The role of graphitic C3N4 in improving the photovoltaic performance of CdS quantum dots sensitized solar cells

Abstract

Graphite-like C3N4 in layered structure (graphitic C3N4, g-C3N4) was introduced into CdS quantum dots sensitized solar cells (QDSCs) to improve the photovoltaic performance. The g-C3N4 enlarges sunlight absorption due to good response to visible light and simultaneously appropriate content g-C3N4 suppresses TiO2 nanoparticle aggregation in QDSC photoanode beneficial from its layered structure. Compared with the melamine prepared g-C3N4, the layer thickness of g-C3N4 prepared from urea is smaller and the specific surface area is larger. The g-C3N4/TiO2 composite for photoanode is prepared through one-step calcining the mixture of urea and TiO2 precursors and then, the prepared g-C3N4/TiO2 photoanode was deposited with CdS QDs. The results showed that g-C3N4 improved not only sunlight absorption, but also the efficiency of electron injection into TiO2 photoanode. The nonlinear synergistic effect existed when g-C3N4 and CdS QDs served as sunlight harvester at the same time, since g-C3N4 and CdS formed hetero-junction in QDSCs. The urea amount in the precursor is modified to optimize photovoltaic properties of QDSCs. The mechanism of g-C3N4 content effect on QDSC photovoltaic performance was investigated systematically through combining photoanodes micro-structural characterization with electrochemical impedance spectrum (EIS) and current density–voltage (J-V) curve measurement.