5th PolyU-SNU Bilateral Workshop on Flexible Organic and Perovskite Electronics
Co-chair
Department of Materials Science and Engineering,
Seoul National University
Co-chair
Chair Professor of Organic Electronics,
Department of Physics and Materials,
The Hong Kong Polytechnic University
Member
Associate Professor,
Department of Chemistry,
The Hong Kong Polytechnic University
Member
Associate Professor, Department of Physics and Materials, The Hong Kong Polytechnic University
Member
Research Assistant Professor,
Department of Chemistry,
The Hong Kong Polytechnic UniversitySpeakers from Korea
 Professor, Department of Materials Science and Engineering |
Stable, Scalable, and Efficient Perovskite Nanocrystal Emitters for Vivid DisplaysAbstract Metal halide perovskites (MHPs) have emerged as promising light emitters for next-generation displays and optoelectronics, owing to their excellent color purity, tunable emission, and high photoluminescence quantum yield (PLQY). However, translating these intrinsic optical merits into practical display devices requires further improvements in efficiency and operational stability. This presentation presents molecular and structural strategies that address both challenges in perovskite light-emitting diodes (PeLEDs). Doping guanidinium (GA) cations into FAPbBr3 nanocrystals (PNCs) with bromide-incorporated overcoating passivates surface defects[1]; surface-binding conjugated molecular multipods strengthen the lattice and reduce dynamic disorder[2]; and benzylphosphonic-acid core/shell structures further boost efficiency and stability[3]. Toward commercialization, a scalable cold-injection synthesis achieves near-unity PLQY at large scale with a high external quantum efficiency (EQE) of 29.6%[4]. Ultra-stable multi-layer-shell PNCs withstand 60°C and 90% relative humidity and high light flux, enabling down-converting LEDs covering over 95% of the Rec. 2020 color space, demonstrating strong commercial potential[5].
|
 Professor, |
Molecular-scale Synaptic Transistors with Redox-Induced Analog StatesAbstract In this talk, I will report a three-terminal, ion-gel-gated, redoxactive molecular transistor that exhibits synaptic plasticity and analog conductance states. The device was composed of a ferrocene-terminated alkanethiolate self-assembled monolayer as the active channel, vertically sandwiched between a monolayer graphene source and a Au drain, and the channel conductance was modulated by an ion-gel gate. Gate voltage pulses induce an electric double layer at the ion-gel/graphene interface, triggering dynamic postsynaptic-like current responses. Our device exhibited neuroinspired plasticity, including short-term plasticity like paired-pulse facilitation and a programmable transition to long-term plasticity upon repeated stimulation. The ferrocene redox moiety was identified as the key enabler of nonvolatile switching behavior, mediating a dynamic, voltage-programmable conductance change via a synergistic mechanism of reversible redox and ion trapping. These results establish vertical molecular transistor systems as a building block for molecular-level neuromorphic hardware, with a three-terminal, read/write-decoupled architecture.
|
 Associate Professor, |
Ionic-Electronic Coupling in Emerging SemiconductorsAbstract Ionic-electronic coupling is a fundamental governing interaction that dictates the generation and transport of ionic and electronic charges in mixed ionic-electronic conductors. Utilising such effect in emerging semiconductors, such as organic mixed ionic-electronic conductors (OMIECs) has demonstrated am impressive ionic-electronic transconduction, in a device form of electrochemical transistors. Here, we present OMIEC material designs for attaining high figure-of-merit (µC*) and excellent operational stability by developing a robust mixed-conductors in aqueous environment. In addition to the balanced mixed conduction, efficient ionic-electronic coupling, the system exhibits a remarkable doping stability, a key factor for reliable OECT function. This work aims to offer insights into rational and versatile design strategies to fundamentally decouple ionic mobility from structural instability, providing routes for developing organic electrochemical devices practically relevant for bio-and neuromorphic electronics.
