Reduced Series Resistance Research Articles

Chitosan/Nitrogen-doped graphene nanocomposite for supercapacitor application

Abstract In this study, we explore the chitosan/nitrogen-doped graphene oxide (CS-NGO) nanocomposite using the hydrothermal method and incorporate it onto carbon paper by a deep coating technique for supercapacitor applications. The incorporation of CS-NGO, a non-toxic and environmentally friendly material, significantly enhances the electrochemical performance. The electrochemical properties are explored by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectrum (EIS). The analyses reveal a specific capacitance increase from 2.84 μF cm−2 to 3.96 μF cm−2, a reduction in charge transfer resistance (Rct) from 24.75 Ω to 16.74 Ω, a decrease in Rs resistance from 4.9 Ω to 0 Ω, and a reduction of equivalent series resistance (ESR) from 12.87 Ω to 6.41 Ω. In addition, the results demonstrate remarkable enhancements in energy density and power density and an excellent cyclic stability of 100% over up to 1000 CV cycles of the CS-NGO electrode. These improvements are due to the potential of CS-NGO nanocomposite in developing high-performance, sustainable supercapacitors with the growing demand for green and safe energy storage solutions. This sign of success in this research is due to the new nanocomposite.

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Comparing Effects of Back Diffusion and Membrane Resistance on the Performance of a Low Temperature Electrochemical Hydrogen Pump

“Green” hydrogen produced via electrolysis using electricity from renewable energy sources is seen as a promising energy carrier to aid in the transition from fossil fuels because its production emits no carbon and consumes only water as a reactant. However, the high energy demand required to compress hydrogen to higher energy densities required for efficient transport and storage remains a bottleneck for its deployment1-4. Electrochemical hydrogen pumps (EHPs) are an attractive solution since they operate via isothermal compression and are thus more efficient than typical mechanical compressors which operate adiabatically1,2,5. EHPs also have the advantage of low noise, absence of moving parts, and ability to simultaneously purify hydrogen during compression1-4.In this study, an in-house built EHP test cell with an active geometric area of 25 cm2 was constructed using membrane electrode assemblies (MEA) based on a proton exchange membrane (PEM) and a platinum catalyst. The cell was used to pressurize hydrogen from atmospheric pressure to 10 barg. The net performance of EHPs is a result of the tradeoff between the two major losses that is, back diffusion of H2 and membrane resistance3-5. Thus, we compared the effect of varying temperature, in the range of 30-75°C, on cell performance. Current densities reaching 1.0 A cm-2 (corresponding to a specific hydrogen flow rate of 7.45 mLs min-1 cm-²) were achieved during testing. Linear sweep voltammetry was used to quantify the back diffusion of hydrogen with temperature, see Figure 1(a). Electrochemical impedance spectroscopy was used to determine the series resistance of the EHP. Figure 1(b) shows the increase in voltage with increasing high frequency resistance, whose largest contribution comes from the membrane, with reducing cell temperatures. Stepped chronopotentiometry measurements were used to characterize the overall cell performance. Figure 1 (c) and (d) show the effect of temperature on the polarization curves at a cathode pressure of 5 and 10 barg, respectively, of the EHP operating with an Aquivion E98-09S membrane with 0.25 mg cm-2 Pt per electrode. At 0.5 A cm-2, an applied voltage of 195 mV was required to compress hydrogen at atmospheric pressure in one step to 10 barg operating at 30°C, corresponding to an overall efficiency of 16%. When the cell temperature is raised to 75°C, a lower voltage of 132 mV is required at 0.5 A cm-2 due to the stronger effect of the reduced series resistance that leads to a higher cell efficiency of 27%. This work shows that membrane resistance has a greater effect than back diffusion on the overall EHP performance to pressures of 10 barg.Future work is focused on coupling this EHP with a photovoltaic driven electrolyser and further decreasing the energy demand required to compress hydrogen. References J. Zou, N. Han, J. Yan, Q. Feng, Y. Wang, Z. Zhai, J. Fan, L. Zeng, H. Li, H. Wang., Electrochemical Energy Reviews 2020, 3, 690–729.G. Sdanghi, J. Dillet, S. Didierjean, V. Fierro, G. Maranzana., Fuel Cells 2020, 3, 370-380Y. Hao, H. Nakajima, H. Yoshizumi, A. Inada, K. Sasaki, K. Ito., International Journal of Hydrogen Energy 2016, 41, 13879-13887.M. Ivanova, R. Peters, M. Müller, S. Haas, M. Seidler, G. Mutschke, K. Eckert, P. Röse, S. Calnan, R. Bagacki, R. Schlatmann, C. Grosselindemann, L. Schäfer, N. Menzler, A. Weber, R. Van de Krol, F. Liang, F. Abdi, S. Brendelberger, N. Neumann, J. Grobbel, M. Roeb, C. Sattler, I. Duran, B. Dietrich, C. Hofberger, L. Stoppel, N. Uhlenbruck, T. Wetzel, D. Rauner, A. Hecimovic, U. Fantz, N. Kulyk, J. Harting, O. Guillon., Angewandte Chemie, 2023, 62, e202218850B. Kee, D. Curran, H. Zhu, R. Braun, S. DeCaluwe, R. Kee, S. Ricote., Membranes 2019, 9,77. Figure 1

