Bulk resistivity optimization for low-bulk-lifetime silicon solar cells

• Published in: Progress in photovoltaics 2001-07, Vol.9 (4), p.273-285
• Main Authors: Brody, Jed, Rohatgi, Ajeet, Yelundur, Vijay
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Exact sciences and technology; Natural energy; Photovoltaic conversion; Solar cells. Photoelectrochemical cells; Solar energy
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.380

Guidelines are presented which are designed to achieve planar solar cell efficiencies as high as 17.5% using existing fabrication technologies and silicon substrates with lifetimes as low as 20 μs. Device simulations are performed to elucidate the need and impact of base doping optimization for different back‐surface passivation schemes, cell thicknesses, emitter profiles, and degrees of dopant–defect interaction. Results indicate that optimal resistivity is a function of back‐surface passivation, with the aluminum back‐surface field (BSF) requiring the highest resistivity, the oxide/nitride stack passivation excelling at an intermediate resistivity, and the ohmic contact needing the lowest resistivity. A comparison of simulated 300 and 100 μm cells shows that thinner cells magnify the differences in optimal resistivity for the three back‐surface passivation schemes. A lifetime model is used to account for dopant–defect interaction that can lower bulk lifetime at higher doping levels. It is demonstrated that cell efficiency decreases and optimal resistivity increases at higher levels of dopant–defect interaction. Simulated devices with an optimized base doping showed an efficiency improvement of as much as 2% (absolute) compared with identical devices with a typical base doping level (1.6 or 1.8 Ω cm) and bulk lifetime of 20 μs. Copyright © 2001 John Wiley & Sons, Ltd.