Applied Research Of Quaternary Cobalt-based Spinel Sulfide Counter Electrode In Quantum Dot Sensitized Solar Cell

Quantum dot sensitized solar cells(QDSSCs)is a new type of solar cell developed to solve energy and environmental problems.The catalytic activity of the counter electrode(CE)is one of the key factors affecting the photovoltaic performance of the device.Spinel sulfides have been widely used in the field of electrochemistry due to their excellent physicochemical properties.And the unique lattice structure of spinel can accommodate a variety of transition metal cations,which provides a rich channel for controlling the properties of spinel materials.In this paper,Mn-Ni-CO,Cu-Ni-CO spinel sulfides and their composites were prepared.A series of structure,morphology and electrochemical performance tests were conducted,and QDSSCs were assembled with Ti O₂/Cd S/Cd Se photoanode for photovoltaic performance test.The main contents are as follows.Quaternary cobalt-based spinel sulfides were prepared by two-step method contained oxide preparation and subsequent hydrothermal vulcanization or one-step solvent-thermal method.In the two-step method,spinel sulfide prepared by hydrothermal sulfurization for 24 h has good crystallinity.While Mn_0.5Ni_0.5Co₂S₄ with high crystallinity and improved electrocatalytic activity can be prepared by one-step solvent thermal method.SEM was used to observe the irregular morphology of Mn_0.5Ni_0.5Co₂S₄ made of nano-flakes and small particles stacked in disorder,which increased more active sites on the surface,facilitating the infiltration of multi-sulfur electrolyte and catalytic reduction reaction.The QDSSCs based on Mn_0.5Ni_0.5Co₂S₄ CE finally achieved 4.57%photoelectric conversion efficiency.The Cu_0.5Ni_0.5Co₂S₄ and Mn_0.5Ni_0.5Co₂S₄ prepared by one-step solvent thermal method.Compared with Ni Co₂S₄ CE,the series impedance R_s(3.06?)and charge transfer impedance R_ct(2.04?)of Cu_0.5Ni_0.5Co₂S₄ CE decreased by 13.73%and 61.27%,respectively.The excellent electrochemical performance of Cu_0.5Ni_0.5Co₂S₄ CE is attributed to the synergistic effect of three metal ions and abundant catalytic active sites,while the improvement of stability may be caused by lattice distortion in the structure of quaternary spinel.The QDSSCs based on Cu_0.5Ni_0.5Co₂S₄ CE obtained the optimal photovoltaic performance,and itsJ_sc?V_oc?FF and PCE were 18.11 m A·cm^-2?0.59 V?0.49 and 5.20%,respectively.For the CNCS/RGO composite materials prepared by one-step solvent thermal method,the introduction of two-dimensional RGO reduces the stack of spinel nanoparticles.However,the larger size of the sheet RGO leads to the increase of the contact resistance between the composite and the titanium mesh substrate,which hinders the rapid transmission of electrons.The QDSSCs based on the best performance composite CE reached 5.09%of the photoelectric conversion efficiency,which was slightly lower than Cu_0.5Ni_0.5Co₂S₄-based cell efficiency.