Optimization strategies for metallization in n-type crystalline silicon TOPCon solar cells: Pathways to elevated fill factor and enhanced efficiency

In advancing photovoltaic technology, optimizing the metallization process is crucial for balancing electrical conductivity and optical performance in solar cell fabrication. This process directly impacts the efficiency and quality of solar cells, traditionally measured by the fill factor (FF). Historically, efforts have focused on evolving metal contacts to reduce optical shading and series resistance, which degrade solar cell efficiency. Our study enhances n-type Tunnel Oxide Passivated Contact (n-TOPCon) solar cells by optimizing screen-printing metallization, particularly by examining the effects of squeegee speeds. Employing a mix of experimental and analytical methodologies, we aimed to identify optimal conditions that improve electrical and optical performance, thereby elevating cell efficiency. Our findings indicate that a squeegee speed of 170 mm/s substantially boosts solar cell performance, evidenced by a current density (Jsc) of 38.96 mA/cm2, open-circuit voltage (Voc) of 684.29 mV, fill factor (FF) of 78.77 %, and a power conversion efficiency (PCE) of 21.00 %. Further, dark I–V measurements confirmed a shunt resistance (Rsh) of 6.25 × 106 Ω and a reduced series resistance (Rs) of 6.48 Ω, underscoring the significance of precise metallization in reducing resistive losses and enhancing efficiency. Future research will explore innovative materials and cutting-edge printing techniques beyond squeegee speed adjustments. The potential incorporation of nanomaterials and conducting polymers aims to refine the metallization process further, promising to push the boundaries of efficiency and cost-effectiveness. This progression is essential for advancing n-TOPCon solar cell development, setting new industry standards, and propelling the sustainable energy movement.

Reactive DC Sputtered TiO2 Electron Transport Layers for Cadmium‐Free Sb2Se3 Solar Cells

AbstractThe evolution of Sb2Se3 heterojunction devices away from CdS electron transport layers (ETL) to wide bandgap metal oxide alternatives is a critical target in the development of this emerging photovoltaic material. Metal oxide ETL/Sb2Se3 device performance has historically been limited by relatively low fill factors, despite offering clear advantages with regards to photocurrent collection. In this study, TiO2 ETLs are fabricated via direct current reactive sputtering and tested in complete Sb2Se3 devices. A strong correlation between TiO2 ETL processing conditions and the Sb2Se3 solar cell device response under forward bias conditions is observed and optimized. Numerical device models support experimental evidence of a spike‐like conduction band offset, which can be mediated, provided a sufficiently high conductivity and low interfacial defect density can be achieved in the TiO2 ETL. Ultimately, a SnO2:F/TiO2/Sb2Se3/P3HT/Au device with the reactively sputtered TiO2 ETL delivers an 8.12% power conversion efficiency (η), the highest TiO2/Sb2Se3 device reported to‐date. This is achieved by a substantial reduction in series resistance, driven by improved crystallinity of the reactively sputtered anatase‐TiO2 ETL, whilst maintaining almost maximum current collection for this device architecture.

