Enhanced photovoltaic performance of dye-sensitized solar cells based on Co9S8 nanotube array counter electrode and TiO2/g-C3N4 heterostructure nanosheet photoanode

High-performance dye-sensitized solar cells (DSSCs) are for the first time reported based on rationally designing g-C3N4 modified TiO2 nanosheets as photoanodes and Co9S8 nanotube arrays (ANTAs) as counter electrodes (CEs). The coupling of g-C3N4 with TiO2 to form a heterojunction extends optical response behavior of TiO2 to visible-light region, and simultaneously restrains the recombination rate of photogenerated charges, thus greatly enhances the photovoltaic performance of TiO2 DSSCs. The smaller electron transport resistance of DSSCs based on TiO2/g-C3N4 photoanodes indicates higher charge transfer ability. Compared with Pt CE, Co9S8 ANTAs CEs show higher electrocatalytic ability towards I−/I3− reaction. It can be proved by cyclic voltammetry and Tafel polarization techniques, which show higher anodic and cathodic peak current density. Longer carrier lifetime is observed for DSSCs based on Co9S8 ANTAs CEs and TiO2/g-C3N4 photoanodes, which indicate the decrease of the combination of the injected electrons with the I3− ions in the electrolyte. DSSCs based on Co9S8 ANTAs CEs and TiO2/g-C3N4 photoanodes show a power conversion efficiency of 8.07%, much higher that of pure TiO2 photoanode.