|
 Professor, |
Electron-Beam–Assisted Mechanical Deformation in Oxide CeramicsAbstract Electron-beam–induced electronic excitation offers a non-thermal pathway to modify deformation mechanisms and drive nanostructure evolution in oxide ceramics. In this study, we demonstrate that electron–matter interactions significantly alter size-dependent mechanical behavior in both amorphous and crystalline systems, enabling precise nanoscale structural control. In amorphous silica, in-situ mechanical compression with focused low-voltage electron irradiation induces athermal viscoplastic deformation and densification at room temperature, permitting localized shaping without external heating. Furthermore, irradiation promotes the solid-state mechanical amorphization of crystalline α-quartz under ambient conditions. These phenomena are attributed to beam-induced delocalized electrons that screen interatomic repulsive forces, thereby lowering the energy barriers for atomic rearrangement. We believe that these findings establish electronic-structure manipulation as a robust strategy for defect engineering and deformation control in ceramics. This work provides a framework for designing nanostructured materials with tailored mechanical performance for extreme environments.
|
|
Assistant Professor, |
Atomic Reconstruction at Engineered Van der Waals InterfacesAbstract Twisted interfaces between two-dimensional (2D) van der Waals (vdW) materials enable control of structural symmetry and functionality at the atomic scale. Varying the stacking angle produces moiré superlattices and lattice reconstruction, where interlayer registry competes with intralayer strain to form ordered domains with emergent electronic, optical, or ferroic properties. This talk will show how stacking configurations and reconstruction govern domain formation and functionality, examined by electron diffraction contrast in transmission electron microscopy (TEM). By integrating TEM with semiconductor device fabrication, we perform operando measurements of domain dynamics in working devices, directly linking local symmetry breaking to macroscopic responses such as ferroelectric switching in twisted bilayer TMDs. Extending to multilayers introduces additional interfaces and symmetry degrees of freedom, yielding complex tessellations with distinctive structural and functional characteristics. Understanding these reconstructions is key to controlling emergent phenomena in twisted vdW materials. |
 Associate Professor, |
Designing Light at the Source: k-Space Mode Engineering for Directional and Chiral Thin-Film EmittersAbstract Controlling the direction and polarization of light at the emission stage is a key challenge for thin-film optoelectronics, where spontaneous emission is intrinsically broad and post-emission optics add loss and system complexity. In this talk, I will discuss k-space mode engineering in photonic-crystal platforms as a route to design how light is generated, extracted, and polarized. I will first show how all-dielectric photonic crystals coupled to thin-film emitters convert trapped guided modes into radiative channels, enabling brighter and highly directional emission. I will then describe symmetry-broken quasi-bound states in the continuum that provide deterministic control of chiral emission at the normal direction. Finally, I will discuss electrically driven photonic-crystal surface-emitting devices, highlighting how band-edge feedback can be implemented in practical laser-diode structures. These examples illustrate how subwavelength optical structures can turn thin-film emitters into efficient, directional, and polarization-controlled light sources for future photonic and display applications.
|
|
Professor, |
Tailoring the Electrical–thermal Properties of Polymers for Thin-film ThermoelectricsAbstract Thin-film thermoelectrics based on solution-processable soft materials, including conducting polymers, carbon nanotubes, and colloidal quantum dots, are promising for flexible and wearable energy harvesting, but remain limited by coupled electrical and thermal transport. In this presentation, a variety of strategies are presented for tailoring electrical and thermal properties through independent control of charge and heat pathways. Electrical transport is enhanced by tuning microstructure, electronic coupling, and carrier density, enabling semi-metallic or highly conductive behavior while maintaining favorable thermopower. Thermal transport is suppressed or redirected through phonon-scattering interfaces, low-conductivity phases, and thermally anisotropic architectures that convert out-of-plane heat flow into in-plane voltage generation. By decoupling electron and phonon transport across material and device length scales, these approaches provide general design principles for high-performance, scalable, and mechanically compliant energy-harvesting platforms. |
 Department Chair & Distinguished Professor, |
Sustainable Silicone Lithography of Organic Semiconductors for Human-interactive, High-resolution RGB OLED MicrodisplayAbstract Ultrahigh-resolution patterning with high throughput and fidelity is critical for extending organic light-emitting diodes (OLEDs) from conventional displays to near-eye microdisplays. However, existing patterning approaches remain limited by insufficient resolution, poor pattern fidelity, and constraints in scalable RGB integration. Here, we introduce a silicone-engineered anisotropic lithography for organic light-emitting semiconductors (OLES), in which a non-volatile etch-blocking layer is formed in situ during reactive ion etching. This self-limiting mechanism simultaneously suppresses lateral etching and enhances directional anisotropy, enabling precise and reproducible pattern definition. As a result, ultrahigh-density OLES patterns exceeding 10,000 pixels per inch are achieved through anisotropic photolithography, providing unprecedented control over sub-micron pixel architectures. By translating principles from silicon etching chemistry into organic semiconductor processing, this strategy establishes a new pathway toward scalable, high-resolution RGB patterning in OLED-on-silicon (OLEDoS) platforms for next-generation extended reality (XR) displays.
