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A popular substance in the MXene family, titanium carbide (Ti

CdS has been known to be one of the best junction partners for Cu(In,Ga)Se2 (CIGS) in CIGS solar cells. However, the use of thick CdS buffer decreases the short-circuit current density of CIGS solar cells. There are two obstacles that limit the use of ultrathin CdS. The first is plasma damage to CIGS during the preparation of transparent conducting windows and the second is a low shunt resistance due to the direct contact between the window and CIGS via pinholes in the thin CdS buffer. In other words, to avoid plasma damage and shunt paths, we may have to use a CdS buffer that is thicker than necessary to form a high-quality CdS/CIGS junction. This work aims to determine how thin the CdS buffer can be employed without sacrificing device performance while also eliminating the above two obstacles. We investigate the effect of CdS thickness on the performance of CIGS solar cells with silver nanowire-based window layers, which can eliminate both obstacles. An approximately 13 nm thick CdS buffer allows us to achieve high short-circuit current density and fill factor values. To attain an even high open-circuit voltage, an additional CdS buffer with a thickness of 13 nm is needed. The data from this study imply that an approximately 26 nm thick CdS buffer is sufficient to form a high-quality CdS/CIGS junction.

We study the electronic and optoelectronic properties of a broken-gap heterojunction composed of SnSe2 and MoTe2 with gate-controlled junction modes. Owing to the interband tunneling current, our device can act as an Esaki diode and a backward diode with a peak-to-valley current ratio approaching 5.7 at room temperature. Furthermore, under an 811 nm laser irradiation the heterostructure exhibits a photodetectivity of up to 7.5 × 1012 Jones. In addition, to harness the electrostatic gate bias, Voc can be tuned from negative to positive by switching from the accumulation mode to the depletion mode of the heterojunction. Additionally, a photovoltaic effect with a fill factor exceeding 41% was observed, which highlights the significant potential for optoelectronic applications. This study not only demonstrates high-performance multifunctional optoelectronics based on the SnSe2/MoTe2 heterostructure but also provides a comprehensive understanding of broken-band alignment and its applications.

The instability of van der Waals (vdW) materials leads to spontaneous morphological and chemical transformations in the air. Although the passivation of vdW materials with other resistive materials is often used to solve stability issues, this passivation layer can block carrier injection and thus interfere with charge transfer doping. In this study, a facile method is proposed for n-doping and mediation of Se vacancies in tungsten diselenide (WSe2) by poly(vinylpyrrolidone) (PVP) coating. The major carrier type of the PVP-coated WSe2-based field-effect transistor (FET) was converted from hole (p-type) to electron (n-type). Furthermore, the vacancy-induced interface trap density was reduced by approximately 500 times. This study provides a practical doping and passivation method for the van der Waals materials, as well as a comprehensive understanding of the chemical reaction and electronic transport in these materials.

Transparent conducting electrodes are essential components in various optoelectrical devices. Although indium tin oxide thin films have been widely used for transparent conducting electrodes, silver nanowire network is a promising alternative to indium tin oxide thin films owing to its lower processing cost and greater suitability for flexible device application. In order to widen the application of silver nanowire network, the electrical conductance has to be improved while maintaining high optical transparency. In this study, we report the enhancement of the electrical conductance of silver nanowire network transparent electrodes by copper electrodeposition on the silver nanowire networks. The electrodeposited copper lowered the sheet resistance of the silver nanowire networks from 21.9 Ω/□ to 12.6 Ω/□. We perform detailed X-ray diffraction analysis revealing the effect of the amount of electrodeposited copper-shell on the sheet resistance of the core-shell(silver/copper) nanowire network transparent electrodes. From the relationship between the cross-sectional area of the copper-shell and the sheet resistance of the transparent electrodes, we deduce the electrical resistivity of electrodeposited copper to be approximately 4.5 times that of copper bulk.

Silver nanowire (AgNW) electrodes have been employed in solar cells as transparent conducting electrodes (TCEs). When a AgNW electrode is used as a network-type TCE in solar cells, photogenerated charge carriers must laterally travel to reach AgNW networks. If the empty space of the network is larger than the lateral collection length of the charge carriers ( L lc ), a significant fraction of the charge carriers will be lost. Therefore, determination of L lc is essential for choosing and/or designing a suitable network for solar cells. Here, we develop a method to relate the lateral photocurrent measured from a specially designed pattern to the L lc value. We apply this method to Cu(In,Ga)Se2 thin-film solar cells with AgNW TCEs. The L lc value was determined to be ≈ 26 μm in the CdS/CIGS/Mo structure under 1-sun illumination. The measured lateral collection length is much larger than the normal spacing between AgNWs, indicating a high lateral collection efficiency in AgNW TCE-based CIGS thin-film solar cells.

