Perovskite Nanocrystal Surface Modification For High-performance Polymer Hybrid Optical Function Materials

Perovskite nanocrystals（PNCs）,as a new type of semiconductor nanocrystals,have drawn much attention due to its superior optoelectronic characteristics,facile synthesis,flexible component adjustment,etc.Therefore,it has tremendous potential in optical function related fields,such as solar cell,illumination,nanocrystal/polymer composite optical material and so on,which means technical innovation may be realized in traditional semiconductor nanocrystal related applications.However,as well as traditional semiconductor nanocrystals,the small size of PNCs makes it have a huge specific surface area.As such,the surface property is crucial to the whole nanocrystal property.Furthermore,there is no doubt that the highly ionic crystal structure and dynamic ligand binding characteristic make the PNC surface property complicated.It can be argued that the property of PNCs can be controlled if the surface property can be controlled,leading to a performance improvement in related applications.Targeted at this key scientific issue,this paper focuses on the surface chemistry of PNCs and studies the structure-activity relationship between PNC surface and corresponding material properties systematically.A series of innovative research works has been carried out.In terms of research significance,the innovations of this paper are as followings:we adapt a method of controlling surface ligand density to enhance the conversion efficiency of photovoltaic device fabricated by PNCs;we propose a dual-ligand strategy to fabricate bulk PNCs/polymer nanocomposite materials with high transparency under high doping content;based on the dual-ligand strategy,we further explore the potential of this PNCs/polymer nanocomposite to serve as light guide plate,which extends the application field of PNCs;from the point of surface element environment,we control the surface element ratio of PNCs to control the interaction sites of polymerizable surfactant on PNC surface and fabricate high transparent PNCs/polymer nanocomposite film with excellent fluorescence properties.Specifically,the detailed works of this paper can be described as the following four parts:1.In chapter two,we control and quantify the ligand density on PNC surface effectively by taking advantage of the dynamic ligand binding characteristic.We systematically study the influence of different ligand density on the active layer morphology,energy level alignment,carrier dynamics,etc.In the range of proper ligand density,the device fabricated by PNCs with lower ligand density exhibits obvious improvement in short-circuit current,open-circuit voltage and fill factor.The best-performing device shows a 12.2%power conversion efficiency,which is the highest one of the solar cells fabricated by Br-contained PNCs at that time.2.In chapter three,we adapt a dual-ligand strategy to fabricate bulk nanocomposite material by copolymerizing PNCs with styrene.The bulk PNCs/polystyrene nanocomposite still shows extremely high transparency even the doping content is up to 5 wt%.One type of ligand is modified on PNC surface by ligand exchange process to ensure the dispersion of the PNCs in styrene.The other type of ligand with polymerization activity is introduced by copolymerization to link the PNCs with polystyrene matrix and suppress phase separation.Thanks to the high refractive index of the PNCs and excellent dispersion in polystyrene matrix,we exploit the potential of this PNCs/polymer nanocomposite to serve as light guide plate,which extends the application field of PNCs.3.In chapter four,we further approve the university of the dual-ligand strategy to other component PNCs.In consideration of the refractive index,absorption coefficient,particle size and particle number per unit,we calculate the related optical parameters of bulk CsPbCl_xBr_3-x（1≤x≤3）PNCs/polystyrene nanocomposites,including volume scattering coefficient and optical radiation efficiency,to analyze the performances of light guide plates fabricated by corresponding bulk PNCs/polystyrene nanocomposite.In addition,we also systematically study the influence of different PNCs component on the display performance of liquid crystal display module based on this type of light guide plate.Under the optimal condition,the surface illumination of the light guide plate and the uniformity of the backlight unit shows about 20.5 times and 1.8 times improvement,respectively.4.In chapter five,we successfully adjust and control the surface element ratio of PNCs by changing the synthesis environment.Thus,the interaction sites of polymerizable surfactant on PNC surface can be controlled,resulting in adjustable optical properties of CsPbBr₃ PNCs/polymer nanocomposite films.We first study the modifying mechanism of the polymerizable surfactant and its positive effect on the properties of the PNCs and the following nanocomposite films.Subsequently,we systematically study the influence of surface element ratio on defect,the amount of polymerizable surfactants bonding on PNCs,fluorescence quantum yield and the optical related characteristics of corresponding nanocomposite films.Finally,based on the interaction site adjustment strategy,the fabrication of PNCs/polymer nanocomposite film with high transparency and high fluorescence quantum yield can be realized under various doping contents.In conclusion,from the point of PNC surface,this paper is dedicated to modulating and controlling the PNC surface chemistry,leading to the improvements of material properties or the developments of potential applications.We not only solve the fundamental scientific problems in optical function related fields,but also focus on the establishment of the structure-activity relationship.This paper is of great significance to deepen the understanding of PNC surface properties and provide valuable reference experience or new research ideas for the developments of PNCs in optical function related fields.