic Photovoltaics Enables Efficient and Stable In-Door Operation.

Organic photovoltaics (OPVs) have great potential to drive low-power consumption electronic devices under indoor light due to their highly tunable optoelectronic properties. Thick devices (>300nm photo-active junctions) are desirable to maximize photocurrent and to manufacture large-scale modules via solution-processing. However, thick devices usually suffer from severe charge recombination, deteriorating device performances. Herein, the study demonstrates excellent thickness tolerance of all-polymer-based PVs for efficient and stable indoor applications. Under indoor light, device performance is less dependent on photoactive layer thickness, exhibiting the best maximum power output in thick devices (34.7 µW cm-2 in 320-475nm devices). Thick devices also exhibit much better photostability compared with thin devices. Such high thickness tolerance of all-polymer-based PV devices under indoor operation is attributed to strongly suppressed space-charge effects, leading to reduced bimolecular recombination losses in thick devices. The unbalanced charge carrier mobilities are identified as the main cause for significant space-charge effects, which is confirmed by drift-diffusion simulations. This work suggests that all-polymer-based PVs, even with unbalanced mobilities, are highly desirable for thick, efficient, and stable devices for indoor applications.

Transition Metal‐Derived 2D Layered Perovskites: A Promising Alternative to Pb in Photovoltaic Systems

AbstractThe high sensitivity of 3D perovskites toward air and moisture hampers their commercialization due to material decomposition. Introducing their 2D counterparts may provide a remedy to these stability issues, as hydrophobic bulky organic cations can resist direct contact of [ sheets with moisture in the air. In addition to air and water stability, 2D perovskites offer tunable optoelectronic properties through structural modulation, similar to their 3D counterparts. In this study, six different transition metal (TM)‐based 2D hybrid halide perovskites are designed: , , , , , and as alternatives for Pb‐based perovskites. Analysis of structural and thermodynamic parameters demonstrate that these designed perovskite materials can form structurally and thermodynamically stable compounds. Additionally, optical properties analysis reveals that the intended compounds exhibit absorption maxima in the visible range of the electromagnetic spectrum. Among the designed compounds, shows a promising power conversion efficiency (PCE) of 19.63%. Thus, these designed 2D perovskite materials hold potential as substitutes for conventional 3D materials in photovoltaic applications.

Electro-Optically Configurable Synaptic Transistors With Cluster-Induced Photoactive Dielectric Layer for Visual Simulation and Biomotor Stimuli.

The integration of visual simulation and biorehabilitation devices promises great applications for sustainable electronics, on-demand integration and neuroscience. However, achieving a multifunctional synergistic biomimetic system with tunable optoelectronic properties at the individual device level remains a challenge. Here, an electro-optically configurable transistor employing conjugated-polymer as semiconductor layer and an insulating polymer (poly(1,8-octanediol-co-citrate) (POC)) with clusterization-triggered photoactive properties as dielectric layer is shown. These devices realize adeptly transition from electrical to optical synapses, featuring multiwavelength and multilevel optical synaptic memory properties exceeding 3 bits. Utilizing enhanced optical memory, the images learning and memory function for visual simulation are achieved. Benefiting from rapid electrical response akin to biological muscle activation, increased actuation occurs under increased stimulus frequency of gate voltage. Additionally, the transistor on POC substrate can be effectively degraded in NaOH solution due to degradation of POC. Pioneeringly, the electro-optically configurability stems from light absorption and photoluminescence of the aggregation cluster in POC layer after 200°C annealing. The enhancement of optical synaptic plasticity and integration of motion-activation functions within a single device opens new avenues at the intersection of optoelectronics, synaptic computing, and bioengineering.

Enhancing Conductivity in Silicon Heterojunction Solar Cells with Silver Nanowire-Assisted Ti3C2Tx MXene Electrodes for Cost-Effective and Scalable Photovoltaics.

