Development of poly-Si/SiOx passivating contacts for advanced Si photovoltaics
As the Earth's population grows and nations become more developed the need for energy continues to rise. The climate change brought about by warming temperatures from humanity's greenhouse gas emissions makes it apparent that any future energy sources must be clean and renewable. Of the commonly known renewable energy sources: solar, wind, geothermal, and hydroelectric, the Sun provides by far the largest amount of power to the Earth daily at around ~1000 time more than global power consumption. Because of this incredible potential, solar photovoltaics (PV) are one of the most promising and most studied renewable energy sources. The current solar PV market is dominated by Si solar cells based on the passivated emitter rear cell (PERC) architecture, but newer technologies which can provide higher efficiencies are on the rise. One such technology is the poly-Si/SiOx passivating contact, which provides better passivation and enhanced carrier selectivity compared to PERC contacts. Cells based on the poly-Si/SiOx contacting scheme reach efficiencies >25% in two-sided devices, >26% in the interdigitated back-contact (IBC) architecture, and show promise of reaching high efficiencies in more specialty applications such as long-distance power transfer. We develop the field of poly-Si/SiOx passivating contacts further through studies at atomistic and device levels, using experimental and simulation techniques to solve mechanistic and practical problems. We first study how hydrogen transports from passivating dielectric layers into the passivating contacts to provide passivation. Our results demonstrate that using Al2O3 as a capping layer on SiNx provides enhanced passivation following fast-firing. Next, we study poly-Si/SiOx passivating contacts in the IBC architecture. We see how dopants can contaminate the isolation region between doped fingers to cause shunting. We also demonstrate how this shunting can be prevented by a proposed trap-assisted compensation mechanism. Next, we provide a process by which shunting across this region can be mitigated in complete cells through a self-aligned etching process. Lastly, we demonstrate the use of poly-Si/SiOx passivating contacts in a novel "minicell" architecture designed for high-illumination laser power beaming applications and show that poly-Si/SiOx contacts enable these devices to achieve efficiencies >40% without being limited by series resistance.
modelling, passivating contacts, photovoltaics, silicon, simulations
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Colorado School of Mines. Arthur Lakes Library