Additional Passivation Layer Research Articles

Strategic approach for achieving high indoor efficiency of perovskite solar Cells: Frustration of charge recombination by dipole induced homogeneous charge distribution

Indoor-light harvesting-technology based on perovskite solar cells have attracted significant attention owing to their promising photovoltaic properties as indoor power generators. We investigated the effect of interfacial dipoles on the performance of perovskite solar cells in low-intensity indoor light environments. Interfacial dipoles were controlled by inserting different polar layers with different molecular dipole moments (BCP, QPPO and QDPPO) on top of electron transport layers (ETLs). Significantly improved uniformity of interfacial dipoles, in the QDPPO layer, effectively reduced charge recombination and enabled persistent fill factors (FF’s) under low-intensity light environments. Perovskite solar cells based on QDPPO exhibited indoor power density (iPD) and indoor power conversion efficiency (iPCE) of 65.63 μW/cm2 and 27.49 % under 800 lux LED, which were further enhanced up to 88.09 μW/cm2 and 36.90 % by employing additional passivation layer under 800 lux LED. Finally, using QDPPO, we successfully demonstrated perovskite photovoltaic mini-modules with a high power output of 2.4 mW under a 1,000 lux halogen, which can be applied in Internet-of-Things sensors under indoor light conditions.

Highly tunable and strongly bound exciton in MoSi2N4 via strain engineering

Motivated by the recently synthesized layered material MoSi2N4, we investigated excitonic response of quasiparticle of monolayer MoSi2N4 by using G0W0 and Bethe-Salpeter equation (BSE) calculations. With a dually sandwiched structure consisting of a central MoN2 layer analogue of 2H-MoS2 capped with silicon-nitrogen (SiN) honeycomb outer layers, MoSi2N4 possesses frontier orbitals confined at the central MoN2 layer with similar sub-valley at K-point as 2H-MoS2. The valley splitting (~130 meV) due to the spin-orbital coupling (SOC) gives rise to a doublet in the spectrum. Excitons in MoSi2N4 shows a strong binding energy up to 0.95 eV with the optical bandgap of 2.44 eV. Both electronic and optical gaps are highly sensitive to tensile strains and become redshift albeit a marginal change of exciton binding energy. With the protection of capped SiN layers, quantum confined excitons in MoSi2N4 without the need of additional passivation layer like BN would provide a bright new platform for robust emission with partially screened disturbance from environment.

Electrochemical Corrosion Investigations on Binary and Ternary Zinc Alloy Coatings using Gel Electrolytes

Novel agar‐based test electrolytes are used to perform electrochemical corrosion investigations on ZnFe and ZnNi binary as well as ZnFeMo ternary zinc coatings. The objectives of the electrochemical investigations include the characterization of the corrosion behavior, the description of the protective effect of the coatings as well as the investigation of the layer formation and degradation under artificial aging. ZnFe and ZnFeMo coatings are applied with varying iron content as well as an additional passivation layer, respectively, to study the effect on corrosion resistance. The results show that the protective effect of the coatings is not negatively influenced by different iron contents or the addition of molybdenum. Additional passivation of the ZnFe‐containing coatings by means of a passivating agent leads to a significant improvement in the protective effect. Artificial aging leads to a slight degradation of the additional passivation layer whereas coatings without post‐treatment enhance their protective effect by the formation of corrosion product layers.

Real Impacts of Ligand-Capped Nanocrystals in Perovskite Solar Cells

Perovskite solar cells (PSCs) has been reached the certified power conversion efficiency (PCE) of 25.2 % in 2019. They are having received large attention because of their superior optoelectronic properties (such as high charge carrier mobility, tunable bandgap, high absorption coefficient) and even the cost-effective process.In the latest fabrication process for high-efficiency PSCs, surface-defect engineering of perovskite film has attracted tremendous attention. Because, the control of surface-defects can play a critical role in grain boundaries of perovskite, and interfaces between perovskite and charge transport layer, leading to PSCs with further improved photovoltaic (PV) performance and long-term stability. There are many exertion for reducing surface-defects state densities of perovskite film by applying an additional passivation layer, for instance cross-linked molecules and two-dimensional (2D) materials (2D-perovskite, graphene, and MoS2) at surface of perovskite film.Most recently, perovskite nanocrystals (NCs) are being investigated as an additional layer for high-efficiency PSCs owing to anticipation of their multifunctional properties including high light-harvesting properties, efficient charge transport by carrier cascade effect, and surface passivation effect. However, it seems to remain under question whether these functions are related to the light-harvesting, suitable band alignment, and surface passivation for PSCs, due to ligand capped NCs.In this study, we investigated that the functions of NCs layer in PSCs with various NCs capped same ligand. To confirm the effects of NC layer in PSCs, we fabricated n-i-p planar devices, which follow FTO/c-TiO2/Perovskite/NC layer/Spiro-OMeTAD/Au structure with three kinds of NCs (CsPbBr3, CsPbI3, and InP). All these NCs have different electrical and optical properties, but nevertheless the devices with each NC layer showed similarly improved PV performance.In analysis results of each function of the NC layer, there were no light-harvesting effects by all NCs layer due to high absorption coefficient and sufficient thickness of perovskite film. In addition, NC layer could not work as a carrier cascade layer at the interface between the perovskite film and hole transport layer due to poor electrical properties of capping ligand. Finally, the NC layer affected only on the surface passivation of perovskite film, and furthermore we found that Oleylamine (OLA) ligand of the NCs was a major cause of the surface passivation effect. We believe that the optimization of the surface passivation effect of fatty amine ligands can further improve the PV performance of PSCs.