The electrical and dielectric features of Al/YbFeO3/p-Si/Al and Al/YbFe0.90Co0.10O3/p-Si/Al structures with interfacial perovskite-oxide layer depending on bias voltage and frequency

In this investigation, thin films of YbFeO3, both in its pure form and doped with 10% Co, were fabricated on a p-Si substrate at 500 °C through the radio-frequency magnetron sputtering method. Examination via Scanning Electron Microscopy demonstrated a porous texture for the pure sample, contrasting with a smooth and crack-free surface post-Co doping. Analysis via X-ray photoelectron spectroscopy unveiled Yb’s 3 + oxidation state, alongside the presence of lattice oxygen, oxygen vacancies, and adsorbed oxygen evident in Gaussian fitting curves. Photoluminescence spectroscopy revealed an augmented emission intensity, likely attributed to increased defect initiation in the Co-doped specimen. Moreover, Raman spectroscopy was employed to identify vibration modes in the examined samples, demonstrating shifts in Raman peaks indicative of Co substitution and subsequent distortion in the crystal structure of YbFeO3. Electrical assessments were conducted at room temperature (300 K) under ambient conditions, employing voltage and frequency as variables. Capacitance–voltage measurements illustrated the emergence of an accumulation, with depletion and inversion regions manifesting at different frequencies based on the applied voltage, attributed to the YbFeO3 interfacial layer at the Al and p-Si interface. The conductance-voltage characteristics indicated that the structure exhibited maximum conductance in the accumulation region. Series resistance for these configurations was deduced from capacitance-conductance-voltage measurements, indicating a dependence on both bias voltage and frequency. The doping process led to a reduction in capacitance and series resistance, accompanied by an increase in conductance values. After obtaining corrected capacitance and conductance parameters, it became evident that series resistance significantly influences both parameters. Interface state density (Nss), determined through the Hill-Coleman relation demonstrated a decreasing trend with increasing frequency. The pure sample exhibited higher interface state density compared to the Co-doped sample at each frequency, highlighting that the 10% Co-doped YbFeO3 thin film enhances the quality of the metal–semiconductor interface properties compared to the pure contact.

Advances in low-temperature solid oxide fuel cells: An explanatory review

This review article explores recent advancements and potential advantages of low-temperature solid oxide fuel cells (LT-SOFCs), offering a comprehensive overview of critical developments in the field. It highlights the significance of utilizing oxygen ion conducting electrolytes such as La0.8Sr0.2Ga0.8Mg0.2O3–type (LSGM) perovskties and yttria-stabilized zirconia (YSZ) in LT-SOFCs, emphasizing their role in facilitating efficient oxygen transport at lower temperatures. Furthermore, the review discusses the importance of electrode tailoring at the nanoscale using techniques like sol-gel and pulsed laser deposition (PLD), which have been shown to enhance the oxygen reduction reaction (ORR) at the cathode, thereby improving overall cell performance. One of the key focal points of the review is the exploration of perovskite structures and their imperative characteristics in LT-SOFCs. Specifically, it elucidates how oxygen defects within perovskites contribute to the migration of oxygen ions, consequently augmenting electrical conductivity within the cell. This discussion underscores the significance of understanding the fundamental principles governing ion transport mechanisms in electrolyte materials, which is crucial for the development of next-generation LT-SOFCs with improved efficiency and performance. Moreover, the review highlights recent advancements in the fabrication of nanoscale electrolyte films, which have shown promising results in reducing series resistance and enhancing cell performance at lower temperatures. Techniques such as atomic layer deposition (ALD), and spark plasma sintering (SPS) are discussed in the context of fabricating these nanoscale membranes, underscoring their potential for revolutionizing LT-SOFC technology. Overall, this review consolidates recent research findings and technological advancements in the field of LT-SOFCs, shedding light on the novel approaches and strategies employed to overcome existing challenges and propel the development of more efficient and practical fuel cell systems. By synthesizing key insights and highlighting future research directions, this review serves as a valuable resource for researchers and engineers working towards the advancement of LT-SOFC technology.

