N-type Electrodes Research Articles

Diazonium-Functionalized Silicon Hybrid Photoelectrodes: Film Thickness and Composition Effects on Photoelectrochemical Behavior.

Aryl diazonium electrografting is a powerful method for imparting molecular functionality onto various substrates by forming a stable carbon-surface covalent bond. While the high reactivity of the aryl radical intermediate makes this method fast and reliable, it can also lead to the formation of an insulating and disordered multilayer film. These thick films affect electrochemical performance, especially for semiconductor substrates used in photoelectrochemical applications. We studied the effects of film thickness and composition by electrografting in situ-generated aminobenzene diazonium salts onto both n-type and p-type silicon electrodes at fixed potentials. Next, we attached ferrocene to the amine-terminated films and probed their (photo)electrochemical behavior. Cyclic voltammetry measurements showed decreased electrochemical reversibility with increasing diazonium film thickness; this reversibility was restored when ferrocene was incorporated throughout the film with a layer-by-layer deposition process. Finally, we compared the behavior of dark p-type electrodes to n-type photoelectrodes and observed differences in the electrochemical reversibility that we attribute to the change in potential drop across the two interfaces.

High Efficiency Flat-Type GaN-Based Light-Emitting Diodes with Multiple Local Breakdown Conductive Channels.

We investigated a flat-type p*-p LED composed of a p*-electrode with a local breakdown conductive channel (LBCC) formed in the p-type electrode region by applying reverse bias. By locally connecting the p*-electrode to the n-type layer via an LBCC, a flat-type LED structure is applied that can replace the n-type electrode without a mesa-etching process. Flat-type p*-p LEDs, devoid of the mesa process, demonstrate outstanding characteristics, boasting comparable light output power to conventional mesa-type n-p LEDs at the same injection current. However, they incur higher operating voltages, attributed to the smaller size of the p* region used as the n-type electrode compared to conventional n-p LEDs. Therefore, despite having comparable external quantum efficiency stemming from similar light output, flat-type p*-p LEDs exhibit diminished wall-plug efficiency (WPE) and voltage efficiency (VE) owing to elevated operating voltages. To address this, our study aimed to mitigate the series resistance of flat-type p*-p LEDs by augmenting the number of LBCCs to enhance the contact area, thereby reducing overall resistance. This structure holds promise for elevating WPE and VE by aligning the operating voltage more closely with that of mesa-type n-p LEDs. Consequently, rectifying the issue of high operating voltages in planar p*-p LEDs enables the creation of efficient LEDs devoid of crystal defects resulting from mesa-etching processes.

Thermoelectric response of textured Sb2Te3–BiSb and Sb2Te3–Bi2Te3 thin film junctions

Surface mounted thin film thermoelectric (TE) devices for localized cooling, power generation, and sensing are topics of immense current interest. Here, we establish the superior TE performance of thin film junctions made of topological insulators (TIs) Bi85Sb15 (BiSb) and Sb2Te3 by comparing their performance with those of Bi2Te3 and Sb2Te3. Thin films of these TIs were first evaluated for their carrier concentration, Hall mobility, resistivity, and thermopower. The Seebeck coefficient of BiSb, Sb2Te3, and Bi2Te3 measured against copper at ambient temperature is −100, +160, and −70 (±10) μV/K, while their power factors are 0.5, 0.5, and 0.45 (±0.05) 10−3 W m−1 K−2, respectively. Single TE junctions of BiSb–Sb2Te3 and Bi2Te3–Sb2Te3 yield a response of 272 and 240 (±10) μV/K, respectively. This comparative study shows that BiSb is a superior n-type counter electrode for Sb2Te3 compared to the n-type Bi2Te3. Moreover, Bi2Te3 is prone to tellurium antisite disorder, which affects its TE properties significantly.

Chip-level mass detection for micro-LED displays based on regression analysis and deep learning.

