In-situ Passivation Of Metal Halide Perovskite Nanocrystals For Photovoltaic Application

Recently,metal halide perovskite semiconductors are poised to be tremendously important for low-cost solution-processed optoelectronic applications.In this project,we reported efficient perovskite nanocrystals(NCs)materials through rational in-situ passivation and further applied them to photovoltaic application.The projects can be divided into the following four parts:Part I:In order to access high efficiency perovskite device fabrication protocls,a simple yet efficient method was introduced to prepare perovskite film with excellent optoelectronic properties by adding acetic acid(Ac)into anti-solvent(chlorobenzene)to assit perovskite crystallization.The best perovskite solar cell exhibits an effiency of 23.0%based on Cs0.05FA0.90MA0.05Pb(I0.95Br0.05)3 hybrid perovskites.Part II:CsPbI3 NCs have been successfully synthesized and showed improved optoelectrical properties by implementing an in-situ ytterbium(Yb)doping strategy during synthesis.Preliminary experimental results indicated that Yb lanthanide cations could effectively reduce defects and trap states caused by surface and lattice vacancies,leading to an improvement in NCs photoluminescence quantum yield(PLQY),crystallinity,thermal stability and carrier transport.Consequently,the CsPbl3 NCs solar cells with optimal Yb doping achieved the best power conversion efficiency(PCE)of 13.12%and showed significantly improved devices stability under ambient conditions.These results indicate that in situ doping strategy is greatly helpful to improve the quality of the resultant perovskite NCs.This approach can provide a new path to achieve a breakthrough in NCs based solar cell technology.Part III:The capping ligands of perovskite nanocrystals play a crucial role in the resultant device performance.To fine-tune the surface ligand towards high-performance devices,we first developed an in-situ passivation process for all-inorganic cesium lead iodide(CsPbI3)perovskite NCs by using a bidentate ligand,namely L-phenylalanine(L-PHE).Through the addition of this capping ligand into the precursor solution during synthesis,our in-situ treated CsPbI3 NCs show significantly higher photoluminescence quantum yields(close to unity),improved material stability,reduction of traps states,increased exciton binding energy,and enhanced electronic coupling between neighboring NCs.Consequently,CsPbI3 NCs passivated by L-PHE realize NCs solar cells with a record efficiency of 14.62%and red light-emitting diodes(LEDs)with a highest external quantum efficiency(EQE)of 10.21%,respectively,surpassing by far both solar cells and LEDs efficiency made from the as-synthesized CsPbI3 NCs.Part ?:The presence of lead in perovskite raises obvious concerns about the toxicity of these materials upon introduction to the commercial market,and this toxicity may be one of the major factors limiting the widespread industrial applications in the future.Here,we successfully synthesized lead-free Cs2TiBr6 nanocrystals for the first time,and systematical characterizations were performed to confirm the obtained nanocrystals.These enviormntally friendly perovskite NCs show great potiential to be further applied to optoelectronic devices.