Research On The Improvement Of Optoelectronic Properties Of LEDs Based On Monolayer Colloidal Spheres

The monolayer colloidal crystals,evolved from monolayer colloidal spheres array,have the advantages of vivid designs,good repeatability and simple fabrication.They play a key role in optimizing the quality of emissive active layer and improving the performance of light-emitting diode?LED?devices.The aim of this study is to develop a high-quality luminescence layer for the organic-inorganic hybrid perovskite LEDs and improve the performance of GaN LEDs based on the colloidal crystals.The two optimization processes are described as follows:1.For perovskite LEDs,the quality of the organic-inorganic hybrid perovskite film is critical,which is not as good as desired due to the poor coverage of the thin film fabricated by standard method.In order to solve this problem,we develop a method where nanoscale structures are adopted.First,the scaffold is developed by employing polystyrene?PS?nanospheres as sacrificial templates,which gives rise to SiO₂ nanobowl micro-arrays on a substrate.Then,the perovskite thin film was prepared by a‘one-step'solution with the limitation of the two-dimensional space provided by the scaffold structure unit.The morphology,crystallization and optical properties of the perovskite films with nanostructure were characterized by SEM,XRD,UV-Vis,and PL respectively.The results show that the perovskite film with the nanostructure has the advantages of less pores,high coverage and good uniformity in morphology.In particular,the PL intensity of the perovskite film is increased by 77.7%compared with a reference perovskite film obtained on a silicon substrate,which demonstrates the effectiveness of the developed procedure in improving the optical properties of organic-inorganic hybrid perovskite film.2.Nano-patterned sapphire substrate?NPSS?technology is one of the keys in improving the internal quantum efficiency?IQE?and light extraction efficiency?LEE?of GaN LEDs,which enhances the performance of the LED device effectively.Enriching the nano-patterned morphology is important in advancing the research of NPSS.In this work,we develop a new method of forming three-dimensional?3D?nano-patterns and study their application in improving the performance of GaN LEDs.PS nanospheres prepared by colloidal self-assembly method are used as sacrificial templates to etch the photoresist by means of spherical-lens photolithography?SLP?.By designing the appropriate ratio of the illumination wave-length and the diameter of colloidal nanosphere in combination with the proper photoresist thickness during the photolithography process,an applicable 3D nanohole array comprising pore shape with circular upper opening and sexfoil-shaped bottom is obtained,which enriches the nano-patterned morphology produced by etching technique.For comparison,the 3D nanoholes and ordinary circular pores are employed as physical masks,respectively,to etch sapphire substrates to form NPSS.The LEE of the GaN LED grown on NPSS based on the 3D nanoholes was 13.2%higher than that of GaN LEDs grown on the circular NPSS.And GaN LEDs grown on NPSS deliver 44.3%enhancement in light output power compared to that of GaN LEDs grown on flat sapphire substrates.