Strategies for high efficiency silicon solar cells

Abstract

ACKNOWLEDGMENTSI would like to thank my advisor Professor Fatima Toor for her productive feedback of my work and her support and encouragement of my project. I am grateful to have had the opportunity to work in her research group. I would also like to thank my coworker Wenqi Duan for all of her help and support in the fabrication process of my project.iii ABSTRACT The fabrication of low cost, high efficiency solar cells is imperative in competing with existing energy technologies. Many research groups have explored using III-V materials and thin-film technologies to create high efficiency cells; however, the materials and manufacturing processes are very costly as compared to monocrystalline silicon (Si) solar cells. Since commercial Si solar cells typically have efficiencies in the range of 17-19%, techniques such as surface texturing, depositing a surface-passivating film, and creating multi-junction Si cells are used to improve the efficiency without significantly increasing the manufacturing costs. This research focused on two of these techniques: (1) a tandem junction solar cell comprised of a thin-film perovskite top cell and a wafer-based Si bottom cell, and (2) Si solar cells with single-and double-layer silicon nitride (SiNx) anti-reflection coatings (ARC). The perovskite/Si tandem junction cell was modeled using a Matlab analytical program. The model took in material properties such as doping concentrations, diffusion coefficients, and band gap energy and calculated the photocurrents, voltages, and efficiencies of the cells individually and in the tandem configuration. A planar Si bottom cell, a cell with a SiNx coating, or a nanostructured black silicon (bSi) cell can be modeled in either an n-terminal or series-connected configuration with the perovskite top cell. By optimizing the bottom and top cell parameters, a tandem cell with an efficiency of 31.78% was reached. Next, planar Si solar cells were fabricated, and the effects of single-and doublelayer SiNx films deposited on the cells were explored. Silicon nitride was sputtered onto planar Si samples, and the refractive index and thicknesses of the films were measured iv using ellipsometry. A range of refractive indices can be reached by adjusting the gas flow rate ratios of nitrogen (N2) and argon (Ar) in the system. The refractive index and thickness of the film affect where the minimum of the reflection curve is located. For Si, the optimum refractive index of a single-layer passivation film is 1.85 with a thickness of 80nm so that the minimum reflection is at 600nm, which is where the photon flux is maximized. However, using a double-layer film of SiNx, the Si solar cell performance is further improved due to surface passivation and lowered surface reflectivity. A bottom layer film with a higher refractive index passivates the Si cell and reduces surface reflectivity, while the top layer film with a smaller refractive index further reduces the surface reflectivity. The refractive indices and thicknesses of the double-layer films were varied, an...

Investigation of the impact of different ARC layers using PC1D simulation: application to crystalline silicon solar cells

“…Although from 425 to 640 nm the EQE of Si 3 N 4 ARC (Black) curve is slightly greater than EQE of Si 3 N 4 ARC (Red) curve, from 640 nm and overall the EQE is showing the best result for the surface-passivated curve (Red). It is adequate to say, surface passivation increases the overall EQE of solar cell by reducing the number of dangling bonds thus reducing the recombination effects [34,35].…”

Plasma etching: a strategy to enhance the photovoltaic conversion efficiency of ultrathin CdTe solar cells

“…The QE response of the etched device is better than that of the un-etched device at short wavelength. According to the numerical simulation results proposed by Song [23], the relatively heavily doped devices have a stronger built-in electric field, thus the cells with high carrier concentration exhibit a higher QE response at short wavelength. Furthermore, McCandless [14] proposed that the CdTe surface oxides formed during CdCl 2 treatment could retard the delivery of Cu species into CdTe, minimizing the doping effect.…”

On the Performance Limits for Mono Crystalline Silicon Solar Cells: A Comparative Study

“…When the number of impurities is increased, the mobility of the charged carriers (electrons & holes) decreases, consequently the performance of Si solar cell decreases [21]. Experimentally, the maximum efficiency, for absorber doping concentration 2x10 15 cm -3 , was found to be 22.1% [22]. The values of the performance parameters for low and high-doped absorber layers can be seen in Table 4.…”