Si/Ge nanodot superlattices for Si-based photovoltaics
Barletta, P., Dezsi, G., Lee, M., Yi, C., & Venkatasubramanian, R. (2010). Si/Ge nanodot superlattices for Si-based photovoltaics. In Concord, NC. March 18,, pp. 404–407. .
We have grown Si/Ge nanodot superlattices via low-pressure chemical vapor deposition in order to analyze their performance as thin-film solar cells. Self-assembled Ge nanodots are included in the base region in order to boost absorption of near-infrared photons and to increase short-circuit current density, Jsc. At a relatively low dot density of 5.5 Ã? 109 cm-2, both 20- and 40-period cells exhibited a fill factor of 70% and open-circuit voltage (Voc) of 0.51V, closely matching previously reported devices grown by molecular beam epitaxy. The 20- and 40-period cells had similar spectral responsivity for Â¿ = 400-550 nm, but the thicker base of the 40-period cell enabled it to attain higher responsivity for wavelengths in the range of 550-900 nm. When we increased the dot density by 55% while holding the number of periods at 40, Voc dropped significantly due to a combination of lower bandgap and higher dislocation density. Work is in progress to integrate such SiGe-nano-materials based PV devices with ultra-thin Si PV, to obtain higher efficiencies as well as minimize the use of Si.