Theoretical Study On The Intrinsic Properties Of Highly Active Iron Oxide And Their Application In PSCs

Nowadays,iron-based materials,especially iron oxides,have received extensive attention due to their significant applications,such as information transmission,catalytic conversion,fuel cells,and data storage materials.Iron oxides,whether used as catalysis or electron transport layer,are attractive in terms of their thermodynamic stability,synthesis,low toxicity and environmentally benign effects.Although iron oxides are favorable catalysts,current research shows thatα-Fe₂O₃ exhibit low activity in alcohol oxidation reactions,whileγ-Fe₂O₃ possess excellent selectivity and catalytic activity.Based on the above,it is necessary to conduct in-depth research on iron oxides with different crystal structures from the theoretical aspects,so as to clarify the reasons for their differences in catalytic activity.In this paper,based on the periodic density functional theory（DFT）,we provided a deep insight in the intrinsic properties ofα-Fe₂O₃,Fe₃O₄ andγ-Fe₂O₃,considering the effects of activated oxygen molecules on the surface of different catalysts.In addition,with the help of the density of states,charge density distribution and periodic natural bond orbitals,the catalytic active sites of Fe₃O₄ andγ-Fe₂O₃ were explored.The factors affecting the catalytic performance of iron oxide were comprehensively resolved.With the in-depth understanding of iron oxide materials,we noticed that iron oxides have been applied in some promising fields,such as perovskite solar cells.Before exploring the properties of the interface structure between iron oxides and perovskites,we studied the stable and efficient triple cations（MA/FA/Cs）based perovskite solar cells.The role of cations that have been neglected all the time is emphasized firstly in the nanoscale model.This thesis is divided into six chapters.The first chapter is the preface,which outlines the classification of iron oxides and their applications in heterogeneous catalysis.Moreover,the basic components and detailed mechanisms of perovskite solar cells are introduced.The influence of the existing electron transport layer on perovskite solar cell devices is described,and the significance of this research is explained.The second chapter explains the theoretical basis of the first-principles calculations used in this thesis.A comprehensive introduction to the calculation details during the research process is utilized.These contents include the introduction of surface structure,surface energy,molecular adsorption,vacancy formation and non-adiabatic molecular dynamics methods.Chapters 3 and 4 are introductions to the catalytic properties and intrinsic properties of iron oxide.The fifth chapter studies the stability and carrier properties of perovskite materials.The obtained main results are summarized as follows:1.From experimental results,it can be concluded that oxidative dehydrogenation of alcohols is the rate-determining step for imine synthesis.The following step in the coupling of benzaldehyde and aniline is a fast reaction,either onγ-Fe₂O₃ catalyst or onα-Fe₂O₃,and Fe₃O₄ catalysts.Suitability for activating molecular oxygen is the critical factor forγ-Fe₂O₃ in oxidative dehydrogenation of alcohols.Theoretical analysis of surface,geometric structure,and electronic structure shows thatγ-Fe₂O₃possesses excellent capability for molecular oxygen activation.Compared withα-Fe₂O₃ and Fe₃O₄,the surface Fe atoms ofγ-Fe₂O₃ easily transfer electrons to molecular oxygen.This work provides molecular-level insights into the crystal phase effect on catalytic performance in molecular oxygen activation,and can shed light on developing other metal oxide catalysts for molecular oxygen activation related reactions.2.With the preparation of previous work,in Chapter 4,we explore the differences in catalytic activity sites ofγ-Fe₂O₃ and Fe₃O₄.According to the results of adsorption energy,γ-Fe₂O₃ was more favorable to adsorb oxygen than Fe₃O₄.It explains whyγ-Fe₂O₃ has better catalytic performance in the oxidation reaction from another view.Interestingly,although Fe₃O₄ andγ-Fe₂O₃ were the same elements of the same crystal structure,their active sites were not consistent.The octahedral sites of Fe₃O₄ and tetrahedral sites ofγ-Fe₂O₃ acted as CASs.It is noticed that the presence of oxygen vacancies did not alter the active sites of Fe₃O₄ andγ-Fe₂O₃.3.Investigating the role of cations in the perovskite structure that have been neglected.When Cs ratio is 5%,it owns a suitable band gap and less overlap between VBM and CBM,thereby reducing the overlap of electron and hole.Although Cs sites have little influence on structural stability,the position of other cations around Cs play a vital role.When Cs cations is surrounded by a MA:FA molar ratio of 2:4,the configuration is more advantageous,resulting in a more suitable lattice match.Cs cations can stabilize the inorganic framework in hybrid lead halide perovskites at room temperature.The simulations of ab initio NA molecular dynamics show that lattice contraction of FAMACs-O increases the coherence time slightly and octahedral tilting decreases the NA coupling and coherence time.Overall,the recombination times of two systems are slow due to the NA coupling smaller（sub-1.5 meV）,and the coherence time shorter（sub-10fs）.This detailed time-domain atomistic analysis of charge carrier dynamics advances our comprehension of the key factors governing the unique properties of hybrid lead halide perovskites.The sixth chapter summarizes and prospects the research results of this thesis.It includes a summary of the research results obtained at this stage and a concise introduction to the ongoing work.