Fundamental understanding and integration of rapid thermal processing, PECVD, and screen printing for cost-effective, high-efficiency silicon photovoltaic devices

The final hurdle preventing widespread application of photovoltaics is cost-effectiveness. Solar cell efficiencies in the laboratory have reached 24%, but industrial cells, constrained by low-cost, high-throughput processes, are limited to 10-15%. This thesis focuses on industrially relevant technologies such as rapid thermal processing (RTP), PECVD, and screen-printing to simplify and speed up cell processing yet maintain the key features that give high efficiencies in the laboratory. RTP utilizes tungsten-halogen and UV lamps as a source of high energy photons that induce thermal and photophysical effects which can significantly increase the kinetics of semiconductor processes such as diffusion, oxidation, and annealing. PECVD also serves as a promising low-cost candidate for SiN/SiO{dollar}sb2{dollar} antireflection coatings and passivation. Finally, screen printing serves as a very high-throughput technology for contact formation as a low-cost alternative to photolithography.; Integration of these technologies into a single cell fabrication sequence, however, revealed the susceptibility to low internal quantum efficiencies in the long and short wavelengths. For example, the inherent rapid cooling during RTP can degrade minority-carrier lifetime and long wavelength response. Lack of knowledge in tailoring RTP emitter diffusion profiles coupled with less than perfect PECVD surface passivation and parasitic SiN absorption was found to limit short wavelength response. Problems like these limited RTP cell efficiencies to only 15.4% prior to this thesis. Through a combination of fundamental understanding of device physics, materials and device characterization, modeling, and cell fabrication these losses were quantified and overcome in this thesis. An in-situ annealing cycle during RTP was optimized to prevent quenching-induced lifetime degradation and to preserve high long wavelength response. Measurement of SiN extinction coefficients to compute parasitic absorption, optimization of emitter profiles, and engineering of a high-quality rapid thermal oxide (RTO) for surface passivation, eliminated short wavelength losses. Identical performance to conventional furnace-processed cells was achieved in half the processing time. Record-high RTP efficiencies {dollar}>{dollar}19% were achieved using photolithography. Screen-printed contacts on RTP cells reduced processing time by another factor of {dollar}>{dollar}four and resulted in {dollar}>{dollar}16%-efficient manufacturable cells. These results have brought photovoltaics one step closer to cost-effective commercialization.