| Abstract
| - We have fabricated organic photovoltaic devices with blends of regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as anelectron donor and an electron acceptor, respectively. Several fabrication parameters suchas blend composition, film thickness, solvent, and presence of LiF layer were varied in orderto find the maximum device performance. The highest external quantum and powerconversion efficiencies were achieved for the blend film with 60 wt % P3HT using p-xyleneas a solvent. Insertion of a LiF layer further improved the power conversion efficiency from0.02% to 0.13% under AM1.5 condition (1 Sun). To understand the relatively poor efficiencyeven in the optimized device, this polymer blend system was analyzed in relation to thefollowing factors: charge separation efficiency, as measured by photoluminescence quantumefficiency; charge carrier mobility, measured by time-of-flight; and charge recombinationdynamics, measured by transient absorption spectroscopy. The results showed that theelectron mobility of F8BT is responsible mainly for the low efficiency in the presence ofminor contribution of the charge separation efficiency.
- AFM images of polymer blend films prepared using (A) chloroform and (B) p-xylene, where the image scan size is 5 × 5 μm. The image C is the enlarged one of A to show the phase segregation. Bottom drawings show schematic diagrams for the film morphology in the thickness direction inside the blend films prepared using chloroform (D) and p-xylene (E).
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