Solution‐Processed Sb2(S,Se)3 Seed‐Assisted Sb2Se3 Thin Film Growth for High Efficiency Solar Cell

Antimony selenide (Sb2Se3) emerges as a promising sunlight absorber in thin film photovoltaic applications due to its excellent light absorption properties and carrier transport behavior, attributed to the quasi‐one‐dimensional Sb4Se6‐nanoribbon crystal structure. Overcoming the challenge of aligning Sb2Se3‐nanoribbons normal to substrates for efficient photogenerated carrier extraction, a solution‐processed nanocrystalline Sb2(S,Se)3‐seeds are employed on the CdS buffer layer. These seeds facilitate superstrated Sb2Se3 thin film solar cell growth through a close‐space sublimation approach. The Sb2(S,Se)3‐seeds guided the Sb2Se3 absorber growth along a [002]‐preferred crystal orientation, ensuring a smoother interface with the CdS window layer. Remarkably, Sb2(S,Se)3‐seeds improve carrier transport, reduce series resistance, and increase charge recombination resistance, resulting in an enhanced power conversion efficiency of 7.52%. This cost‐effective solution‐processed seeds planting approach holds promise for advancing chalcogenide‐based thin film solar cells in large‐scale manufacturing.

High-beam-quality low-resistance vertical-cavity surface-emitting laser array with graphene electrode.

Thermal crosstalk and current crowding effects are pressing issues that significantly impact the beam quality and efficiency of vertical-cavity surface-emitting laser (VCSEL) arrays. In this paper, by taking advantage of the excellent current transmission characteristics of graphene, what we believe to be a novel VCSEL array based on graphene electrode is designed to realize vertical current injections. The series resistance and self-heating of arrays are reduced by controlling the transport direction of the current, effectively suppressing the thermal crosstalk effect. Furthermore, high array beam quality is obtained by optimizing the current density distribution in active regions. Ultimately, the high-power quasi-single mode emission of VCSEL arrays is achieved by introducing graphene electrodes (Gr-VCSEL array) designs. Compared to traditional VCSEL arrays, the 10 × 10 Gr-VCSEL array demonstrates a 41% reduction in series resistance, a side mode suppression ratio of 32 dB, and a divergence angle around 12 °. This structure simultaneously achieves quasi-single mode emission and effectively suppresses the thermal crosstalk effect, providing a new method for the development of high-beam quality VCSEL arrays.

Low-resistive gate module for RF GaN-HFETs by electroplating

This paper presents a novel approach for reducing the gate resistance (R g) of K and Ka-band GaN HFETs with 150 nm gate length through a new gate metallization technique. The method involves increasing the gate cross-section via galvanic metallization using FBH’s Ir-sputter gate technology, which allows an increase in gate metal thickness from the current 0.4 μm to approximately 1.0 μm for the transistors under investigation. This optimization leads to a substantial 50% reduction in gate series resistance, resulting in significant improvements in the RF performance. Specifically, the devices achieve 20% higher output power density and 10% better power-added efficiency at 20 GHz and V ds = 20 V. The decreased gate resistance enables new degrees of freedom in design, such as longer gate fingers and/or shorter gate lengths, for more efficient power cells operating in this frequency range.

