Enhanced Device Performance Research Articles

Passivation of iodine vacancies of perovskite films by reducing iodine to triiodide anions for high-performance photovoltaics

Inverted perovskite solar cells (PSCs) exhibit great potential in large-scale fabrication due to the low-temperature manufacturing process and low cost compared to normal PSCs. However, defects at the surface and grain boundaries (GBs) of perovskite films, such as iodine vacancies, lead to low efficiency and poor stability. Herein, we report a strategy to passivate the defects in situ with tetrabutylammonium chloride (TABCl). Both the surface defects and GB defects are passivated after perovskite film growth. Moreover, TABCl modifies iodine vacancies by reducing I2 to iodide ions, leading to a decrease in charge recombination in the films and enhanced device performance. The power conversion efficiency (PCE) of devices increases from 18.52% to 20.36 % by TBACl modification, and TBACl also reduces the Voc loss in the PSCs. Meanwhile, TBACl enhances the UV light stability of devices tested by continuous UV light irradiation due to the decreased defects by TBACl. The PSCs could maintain over 90% PCE under continuous UV light irradiation for 450 min. This work not only presents a method to effectively passivate the defects in situ including the surface defects and GB defects but also demonstrates a novel strategy to modify the iodine vacancies by the reducibility of TBACl. In addition, the reducibility of TBACl suppresses the degradation of perovskite films, leading to improved stability.

Performance Enhancement and Comparison of Graphene Field Effect Transistor Devices Coated with HMDS Layer

Graphene-based devices show good transfer characteristics, which depend upon the surface morphology of the material and substrate. During fabrication of the device, the substrate morphology is disturbed inappropriately by the surface contamination. In the present study, monolayer Graphene Field Effect Transistor (GFET) has been driven with hydrophobic Hexamethyl Disilazane (HMDS) layer. The HMDS layer is dehydrated before and after the exfoliated monolayer graphene, and the electrical characteristics were measured. The transfer curve of the HMDS coated graphene device demonstrates excellent FET characteristics and prevents contamination from the atmosphere under ambient conditions. Fabrication of GFET device on the hydrophobic substrate enhances the effective ambipolar behavior. It is beginning with an excellent platform and user-friendly device for biosensing applications.

High-Temperature Performance of AlN MESFETs With Epitaxially Grown n-Type AlN Channel Layers

We fabricated AlN metal semiconductor field effect transistors (MESFETs) with an epitaxially grown n-type AlN channel layer and characterized the temperature dependence of their device properties. As the temperature was varied from room temperature to 500°C, maximum drain current increased from 0.42 to 45 mA/mm and maximum transconductance increased from 0.05 to 4.5 mS/mm. This enhanced device performance with increasing temperature is attributed to increased carrier concentration in n-type AlN due to the large ionization energy of Si donors. Owing to a large Schottky barrier height of 2.08 eV for the Ni gate electrode/n-type AlN interface, reverse leakage current is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-{10}}$ </tex-math></inline-formula> A/mm at temperatures ranging from room temperature to 500°C. Off-state breakdown voltage is as high as 1720 V for gate-drain spacing of 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> . These results indicate that AlN MESFETs are promising for high-voltage electronic devices operating at high temperature.

Titanium oxide nanotube film decorated with β-Ga2O3 nanoparticles for enhanced water splitting properties

TiO2 is a wide bandgap material with inherent photogenerated charge carrier recombination problems, which reduces its photoelectrochemical (PEC) water splitting efficiency. Considerable efforts have been dedicated to reducing this charge recombination problems by decorating the film’s surface using transition metal nanoparticles (NP) to enhanced device performance. And considerable numbers of literature reports are available to this respect. However, reports are rare for the surface modification of TiO2 nanotubes (TNT) arrays with metal oxide, specially by β-Ga2O3 nanostructures and its potential applications. Herein, the PEC water splitting properties of β-Ga2O3 NP (GNP)-modified TNT arrays is described. The TNT were synthesized by anodization, whereas the GNP were fabricated by chemical vapour deposition method. X-ray diffraction (XRD) results revealed the presence of weak β-Ga2O3 peaks and reduction in crystallite size upon GNP addition. The integration of GNP on the TNT arrays resulted in a slight increase in optical bandgap from 3.4 to 3.6 eV observed by UV–vis measurements. Linear sweep voltammetry measurement for the modified TNT photocatalyst showed a 32.5% enhancement in photocurrent density compared to the bare TNT photoelectrode, measured in 1 M HCl solution. Elemental analysis confirmed the presence of β-Ga2O3, thereby supporting the XRD and UV–vis results. This study demonstrates that GNP-activated TNT arrays could be used as photoanode for enhanced photocatalytic activity in the PEC cell.

