Position of the anchoring group determined the sensitization efficiency of metal-free D-π-A dyes: Combined experimental and TD–DFT insights

Abstract

We report on the design and synthesis of new D-π-A organic sensitizers incorporating D35 as the electron donor unit and (benzyloxy)benzene as the π- linker. The structure and yield of the synthesized dyes were confirmed via The 1H NMR, 13C NMR, and mass spectrometry analyses. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to get insights on the electronic properties of the synthesized dyes, indicating their capability as photosensitizers. The photophysical characteristics, electrochemical properties, and photovoltaic performance of the sensitizers were investigated. The cyclic voltammetry measurements showed that the oxidation potentials of the excited states of the dyes are more negative than the conduction band edge of anatase TiO2 and their ground state oxidation potentials are more positive than the CoII/III redox shuttle, indicating their potential as photosensitizers. The dye containing benzyloxy group at the para position to the anchoring group showed higher power conversion efficiency (PCE), higher light harvesting efficiency (LHE), wider range of absorption, lower bandgap, higher incident photon-to-current conversion efficiency (IPCE), and higher excitation binding energy than the counterpart dye containing benzyloxy group in the ortho position.