Preparation And Interfacial Control Of High Quality Light Absorbing Layers In Perovskite Solar Cells

Metal halide perovskite materials have attracted great interest in the field of materials and optoelectronic devices due to their excellent photoelectric properties and low-cost solution preparation technology in recent years.The photoelectric conversion efficiency of perovskite solar cells has rapidly increased from the initial 3.8%to 25.5%of the international certification record during only one decade,which is an unprecedented feat in other types of photovoltaic technologies.As a new type of photovoltaic devices,the performance of a perovskite solar cell is greatly determined by the morphology and photoelectric properties of the light absorption layer.A light absorption film in high quality is the basis for obtaining high-performance solar cells.On the other hand,although the conversion efficiency of devices is continuously improving,the stability of the solar cells has gradually become one of the bottlenecks restricting its further commercial development.Generally,the purpose of this thesis is to improve both of the energy conversion efficiency and the stability of perovskite solar cells by promoting the light absorbing layers.As results,The perovskite solar cellss with high efficiency and stability are obtained by means of crystallization control and component engineering of the perovskite films,and interfacial control of the related interface.The details are presented as follows:（1）A new method for preparing high-quality perovskite films in air was developed:liquid-film-covering two-step deposition method.This method can not only adjust the proportion of complex phase in the process of perovskite film formation,but also prevent the adverse effect of water molecules on the crystallization of perovskite film due to the excellent water resistance of terpineol.The conversion efficiency of the planar cell devices fabricated by this method was as high as 18.53%,and still maintained 79.13%of its initial efficiency value after 1000 hours in air environment.（2）A kind of MA₃Bi₂I₉ nanosheets/MAPb I₃ heterostructure perovskite light absorption film was prepared and successfully applied into solar cells.The unique 2D/3D heterostructure not only improved the crystallization quality of MAPb I₃ films,but also greatly improved the stability of MAPb I₃ materials due to the introduction of hydrophobic MA₃Bi₂I₉ nanosheets.The final planar cell device achieved a conversion efficiency of18.97%and a stable output efficiency of 18.57%,with good repeatability.In addition,it can maintained more than 70%of the initial PCE at 25°C and 30%RH for 1000 hours,showing excellent device stability.（3）With Bi I₃ regulating the crystallization of FAPb I₃ perovskite films.Appropriate amount of Bi³⁺can improve the tolerance factor of the cubic phase of FAPb I₃ perovskite structure,and effectively inhibit the transition to non perovskite phase at room temperature.The planar cell devices based on FAPb_0.95Bi_0.05I₃perovskite films achieved a conversion efficiency of 17.78%,which was more than 36%higher than that of the controlled FAPb I₃cell.（4）High quality A₃Bi₂I₉（A=MA⁺,Cs⁺）perovskite nanosheets were successfully prepared by a dissolution-recrystallization method,and the photovoltaic performance of Cs₃Bi₂I₉ devices was systematically studied.In particular,the Cs₃Bi₂I₉ nanosheet thin film based device with inorganic semiconductor Cu I as the hole transport layer had achieved a conversion efficiency of up to 3.20%.It was among one of the highest PCEs of bismuth based perovskite solar cells at that time.Although the conversion efficiency of Cs₃Bi₂I₉thin film solar cells is still lower than that of lead-based perovskite cells,the long-term stability of all inorganic Cs₃Bi₂I₉ thin-film solar cells with Cu I as hole transport material still shows great potential in photovoltaic applications.（5）Application of Bi I₃ modified Ti O₂ electron transport layer in planar perovskite solar cells.The introduction of appropriate concentration of Bi I₃ modified layer can not only effectively improves the crystallization quality and surface morphology of perovskite films on planar substrates,but also effectively inhibits the chemical activity of Ti O₂ surface defects due to the excellent oxidation resistance of Bi I_3.Thus,the using of Bi I₃ modified Ti O₂layer greatly improved the conversion efficiency and stability of the planar devices.Finally,the conversion efficiency of planar solar cells wa s up to 17.79%.This is also one of the highest efficiency of perovskite solar cell prepared by green non-toxic solvent at that time.