Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Omar Manasreh

Committee Member

Simon Ang

Second Committee Member

Jingxian Wu

Keywords

Efficiency Enhancement, Nanoneedle Arrays, Solar Cell, Sol-gel Thin Film

Abstract

The broadband suppression in reflection is one of the primary focuses in high efficiency solar cell research. In this thesis, a moth-eye inspired nanostructure antireflection coating is fabricated on InAs/GaAs quantum dots solar cell in order to enhance the power conversion efficiency. The abrupt refractive index transition between air and GaAs surface is replaced by a tapering zinc oxide nanoneedle on planar tantalum pentoxide coating. The antireflection structure provides gradual reduction of refractive index away from the solar cell top surface.

The nanostructured antireflection coating is fabricated by utilizing chemical bath deposition of tapered zinc oxide nanoneedles on planar tantalum pentoxide coating. A sol-gel method was developed to obtain an air stable tantalum pentoxide solution. The thickness of the planar tantalum pentoxide coating was optimized to suppress the reflection at a single wavelength. In addition, hydrothermally grown zinc oxide nanoneedle arrays were optimized by investigating several growth parameters including pH and growth time to obtain a tapered dimension. A tapering zinc oxide nanoneedle structure coupled with a high refractive index tantalum pentoxide layer suppresses the broadband reflectance to less than 1 %.

The combined antireflection structure significantly increased the performance, not only in reflectance or transmission spectrum, but also in current-voltage characteristic, external quantum efficiency, and spectral response measurements. A power conversion efficiency enhancement of 30 % was obtained by a single quarter wavelength tantalum pentoxide layer. Adding the tapered zinc oxide nanoneedles on top of the planar tantalum pentoxide layer, the power conversion efficiency enhanced by 50 %. Furthermore, a 60 % enhancement in the external quantum efficiency is obtained for the same wavelength range.

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