Exciton Binding Energy of Non‐Fullerene Electron Acceptors

The past three years have witnessed the power conversion efficiency (PCE) of organic solar cells (OSCs) rocketing to over 18%, due to outstanding advantages of non‐fullerene acceptors (NFAs). However, large exciton binding energy (Eb) caused by strong Coulombic force is still one of the main limiting factors for high‐performance OSCs. Thus, it is critical to reduce theEbfor further enhancement of device performance. Many strategies have been developed to reduce theEbof organic materials previously. In this perspective, the calculation methods forEband the relationship betweenEband voltage loss (Vloss) are discussed. Then, the effects of the properties of small‐molecule acceptors onEbfrom the perspectives of fused‐ring donor cores, end groups, side chains, and molecular packing are discussed. Finally, the potential directions for reducingEband pointing out the trade‐off betweenEband bandgaps/miscibility are put forward. It is hoped that this perspective could provide a new thinking of a molecular design for the breakthrough of OSCs.

Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives.

Atmospheric water harvesting (AWH) is emerging as a promising strategy to produce fresh water from abundant airborne moisture to overcome the global clean water shortage. The ubiquitous moisture resources allow AWH to be free from geographical restrictions and potentially realize decentralized applications, making it a vital parallel or supplementary freshwater production approach to liquid water resource-based technologies. Recent advances in regulating chemical properties and micro/nanostructures of moisture-harvesting materials have demonstrated new possibilities to promote enhanced device performance and new understandings. This perspective aims to provide a timely overview on the state-of-the-art materials design and how they serve as the active components in AWH. First, the key processes of AWH, including vapor condensation, droplet nucleation, growth, and departure are outlined, and the desired material properties based on the fundamental mechanisms are discussed. Then, how tailoring materials-water interactions at the molecular level play a vital role in realizing high water uptake and low energy consumption is shown. Last, the challenges and outlook on further improving AWH from material designs and system engineering aspects are highlighted.

Solution-processed bulk heterojunction broadband photodetectors based on perovskites incorporated with PbSe quantum dots

Broadband photodetectors (PDs) have great applications in both scientific and industrial sectors. In this study, we report room-temperature operated solution-processed bulk heterojunction (BHJ) broadband PDs based on perovskites incorporated with highly electrically conductive PbSe quantum dots (QDs). The p-type perovskites incorporated with the n-type PbSe QDs forming the BHJ composite thin film not only extend the spectral response up to the infrared region but also balance charge transport of the photoactive layer, resulting in boosted photocurrent and suppressed dark current, consequently, enhanced device performance of the broadband PDs. As a result, the solution-processed BHJ broadband PDs exhibit a responsibility of 10 mA/W, a detectivity of 10 11 Jones (1 Jones = 1 cm ⋅ Hz 1/2 /W), and a linear dynamic range of 53 dB in the spectral response ranging from 350 nm to 2500 nm, where the BHJ broadband PDs are operated at room temperature. These studies indicate that we provide a facile way to develop room-temperature operated solution-processed broadband PDs. • High electrically conductive n-type PbSe quantum dots and p-type CH 3 NH 3 PbI 3 perovskites. • p-type CH 3 NH 3 PbI 3 perovskites incorporated with n-type PbSe quantum dots forming bulk heterojunction composites. • Solution-processed room-temperature operated broadband photodetectors. • Responsibility, detectivity and a linear dynamic range of broadband photodetectors.

