High-Performance All-Solid-State Dye-Sensitized Solar Cells Utilizing Imidazolium-Type Ionic Crystal as Charge Transfer Layer

An organic ionic crystal, 1-methyl-3-acetyl-imidazolium iodide (MA-II), was synthesized and applied into all-solid-state dye-sensitized solar cells as electrolyte material. We adopted 1-methyl-3-propylimidazolium tetra-fluoroborate as a crystal growth inhibitor, lithium bis-trifluoromethanesulfonylimide as a charge transport enhancer, and 4-tert-butyl pyridine as a carrier recombination inhibitor. The solar cell devices achieved the total conversion efficiencies of 2.6 and 2.0% under half a sun and one sun irradiation, respectively, showing a good stability even without any sealing and protection from ambient condition. The inner work mechanism of solar cell devices was analyzed by measuring the photovoltage, photocurrent transients, and the electrochemical impedance spectra. The results indicated that target solid-state materials from liquid molten salts can be obtained ultimately through molecular design and adjustments of molecular structure, which can be used effectively in photoelectrical devices.