In this work, we present the effect of 1,3,5-trichlorobenzene (TCB) on the morphology and performance of a 1:1(w/w) rr-P3HT:PCBM polymer/fullerene bulk-heterojunction solar cell. The UV-vis spectra of the rr-P3HT:PCBM polymer/fullerene formed from a blend with various TCB concentrations (0-28 mg/ml) indicate an enhanced absorption within the 500-600 nm wavelength range when formed in the presence of the TCB. By increasing the concentration of TCB in the blend, the resultant spun-cast film morphology was improved due to grain size reduction, and the polymer film quality can be further improved via an annealing process. Moreover, the device efficiency is also improved due to a good quality thin film nanostructure. With the optimized TCB quantity and annealing temperature, the power conversion efficiency (PCE) achieved with the solar cell was up to 20% better than that attained by a similar device without the presence of TCB. (C) 2009 Elsevier B.V. All rights reserved.