Though micro-light-emitting diode (micro-LED) displays are regarded as the next-generation emerging display technology, challenges such as defects in LED's light output power and radiation patterns are critical to the commercialization success. Here we propose an electroluminescence mass detection method to examine the light output quality from the on-wafer LED arrays before they are transferred to the display substrate. The mass detection method consists of two stages. In the first stage, the luminescent image is captured by a camera by mounting an ITO (indium-tin oxide) transparent conducting glass on the LED wafer. Due to the resistance of the ITO contact pads and on-wafer n-type electrodes, we develop a calibration method based on the circuit model to predict the current flow on each LED. The light output power of each device is thus calibrated back by multi-variable regression analysis. The analysis results in an average variation as low as 6.89% for devices predicted from luminescent image capturing and actual optical power measurement. We also examine the defective or non-uniform micro-LED radiation profiles by constructing a 2-D convolutional neural network (CNN) model. The optimized model is determined among three different approaches. The CNN model can recognize 99.45% functioning LEDs, and show a precision of 96.29% for correctly predicting good devices.

Optimization of preparation conditions and design of device configurations for Cu3AsS4 solar cells: a combined study of first-principles calculations and SCAPS-1D device simulations.

Former studies have investigated the band structure and optoelectronic properties of Cu3AsS4 and suggested that it is a promising photovoltaic (PV) absorber. However, its power conversion efficiency (PCE) from experiments is still unsatisfactory and detailed experimental optimization strategies are lacking. Here, combining first-principles calculations and SCAPS-1D device simulations, we have systematically studied the optoelectronic and defect properties of Cu3AsS4 to find the suitable growth conditions and have performed various device simulations by adjusting the constituent layers to optimize the device configuration of the Cu3AsS4 solar cell. Our results demonstrated that the defect and hole concentrations can be regulated to a reasonable range as the PV absorber in metal-rich and S-poor growth environments with a low growth temperature of 500 K. Owing to the large cliff-like conduction band offset between the traditional buffer layers CdS and Cu3AsS4, the open-circuit voltage loss is large and the corresponding PCE is low. The PCE can be improved by adopting the new buffer layers with low electron affinity. The corresponding n-type transparent electrode is further optimized. Finally, the solar cell with the configuration of FTO/WO3/Cu3AsS4/Mo is suggested and its PCE can reach an optimal value of 17.82%.

Towards the 4 V-class n-type organic lithium-ion positive electrode materials: the case of conjugated triflimides and cyanamides.

Organic electrode materials have garnered a great deal of interest owing to their sustainability, cost-efficiency, and design flexibility metrics. Despite numerous endeavors to fine-tune their redox potential, the pool of organic positive electrode materials with a redox potential above 3 V versus Li+/Li0, and maintaining air stability in the Li-reservoir configuration remains limited. This study expands the chemical landscape of organic Li-ion positive electrode chemistries towards the 4 V-class through molecular design based on electron density depletion within the redox center via the mesomeric effect of electron-withdrawing groups (EWGs). This results in the development of novel families of conjugated triflimides and cyanamides as high-voltage electrode materials for organic lithium-ion batteries. These are found to exhibit ambient air stability and demonstrate reversible electrochemistry with redox potentials spanning the range of 3.1 V to 3.8 V (versus Li+/Li0), marking the highest reported values so far within the realm of n-type organic chemistries. Through comprehensive structural analysis and extensive electrochemical studies, we elucidate the relationship between the molecular structure and the ability to fine-tune the redox potential. These findings offer promising opportunities to customize the redox properties of organic electrodes, bridging the gap with their inorganic counterparts for application in sustainable and eco-friendly electrochemical energy storage devices.

Interface engineering of multilayer cubic boron nitride terminated diamond (111): Rational regulation of Au/diamond Schottky barriers for ambipolar applications