Tuning the Threshold Voltage of a SnO2 Nanowire Transistor Through Microwave-assisted Metal-oxide Reduction

Numerous studies have suggested that n-type semiconductor nanowires provide excellent electrical properties, as well as notable mechanical flexibility, to electronic devices. However, the dynamic threshold voltages of these devices significantly reduce our ability to produce robust and stable transistors consistently. In this study, tuning of the threshold voltage (Vth) of a SnO2 nanowire transistor was investigated by using a household microwave oven to control the oxygen vacancies on the surface of the SnO2 nanowire. The extent of the negative shift in the Vth of the SnO2 nanowire transistor was controlled by varying the applied power and time of the microwave irradiation in the atomic weight percentage of oxygen on the SnO2 nanowire’s surface. A Vth shift of −0.42 ± 0.69 to −4.25 ± 0.52 V was observed when the applied power was varied from 200 to 1000 W while a shift of −0.46 ± 0.27 to −9.87 ± 0.67 V occurred for microwave irradiation times of 20 to 80 s. Thus, the Vth could be tuned over a wide range by controlling the irradiation time while it could be fine-tuned using the applied power. The Vth characteristics of the controlled SnO2 nanowire transistors were monitored over 20 days in a normal atmosphere and were observed to remain unchanged. Notably, these characteristics were achieved without the application of an additional passivation layer. This method, which is simpler and more effective than other existing methods, can be readily applied for the production of SnO2 nanowire transistors.

An aluminium nitride based multilayer structure for Love mode surface acoustic wave devices

Love mode surface acoustic wave (SAW) devices are very useful for sensing in liquid environments. Earlier work on such devices mainly made use of zinc oxide (ZnO) thin films on silicon (Si) or silicon dioxide (). However, using them for sensing still required protection from contamination from zinc (Zn) in the form of some additional passivation layer. In this work, the objective has been to study an aluminium nitride (AlN)-based multilayer structure that is able to generate SAW Love modes very efficiently. A layer of on top of the AlN layer does the trick. A 3D finite element method simulation analysis of the proposed structure () is accordingly performed, and phase velocities, electromechanical coupling coefficients and frequency shift due to mass loading are simulated as a function of the normalized thicknesses of AlN and films. It is shown that the optimal normalized thickness identified to be = 0.18, = 0.45 with AlN c-axis orientation of and the maximum value of the electromechanical coupling coefficient = 0.58% can be achieved. Even though the value of is comparable to ZnO-based Love mode devices, the phase velocity is 1.5 times higher (5530 m s−1 compared to 3652 m s−1). Equally importantly, it is seen that the frequency shift due to mass loading of deionized water (the AlN-based multilayer Love mode sensor) is much higher for that using the ZnO-based multilayer Love mode sensor.

Effect of Metal Capping on the Stability of Amorphous Si-Zn-Sn-O Thin Film Transistor by Suppressing Ambient Effect.

By adopting metal capping layer (MC layer), electrical properties, such as field effect mobility, on current, and subthreshold swing showed enhanced characteristics with 24.996 cm²/Vs, 2.1×10-4 and 0.34 V/decade, respectively. In addition, the stability of the negative bias thermal stress (NBTS) against the ambient environment has been shown to be enhanced by the MC layer which acts like passivation layer. Without additional passivation layer, MC layer alone sufficiently inhibited the ambient effect to show low threshold voltage shift of 0.21 V compared with 0.89 V of conventional TFT. MC layer structure, enhancing the electrical characteristic and stability, had the advantages of a process that was much simpler than conventional process for high performance and stability.

