Novel random copolymers for optimizing the morphology of the active layer for high performance organic photovoltaic devices have been demonstrated. Three ternary random copolymers PTBDTDPPSiCN(3/7)

PTBDTDPPSiCN(5/5)

PTBDTDPPSiCN(7/3) were prepared by polymerization of electron-donating thienyl-substituted benzodithiophene (TBDT) with 2

5-bis[8-(1

1

3

3

5

5

5-heptamethyltrisiloxane-3-yl)octly]-pyrrolo[3

4-c]

pyrrole-1

4-dione (DPPSi) and 2

5-dio[5-(5-cyano-5

5-dimethyl-pentyl)]-3

6-dithiophen-2-yl-pyrrolo[3

4-c]

pyrrole-1

4-dione (DPPCN) of different ratios. The DPPCN block can well-tune the light absorption and molecular packing

while the DPPSi block is in favor of enhancing the charge mobility. And the formation of organic Si―O―Si networks is beneficial to stabilize the morphology of the active layer. These new copolymers have narrow bandgaps and broaden visible light absorption from 500 nm to 1000 nm. Careful balance of the contents of the trimethoxysilyl group and the cyano group can well-tune the surface energy and morphology of the copolymers. Incorporation of these novel copolymers as additives into the blend of poly(3-hexylthiophene) (P3HT) and [6

6]-phenyl-C

60

-butyric acid methyl ester (PC

61

BM) is found to effectively broaden the light absorption

improve the compatibility and morphology of the active layer. As a result

some devices with certain ratios of these copolymers as additives achieve the enhanced efficiency compared with the device based on pristine P3HT:PC

61

BM.