Effect of the end group of regioregular poly(3-hexylthiophene) polymers on the performance of polymer/fullerene solar cells - Kim, Y; Cook, S; Kirkpatrick, J; Nelson, J; Durrant, JR; Bradley, DDC; Giles, M; Heeney, M; Hamilton, R; McCulloch, I (JOURNAL OF PHYSICAL CHEMISTRY C, 2007)