Effect of π-spacers and anchoring groups on the photovoltaic performances of ullazine-based dyes

Abstract

Three ullazine-based organic sensitizers (QD1, QD2 and QD3) have been designed, synthesized, and characterized for dye-sensitized solar cells (DSSCs). Ullazine possesses some attractive properties, such as a planar π-system to promote intensely the intramolecular charge transfer (ICT) between ullazine donor units and cyanoacrylic acid or carboxylic acid acceptor units. The tuning of π-spacers and anchoring groups led to variation of the photovoltaic performances. The DSSC based on QD1 with a cyanoacrylic acid and ethylene, obtained a PCE of 5.28%, which was higher than that of QD2 with a carboxylic acid and phenylethylene, and QD3 with a carboxylic acid and thiophene ethylene. The absorption spectra of QD2 and QD3 with the increasing of the length of the π-spacers are blue-shifted compared to that of QD1. The absorbed amount of QD1 was the highest of all, contributing to the highest J_sc of 12.28 mA cm⁻². The different V_oc values, in the order of QD1 (0.65 V) > QD2 (0.60 V) > QD3 (0.53 V), are caused by the charge recombination rates at the TiO₂/dye/electrolyte interface and the electron lifetimes.