Three two-dimensional (2D) conjugated polymers, named PBDTSDPP-1, PBDTSDPP-2, and PBDTSDPP-3, based on benzo[1,2-b:4,5-b']dithiophene (BDT) donor unit with conjugated alkylthiothiophene side chain and diketopyrrolopyrrole (DPP) acceptor unit, were designed and synthesized via palladium catalyzed Stille-coupling reaction. The resulting polymers exhibited good thermal stability with a high decomposition temperature over 350 degrees C and a broad absorption in the range from 400 to 900 nm. The HOMO energy levels of the polymers are deeper than -5.39 eV and the LUMO energy levels of them are higher than -4.09 eV. The field effect transistors prepared from PBDTSDPP-1, PBDTSDPP-2 and PBDTSDPP-3 provide a hole mobility of 3.52 x 10(-3), 3.85 x 10(-4) and 436 x 10(-3) cm(2) v(-1) s(-1) respectively. The photovoltaic properties of the polymer as donor was investigated with an inverted structure of ITO/PEIE/polymer:PC71BM/MoO3/Ag. As a preliminary result, PBDTSDPP-1, PBDTSDPP-2, and PBDTSDPP3 showed power conversion efficiency (PCE) of 4.75%, 3.56%, and 5.28%, respectively. The short-circuit current density (Jsc) and PCE value of PSCs based on PBDTSDPP-3 are higher than those of the other two polymers because of better morphology, higher and more balanced charge -carrier mobilities, leading to less recombination loss. (C) 2017 Elsevier Ltd. All rights reserved.