Organic-Inorganic Hybrid Perovskite Nanocrystals For LightEmitting Diodes

Organic-inorganic hybrid perovskite(OHP)nanocrystals(NCs)with high photoluminescence quantum yield(PLQY),large exciton binding energy,and high color purity,are regarded as ideal materials for next-generation optoelectronic devices,particularly for light-emitting diodes(LEDs).However,it is hard to form films from the OHP-NCs suspension because of the relatively low concentration.In addition,the devices based on OHP NCs suffer from poor stability and are lack of blue LEDs,which seriously impede their further development.In this thesis,facile assembly of high-quality OHP NCs thin films has been achieved via an electric-field-assisted method.Also,the highperformance LEDs based on OPH NCs are fabricated.These results are summarized as follows:1.Assembly of high-quality organic-inorganic hybrid perovskite nanocrystals films for light-emitting diodesFor high PLQY and high stability of OHP NCs suspension,we successfully developed an electric-field-assisted assembly method to fabricate CH3NH3 Pb Br3 NCs thin films with high PLQY(80%-90%).The relationship between electric field intensity,external electric field time,solution concentration and coverage rate,thickness and roughness of perovskite NCs film was established,and the optimal experimental conditions were obtained.At the same time,the method was successfully extended to the other components of the perovskite NCs,and the NCs luminescence layer from blue to red was realized.The CH3NH3 Pb Br3 NCs thin film-based LEDs exhibit highly bright and color-purity green electroluminescence(EL)with maximum luminance up to 12450 cd/m2 under 10 V.Furthermore,a current efficiency of 12.7 cd/A,a power efficiency of 9.7 lm/W,and an external quantum efficiency(EQE)of 3.2% can be achieved by optimizing the mobility of hole electron-transporting layer.These values represent the highest values for CH3NH3 Pb Br3 NCs-based LEDs and are better than some of allinorganic NCs-based LEDs.Finally,we showed its application in the flexible LEDs,and the device exhibited stable and bright light emitting even after bending.Our work lays the foundation for the application of perovskite NCs in high-performance and low-cost display fields.2.Structure and morphology regulation of organic-inorganic hybrid perovskite for highly stable and efficient deep-blue light-emitting diodesA new strategy for highly stable and efficient deep-blue perovskite LEDs is proposed by using the dual dimension of structure and morphology.First,in two-dimension(2D)layered phenylethyl ammonium lead bromide((C6H5C2H4NH3)2Pb Br4,(PEA)2Pb Br4)perovskite,the amine groups of PEA cations are bonded to the Pb X4 framework by hydrogen and ionic bonding,and the phenethyl groups stand outwards.As a result,the prepared perovskite layers can be dispersed and stabilized in solvents with chemical structures similar to the phenethyl groups.Second,few-layer 2D(PEA)2Pb Br4 nanosheets fabricated from solvent exchange method increase the exciton binding energy,which can promote radiative recombination.Using these synergistic effects,we first obtained the 2D(PEA)2Pb Br4 nanosheets with PLQY over 15%.Their emission peak is located in the deep-blue range(410 nm),and the half peak width is only ~10.8 nm.Combining with electric-field-assisted assembly method,the LEDs based on 2D(PEA)2Pb Br4 nanosheets have been successfully fabricated.The devices exhibit a deep-blue emission with the maximum brightness up to 147.6 cd/m2.The current efficiency and EQE of the device are 0.19 cd/A and 0.31%,respectively,which are the highest values reported to date for all perovskite blue LEDs.More importantly,the LEDs based on(PEA)2Pb Br4 nanosheets show long-term stability,and can continuously work over 65 h under 50% relative humidity.This work provides a new idea for the design and preparation of highly stable and efficient deep-blue LEDs.