Ulsan National Institute of Science and Technology
Abstract
School of Energy and Chemical Engineering (Energy Engineering)My MS research has focused on light-emitting diodes (LEDs) devices based on perovskite nanocrystals (PeNCs). All-inorganic PeNCs are promising material for optoelectronic devices due to their easily tunable bandgap, narrow full width at half maximum (FWHM), and high photoluminescence (PL) quantum yield. Moreover, all-inorganic perovskite material has better stability than the other perovskite material that employs hybrid or organic part at A site of perovskite. These outstanding physical properties caused lot of interest in PeNCs for LEDs devices. To make highly efficient LEDs devices, there are several important factors. Those are smooth film morphology, energy band alignment for low charge injection barrier, and charge balance between hole and electron. Especially, perovskite material has low exciton binding energy (Eb), therefore, confining electron and hole into nanocrystals is very important to make exciton. By considering these factors, a lot of research is going on. However, blue-emitting PeNCs have resulted lower quantum yield compared to red or green-emitting PeNCs due to their large bandgap and anion segregation. To achieve commercialization of PeNCs for future display, white LEDs are indispensable, therefore, great development of blue-emitting LEDs is required. From this point of view for high-efficiency blue LEDs devices, 1,8-diiodooctane (DIO) additive has been used for our research. DIO is added to poly[bis(4-phenyl)(4-butylphenyl)amine] (poly-TPD) solution that is employed in hole transporting layer (HTL) to improve hole injection and passivate trap states between poly-TPD layer and perovskite NC layer. By adopting DIO additive to HTL, external quantum efficiency (EQE) of green PeNCs LEDs was enhanced from 2.89 % to 5.17 % compared to the reference device, and EQE of blue PeNCs LEDs was enhanced from 0.58 % to 1.34 % compared to the reference device.ope