Low‐Cost Fabrication of Sb2S3 Solar Cells: Direct Evaporation from Raw Stibnite Ore

Antimony sulfide is an emerging 1D nontoxic Earth‐abundant photovoltaic material with favorable wide bandgap as a suitable top‐cell candidate for multijunction tandem solar cells. However, the current fabrication technology for Sb2S3 solar cells relies heavily on a high‐purity Sb2S3 source, which limits its large‐scale deployment. Therefore, it is attractive to fabricate the Sb2S3 solar cells directly from the raw stibnite source, which can be cost effective by avoiding the complicated, costly purification and refinement process of the stibnite ore, while reducing process‐emitted pollution. Herein, high‐quality Sb2S3 films (thickness: ≈1 μm) by the vapor transport deposition of raw stibnite ore powder are obtained, followed by a sulfurization process to remove the surface oxides and facilitate alkali element redistribution. In this way, the particle size is increased from ≈500 nm to ≈1.5 μm, the carrier concentration of the Sb2S3 film is increased from ≈1015 to ≈1016 cm−3, and the power conversion efficiency of Sb2S3 solar cell is increased by more than two times. Through the elemental distribution analysis, it is found that it is the redistribution of alkali elements introduced from the natural stibnite ore that induces the grain growth, contributes toward defect suppression, and leads toward enhanced device performance.

Long‐Range‐Ordered Assembly of Micro‐/Nanostructures at Superwetting Interfaces

On-chip integration of solution-processable materials imposes stringent and simultaneous requirements of controlled nucleation and growth, tunable geometry and dimensions, and long-range-ordered assembly, which is challenging in solution process far from thermodynamic equilibrium. Superwetting interfaces, underpinned by programmable surface chemistry and topography, are promising for steering transport, dewetting, and microfluid dynamics of liquids, thus opening a new paradigm for micro-/nanostructure assembly in solution process. Herein, assembly methods on the basis of superwetting interfaces are reviewed for constructing long-range-ordered micro-/nanostructures. Confined capillary liquids, including capillary bridges and capillary corner menisci realized by controlling local wettability and surface topography, are highlighted for simultaneously attained deterministic patterning and long-range order. The versatility and robustness of confined capillary liquids are discussed with assembly of single-crystalline micro-/nanostructures of organic semiconductors, metal-halide perovskites, and colloidal-nanoparticle superlattices, which lead to enhanced device performances and exotic functionalities. Finally, a perspective for promising directions in this realm is provided.

Silver incorporated bilayer Kesterite solar cell for enhanced device performance: A numerical study

In this work, the analytical results pertaining to modeling of silver substituted Kesterite absorber (Cu1-xAgx)2ZnSnSe4 (ACZTSe) and (Cu1-xAgx)2ZnSnS4 (ACZTS) materials are demonstrated. The basic approach adopted here is the tailoring of bandgap and electron affinity of the modified Kesterite structure so as to enhance the performance. The promising Ag incorporated materials exhibit improvement in open circuit voltage which is one of the bottlenecks in the Kesterite structure. The pure Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) are considered and modeled as the baseline structures for simulation in SCAPS. To improve the performance parameters, the analysis was carried out for tandem structures with silver substituted in place of copper in the Kesterite material. As Ag has got favorable atomic properties which makes it an ideal candidate to substitute against copper. The equations of bandgap and electron affinity for Ag doped CZTS and CZTSe with a tuning factor of [Ag]Ag+[Cu] is modeled for optimizing the tandem structures. The front linear grading with reverse linear bandgap profile is used for the improvement of the overall performance of the device with variation in absorber layer thickness, acceptor doping density. The modeled Ag substituted tandem devices ACZTSe/CZTSe and CZTS/ACZTS results in efficiency of 19.37% and 23.50% respectively. Finally, the impact of temperature variation on Capacitance-Frequency calculation along with the influence of series and shunt on the device performance is investigated and discussed.

Performance enhancement of WS2 transistors via double annealing

Herein, we report the double annealing strategy to improve the device performance of WS2 transistors fabricated using multilayer WS2 flakes on SiO2/p++-Si substrates. In the double annealing approach, the annealing is performed twice, both before and after electrode formation. The statistical analysis of 50 WS2 transistors indicated that, compared to the conventional single annealing, the double annealing increased the average field-effect mobility and reduced the average contact resistance. The enhanced device performance could be attributed to the improved interface quality between WS2 and the electrodes, owing to the removal of organic residues and desorption of surface adsorbents during the first annealing before the electrode formation. These results demonstrate the effectiveness of double annealing in enhancing the device performance of WS2 transistors, suggesting the important role of process optimization in fabricating WS2 transistors and other transition metal dichalcogenide devices.

