Research On High Performance CdS/CdSe Quantum Dot Sensitized Solar Cells And Flexible Devices

Since the 21st century,energy shortages and environmental deterioration have become increasingly serious.Mankind urgently needs to develop efficient,clean,cheap and sustainable energy to solve the current energy crisis.After unremitting exploration and practice,solar energy has become an important part of replacing fossil fuels as a new energy source.Among them,photo-to-electronic conversion as one of the most important form of utilizing the solar energy resource has attracted much attention.Due to many advantages such as adjustable band gap,high molar extinction coefficient,multi-exciton generation effect,resistance to water and oxygen,low cost and simple process,the quantum dot sensitized solar cell?QDSSC?has been intensively studied and made great progress.However,due to factors such as high charge transfer resistance,severe charge recombination,and narrow light absorption range,the power conversion efficiency of the cell is still relatively low compared to theoretical values,which greatly limits its further development and application.At the same time,photovoltaic devices must also have the characteristics of flexibility and diversity in practical applications.Thick substrate materials,cumbersome processes and high costs limit the development and application of QDSSC.On this basis,we have carried out our research work from improving the photovoltaic performance of QDSSC and exploring the application of flexible devices:?1?CdS/CdSe quantum dots have been extremely limited absorption and utilization of ultraviolet light and near-infrared light.Therefore,broadening the light absorption range of CdS/CdSe QDSSC and improving the photo-to-electron conversion are essential to enhance the performance of the solar cell.In this part of the work,a multifunctional long persistence phosphors structure layer was introduced into the CdS/CdSe QDSSC,and the material properties of the structure layer and its impact on solar cells have carefully studied.After the microscopic morphology characterization,optical performance test,electrochemical test and monochromatic incident photon-to-electron conversion efficiency test of electrode materials and devices,we have found that the long persistence phosphors structure layer can absorb and convert the ultraviolet light,radiate and reflect visible light,then broaden the absorption range and improve the light harvesting efficiency.Compared with traditional CdS/CdSe QDSSC,it can be found that the short-circuit current density of cells is significantly enhanced,and the conversion efficiency is increased from 4.08%to 5.07%,an increase of about24%.?2?Based on the development demand of portable solar cells,it is imperative to enhance the flexibility of QDSSC and simplify the tedious preparation process.Therefore,it is urgent for us to develop a flexible QDSSC with the advantages of low production cost,light quality,simple process and excellent adaptability.In this part,sputtering/hydrothermal method and coating method were used to prepare flexible QDSSC,respectively,and the process and performance of flexible CdS/CdSe QDSSC photoanode have been thoroughly investigated.It can be found that the photovoltaic performance of the flexible CdS/CdSe QDSSC prepared by sputtering/hydrothermal method is poor.And by adopting strategies such as introducing additives and optimizing the preparation process,the flexible CdS/CdSe QDSSC prepared by the coating method has significantly improved the bonding performance between materials and the bending performance of the photoanode.After the micro-morphology characterization for the photoanode,it can be found that many cracks appeared on the surface of the flexible photoanode prepared by the rapid temperature change process,and the wide bandgap semiconductor was divided into small cells,which effectively enhanced the bending stability of the photoanode.We have also assembled flexible device using a quasi-solid electrolyte and a flexible Cu₂S counter electrode.Compared with traditional hard CdS/CdSe QDSSC,the series resistance of flexible devices is significantly increased,the light absorption performance and monochromatic incident photon-to-electron conversion efficiency are low,resulting in a decrease in short-circuit current density,and then the conversion efficiency is more than 3%.After 500 times of high-angle bending,the conversion efficiency of all samples remained above 60%of the initial,showing an excellent bending stability.