We study the electronic and optoelectronic properties of a broken-gap heterojunction composed of SnSe

We demonstrate the ability to fabricate high-quality nanoscale electrical contact between silver nanowires (AgNWs) and underlying semiconducting layers in chalcogenide thin film solar cells. AgNW electrodes have attracted many interests due to their ability for low temperature solution processing. However, they have a drawback that the interfacial defects can be generated between AgNWs and underlying rugged semiconductor layers making it difficult to form high-quality junction. To enhance the junction properties, conducting matrix layers have been adapted. Yet, the issues regarding the AgNW/semiconductor junction have not been fully resolved. We developed a facile method to form robust nanoscale contact between AgNWs and semiconducting thin films to achieve high performance chalcogenide thin film solar cells. The method is to deposit an ultra-thin semiconductor layer on devices using aqueous chemical bath deposition. The chemical bath deposition has capability to effectively fill even nanoscale gap and to form chemically stable bonds as well as an intimate junction. As a proof of concept, a CdS layer (~ 10 nm) was deposited using the chemical bath deposition on Cu(In,Ga)Se2 (CIGS) solar cells with a structure of AgNW/CdS/CIGS/Mo/Glass. We also identified that the key factor governing the current-voltage characteristic is the electrical contact between the AgNW electrode and the CdS buffer layer in CIGS thin film solar cells. The power conversion efficiency of the CIGS cell was dramatically improved from 4.9% to 14.2% owing to high-quality AgNW-CdS electrical contact produced by chemical bath deposition of the additional CdS layer as thin as 10 nm.

We quantitatively and analytically investigate the properties of buffer/window junctions and their effects on the energy band alignment and the current-voltage characteristics of Cu(In,Ga)Se2 (CIGS) thin film solar cells with solution processed silver nanowire (AgNW) composite window layers. AgNWs are generally embedded in a moderately conductive matrix layer to ensure lateral collection efficiency of charge carriers photogenerated in the lateral gaps present between AgNWs. Studies on the junctions between a buffer and AgNW-composite window layers and their effects on the performances of CIGS thin film solar cells have seldom been addressed. Here, we show that solution processed AgNW-composite window layers could induce defect states at the buffer/window interface, resulting in poor energy band alignment impeding carrier transport in the solar cells. On the basis of our analysis, we suggest an analytical expression of nmatrixDi2≥3.46×10−5e cm to avoid losses in the power conversion efficiency of the solar cells. nmatrix is the carrier concentration in a matrix layer embedding AgNWs, Di is the negative defect density at the buffer/window interface, and e is the relative dielectric constant of the matrix layer embedding AgNWs.

Silver nanowire (AgNW) networks have demonstrated high optical and electrical properties, even better than those of indium tin oxide thin films, and are expected to be a next-generation transparent conducting electrode (TCE). Enhanced electrical and optical properties are achieved when the diameter of the AgNWs in the network is fairly small, that is, typically less than 30 nm. However, when AgNWs with such small diameters are used in the network, stability issues arise. One method to resolve the stability issues is to increase the diameter of the AgNWs, but the use of AgNWs with large diameters has the disadvantage of causing a rough surface morphology. In this work, we resolve all of the aforementioned issues with AgNW TCEs by the electrodeposition of Ag onto as-spin-coated thin AgNW TCEs. The electrodeposition of Ag offers many advantages, including the precise adjustment of the AgNW diameter and wire-to-wire welding to improve the junction conductance while minimizing the increase in protrusion height because of the overlap of AgNWs upon increasing the diameter. In addition, Ag electrodeposition on AgNW TCEs can provide higher conductance than that of as-spin-coated AgNW TCEs at the same transparency because of the reduced junction resistance, which generates a superior figure of merit. We applied the electrodeposited (ED) AgNW network to a Cu(In,Ga)Se2 thin-film solar cell and compared the device performance to a device with a standard sputtered transparent conducting oxide (TCO). The cell fabricated by the electrodeposition method showed nearly equal performance to that of a cell with the sputtered TCO. We expect that ED AgNW networks can be used as high-performance and robust TCEs for various optoelectronic applications.

