Study On The Preparation And Performance Of G-C₃N₄ Composite Electrode Of Quantum Dot Sensitized Solar Cell

As a green and environmentally friendly renewable resource,solar energy is currently attracting more and more attention from countries and energy scientists.At present,quantum dot-sensitized solar cells（QDSSCs）have become one of the main research directionsfor solar energy utilization due to their high theoretical energy conversion efficiency and low fabrication cost.Due to the large resistance and severe limitation of interfacial charge recombination,their photoelectric conversion efficiency are still far from the theoretical value.As one of the important components of quantum dot sensitized solar cells,the counter electrode not only enable the electrons transmitted from the external circuit,but also acts as a redox electrolyte in the battery,so the conductivity and stability of the counter electrode directly affects the optoelectronic properties of QDSSCs.Metal sulfides have been widely used in the research of QDSSCs counter electrode materials due to their good electrical conductivity and excellent catalytic activity.However,polysulfide electrolytes in QDSSCs can affect the stability of metal sulfides.Therefore,it is necessary to prepare a metal sulfide counter electrode with good stability,excellent electrical conductivity and catalytic activity to improve the photoelectric conversion efficiency.The research contents of this thesis are as follows:（1）Preparation and study of g-C₃N₄/CuS composite counter electrode.The g-C3N4 mesoporous film was prepared by the sol-gel method,and the g-C₃N₄/CuS composite counter electrode was prepared by the continuous ionic layer adsorption and reaction（SILAR）method on the g-C₃N₄ film.The Ti O₂/Cd S/Cd Se/Zn S photoanode was assembled into QDSSCs cells for photoelectric performance testing.Since the g-C₃N₄/CuS counter electrode combines the efficient catalytic activity of g-C₃N₄ and the good electrical conductivity of CuS,the cell performance is effectively improved.By controlling the deposition period of CuS on g-C₃N₄ thin films,the adhesion amount of CuS on g-C₃N₄ can be optimized to achieve the best performance.The CuS with 6 cycles showed the best performance with photoelectric conversion efficiency of 3.65%.（2）Preparation and study of g-C₃N₄/CuS/PbS composite counter electrode.The g-C₃N₄/CuS/PbS composite electrodes were prepared by sol-gel method and SILAR method,and QDSSCs were assembled with g-C₃N₄/Ti O₂ photoanode for testing.The experimental results showed that for g-C₃N₄/CuS counter electrode deposited 2 cycle PbS layer,the photoelectric conversion efficiency was increased to 4.1%,and the fill factor（FF）,short-circuit current density（Jsc）and open circuit voltage（Voc）were also increased to 35.67%、19.41 m A/cm^-2and 0.62V.The improved performance was attributed to the fact that the counter electrode of g-C₃N₄/CuS/PbS not only provided a large number of active sites for the redox of the counter electrode,but also accelerated the reaction rate of the counter electrode.According to Tafel and cyclic voltammetry（CV）curves,the exchange currentdensity（J₀）and limiting diffusion current density(J_lim)reach the maximum at two cycles.It is proved that g-C₃N₄/CuS/PbS composite electrode has better catalytic activity.