Improved charge extraction with N-doped carbon quantum dots in dye-sensitized solar cells

Highlights: • Up-converting N-CQDs are converted from strawberry powders. • N-CQDs and N719 are applied to co-sensitize m-TiO₂ for high-efficiency DSSCs. • The N-CQDs markedly increase charge extraction of DSSC devices. • A maximized PCE of 9.29% is achieved for N₃₀₀-CQDs/N719 co-sensitized DSSCs. • LPPs make the solar cell persistently generate electricity in the dark. Dye-sensitized solar cells (DSSC) have narrow spectral response and serious electron-hole recombination, which are two burdens for photovoltaic performance enhancement. In order to make high-performance DSSCs featured by wide-spectral absorption and fast charge extraction, we present here experimental realization of co-sensitization of nitrogen (N)-doped carbon quantum dots (N-CQDs) with N719 dye. Arising from up-conversion and hole extraction behaviors of N-CQDs, a maximized power conversion efficiency (PCE) as high as 9.29% under one sun illumination is achieved for N₃₀₀-CQDs/N719 co-sensitized DSSC in comparison with 8.09% for N₃₀₀-CQDs-free device. Due to light storing and emitting characteristics of photofluorescent long persistence phosphors in mesoscopic titanium dioxide/long persistence phosphor (m-TiO₂/LPP) photoanode, electricity is persistently generated when ceasing sunlight illumination. This work is far from optimization, but the physical proof-of-concept co-sensitization and fast charge extraction may remarkably widen light-response windows and promote electron-hole separation for advanced photovoltaic devices.