Effects of Metal Oxyhydroxide Coatings on Photoanode in Quantum Dot Sensitized Solar Cells

Exploring facile modifications on photoanode to suppress charge recombination at photoanode/electrolyte interfaces is an efficient way to improve the performance of quantum dot sensitized solar cells (QDSCs). Herein, a series of metal oxyhydroxide gels have been overcoated on CdSeTe QD sensitized photoanodes via a hydrolysis and condensation process from the corresponding metal chloride (NbCl5, ZrOCl2, SnCl4, FeCl3, AlCl3, CoCl2, CuCl2, MgCl2, and ZnCl2) aqueous solutions, and their effects on the photovoltaic performance are systematically investigated. Photovoltaic measurement results indicate that the NbCl5 and ZrOCl2 modifications offer a remarkable enhancement in photovoltaic performance, especially in photovoltage. The SnCl4 AlCl3, MgCl2, and ZnCl2 treatments give a negligible influence, and the FeCl3, CuCl2, and CoCl2 treatments present a negative effect on the performance. DFT calculations suggest that different metal oxyhydroxide coatings bring forward distinct densities of empty states at the surface of TiO2, which correspond to different charge recombination kinetics and therefore different photovoltaic performance. Electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements confirm further the suppressed charge recombination process after coating with the amorphous Zr or Nb oxyhydroxide layer. In all, an impressive power conversion efficiency (PCE) of 9.73% (Jsc = 21.04 mA/cm2, Voc = 0.720 V, FF = 0.642) was obtained for CdSeTe-based QDSCs with ZrOCl2 modification on photoanode.