The Through-Flow Electrochemical Cell - a Breakthrough Technology

The paper describes a new approach to energy-storage electrochemical cells that is “chemistry-agnostic” and promises to solve several problems of existing batteries. These problems include: Charging rates are too slowIntrinsic failure-mechanisms compromise safetyEnergy Density is inadequate for mobile applicationsLifetime is too short for large-scale permanent installations The key idea of the “Through-Flow Cell” is that the electrolyte is pumped continuously in a closed loop through a porous anode, porous separator, and porous cathode, in a direction aiding the active ionic flow. Although the idea of moving a liquid electrolyte is not new, there have not been any successful commercial products until now. It should not be confused with the “Flow-Battery”, an entirely different concept where two different fluids flow separately within anode and cathode. Previous attempts to develop a reliable Through-Flow Cell foundered on the difficulty of immobilizing active materials on the anode and cathode collectors while fluid flows freely through surrounding pore-spaces. I describe a new active-material encapsulation method to achieve that crucial objective, and a new more convenient cell configuration.Applications will include large grid-scale installations and could include high-power transportation vehicles such as trains and buses. The basic cell is configured as a stack-able, de-mountable, and repairable module. It is a completely self-contained package incorporating an adaptive electrolyte pumping system with optional heating and/or cooling to optimize efficiency in a wide range of environmental conditions. In grid-scale systems the ability to easily remove a low-performing cell from a stack, repair, and replace it is a very desirable feature that extends the life of a high-CAPEX installation almost indefinitely.The new cell design has a conservative capacity rating of 3000 Amp.hr (using 300 mA.hr/gm active materials) and a continuous current rating of 2000 Amps, with the cell voltage being determined by the chemistry employed. For the Lithium-ion chemistry with a nominal voltage of 3.7v it has 10 KW.hr energy capacity @ 90% discharge. A linear stack of 100 cells makes a battery storing 1 MW.hr on a rack 9 meters in length; easily accommodated in an enclosure the size of a shipping container that could contain up to eight such racks.For some people the idea of a battery with moving parts runs counter to notions of simplicity found in the standard sealed cylindrical cells. In practice, however, large assemblies of such cells require complex external liquid cooling and possibly fire-suppression systems. When individual cells fail, they are usually disconnected by blowing fuses, resulting in a steady degradation that is not easily repairable.In contrast to sealed cells, some unique advantages of the electrolyte circulation technique can be summarized as follows: Effective Mobility of active-species ions is dramatically boosted by the flow velocity, translating into reduced series resistance between electrodes. Peak charging or discharging currents can be ten times higher without overheating or loss of charge capacity when the flow velocity is only one centimeter per second.Flow direction is reversed when switching from charging to discharging, which reverses dendrite growth that is a potential source of catastrophic failure.The interior temperature of the cell can be directly controlled and excess heat removed from the electrolyte by an external heat-exchanger, or added in cold climates.The Anode and Cathode, being 3-Dimensional porous structures, incorporate greatly increased volumes of active material compared to typical 2-Dimensional foil electrodes.Electrolyte flowing across the surface of active material inside porous electrodes efficiently sweeps away ion-deficient liquid from within the Slipping-Plane near the Solid-Electrolyte Interface (SEI), reducing the parasitic Zeta-Potential. Results from a proof-of-principle laboratory cell using the Nickel Metal-Hydride chemistry will be briefly described, and a full-scale commercial cell design presented in more detail. The very important active-material encapsulation technique is also described along with its unique ability to tolerate large changes in volume of the active material without degradation. Current cylindrical “jelly-roll” format cells cannot tolerate significant volume change caused by ion-intercalation inside active materials without physical destruction.The new technology may enable complete replacement of Graphite by Silicon in the Anodes of Lithium-ion cells. Silicon has a charge capacity almost four times greater than Graphite, but expands up to 400%. In another example, Cathodes in the Lithium-Sulfur chemistry may tolerate far higher Sulfur loading with corresponding increased energy density.In summary, this new focus on the mechanics of energy-storage cells shows promise for a step-change increase in power-density, reliability, and safety. As described, the idea can be applied to any new improvement in chemistry that uses a liquid electrolyte as soon as it achieves maturity. Figure 1

Structural energy storage system using electrospun carbon nanofibers with carbon nanotubes

