Conjugated polymers are highly desirable for the photovoltaic applications. We report the synthesis, characterization, optoelectronic properties, and solar cell application of two polymers, namely, poly[(9,9-didodecylfluorene-2,7-diyl)-alt-(2,2 0 :5 0 ,2 00 -terthiophene-5,5 00 -diyl)] (P1) and poly[(1,4-bis(dodecyloxy)benzene-2,5-diyl)-alt-(2,2 0 :5 0 ,2 00 -terthiophene-5,5 00 -diyl)] (P2). The polymers were synthesized via Stille cross-coupling reaction, and were characterized by the gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared, UV-vis, thermogravimetric analysis, and cyclic voltammetry analyses. The two copolymers are processable due to their good solubility in organic solvents (tetrahydrofuran, CHCl 3 , toluene, chlorobenzene, and o-dichlorobenzene). The optical band gaps (UV-vis, film, and E g opt ) of the P1 and P2 are 2.04 and 2.00 eV, respectively. The density functional theory output structures showed that S . . . O space interaction is likely responsible for the higher planarity of P2. The polymers showed low HOMO energy levels (P1: 25.33 eV, P2: 25.05 eV). The E HOMO for P1 is close to the E HOMO (25.4 eV) of an ideal polymer, which is an important, rare, and main origin of the observed higher V oc (801-808 mV). The onset decomposition temperatures (T d ) for the P1 and P2 are 418 C and 365 C, respectively. The polymer solar cell based on the P1: C 60 (1: 1) and P2: C 60 (1: 1) blend showed a power conversion efficiency (PCE) of 0.94 and 0.71%, respectively. The composite polymer : PC 60 BM 5 1 : 2 increased PCE of the P1 (1.65%) and P2 (1.09%) under AM 1.5 illumination (100 mW/cm 2 ). The study provided important examples to design donor-donor (D-D) polymers for the photovoltaic applications.
