A diminutive modification in arylamine electron donors: synthesis, photophysics and solvatochromic analysis – towards the understanding of dye sensitized solar cell performances

An electron rich donor moiety plays an important role in dye sensitized solar cells (DSCs). In order to attain a suitable donor moiety for DSCs, a deeper understanding of the role of a donor moiety in the dye excited state is significant. In this context, different arylamine dye-based electron donor moieties (TRA, CRA and PyRA) were successfully synthesized and well characterized using 1H-NMR, 13C-NMR and EI-MS spectrometry. Their photophysical properties and solvatochromic behavior were studied using UV-visible absorption, steady state and time resolved fluorescence spectroscopic techniques. The absorption of arylamine dyes is due to intramolecular charge transfer (ICT) between the donor and rhodanine-3-acetic acid via a π-bridge, which is further confirmed by DFT calculations. Lippert–Mataga analysis on the solvatochromic data implies that these molecules are more polar in the excited state, which is additional support for ICT. Furthermore, nanocrystalline TiO2-based dye sensitized solar cells (DSCs) were fabricated using these dyes to investigate the influence of donor moieties on their photovoltaic performance. The overall power conversion efficiencies of 2.57%, 1.68% and 1.25% were obtained for the TRA, PyRA and CRA dyes, respectively. The enhanced power conversion efficiency of TRA is due to a longer lifetime of injected electrons as demonstrated by the electrochemical impedance spectroscopy (EIS) measurements.