FABRICATION OF QUANTUM DOT LIGHT EMITTING DEVICES

Abstract

Since the advent of organic light emitting devices, a lot of research has been devoted to maximizing the efficiency, reducing the fabrication cost, improving quality etc. Band engineering is to choose the suitable materials for various layers in the stacked device structure. Materials are chosen according the band step, mobility we need in our device which leads to smooth transport of charge carriers. In this report, a literature survey has been carried out to find out the possible materials for different layers of OLED. A device structure ITO/PEDOT:PSS/PVK/Alq3/Al has been fabricated and characterized. Low cost solution processed fabrication procedure is followed in which some of layers are deposited using spin coating. A review of spin coating deposition technique is presented in the report with a focus on static dispense spin coating procedure. We report the effect of evaporation rate of solvents (chloroform and chlorobenzene) over the thickness of spin coated PVK thin films and turn-on voltage of fabricated organic light emitting devices(OLEDs). In this work, experiments are performed for static dispense spin coating procedure in which the dispensed drops of PVK solution are made to wait for a finite time before spinning. It is found that the high evaporation rate solvent has higher sensitivity to wait-time-to- spin as opposed to low evaporation rate solvent. The increased turn-on voltage for devices with high evaporation rate solvent proved that the thickness of PVK thin film increases with wait time for chloroform. We observed relatively lesser change in turn-on voltages for chlorobenzene based OLEDs possibly because of low evaporation rate resulting in smaller changes in thickness of PVK layer. Further, a review study of recent advances in OLED revealed the addition of quantum dots as emissive layer. Using the reference from the research work in the literature, the CdSe nanoparticles are synthesized and characterized. An attempt is made to use the synthesized quantum dots in the device structure ITO/PEDOT:PSS/PVK:CdSe/BCP/Al. The devices are fabricated in different PVK:CdSe combinations; once in bilayer and other in bulk. Because the encouraging results are not obtained for QD based OLEDs, perhaps due to the improper technique of depositing quantum dots in the device, a survey of other nanoparticle deposition technique is presented. The contact printing method is being discussed and first step of silicon master mold fabrication using Su-8 negative photoresist has been carried out. The work can be extended to complete the QD deposition using the contact printing method.