Molecular design and synthesis of 3,6-heterocyclic substituted carbazole with (D1-D-π-A) architecture for efficient dye-sensitized solar cell applications

Herein, three metal- free organic dyes based on 3,6-heterocyclic carbazole (CZ) namely IMZ-CZB, BIQ-CZB, and PRD-CZB were molecularly designed, synthesized and characterized as photosensitizers for dye-sensitized solar cell (DSSC). An efficient electron-donating species were made by incorporating (benzimidazole (IMZ) or benzimidazole-quinazoline (BIQ) or perimidin (PRD)) at 3,6-carbazole (D1-D), phenyl as π-bridge (π), and carboxylic acid as anchoring (A) unit leading to formation of (D1-D-π-A) framework. The molecular structures of these dyes were validated utilizing comprehensive spectroscopy measurements. In order to examine the influence of 3,6-heterocyclic substituted carbazole on electronic structures, energy levels, and photophysical properties, density functional theory (DFT) and time-dependent DFT (TD-DFT) techniques were launched. Moreover, these dyes exhibited strong absorption band in UV–vis region range of 440–528 nm that can be interpreted as a robust light-harvesting capability caused by high conjugations. Based on CZ sensitizers and in conjunction with TiO2-based photoanode and I−/I3− based electrolyte, DSSC devices were fabricated and achieved remarkable power conversion efficiency (3.14 % for IMZ-CZB, 2.15 % for BIQ-CZB, 2.39 % for PRD-CZB). Furthermore, the electrochemical impedance spectroscopy (EIS) was carried out in order to evaluate the charge regeneration/recombination as well as electron lifetime (τeff). The findings revealed that IMZ-CZB exhibited higher τeffof 11.27 (ms) and charge recombination resistance (Rrec = 11.50) compared to other dyes which is consist with value of Voc, due to the inhibits dye aggregation caused by benzimidazole. This study indicates that the current designed metal-free dyes hold potential for enhancing the performance of DSSCs.

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