Enhanced light harvesting and charge recombination control with TiO₂/PbCdS/CdS based quantum dot-sensitized solar cells

Charge recombination is considered as one of the most significant factors in hindering the photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs). In addition, expand the light absorption range to the near-infrared region in QDSSCs increasing the generated photocurrent. A significant enhancement in the power conversion efficiency (PCE) of QDSSCs has been obtained by charge recombination control and enhanced light harvesting. In this respect, PbCdS layer is introduced between TiO₂ and CdS QDs via a facile successive ionic layer absorption and reaction (SILAR) method in order to further improve the cell performance. For the first time a photoanode assembly composed of TiO₂/PbCdS/CdS was prepared in QDSSCs. The photovoltaic parameters were significantly enhanced with the incorporation of a PbCdS intermediate layer between TiO₂ and CdS QDs but varied appreciably with the SILAR cycles of PbCdS. When four SILAR cycle layer was applied, the PCE is as high as 3.35%, which is higher than the efficiency of 1.84% for the solar cell without PbCdS layer. The improved performance of the TiO₂/PbCdS/CdS-based QDSSCs was attributed to the PbCdS layer can enhance the light harvesting to release more excitons. In addition, the PbCdS layer accelerates the electron injection kinetics and also functioning as a blocking layer to cover the TiO₂ core from the outer QDs and redox couple, thereby reducing the recombination of electrons from the TiO₂ with the electrolyte or with the QDs. Electrochemical impedance measurements has been measured and discussed in detail providing a detailed analysis of charge transport processes in QDSSCs.