Designing Novel Poly(oxyalkylene)-Segmented Ester-Based Polymeric Dispersants for Efficient TiO₂ Photoanodes of Dye-Sensitized Solar Cells

A family of new polymeric dispersants, branched poly(oxyethylene)-segmented esters of trimellitic anhydride adduct (polyethylene glycol–trimethylolpropane–trimellitic anhydride, designated as PTT), were synthesized and utilized to homogeneously disperse TiO2 nanoparticles. The weight fraction of poly(oxyethylene)-segment in the dispersants and the molecular architecture in favoring the branched shape are two predominant factors for designing the effective dispersants. In particular, the poly(oxyethylene) block of 1000 g/mol from PEG1000 as the starting material and a total molecular weight of 12 000 g/mol have constituted the polymeric dispersants for the best performance for homogenizing TiO2 nanoparticles. The dispersant structures were characterized by using Fourier-transform infrared spectroscopy, acid value determination, and gel permeation chromatography. The TiO2 dispersibility was evaluated by dynamic light scattering and transmission electron microscopy. The synthesized dispersants were utilized to homogenize the as-prepared TiO2, further fabricated into films of photoanodes for dye-sensitized solar cells (DSSCs). The ultimate performance of DSSC was measured to be 8.17 ± 0.13% for the device efficiency (η) which was significantly higher than the conventional TiO2 photoanode at η = 7.14 ± 0.12%. The photoanode film was characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area, and dye-loading amount measurements. The kinetics of photogenerated electron in the photoanode, including electron lifetime and electron transit time of the film, was studied via electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy.