We report the characteristics of polymer/quantum dot solar cells fabricated using a water-soluble polymer and carbon nanotubes in a bulk heterojunction configuration. The water-soluble polythiophene polymer showed significant photoresponse and the potential for use in photovoltaics. The addition of carbon nanotubes to the polymer resulted in an order of magnitude increase in the photoconductivity. Improved charge separation and collection was evidenced by the large difference between light and dark conductivities as well as the increase in both open circuit voltage and short circuit current. Finally, photovoltaic cells using aligned nanotubes showed further improvement in the photoconductivity and IV characteristics. (C) 2005 Springer Science + Business Media, Inc.