Significant improvement of dye-sensitized solar cell performance using low-band-gap chromophores based on triphenylamine and carbazole as strong donors

Abstract

A series of new metal-free D–D-π–A dyes (TMS-1-4) based on triphenylamine (TPA) and carbazole (Cz) that work as strong donor species have been made and used in dye-sensitized solar cells (DSSCs). Malononitrile (-MN), cyanoacrylic acid (-CA), nitrophenylacetonitrile (-NAN) and iminophenylcarboxylic acid (-CH) are the four electron-withdrawing entities connected to the electron-rich TPA-Cz unit in this innovative design. Their molecular structures were identified using all required spectral analyses, as well as by investigating their optical and electrochemical properties. Molecular geometries designed using DFT have also been used to understand how the structures of TMS-1-4 affect their photovoltaic capabilities. The dyes exhibited a strong absorption band in the wavelength range (686 nm–730 nm) that can be translated to a strong light harvesting ability. The photovoltaic conversion efficiencies (PCEs) of TMS-1-4 and the reference dye N719 were also studied, and the rankings were as follows: TMS-2 (8.81%) > TMS-4 (8.03%) > N719 (7.60%) > TMS-3 (6.85%) > TMS-1 (6.51%). Furthermore, the behavior of the dyes was studied after using CDCA, which causes an increase in PCE for all dyes due to an increase in short current value. This work suggests that metal-free dyes (TMS-1-4) are promising candidates for improving the DSSC performance.