Controlled Preparation Of Organic-inorganic Perovskite Films And Their Applications In Solution-processed Light Emitting Diodes

Organic-inorganic hybrid perovskites are a new type of direct bandgap semiconductor materials which can be obtained through low temperature solution process method.Compared with other solution processable semiconductor materials,the hybrid perovskites exhibit excellent optoelectronic properties such as broad-spectrum absorption,long carrier diffusion length and remarkable ambipolar transport properties,which make perovskite solar cells one of the most promising low-cost photovoltaic technologies.In addition,hybrid perovskites also have excellent luminescent properties,such as tuneable light emission wavelengths,high color purity,making them ideal emitter candidate for lignt emitting diodes.However,researches of light-emitting diodes based on organic-inorganic hybrid perovskites(PeLED)is still in its infancy.Many factors still restrict the performance of PeLED devices,including the porous surface morphology of the perovskite layer,low photoluminescence quantum yield(PLQY),and the instability of the perovskites.This thesis mainly studies the effect of controllable preparation of perovskite films on the performance of PeLED devices.Our work starts from a variety of perspectives,including the material system,film formation process,interface control and device structure design,to establish the relationship between the property of the perovskite layer and the performance of the PeLED device.And those works provide novel perspectives for the improvement of performance for PeLED device in the future.First,we focus our research on improving the surface morphology and PLQY of three-dimensional perovskite materials.For the solution-processed methylamine-based perovskite film,the surface morphology is porous and full of pin-hole,which deteriorates PeLED performance.We modified the film formation procedure by introducing Cs ions into the perovskite material,which in turn affected the perovskites crystalline properties.With structural and morphological characterizations,we find the perovskite crystallites becomes significantly smaller and the film surface coverage has been improved.Apart from the improvement of the film morphology,Cs ions also reduces defect density in perovskite films,which reduces the non-radiative recombination rate and improves the photoluminescence quantum yield of the film.Based on this perovskite film,we fabricated a high-performance green PeLED device with external quantum efficiency(EQE)increased by 20 times than the countparts without adding Cs ions.Furthermore,we introduce long-chain ammonium ions into the perovskite to reduce the dimension of perovskites.Combining the optimization of the film forming process,we fabricated a thin film made of thickness-uniform perovskite nanoplates by in-situ grown method.This kind of perovskite film possesses color purity and PLQY comparable to those of perovskite nanocrystals.Moreover,the in-situ approach does not need complicated surface chemistry compared to the colloidal perovskite nanocrystals because only the solid-state optoelectronic properties need to be taken into consideration.This excellent light-emitting layer integrating with suitable device structure result in high-color-purity green and red PeLEDs with remarkably high EQE of up to 10.4%and 7.3%,respectively,reperesting the highest value reported at that time.