New carbazole based metal-free organic dyes with D-π-A-π-A architecture for DSSCs: Synthesis, theoretical and cell performance studies

Herein we report the design, synthesis and photovoltaic performance studies of three new D-pi-A-pi-A architectured organic chromophores (N1-3) derived from (Z)-3-(9-hexyl-9H-carbazol-3-yl)-2-(thiophen-2-yl) acrylonitrile scaffold. In the new design, the electron rich carbazole unit is connected to three different electron withdrawing/anchoring species, viz. cyano acetic acid, rhodanine-3-acetic acid and barbituric acid via cyano vinyl thiophene as pi-spacer. Newly synthesized dyes were characterized by spectral, photophysical and electrochemical analyses. Their optical band-gap, GSOP and ESOP values, as calculated from the optical and CV studies were found to be in the range of 2.12-2.21, -5.52 to -5.43 and -5.40 to -3.25 eV respectively. The DFT and TD-DFT studies were performed using Turbomole 7.1V software and the results indicated the existence of proper charge separation between HOMO and LUMO levels of the dyes. Also, the results revealed good matching of theoretically generated optical spectral data with the experimental values. Finally, DSSC devices were fabricated using these three dyes and the dye N-1 containing cyanoacetic acid as an acceptor unit showed better photo conversion efficiency (eta) of 3.55% than the other two dyes. It's J(sc). V-OC, and IPCE parameters were shown to be 9.06 mA cm(-2), 0.577 V and 48%, respectively. The obtained EIS data and electron lifetimes of N1-3 sensitized devices are well in accordance with experimental photovoltaic parameters. (C) 2017 Elsevier Ltd. All rights reserved.