Diphenylamino-substituted derivatives of 9-phenylcarbazole as glass-forming hole-transporting materials for solid state dye sensitized solar cells

The synthesis and properties of glass-forming diphenylamino-substituted derivatives of 9-phenylcarbazole with methoxy groups in the different position of diphenylamino moieties are reported. A comparative study on their thermal, optical, photoelectrical and electrochemical properties is presented. The synthesized compounds exhibit high thermal stability with 5% weight loss temperatures ranging from 344 to 475 °C. The derivatives absorb electromagnetic irradiation in the range of 225–425 nm with the band gaps of 2.94–3.08 eV. The ionization energies of the synthesized compounds range from 5.04 to 5.56 eV. The lowest ionization energies and band gaps are observed for compounds containing para methoxy-substituted phenyl rings of diphenylamino moieties and for disubstituted carbazole derivatives. Charge-transporting properties of the selected compounds were tested by time-of-flight technique. Hole drift mobilities in the amorphous layers of the materials reach 10⁻³ cm²/V s at high electric fields. The derivatives were tested as hole transport materials in solid-state dye sensitized solar cells and showed conversion efficiency up to 0.54%.     

Effect of process parameters on the efficiency of dye sensitized solar cells

The impact of process parameters on the efficiency of dye-sensitized solar cell (DSSC) was studied in order to improve its performance. TiO₂ working electrodes were prepared on FTO glass for various TiO₂ mixing time. Also these electrodes were sintered at four different temperatures (400, 450, 500, and 550°C) for one hour in ambient atmosphere. Platinum-sputtered counter electrodes were prepared at different light transmittance (70, 50, 30, and 0%). Microstructural charecterization of these electrodes were studied by X-ray diffraction method (XRD) and Scanning electron microscope (SEM). I–V characteristics of DSSCs made up of different working and counter electrodes were studied using solar simulator. Maximum efficiency (open circuit voltage (V_oc)∼0.68 V and short-circuit current density (J_sc) ∼ 12.3 mA/cm²) was observed for DSSC consisting of TiO₂ working electrode (12h mixing time, 500°C sintering temperature) and 0% transmittance Pt counter electrode. These results indicate that enhancement possibility of overall performance in DSSC was obtained by controlling process parameters, especially TiO₂ mixing time, sintering temperature and counter electrode transmittance.