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.