TOWARDS LIGHTWEIGHT AND FLEXIBLE HIGH PERFORMANCE NANOCRYSTALLINE SILICON SOLAR CELLS THROUGH LIGHT TRAPPING AND TRANSPORT LAYERS

Open Access
Author:
Gray, Zachary R
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 17, 2016
Committee Members:
  • Wook Jun Nam, Dissertation Advisor
  • Wook Jun Nam, Committee Chair
  • Suzanne Mohney, Committee Member
  • Osama O. Awadelkarim, Committee Member
  • Susan Trolier-McKinstry, Outside Member
Keywords:
  • light trapping
  • nano-element array
  • hole transport layer
  • electron blocking layer
  • nickel oxide
  • nanocrystalline silicon
  • aluminum doped zinc oxide
  • atomic layer deposition
  • plasma enhanced chemical vapor deposition
  • electron beam lithography
  • ANSYS HFSS
Abstract:
This thesis investigates ways to enhance the efficiency of thin film solar cells through the application of both novel nano-element array light trapping architectures and nickel oxide hole transport/electron blocking layers. Experimental results independently demonstrate a 22% enhancement in short circuit current density (JSC) resulting from a nano-element array light trapping architecture and a ~23% enhancement in fill factor (FF) and ~16% enhancement in open circuit voltage (VOC) resulting from a nickel oxide transport layer. In each case, the overall efficiency of the device employing the light trapping or transport layer was superior to that of the corresponding control device. Since the efficiency of a solar cell scales with the product of JSC, FF, and VOC, it follows that the results of this thesis suggest high performance thin film solar cells can be realized in the event light trapping architectures and transport layers can be simultaneously optimized. The realizations of these performance enhancements stem from extensive process optimization for numerous light trapping and transport layer fabrication approaches. These approaches were guided by numerical modeling techniques which will also be discussed. Key developments in this thesis include (1) the fabrication of nano-element topographies conducive to light trapping using various fabrication approaches, (2) the deposition of defect free nc-Si:H onto structured topographies by switching from SiH4 to SiF4 PECVD gas chemistry, and (3) the development of the atomic layer deposition (ALD) growth conditions for NiO.