3,6-Carbazole Incorporated
into Poly[9,9-dioctylfluorene-<i>alt</i>-(bisthienyl)benzothiadiazole]s
Improving the Power Conversion
Efficiency
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Abstract
A novel concept of D–A-type copolymers based on
fluorene
polymer incorporated with 3,6-carbazole unit enhances the device performance
for organic photovoltaic cells. <b>P(F</b><sub><b>45</b></sub><b>C</b><sub><b>5</b></sub><b>-DTBT)</b>,
incorporating 5 mol % 3,6-carbazole into <b>P(2,7F-DTBT)</b>, shows an almost 2-fold improvement (5.1%) in power conversion efficiency
relative to <b>P(2,7F-DTBT)</b> (2.6%). This results is ascribed
to the good balance between electron and hole mobilities in the devices
(μ<sub>e</sub>/μ<sub>h</sub> ∼ 1.8 for <b>P(F</b><sub><b>45</b></sub><b>C</b><sub><b>5</b></sub><b>-DTBT)</b> vs 152 for <b>P(2,7F-DTBT)</b>), and the
formation of a nanoscale morphology in the blend of the copolymer
and [6,6]-phenyl C71-butyric acid methyl ester (PC<sub>71</sub>BM)