Stress enhanced photoelectric response in flexible AlN single-crystalline thin films

The integration of wide-bandgap (WBG) semiconductors with flexible electronics are anticipated to enhance device performance far beyond the limit of the conventional devices. However, it is challenging to attain robust flexibility and single crystallinity in WBG semiconductors. We fabricated a free-standing AlN film, which can be transferred to any host substrates. Based on this outcome, we further investigated the flexibility of the AlN, as well as the strain-induced properties. It is found that the bending strain can effectively reduce the bandgap of AlN film from 6.2 to 4.8 eV, while no obvious fracture effects after several runs of bent-unbent cycles were observed. Moreover, flexible ultraviolet photodetectors as a platform for exploring the effect of bending stress were demonstrated. The as-obtained photodetector divulges improved responsivity of 161% and a faster rise time response of 31% at a bending radius of 0.5 cm, compared with a control sample. This enhanced performance could originate from the modulation of the bandgap or the piezo-phototronic effect, which influences the migration of carriers during the optoelectronic processes. Our work provides a promising approach for the study of the coupling effect between the flexibility and strain-modulated properties in both WBG semiconductors and devices.

Nanostructuring Electrode Surfaces and Hydrogels for Enhanced Thermocapacitance

Thermogalvanic cells have the ability to convert low-temperature waste heat energy (<200 °C) into electrical energy. However, these systems cannot store this electrical energy. Thermocapacitors use analogous mechanisms to convert heat into electrical energy, but crucially can store this electrical energy. Previous work has used polyelectrolyte gels to frustrate the mobility of a redox couple, causing an accumulation of charge imbalance at the two electode:gelled electrolyte interfaces, resulting in stored thermocapacitance. Here we report an investigation into two methods of utilizing nanostructuring to increase the thermocapacitance performance of a [Fe(CN)6]3–/4– containing polyacrylate hydrogel; specifically, nanostructuring the bulk of the hydrogel and modifying the electrode with carbon nanotubes and liquid crystalline graphene oxide. Nanomaterial-enhanced carbon cloth electrodes significantly increased the available electroactive surface area and charging–discharging rates of these hydrogels, but only resulted in a modest increase in thermocapacitance. Conversely nanostructuring of the hydrogels by changing the degree of neutralization of the hydrogels resulted in significant improvement in thermocapacitance, but only when high concentrations (1 M) of ferricyanide/ferrocyanide electrolyte are available. This study indicates how two different aspects of the system can be nanostructured to enhance device performance.

Constrain Effect of Charge Traps in Organic Field-Effect Transistors with Ferroelectric Polymer as a Dielectric Interfacial Layer.

Traps play crucial roles in the charge transport of disordered organic semiconductors and can significantly influence the electrical performance of organic functional devices. The constrain effect of charge traps in organic field-effect transistors with a ferroelectric polymer as a dielectric interfacial layer has been studied at temperatures ranging from 30 °C to temperature beyond the Curie point of the ferroelectric polymers by utilizing a thermally stable polymer as the semiconducting channel. It has been observed that the charge traps are constrained within a shallow energy level with the ferroelectric interfacial layer. The change in the density of traps involved in the trap-filling process at temperatures across the Curie point shows that the decrease in shallow traps is almost proportional to the increase in deep traps, indicating the transition between shallow and deep traps in the semiconducting channel. These findings suggest potential in stability increase and performance enhancement of future organic functional devices via modulation of traps by a ferroelectric interfacial layer.

Piezo-phototronics in quantum well structures

Quantum well (QW) structures are formed in nanometer-thickness-scale semiconductors with different bandgaps in sandwiched configurations and can offer a wide variety of advantages as active layers for optoelectronic devices, e.g., laser diodes, light emit diodes, photodetectors, and solar cells. Due to the non-centrosymmetric crystal structure, the third-generation semiconductor, such as ZnO, AlN, GaN, and InN, can generate a piezopotential within the crystal by applying an external or internal strain and lead to an effective modulation of the optoelectronic device performance, which is also called piezo-phototronics. With reducing the feature size of materials into several tens of nanometers (e.g., forming QW structures), the multiway coupling effects of quantum physics and piezo-phototronics (coupling with piezoelectricity, photoexcitation, and semiconductor properties) make this research topic more attractive and open a new window for fabricating advanced intelligent optoelectronic devices. This Perspective reviews the recent advances of piezo-phototronics in QW structures, including the fundamental theories and device performance enhancements, and aims to offer a summary and outlook for future research directions and practical applications of piezo-phototronic QW devices.

