Star-shaped triphenylamine-based molecular glass for solid state dye sensitized solar cell application

• Synthesis of a star-shaped triphenylamine molecular glass based on carbazole moities.
• High purity, high thermal stability and low hole drift mobility have been measured.
• Application in solid-state dye sensitized solar cells shows promising results as HTM.

The synthesis by Suzuki cross-coupling and properties of a glass-forming star-shaped compound tris(9-(3-methylphenyl)carbazol-3-yl)-triphenylamine are reported. The thermal, optical, photoelectrical and electrochemical properties of the hole-transporting compound were studied by differencial scanning calorimetry, thermogravimetric analysis, UV/vis spectroscopy, electron photoemission, time-of-flight technique and cyclic voltammetry. The compound exhibits high thermal stability with a the temperature of the onset of the thermal degradation of 510 °C. The compound absorbs in 200–400 nm range and possesses an optical band gap of 3.15 eV, avoiding any screening effect with the dye. The solid state ionization potential (IPss) of the molecule, measured by electron photoemission and cyclic voltammetry is around 5 eV similar to the standard spiroOMeTAD hole-transporting material. The hole drift mobility in the amorphous layer of reported compound reach 6.4 × 10−5 cm2/Vs under high electrical field (6.4 × 105 V/cm). This synthesized derivative was finally assessed as hole transporting material in the solid state dye-senstized solar cells with (5-(1,2,3,3a,4,8b-hexahydro-4-[4-(2,2-diphenylvinyl)phenyl]-cyclopeanta[b]indole-7-ylmethylene)-4-oxo-2-thioxo-thiazolidin-3-yl)acetic acid (D102) as sensitizer and showed a power conversion efficiency of 0.63% under standard solar irradiation (100 mW/cm2, AM1.5).

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