AbstractIn the present study, carbon nanofibers containing multi‐walled carbon nanotubes (MWCNTs) were fabricated and employed as electrodes for structural supercapacitors. Carbon nanofibers were utilized as the electrode material in structural supercapacitors to increase the specific surface area. Electrospun polyacrylonitrile (PAN) nanofibers underwent conversion to carbon nanofibers through stabilization and carbonization processes aided by thermal treatment. The specific surface area of the electrospun carbon nanofiber electrodes was further increased approximately 118 times (1946.9 m2/g) using an activation process in comparison with that of non‐activated carbon nanofibers (16.43 m2/g). Multifunctional supercapacitors were fabricated by employing electrospun carbon nanofibers and a vacuum resin infusion technique. The specific capacitance of activated carbon nanofibers (ACNF) and ACNF‐MWCNT exhibited significant improvement (14.87 and 48.25 mF/cm2, respectively) compared to non‐activated carbon nanofibers (CNF‐MWCNT: 1.71 mF/cm2). This improvement was attributed to the reduction in equivalent series resistance and the increase of the surface area of the nanofiber electrodes. Additionally, the carbon nanofiber electrodes contributed to an increased interlaminar fracture toughness of structural supercapacitors, acting akin to “Velcro” between fabric interfaces. This work serves as a “proof of concept” for a straightforward and efficient method to manufacture electrodes for structural supercapacitors based on the electrospinning technique.Highlights Fabrication of carbon nanofibers containing MWCNTs using electrospinning. The carbon nanofiber as an electrode for structural supercapacitors. Simple and effective method. Dramatically improving specific capacitance of the supercapacitors.

Structure Influence of Amine-Containing Additives on the Solution State and Out-of-Plane Conductivity of PEDOT:PSS for Efficient Organic Solar Cells.

Additives are extensively explored for improving PEDOT:PSS performances mainly through the removal of excess PSS and as a secondary dopant. In this work, amine-containing additives are introduced to PEDOT:PSS solutions as processing additives where the interactions to the PSS are anticipated through electrostatic interactions. Such interactions affected solution property where the increased viscosity is found to significantly increase the out-of-plane conductivity of the PEDOT:PSS thin films. Organic solar cells adopting these additive-assisted processed PEDOT:PSS layers as hole transporting layers (HTL) showed the improved device performances that resulted from the reduced series resistance provided by the PEDOT:PSS HTL. A top power conversion efficiency of 18.28% is achieved with para-phenylenediamine (PPD) additive in the PEDOT:PSS HTL, which is 3.5% higher compared to devices with neat PEDOT:PSS thin film as the HTL.

Enabling durable hydrogen production and preventing the catastrophic delamination in the solid oxide electrolysis cells by infiltrating SrFe2O4-δ solutions into LSM/YSZ -based air electrode

Solid oxide cells with La0.8Sr0.2MnO3/yttria-stabilized zirconia (LSM/YSZ) air electrodes exhibit accelerated performance degradation during electrolysis of hydrogen production. Under galvanic mode with a current density of 0.5 A/cm2, baseline electrolysis cells exhibit a rapid increase in resistance upon 200 h of operation and become utterly delaminated after 350 h at 800 °C. To prevent such catastrophic delamination, SrFe2O4-δ solutions are infiltrated into the LSM/YSZ air electrode of as-fabricated cell. Under the identical operation condition, SrFe2O4-δ infiltrated cells exhibit performance enhancement manifested by an immediate decrease in electrolysis operation voltage and reduction of both series and polarization resistance and sustainability of 900 h continuous electrolysis operation without delamination. Nanostructure examination reveals active interaction of the SrFe2O4-δ infiltrate with cells after calcination, Fe diffusion into the LSM backbones, and formation of nanoparticles on the surface of the backbones. During electrolysis, the nanoparticles maintain intact morphology and constant particle size, while there is continuous cation exchange between the nanoparticles and the backbone. The nanostructure origin of the increased electrolysis performance, reduced resistance, and increased durability induced by infiltration are discussed. The present study demonstrates a feasible and viable approach to preventing electrode delamination while increasing the durability of hydrogen production for electrolysis cells.