Eliminating the Perovskite Solar Cell Manufacturing Bottleneck via High‐Speed Flexography

AbstractPerovskite solar cells have potential to deliver terawatt‐scale power via low‐cost manufacturing. However, scaling is limited by slow, high‐temperature annealing of the inorganic transport layers and the lack of reliable, large‐area methods for depositing thin (&lt;30 nm) charge transport layers (CTLs). We present a method for scaling ultrathin NiOx hole transport layers (HTLs) by pairing high‐speed (60 m min−1) flexographic printing with rapidly annealed sol–gel inks to achieve the fastest reported process for fabrication of inorganic CTLs for perovskites. By engineering precursor rheology for rapid film‐leveling, NiOx HTLs were printed with high uniformity and ultralow pinhole densities resulting in photovoltaic performance exceeding that of spin‐coated devices. Integrating these printed transport layers in planar inverted PSCs allows rapid fabrication of high‐efficiency (PCE &gt; 15%) CsxFA1−xPbI solar cells with improved short circuit currents (Jsc) of 22.4 mA cm−2. Rapid annealing of the HTL accelerates total processing time by 60X, while maintaining the required balance of optoelectronic properties and the chemical composition for effective hole collection. These results build an improved understanding of ultrathin NiOx and reveal opportunities to enhance device performance via scalable manufacturing of inorganic CTLs.

Controlled local orientation of 2D nanomaterials in 3D devices: methods and prospects for multifunctional designs and enhanced performance

The review provides the recent progress in the processing of functional devices using oriented 2D nanomaterials and highlights the alignment strategies that contributed to the enhancement of device performance.

Enhanced Device Performance of Cs2agbibr­6 Double Perovskite Photodetector by Sno2/Zno Double Electron Transport Layer

Enhanced Device Performance of Cs2agbibr­6 Double Perovskite Photodetector by Sno2/Zno Double Electron Transport Layer

Influence of defect densities on perovskite (CH3NH3PbI3) solar Cells: Correlation of experiment and simulation

In the present report, a device model Al/PEDOT:PSS/CH3NH3PbI3/PCBM/FTO has been revisited in order to enhance device performance. The device has been simulated using SCAPS-1D and after optimization, the efficiency increases significantly from previously reported, 13.1 % to 17.23 %. A brief study on the impact of defect density of the absorber layer and the interface defect density of PEDOT:PSS/CH3NH3PbI3 and CH3NH3PbI3/PCBM on the output of the cell has been investigated. A new device model Al/CH3NH3PbI3/PCBM/FTO has also been proposed, which is a hole transport layer free structure and it yields an efficiency of about 15.23 %. The device without a hole transport layer is the most convenient one as it has a simple structure. The current–voltage output characteristics of the two simulated models are compared with the experimental results reported earlier.

Influence of solvent additive on the performance and aging behavior of non-fullerene organic solar cells

The performance of organic solar cells has improved significantly in recent years due to the use of non-fullerene acceptors (NFA). While processing additives are typically added to the active layer blends to enhance device performance in NFA organic solar cells, their impact on device degradation remains unclear. In this work we have compared the performance, in pristine and degraded state, between air-processed slot-die coated NFA ITO-free organic solar cells with and without the processing additive DIO, using a structure of PET/Ag/ZnO/PBDB-T:ITIC/FHC PEDOT:PSS. We observed an improvement in the power conversion efficiency of the devices when adding DIO, from 4.03% up to 4.97%. The evolution of the performance for both devices under ISOS-L1 life testing protocol reveals that the drop in efficiency is mainly due to a decay of JSC for both cells. In the short time scale the efficiency of non-DIO cells decays faster than the DIO cells, whereas in the long time scale the efficiency of non-DIO cells tends to stabilize sooner. Carrier mobilities estimated from impedance measurements decrease with time at similar rate for both degraded samples. Besides, DIO devices present a steep increase of the series resistance with time causing a decrease of the FF and thus of the efficiency. Moreover, in both degraded devices, the open-circuit voltage saturates with increasing illumination intensity. Numerical simulations reveal that a reduced anode work function of 5 eV is needed to fit experimental data.