Ferrocene Appended D−π−A chromophores for Dye-Sensitized Solar Cells: Synthesis, Photophysical, Effect of Co-adsorbent on Photovoltaic Efficiencies and DFT studies

A new ferrocene conjugated donor–π–acceptor type of dyes 1 and 2 were synthesized and characterized using different spectroscopic techniques (FT-IR, NMR, and ESI-mass). The intramolecular charge transfer process of both the dyes were analysed using the solvatochromic method, which reveals positive solvatochromism due to its well stabilization in the excited states than in the ground states. The electrochemical behavior of the dyes 1 and 2 were carried out by the cyclic voltammetric technique, which shows quasi-reversible in nature, and the potentials were further utilized for the band gap calculation with UV-visible data [2.99 eV (1) and 2.88 eV (2)]. The photovoltaic attainments of the dyes 1 and 2 were studied through the dye-sensitized solar cells (DSSCs) in the presence and absence of co-adsorbent like chenodeoxycholic acid (CDCA), which act as an anti-dye aggregation material. The photovoltaic parameters like short circuit current density (Jsc) = 0.067 mA cm2, open circuit voltage (Voc) = 0.444 V, fill factor (FF) = 0.447, and the cell displayed an overall conversion efficiency of 0.013 % for dye 2. In contrast, the power conversion efficiency (PCE) was found to be enhanced to 0.177 % (Jsc = 0.389 mA/cm2, Voc = 0.577 V, FF =0.790), in the presence of chenodeoxycholic acid (CDCA) co-adsorbent. This enhancement in efficiency is due to reduced dye aggregation and increased electron injection in the presence of CDCA. In addition, chromophore 2 has 1.4 times higher efficiencies than 1, attributing to the presence of an additional phenyl group making an efficient intramolecular process of 2. Furthermore, the incident photon to current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies reveal the dye efficiencies were directly proportional to that of the power conversion efficiency (PCE), respectively. Moreover, the electronic structure and electron density distribution analysis were analysed for both dyes 1 and 2 to confirm the intramolecular charge transfer properties using density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT) calculations using the B3LYP/ 6-31+G** level of theory.