Design And Construction Of Counter Electrode Nickel Cobalt Selenide And Its Application In Photovoltaics

Dye-sensitized solar cells（DSCs）are considered as a new type of photovoltaic devices.Generally,counter electrode is an important part of DSCs.However,the application of dye-sensitized solar cells is limited due to the disadvantages of the traditional platinum counter electrode,such as easy corrosion and high cost.In recent years,the development of platinum-free counter electrode materials has become an important research direction in DSCs.Interestingly,cobalt selenide nanomaterials exhibit excellent electrocatalytic performance for DSCs.However,there are few reports on the application of cobalt selenide nanomaterials in DSCs,which are synthesized by using metal-organic framework as precursor.Therefore,cobalt selenide films with porous structure have been designed through metal organic framework.Furthermore,nickel element has been introduced into cobalt selenide films due to the synergistic effect of bimetallic.The effect of nickel element on the electrocatalytic performance of cobalt selenide films is systematically studied.The aim is to improve the photovoltaic performance of DSCs.（1）Two cobalt diselenide（Co Se₂-D and Co Se₂-S）films are prepared by electrodeposition,solvothermal,and selenization techniques.Co Se₂-S films possess the porous structure composed of small particles,which are beneficial to increase electrocatalytic active sites.And Co Se₂-D films are consisted of particles and sheet structures.In addition,cobalt and selenium elements are uniformly distributed on Co Se₂-S films.Meanwhile,the electron transport distance of Co Se₂-S films is reduced,due to their thin thickness comparing with Co Se₂-D films.The results from XPS and TEM characterization demonstrated that cobalt diselenide films are successfully synthesized.（2）The electrocatalytic activities of Co Se₂-D and Co Se₂-S counter electrodes are analyzed by CV,EIS and Tafel characterization techniques.The results demonstrate that the Co Se₂-S counter electrode has higher electrocatalytic activity than those of the platinum electrode and Co Se₂-D counter electrode.Then,Pt,Co Se₂-S and Co Se₂-D counter electrodes are assembled into DSCs.The photoelectric conversion efficiency of the DSC based on Co Se₂-S counter electrode is up to 6.86%,which is higher than that of the DSCs with Co Se₂-D counter electrode（5.75%）and platinum electrode（6.36%）.In addition,DSCs based on Co Se₂-S counter electrodes also show good repeatability.These results indicate that Co Se₂ nanomaterials show great application potential in DSCs.（3）The synergistic effect of bimetallic is further used to improve the electrocatalytic performance of cobalt selenide counter electrode Ni-Co-based selenides are synthesized by introducing Ni element in solvothermal process.The morphology and phase of Ni-Co-based selenides are adjusted by controlling molar ratio of Ni/Co to optimize their electrocatalytic performance.Specially,the results show that nickel-cobalt selenide film with the Ni/Co molar ratio of 1:1 displays the sheet structure composed of nanoparticles.The EDS and XPS spectra indicate that the atomic ratio of cobalt,nickel,and selenium is approximately 1:1:4.The electrochemical characterization demonstrates that the optimized Ni-Co-based selenide counter electrode exhibits higher electrocatalytic performance than that of Pt electrode.The DSC based on the optimized Ni-Co-based selenide counter electrode show the high photoelectric conversion efficiency of 7.84%,which is larger than those of DSCs based on platinum electrode（6.95%）,cobalt diselenide（5.46%）,and nickel diselenide（6.96%）.The above experimental results indicate that the electrocatalytic performance of Ni-Co-based selenide is improved by the synergistic effect,which is beneficial to the improve the photovoltaic performance of DSCs.