Carbon nanotube films with high nanotube loading were prepared using a vacuum filtration method and their photovoltaic properties as semi-transparent conducting electrodes in nanotube-silicon heterojunction solar cells were investigated. The correlation between the power conversion efficiency of the solar cells and the figure of merit (FM) of the films were obtained. The maximum efficiencies (up to 1.5%) were found for those cells using the films with highest FMs and transmittances. For comparison, the photovoltaic performance of a self-assembled nanotube thin film of high transmittance (91%) was tested and the corresponding solar cell showed a conversion efficiency of similar to 4%. This work provides guidance for future improvement on the photovoltaic properties of nanotube films as window electrode materials. (C) 2010 Elsevier Ltd. All rights reserved.