Seungjin Lee

High‐Performance Planar Perovskite Optoelectronic Devices: A Morphological and Interfacial Control by Polar Solvent Treatment

Highly efficient planar perovskite optoelectronic devices are realized by amine-based solvent treatment on compact TiO2 and by optimizing the morphology of the perovskite layers. Amine-based solvent treatment between the TiO2 and the perovskite layers enhances electron injection and extraction and reduces the recombination of photogenerated charges at the interface.

Amine-Based Polar Solvent Treatment for Highly Efficient Inverted Polymer Solar Cells

The interfacial dipolar polarization in inverted structure polymer solar cells, which arises spontaneously from the absorption of ethanolamine end groups, such as amine and hydroxyl groups on ripple-structure zinc oxide (ZnO-R), lowers the contact barrier for electron transport and extraction and leads to enhanced electron mobility, suppression of bimolecular recombination, reduction of the contact resistance and series resistance, and remarkable enhancement of the power conversion efficiency.

Amine‐Based Interfacial Molecules for Inverted Polymer‐Based Optoelectronic Devices

The change in the work function (WF) of ZnO with amine-based interfacial mole-cules (AIM) can be controlled by the number of amine groups. AIM with a larger amine group can induce a stronger interface dipole between the amine groups and the ZnO surface, leading to a greater reduction of the WF.

Amine-Based Passivating Materials for Enhanced Optical Properties and Performance of Organic–Inorganic Perovskites in Light-Emitting Diodes

The use of hybrid organic-inorganic perovskites in optoelectronic applications are attracting an interest because of their outstanding characteristics, which enable a remarkable enhancement of device efficiency. However, solution-processed perovskite crystals unavoidably contain defect sites that cause hysteresis in perovskite solar cells (PeSCs) and blinking in perovskite light-emitting diodes (PeLEDs). Here, we report significant beneficial effects using a new treatment based on amine-based passivating materials (APMs) to passivate the defect sites of methylammonium lead tribromide (MAPbBr3) through coordinate bonding between the nitrogen atoms and undercoordinated lead ions. This treatment greatly enhanced the PeLEDs efficiency, with an external quantum efficiency (EQE) of 6.2%, enhanced photoluminescence (PL), a lower threshold for amplified spontaneous emission (ASE), a longer PL lifetime, and enhanced device stability. Using confocal microscopy, we observed the cessation of PL blinking in perovskite films treated with ethylenediamine (EDA) due to passivation of the defect sites in the MAPbBr3.

Improved performance of perovskite light-emitting diodes using a PEDOT:PSS and MoO3 composite layer

We demonstrate the enhanced performance of perovskite light-emitting diodes (PeLEDs) using a solution-processable MoO3 and PEDOT:PSS (PEDOT:MoO3) composite layer as the hole transport layer (HTL). The PEDOT:MoO3 composite layer presents improved hole injection through a reduction in the contact barrier between the HTL and the CH3NH3PbBr3 layer and enhanced crystallinity of the perovskite film. The optimized PeLEDs with the PEDOT:MoO3 composite film showed enhanced external quantum efficiency (EQE) and maximum luminous efficiency, compared to a PeLED using a pristine PEDOT:PSS layer.

Combination effect of polar solvent treatment on ZnO and polyfluorene-based polymer blends for highly efficient blue-based hybrid organic–inorganic polymer light-emitting diodes

Highly efficient blue-based hybrid organic–inorganic polymer light-emitting diodes were synthesized by the combination effect of polar solvent treatment on zinc oxide (ZnO) and hole trap using poly(9,9-dioctylfluorene) (F8):poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine (TFB) blend to balance the charge carrier transport, leading to maximized recombination of charge carriers and enhance the device efficiency.

Growth of Nanosized Single Crystals for Efficient Perovskite Light-Emitting Diodes

Organic-inorganic hybrid perovskites are emerging as promising emitting materials due to their narrow full-width at half-maximum emissions, color tunability, and high photoluminescence quantum yields (PLQYs). However, the thermal generation of free charges at room temperature results in a low radiative recombination rate and an excitation-intensity-dependent PLQY, which is associated with the trap density. Here, we report perovskite films composed of uniform nanosized single crystals (average diameter = 31.7 nm) produced by introducing bulky amine ligands and performing the growth at a lower temperature. By effectively controlling the crystal growth, we maximized the radiative bimolecular recombination yield by reducing the trap density and spatially confining the charges. Finally, highly bright and efficient green emissive perovskite light-emitting diodes that do not suffer from electroluminescence blinking were achieved with a luminance of up to 55 400 cd m-2, current efficiency of 55.2 cd A-1, and external quantum efficiency of 12.1%.

Control of Interface Defects for Efficient and Stable Quasi-2D Perovskite Light-Emitting Diodes Using Nickel Oxide Hole Injection Layer

Abstract Metal halide perovskites (MHPs) have emerged as promising materials for light‐emitting diodes owing to their narrow emission spectrum and wide range of color tunability. However, the low exciton binding energy in MHPs leads to a competition between the trap‐mediated nonradiative recombination and the bimolecular radiative recombination. Here, efficient and stable green emissive perovskite light‐emitting diodes (PeLEDs) with an external quantum efficiency of 14.6% are demonstrated through compositional, dimensional, and interfacial modulations of MHPs. The interfacial energetics and optoelectronic properties of the perovskite layer grown on a nickel oxide (NiOx) and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate hole injection interfaces are investigated. The better interface formed between the NiOx/perovskite layers in terms of lower density of traps/defects, as well as more balanced charge carriers in the perovskite layer leading to high recombination yield of carriers are the main reasons for significantly improved device efficiency, photostability of perovskite, and operational stability of PeLEDs.

Conjugated Polyelectrolytes Bearing Various Ion Densities: Spontaneous Dipole Generation, Poling‐Induced Dipole Alignment, and Interfacial Energy Barrier Control for Optoelectronic Device Applications

Conjugated polyelectrolytes (CPEs) with π-delocalized main backbones and ionic pendant groups are intensively studied as interfacial layers for efficient polymer-based optoelectronic devices (POEDs) because they facilitate facile control of charge injection/extraction barriers. Here, a simple and effective method of performing precise interfacial energy level adjustment is presented by employing CPEs with different thicknesses and various ion densities under electric poling to realize efficient charge injection/extraction of POEDs. The effects of the CPE ion densities and electric (positive or negative) poling on the energy level tuning process are investigated by measuring the open-circuit voltages and current densities of devices with the structure indium tin oxide/zinc oxide/CPE/organic active layer/molybdenum oxide/gold while changing the CPE film thickness. The performances of inverted polymer light-emitting diodes and inverted polymer solar cells are remarkably improved by precisely controlling the interfacial energy level matching using optimum CPE conditions.