A United States patent US 9,754,731 B2 was awarded to Prof. Wallace Leung, Chair Professor of Innovative Products and Technologies of the Department of Mechanical Engineering, PolyU, and his PhD student Lijun Yang, for a method of producing dye-sensitized solar cell, the most environmental friendly photovoltaics to-date.
The method concerns a novel configuration of using more than one or more dyes to harvest sunlight for the solar cell. The photo-anode made up of titanium nanofibers and the first dye is adsorbed onto the large surface area provided by the titanium nanofiber with diameter of 60 nanometers. The second dye is coated as a monolayer onto the nanofibers covering the first dye providing a core-shell structure, and likewise the third dye coated onto the second dye, etc. Each dye harvests sunlight independently whereby the photons are converted to electrons. The electrons from each dye pass onto the previous dye at lower energy level in a cascade manner and finally to the titanium nanofibers, which transport all the collected electrons to the electrode. This novel configuration reduces loss of electrons by recombination with the electrolyte/positive holes, thereby increasing the efficiency of the solar cell and each dye can harvest uniquely the wavelength of the solar spectrum thereby maximizing the light harvesting. The efficiency can reach 10% with low loss.
The work was published in LJ Yang, WWF Leung, JC Wang, “Improvement of Light Harvesting in Dye Sensitized Solar Cell Based on Cascade Charge Transfer,” Nanoscale, 2013, 5 (16), 7493-7498.