Jae Choul Yu

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.

Improving the Stability and Performance of Perovskite Light-Emitting Diodes by Thermal Annealing Treatment

A perovskite LED with a perovskite film treated under optimum thermal annealing conditions exhibits a significantly enhanced long-term stability with full coverage of the green electroluminescence emission due to the highly uniform morphology of the perovskite film.

Highly Efficient Polymer-Based Optoelectronic Devices Using PEDOT:PSS and a GO Composite Layer as a Hole Transport Layer

We demonstrate highly efficient polymer light-emitting diodes (PLEDs), as well as polymer solar cells (PSCs), using a solution-processable poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS):graphene oxide (GO) (PEDOT:GO) composite layer as hole transport layers (HTLs). The PEDOT:GO composite HTL layer shows enhanced charge carrier transport due to improved conductivity by benzoid-quinoid transitions with a well-matched work function between GO (4.89 eV) and PEDOT:PSS (4.95 eV). Moreover, it reduces remarkably exciton quenching and suppresses recombinations that bring higher charge extraction in PSCs and increases the recombinations of holes and electrons within the active layer by the blocking behavior of the electrons from a fluorescent semiconductor due to the existence of GO with large bandgap (∼3.6 eV) in the PEDOT:GO composite layer, therefore leading to an enhancement of device efficiency in PLEDs and PSCs. The optimized PLEDs and PSCs with a PEDOT:GO composite HTL layer shows the maximum luminous efficiency of 21.74 cd/A (at 6.4 V) for PLEDs, as well as the power conversion efficiency of 8.21% for PSCs, which were improved by ∼220 and 12%, respectively, compared to reference PLEDs and PSCs with a PEDOT:PSS layer.

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.

Highly efficient flexible optoelectronic devices using metal nanowire-conducting polymer composite transparent electrode

Here, we report a comprehensive analysis of the electrical, optical, mechanical, and surface morphological properties of composite nanostrutures based on silver nanowires (AgNW) and PEDOT:PSS conducting polymer for the use as flexible and transparent electrodes. Compared to ITO or the single material of AgNW or PEDOT:PSS, the AgNW/PEDOT:PSS composite electrode showed high electrical conductivity with a low sheet resistance of 26.8 Ω/sq at 91% transmittance (at 550 nm), improves surface smoothness, and enhances mechanical properties assisted by an amphiphilic fluoro-surfactant. The polymeric light-emitting diodes (PLEDs) and organic solar cells (OSCs) using the AgNW/PEDOT:PSS composite electrode showed higher device performances than those with AgNW and PEDOT:PSS electrodes and excellent flexibility under bending test. These results indicates that the AgNW/PEDOT:PSS composite presented is a good candidate as next-generation transparent elelctrodes for applications into flexible optoelectronic devices.

Highly efficient and stable inverted perovskite solar cell employing PEDOT:GO composite layer as a hole transport layer

The beneficial use of a hole transport layer (HTL) as a substitution for poly(3,4-ethlyenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is regarded as one of the most important approaches for improving the stability and efficiency of inverted perovskite solar cells. Here, we demonstrate highly efficient and stable inverted perovskite solar cells by applying a GO-doped PEDOT:PSS (PEDOT:GO) film as an HTL. The high performance of this solar cell stems from the excellent optical and electrical properties of the PEDOT:GO film, including a higher electrical conductivity, a higher work function related to the reduced contact barrier between the perovskite layer and the PEDOT:GO layer, enhanced crystallinity of the perovskite crystal, and suppressed leakage current. Moreover, the device with the PEDOT:GO layer showed excellent long-term stability in ambient air conditions. Thus, the enhancement in the efficiency and the excellent stability of inverted perovskite solar cells are promising for the eventual commercialization of perovskite optoelectronic devices.