p-Type Single-Wall Carbon Nanotube Network on n-Type Si for Heterojunction Photovoltaic Cells

High-density p-n heterojunctions between single wall carbon nanotubes (SWNTs) and n-type crystalline silicon produced with airbrushing technique were used for light harvesting. The SWNT/n-Si heterojunction is rectifying. Under illumination the numerous heterojunctions formed between the semitransparent SWNT thin coating and the ntype silicon substrate generate electron-hole pairs, which are then split and transported through SWNTs (holes) and n-Si (electrons), respectively. The nanotubes serve as both photogeneration sites and a charge carriers collecting and transport layer. It was also found that the thionyl chloride (SOCl2)-treatment of SWNT coating films can lead to a significant increase in the conversion efficiency through readjusting the Fermi level and increasing the carrier concentration and mobility of the nanotube network. Initial tests have shown a power conversion efficiency of above 4%, proving that SOCl2 treated-SWNT/n-Si is a potentially suitable configuration for making solar cells.