Optimization of performance and stability of quantum dot sensitized solar cells by manipulating the electrical properties of different metal sulfide counter electrodes

TiO2 Passivation Layer on ZnO Hollow Microspheres for Quantum Dots Sensitized Solar Cells with Improved Light Harvesting and Electron Collection

Light harvesting and electron recombination are essential factors that influence photovoltaic performance of quantum dots sensitized solar cells (QDSSCs). ZnO hollow microspheres (HMS) as architectures in QDSSCs are beneficial in improving light scattering, facilitating the enhancement of light harvesting efficiency. However, this advantage is greatly weakened by defects located at the surface of ZnO HMS. Therefore, we prepared a composite hollow microsphere structure consisting of ZnO HMS coated by TiO₂ layer that is obtained by immersing ZnO HMS architectures in TiCl₄ aqueous solution. This TiO₂-passivated ZnO HMS architecture is designed to yield good light harvesting, reduced charge recombination, and longer electron lifetime. As a result, the power conversion efficiency (PCE) of QDSSC reaches to 3.16% with an optimal thickness of TiO₂ passivation layer, which is much higher when compared to 1.54% for QDSSC based on bare ZnO HMS.

Ti Porous Film-Supported NiCo₂S₄ Nanotubes Counter Electrode for Quantum-Dot-Sensitized Solar Cells

In this paper, a novel Ti porous film-supported NiCo₂S₄ nanotube was fabricated by the acid etching and two-step hydrothermal method and then used as a counter electrode in a CdS/CdSe quantum-dot-sensitized solar cell. Measurements of the cyclic voltammetry, Tafel polarization curves, and electrochemical impedance spectroscopy of the symmetric cells revealed that compared with the conventional FTO (fluorine doped tin oxide)/Pt counter electrode, Ti porous film-supported NiCo₂S₄ nanotubes counter electrode exhibited greater electrocatalytic activity toward polysulfide electrolyte and lower charge-transfer resistance at the interface between electrolyte and counter electrode, which remarkably improved the fill factor, short-circuit current density, and power conversion efficiency of the quantum-dot-sensitized solar cell. Under illumination of one sun (100 mW/cm²), the quantum-dot-sensitized solar cell based on Ti porous film-supported NiCo₂S₄ nanotubes counter electrode achieved a power conversion efficiency of 3.14%, which is superior to the cell based on FTO/Pt counter electrode (1.3%).