Naphthalimide-phenothiazine based A’-π-D-π-A featured organic dyes for dye sensitized solar cell applications

Highlights •To the best of our knowledge, this is the first attempt on a novel structural framework, A’-d-π-A is demonstrated, where an auxiliary acceptor is placed in the terminal position.•The diffuse reflectance UV–vis absorption spectra of the dyes, suggest broader wavelength for absorption (200–750 nm).•EM radiation to current conversion efficiency upto 4.9 % was achieved, with Jsc of 12.21 mA/cm2 and Voc of 648 mV.•Naphthalimide as an auxiliary acceptor did not prevent recombination reaction but rather acted as an electron trap.•This work clearly explains the importance of the choice of an auxiliary acceptor in influencing the efficiency of a device. [Display omitted] The effect of naphthalimide as auxiliary acceptor in the PTz-based dyes for dye-sensitised solar cell (DSSC) application is reported. In this regard, two new organic dyes with N-alkylated phenothiazine (PTz) core were synthesized by substitution of naphthalimide at C-3 of the PTz via triple bond and incorporation of an electron acceptor at C-7 position. Photophysical and electrochemical studies were carried out to assess the performance of the dyes on spectral coverage and to determine the redox energy levels, respectively. Charge distribution and electron transfer process of the optimized dyes were rationalised via theoretical studies. DSSCs fabricated with these dyes showed an optimal efficiency of 4.9 % for a device fabricated with iodide/triiodide electrolyte.