Boosting the power conversion efficiency of quantum dot sensitized solar cells via g-C3N4 modified TiO2 nanoparticles

Abstract

In spite of the great development in quantum dot sensitized solar cells (QDSSCs), enrichment of material system of QDSSCs is still imperial mission for further advances. In this report, two-dimensional graphitic carbon nitride (g-C3N4) prepared from urea was applied to modify porous TiO2 photoanodes, followed by the deposition of CdS and CdSe QDs as sensitizers. In the as-prepared photoanodes, g-C3N4 functioned as barrier for retarding electron backward recombination and assisted to strengthen light absorption. Compared with the pure TiO2 photoanode, the photoelectrical behaviors of g-C3N4 modified TiO2 photoanode were obviously improved. By optimizing the loading amount of g-C3N4, the champion performance was achieved at 15% addition amount of g-C3N4 with shortcircuit current density of 15.1 mA cm−2, open circuit voltage of 0.56 V, and energy conversion efficiency of 4.14% under AM 1.5 illumination. The improvement in cell performance was attributed to the type II alignment between g-C3N4 and TiO2, which induced the fast separation of photogenerated carriers. The transfer of the photogenerated electrons and holes is driven by the conduction band offset of 0.39 eV and the valence band offset of 0.86 eV, respectively. Present results provided a new insight for further optimum photoanode structures of QDSSCs.