Solvent Effect Leading to High Performance of Bulk Heterojunction Polymer Solar Cells by Novel Polysilafluorene Derivatives

An amount of 3% of power conversion efficiency (PCE) was observed from bulk heterojunction (BHJ) polymer, solar cells (PSCs) using a novel stole-containing polymer, poly-(2,7-(9',9'-silafluorene)-alt-5',5'-(4,7-bis(3'-hexyl-2,2'-bithiophen-5-yl)benzo [c] [1,2,5]thiadiazole)) (PSiF-BBT) blended with a fullerene derivative, [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). Moreover, PCEs and short-circuit currents (J(sc)) of BHJ PSCs processed from chloroform solution were 50% increased from that of chlorobenzene solution. The studies of optical and electric properties and morphology information obtained from atomic force microscopy (AFM) and transmission electron microscopy (TEM) showed that the absorption coefficient of polymer thin films was enhanced, and the formed polymer-rich fibrillar domains were responsible for the improved device performance.