Enhance photovoltaic performance of tris(2,2'-bipyridine) cobalt(II)/(III) based dye-sensitized solar cells via modifying TiO2 surface 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 TiO2 films. Compared to the uncoated samples, dye-sensitized solar cells with such films exhibit enhanced open circuit voltage (V-oc) and short circuit current (Jsc) 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 TiO2 working electrodes were found to increase after ZIF-8 treatment, which is responsible for the improvement of Jsc. 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 Voc, as there is no TiO2 conduction band shift after the treatment of ZIF-8. (C) 2017 Elsevier Ltd. All rights reserved.