Passivation capability of carbon black layers for screen-printed battery applications with Ag current collectors

Screen-printed thin-film batteries comprise current collectors typically realised with commercially available conductive silver inks primarily designed for non-critical printed electronics applications. The avoidance of electrochemical interaction of metallic silver with the respective battery chemistry requires printing of an additional passivation layer. The wide range of printing inks available makes it difficult for researchers to select and qualify battery specific inks that ensure a long-life cycle without limitation of relevant battery performance parameters. This study presents a novel method to quantify the passivation capability of carbon black passivation layers for silver current collectors in 6.0 M potassium hydroxide and 5.8 M zinc chloride aqueous electrolyte solutions. Cyclic voltammetry is used to determine possible electrochemical interaction of passivated current collectors with the electrolyte media which constitute battery performance degrading parasitic side reactions. An innovative approach based on Faraday’s law of electrolysis is presented to transform cyclic voltammogram curve progressions into comparable numerical values. The mathematical approach allows quantitative comparison of individually fabricated passivation layers with respect to their passivation capability instead of interpreting a large number of cyclic voltammograms.

Hydrophobic Microfiber Strain Sensor Operating Stably in Sweat and Water Environment

AbstractFiber‐based wearable healthcare sensing devices that can monitor the health status of the human body in real time can be affected by sweat from the human body or water from the outside, which may cause the sensor to malfunction. In this study, it is investigated how the fiber strain sensor can operate stably without being affected by sweat or water, even if no additional passivation layer is formed on the outside of fibers applicable to wearable healthcare sensors. The resistance values ​​of the microfiber strain sensor are monitored in real time with the movement of the elbow and knee wraps stitched with a polyurethane (PU)–tin oxide (SnO2)–carbon nanotube (CNT) composite microfiber. The PU used as a matrix plays a role of naturally increasing or decreasing the fiber according to the movement of the elbow or knee of the body. The CNTs embedded in a PU matrix can monitor the angular movement of the elbow and knee by measuring the changes in electrical resistance. The (1H,1H,2H,2H‐heptadecafluorodec‐1‐yl) phosphonic acid‐coated SnO2 embedded in a PU prevents sweat and water from entering the fiber. This allows to precisely detect elbow and knee movements stably in an external environment exposed to sweat or water.

Improvement in IBC-silicon solar cell performance by insertion of highly doped crystalline layer at heterojunction interfaces

By inserting a thin highly doped crystalline silicon layer between the base region and amorphous silicon layer in an interdigitated back-contact (IBC) silicon solar cell, a new passivation layer is investigated. The passivation layer performance is characterized by numerical simulations. Moreover, the dependence of the output parameters of the solar cell on the additional layer parameters (doping concentration and thickness) is studied. By optimizing the additional passivation layer in terms of doping concentration and thickness, the power conversion efficiency could be improved by a factor of 2.5%, open circuit voltage is increased by 30 mV and the fill factor of the solar cell by 7.4%. The performance enhancement is achieved due to the decrease of recombination rate, a decrease in solar cell resistivity and improvement of field effect passivation at heterojunction interface. The above-mentioned results are compared with reported results of the same conventional interdigitated back-contact silicon solar cell structure. Furthermore, the effect of a-Si:H/c-Si interface defect density on IBC silicon solar cell parameters with a new passivation layer is studied. The additional passivation layer also reduces the sensitivity of output parameter of solar cell to interface defect density.

Periodic nanostructures on unpolished substrates and their integration in solar cells

We present a novel fabrication process based on laser interference lithography, lift-off and reactive ion etching, which allows us to fabricate periodic nanostructures on photovoltaic substrates with an average root mean square (RMS) roughness of 750 nm. We fabricate nanostructures on unpolished crystalline silicon substrates, which reduces their reflectance 30% as fabricated. When an additional passivation layer is deposited, the light trapping grows, achieving a reflectance reduction of 60%. In addition, we have successfully integrated the nanostructured substrates in silicon wafer–based solar cells following standard processes, achieving a final efficiency of 15.56%.

Passivation Effect of Diamond-Like Carbon Films for Organic Light-Emitting Diodes

We have studied organic light-emitting devices (OLEDs) with double-layered inorganic molybdenum trioxide (MoO3)/diamond-like carbon (DLC) as passivation films. The initial device characteristics were identical to those of devices without a passivation film, namely, the maximum luminance and electro luminescence (EL) efficiency were 15,000 cd/m2 and 1.9 lm/W, respectively. However, in the device without a 20 nm MoO3 inorganic film, the device durability was markedly lower than that of the device with a double-layered structure. By adding MoO3 as an additional passivation layer, plasma damage in the peripheral region of the organic layer was markedly reduced, and the resultant device durability was improved significantly.