Simple diphenylamine based D-?-A type sensitizers/co-sensitizers for DSSCs: A comprehensive study on the impact of anchoring groups

Abstract

Herein, we report the design, synthesis and characterization of a new series of simple donor-? spacer-acceptor/anchor (D-?-A) type diphenylamine based metal-free organic dyes possessing three different anchoring groups, viz. 4-aminobenzoic acid (DTP), 2-(4-nitrophenyl)acetonitrile (DTN), and barbituric acid (DTB), connected with 2-(thiophene-2-yl)-acetonitrile, as effective sensitizers and co-sensitizers in Dye Sensitized Solar Cells (DSSCs). They were subjected to photophysical, electrochemical and theoretical studies. The dyes exhibited characteristic ?<inf>abs</inf> and ?<inf>emi</inf> in the range of 445-485 and 545-570 nm, respectively. Both optical and electrochemical band gaps were found to be in the range of 2.2 to 2.35 eV. The driving forces for injection (?G<inf>inj</inf>), recombination (?G<inf>rec</inf>) and regeneration (?G<inf>reg</inf>) processes were evaluated to understand their feasibility. Finally, the DSSC devices were fabricated employing the new dyes as sensitizers as well as co-sensitizers along with the Ru(ii) based N3 dye. Interestingly, DTP carrying 4-aminobenzoic acid as the anchoring group shows the best photoelectrochemical performance, viz. photovoltaic conversion efficiency (PCE) = 4.4%, open circuit potential (V<inf>OC</inf>) = 0.577 V, and short-circuit current density (J<inf>SC</inf>) = 9.06 mA cm-2 with a broad incident photon conversion efficiency (IPCE) spectrum. Co-sensitization of the dyes brought about enhanced V<inf>OC</inf> values, compared to the N3 dye alone. Finally, different interface resistance values obtained from the electrochemical impedance spectroscopy (EIS) circuit fitting were used to study the fundamental processes of energy conversion. © 2019 the Owner Societies.