Design and fabrication of the teepee photonic crystal for high-efficiency thin film solar cell architectures

Abstract

The goal of this thesis is to provide the fabrication foundation and analysis of a photonic crystal-based tunnel oxide passivated contact (TOPCon) solar cell. A theoretical framework will be provided that studies the light interaction with photonic crystals and discusses funda- mental effects associated with photonic crystals such as parallel-to-interface refraction, slow light modes and enhanced light trapping. Additionally, a review of solar cell theory will be given, reviewing semiconductor properties, the generation and recombination of carriers, p-n junction diodes and solar cell efficiency and its limits.The fabrication procedure for the photonic crystal, referred to as the teepee photonic crystal, and the integrated TOPCon solar cell will be discussed, including in-depth discussion of reactive ion etching, the formation of tunnel oxide passivated contacts and each of their challenges. Next, the methods used for the analysis of optical properties of two unique photonic crystals, the teepee and inverted pyramid photonic crystals, and the electronic properties of the teepee photonic crystal TOPCon solar cell will be provided. In our analysis, we demonstrate that the teepee photonic crystal exceeds the Lamber- tian limit, a fundamental upper limit of solar absorption based on statistical ray trapping. When fabricated on a 10 μm silicon-on-insulator substrate, we show that the teepee photonic crystal exceeds this limit for angles of incidence between 0o and 60o over a majority of the AM1.5 Global Solar Spectrum. Finally, we present a teepee photonic crystal TOPCon solar cell that demonstrates an efficiency of 11.7%. The low efficiency is largely due to the presence of a blistered passivated contact region that degrades the passivating quality of our device resulting in very low open- circuit voltages. Alternate methods of fabrication to prevent blistering are presented, laying the ground work for future fabrication.