Silicon heterojunction (SHJ) solar cells have set world-record efficiencies among single-junction silicon solar cells, accelerating their commercial deployment. Despite these clear efficiency advantages, the high costs associated with low-temperature silver pastes (LTSP) for metallization have driven the search for more economical alternatives in mass production. 2D transition metal carbides (MXenes) have attracted significant attention due to their tunable optoelectronic properties and metal-like conductivity, the highest among all solution-processed 2D materials. MXenes have emerged as a cost-effective alternative for rear-side electrodes in SHJ solar cells. However, the use of MXene electrodes has so far been limited to lab-scale SHJ solar cells. The efficiency of these devices has been constrained by a fill factor (FF) of under 73%, primarily due to suboptimal charge transport at the contact layer/MXene interface. Herein, a silver nanowire (AgNW)-assisted Ti3C2Tx MXene electrode contact is introduced and explores the potential of this hybrid electrode in industry-scale solar cells. By incorporating this hybrid electrode into SHJ solar cells, 9.0 cm2 cells are achieved with an efficiency of 24.04% (FF of 81.64%) and 252 cm2 cells with an efficiency of 22.17% (FFof 76.86%), among the top-performing SHJ devices with non-metallic electrodes to date. Additionally, the stability and cost-effectiveness of these solar cells are discussed.

Advancements and Challenges of Vacuum‐Processed Organic Photodiodes: A Comprehensive Review

Organic photodiodes (OPDs) have made remarkable strides and now poised to surpass traditional silicon photodiodes (PDs) in various aspects including linear dynamic range (LDR), detectivity, wavelength selectivity, and versatility.[1] Tunable mechanical and optoelectronic properties of organic semiconductors, coupled with lower process costs, have propelled OPDs into the spotlight across fields such as wearable light fidelity systems, flexible image sensors, and biomedical imaging.[2–5] While most advanced organic imaging systems to date rely on polymer‐based solution processes, challenges such as the use of toxic organic solvents and reproducibility issues hinder their commercialization.[6,7] Vacuum‐processed OPDs offer a promising alternative, boasting eco‐friendliness and compatibility with large‐scale fabrication facilities.[8,9] In this review, recent advancements and challenges in vacuum‐processed OPDs, an area that has received less attention compared to solution‐processed counterparts, are explored. Herein, four primary pathways for development of vacuum‐processed OPDs are outlined: 1) ultraviolet‐selective OPDs, 2) visible‐light‐selective OPDs, 3) near‐infrared or short‐wave‐infrared‐sensitive OPDs, and 4) addressing challenges such as higher noise currents compared to inorganic PDs. In this review, it is aimed to furnish readers with a comprehensive understanding of vacuum‐processed OPDs, spanning from materials design to device engineering.

Synthesis and characterization of new perylenediimide derivatives: Promising low-cost electron transport materials for perovskite solar cells

In organic-inorganic perovskite solar cells (PSCs), the electron transport layer (ETL) plays a crucial role providing efficient electron extraction and transport required for achieving high device performance. Compared to traditional fullerene-based electron-transport materials (ETMs), non-fullerene small molecules have attracted much attention due to their tunable optoelectronic properties, lower cost, and much higher stability. In this work, we synthesized and characterized four perylenediimide (PDI) derivatives and investigated their optoelectronic properties in the context of application as ETMs for PSCs. To establish the compatibility of PDI films with perovskite absorber material, the surface properties of Cs0.12FA0.88PbI3/PDI bilayer stacks were studied using contact angle and infrared scattering scanning near-field microscopy methods. A study of the photochemical stability of these bilayer stacks showed that coating the perovskite film with a layer of PDI improves its tolerance with respect to light. Utilizing these molecules as ETMs in the inverted p-i-n PSCs delivered light power conversion efficiencies ranging from 11.1 % to 15.4 %, thus indicating the considerable effect of the PDI derivative molecular structure on the photovoltaic properties. Further development of this research direction may lead to the rational design of advanced PDI-based electron transport materials for efficient and stable PSCs.