Ultra-wide bandgap semiconductor diamond has become a new hope for developing high power devices owing to excellent properties. We have previously demonstrated that the strong Fermi pinning effect is a critical factor limiting its development. This paper proposes terminal engineering to improve the contact quality between Au and diamond by adjusting the electron affinity of the diamond (111) surface using first-principles calculations. Remarkable changes in interfacial polarity can be achieved by inserting different thicknesses of Cubic Boron Nitride (c-BN) with H/F terminals on the diamond (111) surface. The C-xBNH have the lowest negative electron affinity (−3.80 eV ∼ −2.75 eV), whereas C-xNBF supercells have the highest positive electron affinity (4.52 eV ∼ 8.53 eV). Positive charges accumulate at Diamond/xNB-Au and Diamond/xBNH-Au interfaces, while negative charges build up at the other interlayers. Furthermore, the tunneling probability of the Diamond/xNB-Au interfaces is close to 1, indicating an excellent transmission. The ideal p-type and n-type Schottky barrier heights can be achieved by rational design of the c-BN terminated Diamond contact with Au, and desirable ambipolar regulation can be effectively achieved (Diamond/xNB-Au (x = 2, 3) and Diamond/xNBF-Au (x = 1, 2) for n-type ohmic electrodes and Diamond/xBNF-Au (x = 2, 3) for p-type ohmic electrodes). The proposed strategy allows interface polarity optimization by modifying the surface electron affinity, which can be extended to other high-performance ambipolar diamond devices with the rational design of contact metals.

Silicon-based heterojunction photoanodes modified with copper-bipyridine catalyst for enhanced solar-driven water splitting

In photoelectrochemical (PEC) water splitting, accelerating the carrier transfer from the semiconductor to the catalytic functional layer through the construction of nanostructure-heterojunction interface is an effective method to overcome the intrinsically slow kinetics of the photoanode phase interface. In this work, p-type NiO and n-type TiO2 layers were deposited on the surface of n-type Si electrodes, respectively, to construct p-n and n-n heterojunction photoanodes. Moreover, a copper-bipyridine molecular catalyst, namely Cu(dcbpy), was deposited on the heterojunction photoanodes to furtherly provide transfer path for the photogenerated holes in water splitting. Under the illumination of simulated sunlight, the Si/NiO/Cu(dcbpy) photoanode exhibits a high photocurrent density of 16.63 mA cm−2 at 2.2 VRHE, which is 277.2 times of n-Si and 1.92 times of Si/TiO2/Cu(dcbpy) at the same condition. This result indicates that p-n heterojunction accelerates the photogenerated holes transfer from Si to the electrocatalyst of Cu(dcbpy) to achieve a high water-splitting efficiency. This work provides an approach to designing efficient Si-based photoanodes through nanostructure-heterojunction interface engineering and molecular catalyst modification.

A single n-type semiconducting polymer-based photo-electrochemical transistor

Conjugated polymer films, which can conduct both ionic and electronic charges, are central to building soft electronic sensors and actuators. Despite the possible interplay between light absorption and the mixed conductivity of these materials in aqueous biological media, no single polymer film has been utilized to create a solar-switchable organic bioelectronic circuit that relies on a fully reversible and redox reaction-free potentiometric photodetection and current modulation. Here we demonstrate that the absorption of light by an electron and cation-transporting polymer film reversibly modulates its electrochemical potential and conductivity in an aqueous electrolyte, which is harnessed to design an n-type photo-electrochemical transistor (n-OPECT). By controlling the intensity of light incident on the n-type polymeric gate electrode, we generate transistor output characteristics that mimic the modulation of the polymeric channel current achieved through gate voltage control. The micron-scale n-OPECT exhibits a high signal-to-noise ratio and an excellent sensitivity to low light intensities. We demonstrate three direct applications of the n-OPECT, i.e., a photoplethysmogram recorder, a light-controlled inverter circuit, and a light-gated artificial synapse, underscoring the suitability of this platform for a myriad of biomedical applications that involve light intensity changes.

High-efficiency flat-type nitride-based micro-light emitting diodes using local breakdown conductive channel

A flat-type p-p light-emitting diode (LED) utilizing a local breakdown conductive channel (LBCC) in nitride semiconductor-based LEDs is introduced to replace n-p LEDs with existing mesa etched structures. The flat-type p-p LED, including the LBCC, exhibits similar light output power in the same injection current as the n-p LED of the conventional mesa structure but at a higher operating voltage. Consequently, the flat-type p-p LED with LBCC has lower wall plug efficiency compared to the mesa structured n-p LED. However, when the LED size is small, the flat-type p-p LED can achieve an optical power and operating voltage similar to the conventional n-p LED. As the LED size decreases, the n-type electrode of mesa-type n-p LED decreases to the similar size to the LBCC, providing an alternative to the operating voltage characteristics and wall plug efficiency. In addition, the junction temperature of the LED decreases as the LED size decreases. Based on these results, it is believed that the flat-type P-P LED can be advantageous for achieving high efficiency in smaller LED chips due to the smaller dry-etched mesa area which contains crystal defects that act as non-radiative recombination centers, and higher heat dissipation capacity.

