Metal Nanostructures Based Composite Materials For Organic Light-emitting Device Application

Organic light-emitting devices have gain substantial attention in recent years with ever growing market share,such as mobile phone,TV,wearables,computers,and other consumer electronics.Organic light-emitting devices outperform their alternatives,i.e.,LCD and inorganic counterparts,with their high contrast ratio,lightweight and thin form factors,wide viewing angle,low power consumption,more vivid colors,and manufacturable in large format.In addition,the seemingly infinite design and synthesis options of organic materials provide great versatility of such technology toward marketable consumer products.The trend of future consumer products will be thinner,lighter,and even foldable or stretchable,enabling ultimate product design toward compliant wearables or implantable electronics.Current research and development effort in the area of organic light-emitting devices focuses primarily on further improving device performance and introducing environmental adaptability,such as folding,rolling,stretching,and compressing.These new generations of consumer electronics will for sure influence how people live their everyday life and change how people interact with the world and with each other.However,the realization of such future products requires fundamental innovations of each component within the device,which introduces a series of challenges to both materials and device structures.In this dissertation,we focus our effort on studying metal nanostructure based composite materials.Design,fabrication,and structural engineering of a number of different composite materials leads to notable enhancement in device photoluminescence,efficiency improvement in electroluminescence,and intrinsically stretchable light-emitting diodes.A general summary of the current dissertation is described as follows:1.In situ grown metal nanoparticles-graphene composite material was evidenced to largely enhance its localized surface plasmon resonance and at the same time efficiently passivating the copper nanoparticles from oxidation.This system was also shown to increase the fluorescence intensity of an organic fluorophore by 10 folds.By introducing a single crystal structure of an organic semiconductor molecule,namely BP3 T,such composite structure is able to enhance the PL intensity and lower the threshold of amplified spontaneous emission from 104.5 ?J/cm2 to 37.8 ?J/cm2.2.A metal nanowire-polymer composite electrode has been fabricated by incorporating silver nanowire and its application in stretchable perovskite light-emitting devices was studied.Specifically,stretchable electrode was fabricated by forming an interpenetrated network of silver nanowires within an intrinsically stretchable polyurethane acrylate(Ag NWs/PU)polymer.Stretchable light-emitting layer was prepared by generating perovskite structure from a mixture of perovskite precursors,polyethylene oxide(PEO),and polydimethylsiloxane(PDMS).Device shows a homogeneous electroluminescence when using liquid metal as cathode,which continues working at 60% strain.In a following work,we have fabricated a stretchable light-emitting diode device by combining a silver nanowire/polyimide electrode and perovskite quantum dots light-emitting layer atop a pre-stretched elastic substrate.The device shows a current efficiency of up to 9.1 cd/A.A microscale buckled structure allows for repeatable operations of stretching/releasing cycles up to 50% strain without noticeable changes in device characteristics.3.We have developed a novel ultrathin metal transparent composite electrode(PAI/Ag)by implementing a thermal curable polymer(PAI)as supporting layer for kinetically growing sub-10 nm thin silver thin films.The enrichment of N atoms within the PAI polymer layer introduces sufficient bonding with silver atoms during thermal deposition,suppressing the formation of isolated atomic aggregation.Continuous smooth film can then form even at thickness of ~9 nm.The obtained composite electrode exhibits an optical transmittance of 94.5% at 550 nm and a sheet resistance of 15.1 Ohm/sq upon overcoating a thin anti-reflection layer of PEDOT:PSS.White organic light-emitting diode devices have been prepared to evaluate the composite electrode against ITO.The outstanding optical and electrical characteristics of such composite electrode together with a matching refractive index of PAI(n~1.7)with the organic emitters give rise to a power efficiency maximum of 84.7 lm/W,which is 56.9% higher than for ITO.