Synthesis and studies of carbazole-based donor polymer for organic solar cell applications

We have developed a carbazole-based electron donor material, containing extended thiophene π-conjugated through a cyanovinylene spacer in order to enhance the effective intramolecular charge transfer for bulk heterojunction polymer solar cell (BHJ-PSC) applications. The polymer was synthesized via FeCl 3 oxidative polymerization method, namely poly(2E,2′E)-3,3′-(9-hexyl-9 H -carbazole-3,6-diyl)bis(2-(5-methylthiophen-2yl)acrylonitrile (CN-PICTAN). The CN-PICTAN formation was confirmed by Fourier transformed infrared, nuclear magnetic resonance spectroscopy, and gel permeation chromatography techniques. The CN-PICTAN showed a broad absorption and emission range with optical band gap ( E g opt ) of 2.1 eV. The CN-PICTAN exhibited a high thermal stability with 5% weight loss at 356 °C and deep-lying highest occupied molecular orbital level of − 5.23 eV. The BHJ-PSC device fabricated with CN-PICTAN:PC 61 BM (1:1.5) showed a power conversion efficiency of 1.23%, which was enhanced to 1.73% after the device was annealed at 100 °C.