Nanotube film metallicity and its effect on the performance of carbon nanotube-silicon solar cells

Research into silicon solar cells that use a thin film of single walled carbon nanotubes as the front electrode is an important area of increasing research activity. This paper provides the first ever direct performance comparison between devices fabricated with either semiconducting, metallic or mixed nanotubes to probe the effect of the semiconducting/metallic nature, or 'metallicity', of the nanotube film on solar cell performance and properties. HiPCO nanotube material sorted using the gel chromatography technique is highly purified in either metallic or semiconducting nanotube species. The solar cells fabricated with the metallic nanotubes greatly outperform their semiconducting or mixed counterparts. The operating mechanisms underlying this observation and its implications in regards to current understanding are discussed in light of recent literature. Dramatic increases in performance as well as substantial changes in the effect of metallicity due to subsequent hole doping of the sorted nanotube films are also demonstrated. Using highly pure semiconducting and metallic carbon nanotubes, film metallicity is shown to be a vital factor in the performance of carbon nanotube-silicon solar cells. Using highly pure semiconducting and metallic carbon nanotubes, film metallicity is shown to be a vital factor in the performance of carbon nanotube-silicon solar cells. Metallic nanotubes greatly outperform their semiconducting counterparts unless the films are doped, in which case the difference is reduced but still significant.