Ion Competitive Reaction-induced Crystallization Regulation And Buried Interface Optimization Of Formamidinium-based Perovskites

The development of photovoltaic cell technology is an important measure to achieve the“double carbon”goal and solve current energy and environmental problems.In recent years,organic-inorganic hybrid perovskite materials based on FAPb I₃（HC（NH₂）₂Pb I₃）components have ideal optical band gap（1.48 e V）,excellent optoelectronic properties and outstanding thermal stability,and have become one of the most important research directions in the field of photovoltaic cells.At present,the preparation of FA-based perovskite films is mainly based on a two-step growth method induced by the spontaneous chemical reaction of the upper layer of FA cations and the lower layer of Pb I₂.However,there are difficulties in the controllability of perovskite crystallization kinetics and the suppression of defects formation during the nucleation-growth process of the film,resulting in the disordered distribution of Pb I₂,the formation of grain interface defects at the buried interface at the bottom of perovskite film,and other serious problems,which hinder carrier transport,lead to nonradiative recombination energy loss,and reduce device efficiency and stability.In order to solve the problems of crystallization regulation and buried interface defects,this thesis innovatively designs a strategy for regulating the nucleation and crystallization process of films based on a novel ionic liquid-induced ion competition reaction.Furthermore,by introducing a novel functionalized bridging molecule,the buried interface between the perovskite and the transport layer is optimized.Specifically,the following two research works are included:（1）Ion competition reaction drives the enhancement of crystallization kinetics to construct high-quality perovskite-lead iodide nanosheets heterojunction films.A novel ionic liquid,1-butyl-3-methylimidazolium thiocyanate（BMIMSCN）,was designed as an additive to perovskite precursors,to tune the spontaneous chemical reaction process of FA cation composition and underlying Pb I₂ composition in perovskite films.Through quasi-in situ test and analysis,the mechanism of ion-competitive reaction induced by BMIMSCN in the perovskite nucleation and crystallization process was revealed,and it was proved that BMIMSCN could enhance the crystallization kinetics and regulate the vertically oriented and ordered distribution of Pb I₂ nanosheets in perovskite films.A novel high-quality perovskite-Pb I₂ nanosheets heterojunction film was constructed,which reduced the intrinsic defects of the film and improved the longitudinal transport of carriers.The optimal perovskite solar cell based on BMIMSCN achieved a power conversion efficiency of over 23%,and the unencapsulated device could still maintain above 85%of the initial value after 1000 h storage in a constant humidity environment with a relative humidity of about 10%.This work expands the idea of perovskite crystallization regulation.（2）Optimization of the buried interface of perovskite solar cells by chemical bridging and coordination passivation based on p-aminobenzenesulfonic acid.To solve the problem of buried interface defects of perovskite,a novel double-terminal functional organic small molecular p-aminobenzenesulfonic acid（ABSA）was designed to form a chemically bridged molecular passivation layer at the buried interface between perovskite and Sn O₂.The-SO₃^-on the side of the ABSA molecule could generate new coordination bonds with the uncoordinated Sn atoms on the surface of Sn O₂,filling the oxygen vacancies.While-NH₂ on the other side could suppress uncoordinated Pb²⁺defects in perovskites through the interactions.This double-sided synergistic passivation effect improved the charge transport performance.The ABSA-based perovskite solar cell achieved an optimal power conversion efficiency of 20.94%,and the unencapsulated device could still maintain more than 85%of the initial efficiency after being stored in a constant humidity environment with a relative humidity of about 10%for 240 h.This work provides a new idea and method for the study of defect passivation at the buried interface of perovskites.