In this study, the well-defined coil-rod-coil triblock copolymer poly(4-vinyltriphenylamine)b-poly(3-hexylthiophene)-b-poly(4-vinyltriphenylamin) (PTPA-P3HT-PTPA) was used as a surfactant for P3HT/PCBM (1:1) based solar cells. The power conversion efficiency of the device was enhanced from 3.9 to 4.4% in the presence of the 0-5% PTPA-P3HT-PTPA under illumination of AM 1.5G (100 mW/cm 2 ). The morphology variation and the balance of the hole/electron mobility accounted for such enhancement. In the P3HT/PCBM/PTPA-P3HT-PTPA ternary blends, the fiber-like structure was observed for surfactant ratios of 0-5%, while a sphere-like nanostructure was observed for the surfactant ratio of 1.5%. The sphere-like nanostructure led to a smaller domain size and enhanced interfacial area for charge separation as compared to the fiber-like structure. On the other hand, the increased hole mobility in the blend with the addition of PTPA-P3HT-PTPA resulted in the balanced hole and electron mobility (μ e /μ h ∼1.7 in comparison to the ratio of 3.6 without the surfactant). The incorporated PTPA-P3HT-PTPA surfactant not only extended the lifetime of solar cells but also reduced the PCBM aggregation upon annealing, resulting in better thermal stability. The DSC result confirmed the selective miscibility of the PTPA coil segment with PCBM. These results demonstrated the superior compatibilizing effect of the rod-coil triblock copolymers for solar cell applications.

Seven donor-acceptor copolymers incorporating didecyloxyphenylene (DP) donor and the following acceptorssthieno [3,4-b]pyrazine (TP), 2,1,3-benzothiadiazole (BT), quinoxaline (Q), pyridine (Py), 2,3-dimethyl-5,7-dithien-2-yl-thieno [3,4-b]pyrazine (DTTP), 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT), and 2,3-dimethyl-5,7-dithien-2-yl-quinoxaline (DTQ)swere synthesized by Suzuki coupling polymerization. The effects of the acceptor strength and backbone planarity on the optical, electrochemical, field-effect charge transport, and photovoltaic properties of the donor-acceptor copolymers were investigated. The optical band gap (eV) of the copolymers showed the trend of DP/TP (1.47) < DP/BT (2.37) < DP/Py (2.76) < DP/Q (2.78) < DP/P (3.15). The DP/TP copolymer had a field-effect hole mobility of 1.89 × 10 -3 cm 2 V -1 s -1 . The DP/DTBT and DP/ DTQ copolymers showed hole mobilities of 1.92 × 10 -4 and 2.10 × 10 -3 cm 2 V -1 s -1 , respectively. The strong acceptor strength of TP and coplanar backbone in the DP/TP copolymer resulted in a large intramolecular charge transfer, leading to the observed charge transport and optical properties.. These results show that the backbone planarity of the DP/BT and DP/Q copolymers was significantly improved by incorporating thiophene moieties, leading to enhanced charge transport. Photovoltaic cells fabricated from DP/DTBT and DP/DTQ polymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) showed power conversion efficiencies of 0.40-0.41% under AM 1.5 solar simulator illumination (100 mW/cm 2 ). The results of the present study show that the electronic and optoelectronic properties of dialkoxylphenylene-based donor-acceptor copolymers could be tuned through the acceptor structure and backbone coplanarity.

We report synthesis, properties, and optoelectronic device characteristics of six new indolocarbazole-acceptor conjugated copolymers prepared by Suzuki coupling reaction. Two different linkages of indolocarbazole (28IC and 39IC) and four acceptors of 2,3-didodecylthieno [3,4-b]pyrazine (TP12), 2,3-bis(4-(2-ethylhexyloxy) phenyl)thieno [3,4-b]pyrazine (TPO), 2,1,3-benzothiadiazole (BT), and 2,3-bis(4-(2-ethylhexyloxy)phenyl)quinoxaline (QO) were used to explore the effects of acceptor structure, linkage, and side group on the electronic and optoelectronic properties. The optical band gap (eV) of the studied copolymers were in the following order: P28IC-TPO (1.58) < P39IC-TP12 (1.79) < P28IC-TP12 (1.84) < P28IC-BT (2.09) < P28IC-QO (2.31) < P39IC-QO (2.34). The hole mobility and on-off ratios of the studied copolymers were in the ranges 1.66 × 10 -5 to 4 × 10 -4 cm 2 /V • s and 40-46900, respectively. It basically depended on the degree of intromolecular charge transfer between indolocarbazole and acceptor as well as the HOMO level. The power conversion efficiency (PCE) of the indolocarbazole-acceptor polymer/PC 61 BM or PC 71 BM based photovoltaic cells were in the range 0.14-1.40% under the illumination of AM 1.5G (100 mW/cm 2 ). P28IC-QO showed the best PCE among the studied copolymers because of its suitable HOMO/LUMO energy level, high molecular weight, good hole mobility, efficient PL quenching, and large V oc .

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