|
 Professor, |
Sensory Neuromorphic Displays for Biomedical and Robotic ApplicationsAbstract Human-interactive technologies play a crucial role in intelligent IoT, bioelectronics, and emerging physical AI regimes. Sensory neuromorphic displays (SNDs) integrate sensory processing, computation, memory, and visualization into a unified system, addressing the key limitations of traditional displays such as limited adaptability, high power consumption, and lack of contextual awareness. By leveraging neuromorphic computing principles and advanced device architectures, these displays enable real-time, adaptive responses to environmental stimuli, enhancing energy efficiency and interactivity. The development of innovative one-integrated platforms with optimized architectures where all the functional components are converged is essential to achieve highly efficient and fast information management. The presentation introduces a light-emitting tactile sensory neuromorphic display for real-time monitoring of finger rehabilitation movements. The core structure is based on a polymer electrochemical transistor (OECT) with an elastomeric tactile receptor and an electrochemiluminescent ion gel as the light-emitting layer. The approach presents a highly interactive, low-power solution for personalized rehabilitation monitoring. The SND platform also detects, memorizes, and visualizes magnetic field with an elastomeric gate modified with ferromagnetic fillers, demonstrating its feasibility and versatility for compact, energy-efficient wearable and physical AI robotic applications.
|
 Professor, |
Multi-dimensional Bioelectronic Interfaces and Energy Devices Based on Crystalline PEDOT:PSSAbstract In this research, we report organic bioelectronic interfaces based on highly crystalline poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films and microfibers, designed to overcome the inherent trade-off between electrical/electrochemical performance and long-term stability in aqueous environments. The crystalline PEDOT:PSS films exhibit excellent electrical, electrochemical, and optical properties, alongside robust long-term stability in water, and demonstrate high biocompatibility for primary-cultured cardiomyocytes and neurons over several weeks. Leveraging these properties, we successfully employ these films in high-performance multi-electrode arrays (MEAs) to record and stimulate the electrophysiological activities of primary cardiomyocytes and chicken retina tissues. In parallel, we develop crystalline PEDOT:PSS microfibers and a specialized self-fusion process to create single-strand wearable electrochemical transistors and 3D microfibrillar network-based bioelectronic interfaces. Finally, we discuss ongoing research activities, including the direct crystallization of PEDOT:PSS on plastic substrates, core-shell fibers and 3D sponges for energy storage, and PEDOT:PSS composite materials for electrocatalysis, gas separation membranes, and degradable/sustainable electronics.
|
Speakers from PolyU
 Associate Professor, |
Defects and Phase Transformation in Hybrid Perovskites Revealed by Low-dose Transmission Electron MicroscopyAbstract Organic-inorganic hybrid perovskites have become exciting candidates for use in next-generation solar cells. Further optimizing perovskite materials requires better understanding on the nature of intrinsic defects and their impacts on solar-cell performance. Using low-dose transmission electron microscopy (TEM), we have successfully unravelled the intrinsic defect structure including twinning boundaries in MAPbI3 and stacking faults in FAPbI3. The origin of these defects can be understood based on the stability of perovskite structure described by the Goldschmidt’s tolerance factor. This understanding further guides us to develop a defect-engineering strategy via tailoring MA/FA ratio in MA1-xFAxPbI3 to tune the tolerance factor, which further leads to controlled defect type and density. Measured performance on such defect-engineered sample series revealed the detrimental effect of defects on charge carrier lifetime, open-circuit voltage, and current-voltage hysteresis. In addition, we also applied scanning TEM to unravel the hexagonal-to-cubic phase transition mechanism in FAPbI3.
