Enhancement in the solar efficiency of a dye-sensitized solar cell by molecular engineering of an organic dye incorporating N-alkyl-attached 1,8-naphthalamide derivative

Abstract

Controlling the orientation of the dye molecules adsorbed on the TiO₂ surface needs extensive attention for improving the photovoltaic parameters of dye-sensitized solar cells (DSSCs). The suppression of the charge recombination and self-aggregation of dye molecules on the TiO₂ surface also plays a vital role in the improvement of cell efficiency. In this report, based on the bi-anchored structure containing N-alkyl-attached 1,8-naphthalamide derivative as the donor system and spiroBiproDOT as the π-spacer, an organic dimeric dye (D-Dye) was designed and synthesized by Suzuki coupling, followed by Knoevenagel condensation. The maximum power conversion efficiency of 7.1% with a V_oc and J_sc of 0.70 V and 14.6 mA cm⁻², respectively, was achieved for the DSSC employing D-Dye. A monomeric dye (M-Dye) was also synthesized and the resultant cell efficiency of 4.85% was achieved with V_oc and J_sc of 0.67 V and 9.93 mA cm⁻², respectively, which was 33% lower than that of its dimeric analogue (D-Dye). The photo-physical experiment was carried out for both organic dyes to understand their light absorption characteristics. The incident photon-to-current conversion efficiency (IPCE) and electrochemical impedance measurements were also obtained to rationalize the better photovoltaic performance of DSSCs employing the dimeric D-Dye, which was due to the effective suppression of the charge recombination and self-aggregation of dye molecules. The co-adsorption of D-Dye (0.4 mM) with N-719 (0.4 mM) in the ratio of 10 : 1 v/v (D-Dye:N-719) further enhanced the cell efficiency to 8.34% (V_oc of 0.77 V and J_sc of 14.9 mA cm⁻²).