Ultrahigh Color Conversion Efficiency Nano-Light-Emitting Diode With Single Electrical Contact

Realizing full color GaN-based micro- and nano-light-emitting diode (nLED) displays with quantum dots (QDs) being the color conversion media remains challenging because of the limited QD color conversion efficiency (CCE). In this article, by using GaN-based nanorod LED as the light source and exciting the QDs by nonradiative energy transfer (NRET) method, a nanorod LED with ultrahigh CCE has been realized. At the same time, a single electrical contact alternating current (ac)-driven electroluminescence (EL) method is adopted to investigate the relationship between frequency and nLED performance. Different from the double terminal injection mode, on the premise of lighting up the nanorod LED, the ac-driven can also avoid the necessity of external p-type and n-type electrodes, thus simplified the manufacturing process of LED. The final optical measurement shows that the CCE of this hybrid color conversion nLED driven by single contact electrode can reach up to 86.67% under the ac voltage of 60 V and an ac frequency of 14.2 MHz, which shows that the energy utilization efficiency can be effectively improved by NRET.

Design and Performance of Ultraviolet 368-nm AlGaN-Based Flip-Chip High-Voltage LEDs with Epitaxial Indium Tin Oxide/Al Reflective Mirror and Symmetry Electrode Arrangement

In this letter, we describe the design and fabrication of high-power AlGaN-based ultraviolet (UV) flip-chip high-voltage light-emitting diodes (LEDs) operating at 368 nm with an epitaxial indium tin oxide (ITO)/Al reflecting mirror and symmetry electrode layout. Metal-organic chemical vapor deposition (MOCVD) was used to grow an ITO thin film as a transparent electrode on the LED surface. At 365 nm, epitaxial ITO thin films exhibited a transmittance of up to 93.6%. Additionally, the epitaxial ITO/Al reflective mirror has a reflectance of 81.2% at 365-nm. To investigate the electrical characteristics, four types of HV-LED micro-cells were constructed with varying n-type mesa structures and p-type interconnect electrodes. We demonstrated a forward voltage (Vf) of 7.86 V at 350 mA with a 2 × 2 mico-cells high-voltage ultraviolet 368-nm flip-chip LED after optimising electrode structure and device process.

Highly Conductive and Visibly Transparent p-Type CuCrO2 Films by Ultrasonic Spray Pyrolysis.

The development of high-performing p-type transparent conducting oxides will enable immense progress in the fabrication of optoelectronic devices including invisible electronics and all-oxide power electronics. While n-type transparent electrodes have already reached widespread industrial production, the lack of p-type counterparts with comparable transparency and conductivity has created a bottleneck for the development of next-generation optoelectronic devices. In this work, we present the fabrication of delafossite copper chromium oxide p-type transparent electrodes with outstanding optical and electrical properties. These layers were deposited using ultrasonic spray pyrolysis, a wet chemical method that is fast, simple, and scalable. Through careful screening of the deposition conditions, highly crystalline, dense, and smooth CuCrO2 coatings were obtained. A detailed investigation of the role played by the deposition temperature and the cation ratio enabled the properties of the prepared layers to be reliably tuned, as verified using X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, Hall effect measurements, and electron and atomic force microscopies. We demonstrate record conductivities for solution-processed CuCrO2, exceeding 100 S cm-1, and we also obtained the highest value for two separate figures of merit for p-type transparent conducting oxides. These performances position solution-deposited CuCrO2 as the leading p-type transparent-conducting oxide currently available.

