Effect of donor moiety in organic sensitizer on spectral response, electrochemical and photovoltaic properties

This paper describes the effects of donating ability in a D (donor)-π-A (acceptor) structured organic dye on the HOMO and LUMO energy levels and photovoltaic performance in dye-sensitized solar cell. Two different dyes were synthesized based on the cyanoacetic acid as an acceptor and the phenyl-thiophene as a π-conjugated bridge, where one contains a diethyl amino group (P2) and the other has an ethoxy group (P5) as the donor. The HOMO-LUMO energy gap was significantly influenced by donor group, where change of ethoxy donor with stronger amino one in donating ability decreased the energy gap from 2.84 eV to 2.21 eV. Moreover, it was also found that HOMO energy level was more sensitive to change in donor group than LUMO one. Photovoltaic performances of P2- and P5-dye-sensitized solar cells were systematically investigated in terms of the effects of co-adsorbent concentration, TiO₂ film thickness and TiCl₄ post-treatment. Under the best condition, the P5 dye showed the conversion efficiency of 2.62%, while the P2 dye exhibited much higher efficiency of 5.89% due to broader absorption.