Recently, pneumatic flow control valves having high responses have been developed and are being wide-ly used. It is very important to know the characteristics of the valves for structuring pneumatic servo systems. The method for measuring the dynamic characteristics of the valves has yet to be established, because of the difficulty of the unsteady flow rate measurements of the compressible fluids.In this study, simple methods to measure the input-output characteristics and the frequency characteristic of the flow control valves using an isothermal chamber are proposed. The isothermal chamber is a chamber in which steel wool is stuffed into a normal chamber to make the heat transfer area larger, and could almost simulate an isothermal condition. Therefore, the flow rate could be obtained only by measuring the pressure in the chamber. Two types of servo valves and proportional control valves were tested using the proposed method. At the same time, the spool displacement of the valves were measured. The effectiveness of the proposed method was confirmed by comparing the results obtained from the proposed method and the spool displacement of the valves. In addition, it could be clarified that the frequency response could be measured up to a frequency of 140Hz by this method.

In pneumatically actuated servo mechanisms, accurate and speedy positioning as an electric servo has been regarded as being difficult because of the disturbance caused by fluctuations in the friction force and air compressibility been carried out. Therefore, studies on positioning in a pneumatic servo have concentrated regarding the compensation of nonlinearity according to air compressibility and friction force. In this study, an servo table mounted with externally pressurized air bearings is proposed to compensate for the friction force that has a serious effect on the accurate positioning in the vicinity of the reference dis-placement. The table is driven by two servo valves operating at nearly 100Hz for speedy positioning. As a result, this study was able to confirm that the friction force on this table was nearly zero, therefore, 10μm accuracy could be obtained easily by using this table at positioning and in the case of Ref. 2mm, the table was converged to it in 16ms within an accuracy of ±10μm.

Until recently, a pneumatic cylinder was driven by 2 port electronic valves or speed controllers for point-to-point control but now a proposition and analyze for pneumatic servo mechanism has made progress due to improvements in the performance of control valves and a price decrease in PCs.For point to point as a meter-out, a change in the dynamic characteristics of cylinders resulting from a change in the parameter of the driving system was reported by experiments and analytical studies and temperature changes was known as an important parameter affecting its dynamic characteristics.For the driving systems incorporating a servo mechanism, a variation in the response of a servo system by parameter changes could make an estimation using linearization in the vicinity of an operating point but temperature changes in a cylinder being assumed to be polytropic and it is not known that an actual state of temperature changes during servo driving.This study measured the practice transient temperature changes of air in a cylinder during servo driving using an indirect method and proposed a nonlinear mathematical model including temperature changes for analyzing the pneumatic servo driving system.

To drive a pneumatic cylinder, meter-out circuit is used in many cases, since time to move the piston is constanteven if the load is changed. That is, the meter-out restriction method realized velocity control. However thisprinciple of velocity control has not been explained sufficiently. The purpose of this study is to make clear thevelocity control mechanism. In order to clarify this mechanism, nondimensional equations and their responses are presented. Consequently six parameters governing the cylinder response are obtained. As a result, by drawing theblock diagram of cylinder system, it is found that the compliance of a cylinder makes the feed back loop in cylinder velocity and the flow characteristics of restriction in choking compensates the constant velocity for changing a loadforce.

In case of charging of or discharging from a chamber with a compressible fluid, the temperature change of fluid in chamber affects pressure change as a result of convective heat transfer within the chamber wall. Therefore, in a pressure control system using a compressible fluid, the temperature change has an effect on the control characteristics of the pressure.This study analyzed how a temperature change, owing to heat transfer with the chamber wall, can affect the control characteristics of the pressure in it with a normal chamber and isothermal chamber. An isothermal chamber is a chamber that can almost realize isothermal conditions due to the larger heat transfer area and heat transfer coefficient by filling it with steel wool. As a result, this study could confirm that a slight temperature change can affect the pressure control characteristics and dynamic characteristics of pressure response, making it better by a suppression of the temperature change in a chamber.

In this study, methods for the characteristics measurement of pneumatic elements using isothermal chamber, the methods for the flow rate and dynamic characteristic measurement of pneumatic control valve, are proposed. An isothermal chamber is a chamber in which the steel wool is stuffed and isothermal condition can almost be realized. Therefore, the instantaneous flow rate could be measured only from the pressure response using the state equation of gas. Effectiveness and simplicity of the proposed method are confirmed by comparing the measured results obtained by proposed methods with the methods defined JIS and the ISO standards.