Effects of aromatic π-conjugated bridges on optical and photovoltaic properties of N, N-diphenylhydrazone-based metal-free organic dyes

Abstract

A series of novel D–π–A hydrazone dyes ( HB, HP, HF and HT) containing an N, N-diphenylhydrazone donor and 2-cyanoacetic acid acceptor linked by a different aromatic bridge (benzene, pyrrole, furan, and thiophene) have been designed and synthesized to evaluate the aromatic bridge effects on the photophysical, electrochemical and the photovoltaic properties of the hydrazone-sensitized TiO 2 solar cells. Each of the hydrazone-based dyes exhibited different adsorption behavior, frontier molecular orbitals, and photovoltaic performance depending on the identity of aromatic π-conjugated bridges. Specifically, HP-sensitized TiO 2 solar cell showed an obviously higher photocurrent, photovoltage, and power conversion efficiency than other three dyes. We interpret that these results were stemmed from light-harvesting abilities, the charge recombination rate and electron lifetime of different aromatic bridges. Optical spectroscopy, cyclic voltammetry, density functional theory calculations, electrochemical impedance spectra, and photovoltaic measurements were employed to support our proposal. With the addition of 1 mM chenodeoxycholic acid (CDCA) as the coadsorbent, a maximum power conversion efficiency of a DSSC based on HP was 7.74% ( J sc = 16.17 mA/cm 2, V oc = 0.69 V, FF = 0.694) under simulated AM 1.5 G solar irradiation (100 mW/cm 2). This work suggests that N, N-diphenylhydrazone and N-(2-ethylhexyl) substituted pyrrole moieties can be used as an alternative and effective donor and π-conjugated bridge, respectively, in the construction of efficient D–π–A organic dyes.