In order to explore the effect of bulky side chain substituted benzodithiophene (BDT) based polymers on optoelectronic properties, here we have designed and synthesized two new 2D conjugated donor-acceptor (D-A) copolymers P1 and P2 via Stille coupling of 2,3-bis(4-(2-ethylhexyloxy)phenyl)thiophene (BAPT) substituted BDT as (D) unit and 1,3-di(2-bromothien-5-yl)-5-(2-ethylhexyl)thieno[3,4-c]pyrrole-4,6-dione (TPD) or 2,5-ethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (DPP) as (A) units. The new polymers P1 and P2 showed broad absorption windows with vibronic shoulders indicate pi-pi stacking of polymer backbones. In addition P1 and P2 showed deep highest occupied molecular orbital (HOMO) energy levels of -5.50, -5.35 eV, respectively which allow delivering high open-circuit voltages (V (oc)) in bulk heterojunction polymer solar cells (BHJ PSCs). The donor photon energy loss (E (g)-eV (oc)) of P1 and P2 are 0.87 and 0.57 which is comparable to the previous reports. BHJ PSCs were fabricated with P1 and P2, and they displayed high V (oc) of 0.99 and 0.78 V, respectively, with maximum power conversion efficiency of 2.05 and 0.96 % in additive free BHJ PSCs. The polymer field effect transistor mobilities of P1 and P2 are 8.0 x 10(-3), 9.2 x 10(-5) cm(2)/V s, respectively.