In this work, we demonstrate an improved method to simulate the characteristics of multijunction solar cell by introducing a bias-dependent luminescent coupling efficiency. The standard two-diode equivalent-circuit model with constant luminescent coupling efficiency has limited accuracy because it does not include the recombination current from photogenerated carriers. Therefore, we propose an alternative analytical method with bias-dependent luminescent coupling efficiency to model multijunction cell behavior. We show that there is a noticeable difference in the J-V characteristics and cell performance generated by simulations with a constant vs. bias-dependent coupling efficiency. The results indicate that introducing a bias-dependent coupling efficiency produces more accurate modeling of multijunction cell behavior under real operating conditions.
Indium-doped zinc oxide nanowires grown by vapor-liquid-solid technique with 1.6 at. % indium content show intense room temperature photoluminescence (PL) that is red shifted to 20 meV from band edge. We report on a combination of nanowires and nanobelts-like structures with enhanced optical properties after indium doping. The near band edge emission shift gives an estimate for the carrier density as high as 5.5 Â 10 19 cm À3 for doped nanowires according to Mott's critical density theory. Quenching of the visible green peak is seen for doped nanostructures indicating lesser oxygen vacancies and improved quality. PL and transmission electron microscopy measurements confirm indium doping into the ZnO lattice, whereas temperature dependent PL data give an estimation of the donor and acceptor binding energies that agrees well with indium doped nanowires. This provides a non-destructive technique to estimate doping for 1D structures as compared to the traditional FET approach. Furthermore, these indium doped nanowires can be a potential candidate for transparent conducting oxides applications and spintronic devices with controlled growth mechanism. V
In this study, the growth of three important semiconductor nanowires, Zinc Oxide, Indium Oxide and Cadmium Sulfide nanowires using the vapor-liquid-solid (VLS) method has been investigated. Different growth recipes with different growth parameters were incorporated to synthesize high quality and long NWs. It attempts to provide precise growth recipes which lead to high quality of nanowires. The effect of different growth conditions such as growth temperature, carrier gas flow, presence of metal catalyst and growth time has been investigated. Also, to evaluate the crystal quality of the nanowires, photoluminescence (PL) spectra of the as grown nanowires were investigated.
In this work, the luminescent coupling (LC) effects on photocurrent‐matched and photocurrent‐mismatched multijunction solar cells are investigated from fundamental physical theories and modeled by spice circuit simulations. It is demonstrated that the voltage increase of a photocurrent‐matched cell is constant in the voltage range from maximum power point to open‐circuit point, and this increase depends on the number of junctions and LC efficiency. Through the LC effects, it is shown that at the operation point of a photocurrent‐matched double‐junction (2J) cell, the photons from radiative recombination (which is the dominated recombination mechanism) of the top junction, is not wasted, but instead couples downward to the bottom junction, doubles the second junction's recombination current density, and leads to a significant voltage increase of kT/q lntrue(2true) = 17.8 mV. The same physics extended to a photocurrent‐matched triple‐junction (3J) cell with an increase of kT/q lntrue(2×3true) = 46 mV and n‐junction cell with an increase of kT/q lntrue(n!true). Furthermore, it is shown that the theoretical prediction matches the circuit simulations exactly, and this tens of millivolts enhancement in voltage increases with increasing the number of junctions, consequently leads to a greater improvement in cell performance.
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