Effect of π‑Bridge Chain Rearrangement\nin a Sensitizer on Photovoltaic Performance of Dye-Sensitized Solar\nCells

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