N-Aryl group influences on the properties of umbrella-shaped thiophene-(N-aryl)pyrrole-thiophene dyes

To investigate the N-aryl group influences on the optical, electrochemical and photovoltaic properties of thiophene-(N-aryl)pyrrole-thiophene (N-Aryl TPT)-based dyes, two new dyes (TPTDYE 3 and TPTDYE 4) were prepared by attaching the electron donating and non-planar 4′-(N,N-diphenylamino)biphenyl or 3-fluoro-4′-(N,N-diphenylamino)biphenyl group on the pyrrole nitrogen of the thiophene-pyrrole-thiophene (TPT) unit and the electron accepting cyanoacrylic acid group at the 3-position of pyrrole unit. In addition, another two new dyes (TPTDYE 5 and TPTDYE 6) were obtained by introducing two more triphenylamine groups on the both side of the TPT unit of TPTDYE 3 and TPTDYE 4, respectively. The shapes of the dyes are found to be similar to umbrella, since three electron donor groups are placed around the cyanoacrylic acid group positioned at middle of the dyes. The absorption spectra of dyes TPTDYE 5 and TPTDYE 6 were found to be relativity broad (∼300–475 nm) and red shifted compared to the absorption spectra (∼300–425 nm) of dyes TPTDYE 3 and TPTDYE 4. The electrochemical studies indicate that the HOMO energy levels of the non-fluorinated dyes (TPTDYE 3 and TPTDYE 5) were slightly deeper than fluorinated dyes (TPTDYE 4 and TPTDYE 6). The dye sensitized solar cells (DSSCs) prepared with TPTDYE 5 with and without coadsorbent offered a maximum energy conversion efficiency of 4.02% and 3.42%, respectively.