Preparation and Characterization of High Molecular Weight Low Bandgap Polymers Based on Poly(2,7-carbazole)s for Organic Solar Cells

摘要

We report the PCDTBT {Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]}, an alternating copolymer of 2,7-carbazole and dithienyl-2,1,3-benzothiazole, has high molecular weight and narrow molecular weight distribution. Our PCDTBT can be successfully prepared as good yield by using tetrakis(triphenylphosphine)palladium [Pd(PPh_3)_4] catalyst instead of Pd_2dba_3/P(o-Tol)_3 catalyst. From the UV/Vis absorption spectroscopy, we can observe that absorption bands of PCDTBT are bathochromically shifted by increasing the molecular weight, that is to say, our high molecular weight PCDTBT can absorb much longer wavelength light compare to low molecular weight PCDTBT. The best performance can be obtained from device based on the mixture of PCDTBT (polymer-3O) and PC_(70)BM {[6,6]-phenyl C71-butyric acid methyl ester} (1:4) as an active layer, which shows 4.50% of PCE with 10.1 mA/cm~2 of short-circuit current density (J_(sc)), 0.85 V of open-circuit voltage (V_(oc)), and 52.3% of fill factor which is very similar with Leclerc's published result.