Effect of π-Bridge Chain Rearrangement in a Sensitizer on Photovoltaic Performance of Dye-Sensitized Solar Cells

In this paper, novel triphenylamine (TPA)-based photosensitizers (YY-ThP, YY-PTh, YY-TTP, and YY-PTT) with a donor-π-acceptor (D-π-A) structure are developed for dye-sensitized solar cells by rearrangement of planar thiophene and thienothiophene with a benzene ring as a π-bridging chain. Density functional theory calculations are performed to obtain the HOMO-LUMO electron cloud density distribution, dipole moment (μ), intermolecular torsion angle (θ), three-dimensional (3D) molecular structure, and electrostatic potential surface (ESP) maps of the dyes. The effects of π-bridge chain rearrangement and dye cosensitization on the photophysical, electrochemical, and photovoltaic properties of the devices are investigated through experiment analysis. The results showed that the dye YY-ThP with the thiophene group in the π-bridged chain linked to the TPA donor has the largest μ (14.74 D) and the smallest θ (17.48°), and the electron-withdrawing thiophene group enabled this π-bridged chain with a faster intramolecular charge transfer, which made it exhibit the best energy conversion efficiency (PCE = 4.78%). Furthermore, cosensitization of the YY-ThP+YY-PTh device in an equimolar ratio minimizes lateral electron migration and dark current generation, achieving the highest PCE (5.28%).