Synthesis and characterization of triphenylamine modified azobenzene dyes

A series of triphenylamine modified azobenzenes were synthesized and studied theoretically and experimentally. D-A-D structures of these dyes were revealed with an intramolecular charge transfer (ICT) from both triphenylamine or indoline units (donor) to the central azobenzene unit (acceptor). Both computational and experimental results indicate that a stronger electron donating ability of the donor enhances the degree of ICT and improve their HOMO energies. The absorption spectra indicate an increased light absorption by enhanced ICT effect. The intermolecular interaction also affects their absorption ability. The strongest intermolecular interaction results in the best light absorption ability in films. An obviously increased hole mobility was also found as the ICT was enhanced. These dyes were used as hole transport materials (HTM) of perovskite solar cells to investigate their feasibility. It is revealed that the solubility and filming ability are significant for the photovoltaic performance of devices.