Bottom-up self-assembly of macroporous ZnO nanostructures for photovoltaic applications

The present study utilized a template-assisted electrodeposition route for the bottom-up epitaxial growth of macroporous zinc oxide nanostructures. To this end, the ZnO seed layer was coated on the p-type silicon substrates using a radio frequency magnetron sputtering technique to form a p-n heterojunction. Then, polymer microspheres were implanted on ZnO/Si substrates to act as a template. Subsequently, ZnO nanostructures were electrodeposited through the interstitial spaces between the microspheres. After the deposition, the microspheres were removed by dissolving in chloroform solvent, forming a porous structure. The planar and cross-sectional electron microscopy analyses exhibited a uniform macroporous morphology with an average pore diameter of ∼1 μm. The pores were homogeneously distributed on the surface of the electrodeposited ZnO layer. The advantage of this technique over the top-down approaches, such as electrochemical etching, is that the porosity and size of pores can be easily adjusted by varying the concentration and diameter of microsphere templates. The optical investigations revealed enhancement in photon absorption and photoluminescence (PL) intensity due to multiple light scattering in the pore walls of the deposited ZnO nanostructures. For the templated sample, a PL blue shift was observed due to the reduction in crystallite size of ZnO nanostructures. A heterojunction thin film solar cell was designed by the metallization of ZnO/p-Si samples to study the power conversion capability of macroporous ZnO nanostructures. The photovoltaic performance of the developed devices was evaluated under a solar light simulator. The device based on the templated sample showed increased shunt resistance and reduced series resistance compared to the flat sample. The optoelectrical results indicated an efficiency improvement for the fabricated solar cells based on the macroporous ZnO sample due to its higher exposed area and increased rate of electron-hole generation.

Solution processable polypyrrole nanotubes as an alternative hole transporting material in perovskite solar cells

The major challenge towards the commercialization of perovskite solar cells is to find an alternative stable, low-cost, and solution-processible hole transporting material to unstable and expensive 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenylamine)− 9,9’- spirobifluorene. Despite having all prerequisite properties like the ease of synthesis, low cost, tunability of hole conductivity, the conducting polymers such as polypyrrole are hardly being explored extensively as hole-transporting materials because of their insolubility in common organic solvents. Here, a colloidal solution of hydrophobic polypyrrole nanotubes co-doped with sodium dodecylbenzenesulfonate has been developed and explored for the hole transporting layer in methylammonium lead iodide-based perovskite solar cells. The best device has shown a power conversion efficiency of 7.3% at ambient conditions and without sealing. In terms of stability, the unsealed polypyrrole-based devices maintaining 85% of the initial efficiency at relative humidity 75–80 % with over 120 h have outperformed the unencapsulated poly(3-hexylthiophene)- based devices (average power conversion efficiency ∼11 %) fabricated using the same procedure and measured under same conditions. Frequency response analysis and electroluminescent imaging reveal that the photovoltaic performance of the polypyrrole-based cells can further be improved by reducing series resistance arising due to hole transporting layers. These studies show the polypyrrole colloids as a promising low-cost solution for the hole transporting layer in perovskite solar cells.

Influence of SWCNT on the Electrical Behavior of an Environmentally Friendly CH3NH3SnI3 Perovskite-Based Optoelectronic Schottky Device

The lead-free tin-based halide perovskite CH3NH3SnI3 has recently been explored in a wide range of optoelectronic device applications. However, the charge conduction process of the CH3NH3SnI3 perovskite layer is hindered by the presence of vacancies resulting from tin oxidation, sample defects, and trap states, which limit the performance of the device. In this study, we introduced single-walled carbon nanotubes (SWCNTs) into the perovskite to enhance the charge conduction of the device. To demonstrate this, CH3NH3SnI3 perovskite and its composites with SWCNTs were synthesized and used as an active layer in a sandwich-structured device. Electrical measurements show that the device based on SWCNTs exhibits superior performance compared to the device consisting solely of perovskite. Incorporating SWCNTs into the device improves conductivity and reduces series resistance. Specifically, in the absence of light, SWCNTs increase the conductivity from 3.8 × 10–5 to 1.6 × 10–4 S/m and decrease the series resistance from 348.25 to 34.80 Ω. Under illumination, SWCNTs further increase conductivity to 4.0 × 10–4 S/m from 8.1 × 10–5 S/m and decrease series resistance to 19.20 Ω from 220.56 Ω. The results suggest that SWCNT can serve as a channel for charge extraction. An analysis of space charge limited current (SCLC) conduction indicates that incorporating SWCNT decreases the trap energy from 103.22 to 79.70 meV under dark conditions. This implies that SWCNT also acts as a filler for trap states. Based on these findings, it appears that the SWCNT-CH3NH3SnI3 perovskite composite has the potential to yield high-performance optoelectronic devices. This study presents an intriguing approach for enhancing carrier transfer with minimal recombination loss and could serve as a source of inspiration for future research in the optoelectronics field.