The Effect of B, Al, N, and P Impurities on the Electronic Structure of Si0.3Sn0.7Ge alloy: A First-Principles Approach

This study examines the effect of doping Si0.3Sn0.7Ge with an impurity element X (B, Al, N, or P) on the Sn site, using first-principle calculations based on the fully self-consistent Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). To treat several forms of chemical disorders of Si0.3Sn0.7Ge, X-doping was carried out by substituting small amounts of Sn with each element X, which gives rise to the alloy Si0.3Sn0.7-yXyGe. As the X content increases from y = 0.01 to 0.06, the Fermi level maintains its position in the conduction band edge. While the number of states at the Fermi level decreases. With 1% X impurity added to the alloy Si0.3Sn0.7-yXyGe, the number of carriers (electron and hole) states was generally enhanced. For the case of X = P, when compared to the parent material Si0.3Sn0.7Ge, an enhancement of 0.04 states/eV was observed. Due to the increase in the number of states, which indicates an improvement in thermopower, these alloys Si0.3Sn0.7-yXyGe are promising for application as n-type electrodes in a thermoelectric generator (TEG).

Birhythmicity, intrinsic entrainment, and minimal chimeras in an electrochemical experiment.

The coexistence of limit cycles in a phase space, so called birhythmicity, is a phenomenon known to exist in many systems in various disciplines. Yet, detailed experimental investigations are rare, as are studies on the interaction between birhythmic components. In this article, we present experimental evidence for the existence of birhythmicity during the anodic electrodissolution of Si in a fluoride-containing electrolyte using weakly illuminated n-type Si electrodes. Moreover, we demonstrate several types of interaction between the coexisting limit cycles, in part resulting in peculiar dynamics. The two limit cycles exhibit vastly different sensitivities with respect to a small perturbation of the electrode potential, rendering the coupling essentially unidirectional. A manifestation of this is an asymmetric 1:2 intrinsic entrainment of the coexisting limit cycles on an individual uniformly oscillating electrode. In this state, the phase-space structure mediates the locking of one of the oscillators to the other one across the separatrix. Furthermore, the transition scenarios from one limit cycle to the other one at the borders of the birhythmicity go along with different types of spatial symmetry breaking. Finally, the master-slave type coupling promotes two (within the experimental limits) identical electrodes initialized on the different limit cycles to adopt states of different complexity: one of the electrodes exhibits irregular, most likely chaotic, motion, while the other one exhibits period-1 oscillations. The coexistence of coherence and incoherence is the characteristic property of a chimera state, the two coupled electrodes constituting an experimental example of a smallest chimera state in a minimal network configuration.

Indium Tin-Doped Oxide (ITO) as a High Activity Water Oxidation Photoanode.

Photochemical water oxidation was carried out at a mesoporous nanoparticle film composed of indium tin-doped oxide (nanoITO). Annealing nanoITO at temperatures above 250 °C affects both conducting and semiconducting properties. Impressive photoelectrochemical activity was observed at this degenerate n-type semiconductor electrode, outperforming the traditional semiconductor titanium dioxide (TiO2) under the same conditions. In a 0.1 M HNO3 solution, the nanoITO electrode sustained photocurrents of 1.0 mA/cm2 at an Eapplied = 1.5 V vs saturated calomel electrode (SCE) (η = 0.55 V) under a 90 mW/cm2 UV illumination (375 nm). This activity is compared to ∼0.3 mA/cm2 with a traditional TiO2 electrode under the same potential and conditions. Evidence for oxygen generation in the photolysis experiments was quantified using the collector-generator method, and >70% photocurrent efficiency for O2 production was confirmed at this nanoITO photoanode.

Improved Reliability of AlGaN-Based Deep Ultraviolet LED With Modified Reflective N-Type Electrode

Cr/Al/Ti/Au stacks with two thicknesses of Al layers were employed as reflective n-type electrodes for 274 nm AlGaN-based flip-chip deep ultraviolet light-emitting diodes (DUV LEDs). Large bulges arose in the annealed n-type electrode with 120-nm-thick Al layer, resulting in cracks within the upper rugged SiO2 passivation layer after burn-in test. Sn atoms from solder paste migrated along the cracks and served as leakage current channels, which accelerated device degradation. In contrast, the annealed n-type electrode with 60-nm-thick Al layer retained uniform morphology. And the DUV LEDs with such n-type electrode exhibited good reliability and normalized optical power of 86.8% after burn-in test of 1000 h. This study provides insight into electrode defects related degradation behavior and helps to improve the reliability of AlGaN-based flip-chip DUV LEDs with reflective electrode.

