Abstract
We studied the enhancement mechanism of the photovoltaic conversion efficiency of single-walled carbon nanotube (SWNT)/Si heterojunction solar cells by nitric acid (HNO3) doping in the dried condition. The conversion efficiency enhanced by HNO3 doping strongly depends on the thickness of the SWNT network film. From the analysis of thickness-dependent current–voltage characteristics, we found that the enhancement resulted from not only a decrease in the series resistance of the SWNT network film, but also an increase in the p–n junction density due to an increase in the carrier density of SWNTs.