Solution-Processed Bulk Heterojunction Solar Cells with Silyl End-Capped Sexithiophene
We fabricated solution-processed organic photovoltaic cells (OPVs) using substituted two sexithiophenes, a,w-bis(dimethyl-n-octylsilyl)sexithiophene (DSi-6T) and a,w-dihexylsexithiophene (DH-6T), as electron donors, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor. Solution-processed OPVs usingDH-6TandDSi-6Tshowed good photovoltaic properties in spite of their poor solubility. The best performance was observed onDSi-6T : PCBM 1 : 5 (w/w) blend cell with an open circuit voltage (Voc) of 0.63 V, short circuit current density (Jsc) of 1.34 mA/cm2, fill factor (FF) of 55%, and power conversion efficiency of 0.44% under AM 1.5 G illumination. AlthoughDH-6Thas higher hole mobility thanDSi-6T, theDSi-6T : PCBM blend cell showed higher hole mobility thanDH-6T : PCBM cell. Therefore,DSi-6Tcell showed higher device performance thanDH-6Tcell due to its silyl substitutions, which lead to the increase of the solubility. The incorporation of solution-processed TiO2interfacial layer in theDSi-6T : PCBM devices significantly enhances FF due to the reduced charge recombination near active layer/Al interface.