The vital role of introducing chlorine (Cl) atoms onto conjugated polymers, which affects their semiconducting properties, is not yet well understood. A series of donoracceptor polymers based on dichlorinated-2,1,3-benzothiadiazole (2ClBT) and four different donor moieties with various conjugation lengths (thiophene (T), thieno[3,2-b]thiophene (TT), 2,2'-bithiophene (DT), and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT)) were synthesized and used in organic field-effect transistors (OFETs). The structureproperty relationship associated with the 2ClBT-based polymers was thoroughly investigated via a range of techniques, and it was found that a change in the conjugation length of the main backbone could alter energy levels, morphology, and optoelectronic properties, which had a significant effect on the charge transport property. P2CLBT-TVT exhibited superior qualities relative to the other samples with respect to the degree of uniform film-forming ability and molecular organization and charge carrier transport, which resulted in the best hole mobility of 0.147 cm(2) V-1 s(1). Furthermore, we also emphasize that for all the polymers no substantial changes were observed in the OFET transfer-curve slopes during 200 testing cycles, indicating excellent operational stability. This study demonstrates that the design of semiconducting polymers possessing Cl atoms was effective at improving operating stability in the OFETs manufactured from them.