Applications Of Gold Nanoparticles And Polymers On Highly Efficient Perovskite Light-Emitting Diodes

In recent years,metal halide perovskites(MHPs)have many excellent optoelectronic properties such as narrow emission peaks(full width at half maximum(FWHM)?20 nm),tunable bandgaps(from ultraviolet to near-infrared),high charge-carrier mobilities,and high color purity.Hence,metal halide perovskite light-emitting diodes(Pe LEDs)have wide prospects in displays and lighting applications.However,it is highly impending to improve the luminous efficiency and to study the mechanism of metal halide Pe LEDs.From the aspect of device efficiency,the external quantum efficiency(EQE)of blue Pe LEDs is lower than that of green and red counterparts.In addition,the mechanism of improving the photoluminescence quantum yield(PLQY)of perovskite films by adding polymers is still scarce in the luminescence mechanism of Pe LEDs.In order to solve these problems,in the first part,the gold nanoparticles(Au NPs)are introduced into blue Pe LEDs to improve the luminescence efficiency.Meanwhile,a new mechanism"far field effect"is proposed to explain how Au NPs enhance the EQE of blue Pe LEDs.In the second part,we take advantages of fluorescence lifetime image microscopy and PL spectroscopy on the nano-second scale for the underlying mechanism of PLQY enhancement of formamidine lead bromide perovskite(FAPb Br₃)thin film by poly(ethylene oxide)(PEO).Our results reveal that the PEO assists the energy funneling in the 3D polycrystals perovskite thin films.The main contents are as follows:1.The studies of Au NPs enhance blue Pe LEDs:We introduce Au NPs into the hole transport layer-poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)to simultaneously achieve high photoluminescence(PL)and electroluminescence(EL)enhancements without any change of the emission wavelength.It is the first example to introduce the metallic micro-nano materials into blue Pe LEDs.Consequently,the blue Pe LEDs with a maximum brightness(L_max)and a maximum external quantum efficiencies(EQE_max)of the?1110 cd/m² and?1.64%are achieved,presenting one of the best performances among the blue Pe LEDs reported so far.The influences of Au.NPs on the crystallization property and surface morphology of perovskite films are studied.Moreover,the contributions of"near field plasmonic"effect and"far field plasmonic"effect of Au NPs are compared separately.Finally,the evolutions of Z_theory-PL with distance confirm that the improvement of blue Pe LEDs performance is mainly attributed to the far-field surface plasmonic effect of Au NPs.2.The mechanism studies of PLQY enhancement in FAPb Br₃ thin film by PEO:we fabricate perovskite thin films by mixing PEO with FAPb Br₃ perovskite precursor solution,leading to a high PLQY of?62.1%.It is one of the highest PLQY values in FAPb Br₃ perovskite thin films so far.The morphology studies of PEO:FAPb Br₃perovskite thin film reveal that self-assembled 3D polycrystals with sizes from?20 to?1500 nm are formed.The polycrystals contain inhomogeneous domains with a range of energetic excited states.Through fluorescence lifetime image microscopy,the in situ fluorescence emissions and the lifetimes of the domains are measured simultaneously,indicating energy funneling from the wide-bandgap domains(with small-size grains)into the narrow-bandgap domains(with large-size grains).Moreover,the PL spectroscopy on the nano-second scale is used to study the dynamics of charge transfer.It's found that PEO can assist 3D perovskite forming energy funneling,thereby improving the exciton recombination.In summary,this work is a hot issue in the field of perovskite electroluminescence.The main significances are as follows:In terms of device structure engineering,it is firstly proposed to improve the performance of blue Pe LEDs through the Au NPs,which provides a feasible way to prepare the high efficiency and low cost blue Pe LEDs,which has technical and theoretical significance for the development of blue Pe LEDs.In terms of luminescence mechanism of perovskite thin film,this work provides an important theoretical guidance for improving the PLQY and avoiding the defect-quenching,which is highly targeted and innovative.