Performance enhancement of iii-v multiple-quantum-well photovoltaic devices employing light-harvesting nanohole assembly

Abstract

The thesis focuses on the optimum structural parameters for light-trapping in quantum well solar cells and compares their overall performance with standard single-junction solar cells. There are a variety of structures that facilitate light-trapping, among which nanostructure holes fabricated on the surface of solar cells have been considered in this work. The principle topics addressed in this thesis are 1) assessment of light absorption in periodic and random nanohole structures using FDTD (finite-difference time-domain) tool, 2) an implementation of appropriate physics and methodology for device performance of quantum-well solar cells, 3) exploration of device design issues that will yield the maximum solar conversion efficiency. In this context, we concentrated on the single-junction GaAs cells and AlGaAs/GaAs multiple quantum well solar cells as GaAs cells can achieve high efficiencies due to their near-optimal bandgap [1]. Rigorous optical simulations have been performed to investigate the light-trapping enhancement in ultra-thin GaAs having periodic and random nanostructured holes using open- source electromagnetic simulation software package MEEP [2]. We extensively studied the effects of nanostructures for different nanohole arrangements, heights, and diameters for GaAs material. Our analysis shows that the random structures offer substantially improved light absorption than the periodic nanostructures. Next, the device characteristics of single-junction GaAs solar cell and AlGaAs/GaAs multiple-quantum-well (MQW) solar cell have been studied using Silvaco TCAD (technology computer-aided design) [3]. Finally, we investigated the nanostructure light-trapping effects on the solar conversion efficiency of GaAs single-junction and AlGaAs/GaAs quantum-well solar cells. Our analysis shows that the efficient light trapping characteristics of nanohole arrays will be helpful to realize efficient thin-film photovoltaic devices.