First-principles investigation of the electronic and thermoelectric properties of SiGe doped with Sn and one percent B

Silicon-Germanium (SiGe) has recently attracted much interest as a room temperature thermoelectric (TE) material for converting heat into electrical output power. With the advantage of silicon being non-toxic, cost-effective, and abundant on earth, a silicon base TE material has a promising future. A first-principle calculation based on the fully self-consistent Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) to treat several forms of chemical disorders of SiGe by Sn-doping was carried out. In SiGe1-xSnx, as the Sn content increases the Fermi level shifts to the conduction band edge. Similarly, in Si1-xSnxGe, a high Sn content (x = 0.4 to 0.9) results in the Fermi level shifting to the conduction band edge. On the contrary, a low amount of Sn content (x = 0.1 to 0.3) causes the Fermi level to fluctuate between the conduction band and the valence band states. With the addition of 1% Boron impurity to the alloys Si1-xSnxGe and SiGe1-xSnx, the number of carriers (electron and hole) states was enhanced by 0.05 states/eV. This makes the alloys Si0.3Sn0.69B0.01Ge and SiGe0.4Sn0.59B0.01 promising for application as n-type electrodes in a thermoelectric generator (TEG).

Solution-processed and annealing-free zirconium acetylacetonate electron-selective contacts for efficient crystalline silicon solar cells

The interfaces between n-type silicon (n-Si) and metal electrode contact have enormous influences on the performance and stability of silicon solar cells. Recently, it has been proven that the carrier-selective contact (CSC) is an effective strategy to improve the device efficiency. Herein, a solution-processed and annealing-free zirconium acetylacetonate (ZrAcac) layer is used as an electron-selective contact for fabricating efficient crystalline silicon solar cell. This contact scheme enabled a reduction in both the contact resistivity and the work function at the interface between n-Si and Al, which can be attributed to the dipole formation at the contact interface induced by charge transfer. The application of this ZrAcac based contact was shown to consistently improve all device parameters reaching a maximum power conversion efficiency of 17.8% with a high fill factor of 81.1%, and greatly improve the device stability. This work demonstrated that the ZrAcac layer can provide sufficient energy alignment and enhanced carrier selectivity for efficient and stable photovoltaic devices.

Plasmonic Hydrogen Evolution at p-Type Semiconductor Electorode

The efficient control of the visible light driven hydrogen evolution reaction can be recognized as the one of the promising challenge for the sustainable society. It can be said that the wide-band semiconductor electrode is the promising material for the photo-energy conversion system. However, various semiconductor electrodes have the limitation to the ultraviolet region because of their wide band gap energy. Recently, plasmoic photoelectric conversion system, which is the combination of the plasmon active metal nano-structures with the semiconductor substrate, has been received much attention because the system shows the visible light response characters beyond the limitation of the limitation. In this system, the electrons excited in the metal structures injected into the conduction band of the n-type semiconductor and the remained holes are consumed through the oxidation reaction. Up to now, various plasmon-induced chemical reactions, even the water splitting, have been proposed. As our previous study, we have not only visualized the reaction active sites but also determined the reaction active species through the polymerization reactions of the conductive polymer. Although well-established systems have been reported, the direct control of the reduction reaction at the metal-semiconductor interface by the excited electrons has not been well examined. This is because the almost plasmonic photoconversion systems consist of the n-type semiconductor electrode and applied the generated holes to the reactions. In this study, we have tried to establish the plasmon-induced hydrogen evolution system by the introduction of the plasmon-active metal nano-structures into the p-type semiconductor substrate. By supporting the plasmonic structures, we have confirmed the photo-current generation under the visible light illumination.[1] Through the photocurrent measurements and the incident photon to current conversion efficiency obtained under different pH conditions, we have confirmed the unique pH dependence. In addition to these, we have also investigated the isotopic effect on the hydrogen evolution reaction to clarify the unique surface molecular process. Through the various photoelectrochemical measurements, we are sure that our plasmonic hydrogen evolution system could be one of the good candidate for future light energy conversion system. [1] D. Sato, H. Minamimoto, and K. Murakoshi, Chem. Lett., in press.