Hafnium Doped Zinc Oxide: From Material Optimization to Energy Applications

  • Boulos Alfakes

Student thesis: Doctoral Thesis

Abstract

The need for a high optical spectrum throughput, high conductivity, and controlled energy levels of transparent conductive oxide used in solar cells stresses the importance of developing novel materials that help reduce the existing dependency on indium-based oxides. Zinc Oxide (ZnO) is a promising material in this context, and in this work, we demonstrate how Hafnium (Hf) doping of ZnO films allows the engineering of both electrical and optical properties to fit the requirements of different solar cell architectures and materials. We focus on the lightly doped domain, where Hf substitution is believed to be the key for band gap tunability without negatively affecting the carrier transport behavior. Moreover, Hf-doped ZnO photoelectrochemical (PEC) performance was studied. The resultant doped materials showed a significant improvement in PEC efficiency compared to pristine ZnO, which is linked directly to Hf introduction, revealed by detailed optical, structural, and electrical analyses. The photocurrent obtained in the best performing Hf-doped sample (0.75 wt.% Hf) was roughly threefold higher compared to the undoped ZnO. Finally, first principle Density Functional Theory (DFT) simulations are performed to have better insight into the electronic and electrical properties of Hf-doped ZnO. Additionally, common dopants of ZnO were also simulated, to allow for normalized comparison. Both the Hf-doped ZnO experimental results and the DFT obtained properties of all dopants are applied to a one-II dimensional solar cell simulation tool, to predict the experimental enhancement caused by Hf doping. The simulation results show that over 4% improvement in ZnO/Si heterojunction solar cell conversion efficiency is to be anticipated as a result of Hf doping.
Date of AwardMay 2020
Original languageAmerican English

Keywords

  • Hf-doped ZnO
  • Atomic Layer Deposition
  • Photoelectrochemical Performance First-Principle Calculations
  • ZnO/Si heterojunction Solar Cell.

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