Interface Regulation Of Mesoporous Layer And Optimized Design Of Back Electrode In Perovskite Solar Cells

Perovskite Solar Cells?PSCs?have the advantages of abundant raw materials,easy and large-scale fabrication.The efficiency of PSCs has grown rapidly from 3.8%to 24.2%in recent decade years.In the future,it will become the main trend of the development in the photovoltaic field.In PSCs,series resistance causes loss of energy,which will reduce the power conversion efficiency?PCE?.The mesoporous TiO₂ is still the most efficient and often used for mesostructured PSCs.However,high interfacial charge recombination,poor electron transfer and low open circuit voltage(V_OC)exist in mesostructured PSCs based on intrinsic defect-rich low mobility TiO₂.Therefore,it is important to modify the interface or design the surface of the mesoporous TiO₂ substrate.However,for devices,the introduction of an additional modification layer will increase the series resistance,which will affect the PCE of PSCs.In addition,one-step in-situ modification of TiO₂ surface is rarely reported at present.The resistance of back electrode is an important part of series resistance,which has a large space for optimization.But researchers are paying less attention to the design and optimization of the back electrode now.In this thesis,in order to regulate the interface of mesoporous layer and reduce the series resistance of PSCs,the in-situ modification of the mesoporous layer and the design and optimization of the back electrode were studied.The main works and achievements are as follows:In Chapter 1,both the research background,classification of solar cells,and the development,device structures,working principle and important performance parameters of perovskite solar cells were introduced.In Chapter 2,the device fabrication process was illustrated in detail.Moreover,the characterization and testing methods including the related conditions for film samples and solar cell devices were described.In Chapter 3,the effects of self-assembled ultra-thin MgO coated TiO₂ core/shell nanostructure on mesoporous layer,perovskite layer and device properties were investigated.The effect and mechanism of MgO ultra-thin coating on TiO₂ were studied by analyzing the photophysical properties,photogenerated carrier transport kinetics and carrier recombination.An amorphous ultrathin outer nanolayer of MgO was conformally coated onto TiO₂ core nanoparticles in a one-step bottom-up approach.Such self-assembled MgO/TiO₂ core/shell nanostructures would retain the mesoporous structure feature,supply more contact interface of MgO/TiO₂ and separate the TiO₂ and perovskite directly,which can not only passivate surface defects and reduce charge-recombination,but also facilitate charge-extraction at the mesoporous layer/perovskite interface and electrons transfer in PSCs.Based on the mesoporous layer consisting of optimized MgO-coated TiO₂ nanoparticles,the corresponding open circuit voltage(V_OC)and fill factor?FF?of PSCs were 1.00 V and78.49%,4.2%and 13.8%higher than the uncoated TiO₂ based PSCs,respectively,and the obtained power conversion efficiency?PCE?was increased from 13.13%to 16.30%with well-suppressed J-V hysteresis.Meanwhile,the photovoltaic characteristics and the well-behaved junction property were further clarified by the ideal model,where a much lower series resistance is obtained for the cell based on m-TiO₂ with MgO coating.In addition,we provided an easy regulated uniform coating route to fabricate well-defined core-shell nanoparticles with modified properties.In Chapter 4,the effect of resistance of the back electrode on the PSCs was studied,and the structure,thickness and material of the back electrode were optimized.Seven different structures of back electrode were designed and simulated by COMSOL software to explore the effect of electrode structure,electrode thickness and electrode material on the PSCs.In addition,the effect of back electrode thickness on photoelectric performance was also optimized by experiments.It was found that the back electrode structure affects the performance of the cells by varying the series resistance.Only considering the electrode resistance,the ideal electrode material is Ag,and the optimum thickness of the back electrode is about 100 nm by combining the simulation with the experiment.In Chapter 5,the research works of this thesis were summarized.In addition,the methods of suppressing carrier recombination and the optimization of back electrode to improve the photoelectric performance of the PSCs were prospected.