Hybrid carbon nanotubes-bimetallic composite nanoparticles with sea urchin-like structures (SU-CNTs) were introduced to bulk heterojuction polymer-fullerene solar cells to improve their performance. The SU-CNTs were composed of multi-walled CNTs, which were grown radially over the entire surface of the bimetallic nanoparticles composed of Ni and Al. SU-CNTs with a precisely controlled length of similar to 200 +/- 40 nm were dispersed homogenously in a polymer active layer. Compared with a pristine device (i.e., without SU-CNTs), the SU-CNTs-doped organic photovoltaic (OPV) cells showed an improved short-circuit current density and power conversion efficiency from 7.5 to 9.5 mA/cm(2) and 2.1 +/- 0.1% to 2.2 +/- 0.2% (max. 2.5%), respectively. The specially designed SU-CNTs have strong potential as an effective exciton dissociation medium in the polymer active layer to enhance the performance of organic solar cells. (C) 2009 Elsevier B.V. All rights reserved.