By transitioning to semicrystalline polymers, the performance of polymer-based solar cells has recently increased to over 5% [W. Ma, Adv. Fund. Mater. 15, 1665 (2005); G. Li, Nat. Mater. 4, 864 (2005); M. Reyes-Reyes, Org. Lett. 7, 5749 (2005); J. Y. Kim, Adv. Mater. (Weinheim, Ger.) 18, 572 (2005); J. Peet, Nat. Mater. 6, 497 (2007)]. Poly(2,5-bis(3-tetradecyllthiophen-2-yl) thieno[3,2- b] thiophene) (pBTTT) has caused recent excitement in the organic electronics community because of its high reported hole mobility (0.6 cm2 V-1 s-1) that was measured in field effect transistors and its ability to form large crystals. In this letter, we investigate the potential of pBTTT as light absorber and hole transporter in a bulk heterojunction solar cell. We find that the highest efficiency of 2.3% is achieved by using a 1:4 blend of pBTTT and[6,6]-phenyl C61 -butyric acid methyl ester. The hole mobility as measured by space charge limited current modeling was found to be 3.8× 10-4 cm2 V-1 s-1 in this blend. © 2008 American Institute of Physics.