Enhance photovoltaic performance of tris(2,2″-bipyridine) cobalt(II)/(III) based dye-sensitized solar cells via modifying TiO₂surface with metal-organic frameworks

A very thin blocking layer of a metal organic framework ZIF-8 has been successfully coated on the surface of mesoporous TiO₂films. Compared to the uncoated samples, dye-sensitized solar cells with such films exhibit enhanced open circuit voltage (V_OC) and short circuit current (J_SC) by 3% and 21%, respectively, leading to a 9.42% energy conversion efficiency using tris(2,2′-bipyridine) cobalt(II)/(III) redox mediator. The electron lifetimes as well as dye loading on TiO₂working electrodes were found to increase after ZIF-8 treatment, which is responsible for the improvement of J_SC. An increase of charge recombination resistance between working electrode and organic electrolyte, as is characterized by electrochemical impedance spectra, is proposed to be the reason for the increased V_OC, as there is no TiO₂conduction band shift after the treatment of ZIF-8.