Heteroatom-containing conjugated polymers are promising candidates for designing efficient polymer solar cells. However, fundamental understanding of the role of heteroatoms on structure-property relationships of these polymers is not yet fully understood. This work, based on first-principles calculations at the molecular level, uncovers how fluorine and oxygen introduction on poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) affect structural and electronic properties. Systematic computations of torsional defects, energy gaps, molecular electrostatic potential surfaces and dipole moments are carrier out for PCPDT-BT and its fluorine and oxygen derivatives. We found that oxygen derivative favors lowest energy planar conformation, low energy gaps and high ground to excited state dipole differences. The present results further suggest that oxygenation might increase charge dissociation and reduce charge recombination in the excited state, supporting the recent experimental findings. (C) 2014 Elsevier Ltd. All rights reserved.