We demonstrate self-sustaining electrical oscillations with frequency of MHz range based on out-of-plane voltage-triggered switching in VO2 thin films grown on conductive layers. VO2 films deposited by a reactive sputtering method at a low temperature of 250 °C on conductive TiN layers showed thermally induced out-of-plane insulator-metal transition with two orders of change in resistance. By applying dc voltage to the layered device in a point contact configuration, self-sustaining electrical oscillations were triggered and the highest frequency of 9 MHz was achieved. Dependence of the frequency on the film thickness, as well as on the source voltage and on the series resistance, was examined in order to clarify the oscillation mechanism and the factors that affect the frequency. The oscillation frequency, which is dominated by recovering time from metallic to insulating state, decreased with increasing film thickness, indicating that the resistance of VO2 film determines the time constant for the recovery path. Self-sustaining oscillation phenomena achieved in point contact devices has great potential for applications in MHz band generators and micro-inverters.
In this study, copper bismuth oxide (CuBi2O4) absorber-based thin film heterojunction solar cell structure consisting of Al/FTO/CdS/CuBi2O4/Ni has been proposed. The proposed solar cell device structure has been modeled and analyzed by using the solar cell capacitance simulator in one dimension (SCAPS-1D) software program. The performance of the proposed photovoltaic device is evaluated numerically by varying thickness, doping concentrations, defect density, operating temperature, back metal contact work function, series and shunt resistances. The current density–voltage behaviors at dark and under illumination are investigated. To realize the high efficiency CuBi2O4-based solar cell, the thickness, acceptor and donor densities, defect densities of different layers have been optimized. The present work reveals that the power conversion efficiency can be enhanced by increasing the absorber layer thickness. The efficiency of 26.0% with open-circuit voltage of 0.97 V, short-circuit current density of 31.61 mA/cm2, and fill-factor of 84.58% is achieved for the proposed solar cell at the optimum 2.0-μm-thick CuBi2O4 absorber layer. It is suggested that the p-type CuBi2O4 material proposed in the present study can be employed as a promising absorber layer for applications in the low cost and high efficiency thin-film solar cells.
In this work, the photovoltaic outputs of the lead-free FASnI 3 -based perovskite solar cells are discussed by using Solar Cell Capacitance Simulator in One Dimension. The device outputs estimated theoretically in this study are almost equal to the experimental results, thereby verifying accuracy of this simulation. To find the decent electron transport layer (ETL), herein, various ETLs are presented instead of C 60 /BCP in the experimental FASnI 3 -based perovskite solar cell (PSC). The designed FASnI 3 PSC utilizing niobium pentoxide (Nb 2 O 5 ) as an ETL with an appropriate band alignment and a low lattice mismatch at FASnI 3 /ETL interface provides better efficiency by decreasing recombination at front side. The performances of the proposed PSC are also measured by altering the thickness and doping of ETL and absorber, interface defects, and series and shunt resistances. Furthermore, this paper reports the calculation of recombination coefficients at absorber/ETL interface, depletion region, and quasi-neutral region. An improved efficiency of 22.24% is evaluated at optimized thicknesses of 100 nm for HTL, 500 nm for absorber, 50 nm for ETL, and 50
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