Suppressed Trap Density Leads to Versatile p‐i‐n Heterojunction Photodiode with Enhanced Photovoltaic/Photodetection Dual‐Function

AbstractMultifunctional integration of optoelectronic devices within a single photodiode is in high demand for next‐generation on‐chip multifunctional integration and Internet of Things applications. Owing to the rapidity of nucleation‐crystallization that is associated with the solution method, large trap state densities (Nt), and consequently, severe dark current densities, as well as recombination losses are generally induced, which are detrimental to the detectivity (D*) of organic photodetectors (OPDs) and to the open‐circuit voltage (VOC) of organic photovoltaics (OPVs). Herein, a versatile p‐i‐n heterojunction organic photodiode with optimized vertical phase distribution and rational solid‐state packing is fabricated via a layer‐by‐layer (LBL) deposition procedure entailing the introduction of a rylene‐fullerene hybrid as a morphological modulator. This precisely controlled photodiode displayed suppressed Nt (2.5 × 1016 cm−3), low‐lying Urbach energy Eu (23.2 meV), as well as synergistically reduced series resistance, dark current, and sub‐bandgap radiative/non‐radiative recombination losses. Consequently, this ternary‐pseudo‐bilayer‐type photodiode exhibits excellent dual‐function performance with an outstanding D* of 9.48 × 1011 Jones in self‐powered OPD mode and a surprisingly suppressed energy loss of 0.538 eV in OPV mode. This study provides important insights into the mechanism and effects of trap density and energy disorder suppression in solution‐processed multifunctional integrated photoelectric conversion diodes.

MOSFET series resistance extraction at cryogenic temperatures

A series resistance extraction method proposed recently, which uses multiple drain current versus gate voltage curves at varied drain voltages, was applied to bulk CMOS devices at low temperatures down to 4 K. A moderate reduction of series resistance compared with 300 K was found. Horizontal field dependence of mobility significantly changed with temperature, which was taken into account during the extraction. Anomalous non-linear series resistance was observed at 4 K only for p-channel FETs, suggesting the need for careful source/drain overlap design for low temperature operations.

Enhanced photovoltage production from Canna dyes with surface passivation of ZnO based dye sensitized solar cells

Among the vast number of floras, Canna lily Red (CR) and Canna lily Yellow (CY) flower extracts were used as photosensitizers for natural dye-sensitized solar cells (NDSSC) with ZnO photoanode material. This study incorporates a blocking or compact layer (CL) below the nanoporous ZnO semiconducting metal oxide to reduce the device's recombination rate. A noticeable increment of J SC after adding a compact layer is observed for both the dyes; that is for CR dye from 0.43 to 0.47 mA/cm 2 , and for CY dye, 0.38 to 0.44 mA/cm 2 is obtained with a consistent high V OC of 0.54 to 0.60 V. Moreover, the device's charge collection efficiency has been enhanced from ∼ 93 to ∼ 97 % for CR dye and from ∼ 89 to ∼ 96 % for CY dye-loaded films after adding a compact layer. The enhancement in J SC , V OC , and fill factor ( FF ) is credited to increased electron lifetime, increased diffusion length, reduced series resistance ( Rs ), and exclusively enhanced recombination resistance among the FTO/electrolyte interface due to the compact layer. Despite visible defect states in the ZnO photoanode, a consistent photovoltage of 0.54 V to 0.6 V significantly manifests enhanced photovoltage production of Canna dyes in the device. The effect of compact layers on photovoltaic parameters is well established through the EIS study. • Canna dyes utilized as photosensitizers with ZnO photoanode in DSSC. • The rate of recombination and back transfer of charge carriers was reduced. • V OC and J SC are tunable with electrochemical impedance spectroscopy. • Photovoltage of 0.55V - 0.6V production is the iconic feature of these canna dyes.