Improved photovoltaic performances of Ru (II) complex sensitized DSSCs by co-sensitization of carbazole based chromophores

Abstract

Herein, we report photovoltaic performance studies of three carbazole based dyes (N<inf>1–3</inf>) derived from (Z)-3-(9-hexyl-9H-carbazol-3-yl)-2-(thiophen-2-yl)acrylonitrile scaffold as effective co-sensitizers in Ru (II) complex, i.e. NCSU-10 sensitized DSSCs. From the results it is evident that, the device fabricated using co-sensitizer N<inf>3</inf> with 0.2 mM of NCSU-10 exhibited improved photon conversion efficiency (PCE) of 8.73% with J<inf>SC</inf> of 19.87 mA·cm? 2, V<inf>OC</inf> of 0.655 V and FF of 67.0%, while N<inf>1</inf> displayed PCE of 8.29% with J<inf>SC</inf> of 19.75 mA·cm? 2, V<inf>OC</inf> of 0.671 V and FF of 62.6%, whereas NCSU-10 (0.2 mM) alone displayed PCE of 8.25% with J<inf>SC</inf> of 20.41 mA·cm? 2, V<inf>OC</inf> of 0.667 V and FF of 60.6%. However, their EIS studies confirm that, N<inf>1</inf>, showing higher V<inf>OC</inf> is efficient in suppressing the undesired charge recombination in DSSCs through enhanced surface coverage on TiO<inf>2</inf> and thereby resulting in longer electron lifetime than that of NCSU-10 dye alone. Here, the higher PCE of N<inf>3</inf> can be attributed to its improved light harvesting efficiency, which is due to the presence of highly electron withdrawing barbituric acid in its structure. Conclusively, the results showcase the potential of simple carbazole based dyes as co-sensitizers in improving efficiency of DSSCs. © 2017