|
 Associate Professor, |
Chiral Perovskite Superlattices: From Chiral Superfluorescence to SpintronicsAbstract Achieving room-temperature chiral superfluorescence—a collective quantum phenomenon where disordered dipoles spontaneously synchronize into a coherent, circularly polarized giant dipole—has remained an elusive goal due to rapid dephasing and weak spin-photon coupling. In this talk, I will present how we have realized this phenomenon in vertically aligned chiral perovskite superlattices. This unique architecture facilitates the spontaneous emergence of ultrafast, coherent light bursts from the edge states with a high degree of circular polarization and long dephasing lifetime, establishing a new frontier in chiral quantum optics.
|
 Assistant Dean, Faculty of Science & Associate Professor, |
Low Dimensional Hybrid Perovskites: Large-Scale Growth and Emerging ApplicationsAbstract Low-dimensional organic-inorganic hybrid perovskites (HOIPs) have emerged as a unique class of quantum materials that integrate the structural tunability of organic molecules and inorganic quantum wells. Their hybrid nature enables the design of diverse electronic, optical, ferroic, and spin-related functionalities, offering exciting opportunities for next-generation optoelectronics, spintronics, and neuromorphic computing.
|
|
Assistant Professor, |
Low-dose Scanning Transmission Electron Microscopy (STEM) Characterizations of Halide Perovskite PhotovoltaicsAbstract The long-term stability of halide perovskite (HP) solar cells (PSCs) remains a critical hurdle, making it essential to get a thorough understanding of the microstructural underpinnings of HP degradation. We developed a protective strategy coupled with optimized low-dose scanning transmission electron microscopy (STEM) imaging, allowed us to unveil atomic-scale features within PSCs, including compositional and twin boundaries, stacking faults, and nanoscale impurities such as PbI2 and non-PbI2 nanoclusters. Guided by these insights, we developed targeted passivation strategies, effectively reducing nanoclusters density and enhancing device performance. |
|
Research Assistant Professor, |
High-Performance Flexible Electrochemical Transistors for Health MonitoringAbstract Electrochemical transistors (ECTs) have emerged as a powerful platform for bioelectronics, spanning healthcare diagnostics to human-machine interfaces, due to their efficient coupling of electronic and ionic transport. Their unique volumetric doping enables high transconductance at low operating voltages, making them ideal for various sensing applications. This talk will highlight our recent material and device innovations in high-performance ECTs for advanced bioelectronics. First, Organic Photo-Electrochemical Transistors (OPECTs) with photosensitive gates have been developed, combining signal amplification with photoelectrochemical analysis for ultra-sensitive DNA detection. Second, Perovskite Solar Cell-Gated ECTs are introduced as flexible photodetectors, enabling continuous, wearable, and contactless monitoring of PPG and blood oxygen levels under ambient light. Finally, novel metal-organic framework-based ECTs (MOFECTs) are demonstrated using oriented 2D MOF films. The unique vertical nanopores of these films facilitate efficient ion transfer and ultrahigh transconductance, successfully enabling the creation of ultra-flexible arrays for multi-directional ECG mapping on human skin. |
|
Associate Professor, |
All-in-One Wearable Neuromorphic System for Continuous, Non-Invasive Cardiovascular Monitoring and Closed-Loop TherapyAbstract Neuromorphic bioelectronics have emerged as a promising platform for low-power physiological data processing; however, the integration of sensing, intelligent decision-making, and therapeutic feedback within a single hardware system remains challenging. In this work, we report a wearable neuromorphic platform based on a light-emitting synaptic transistor (LEST) array for closed-loop cardiovascular management. The LEST simultaneously exhibits synaptic plasticity and electrochemiluminescent emission, enabling both neuromorphic computing and optical stimulation in a unified device architecture. An 8 × 8 flexible LEST array is employed to perform parallel in-memory matrix–vector multiplication and hardware-based classification of photoplethysmography (PPG) signals associated with different cardiovascular conditions. Following disease recognition, the array can be reconfigured to generate programmable pulsed red-light emission as a therapeutic output, eliminating the need for additional intervention modules. By seamlessly integrating physiological monitoring, neuromorphic information processing, disease identification, and optical therapy, this system establishes a compact closed-loop bioelectronic framework for intelligent healthcare applications. The proposed strategy highlights the potential of multifunctional neuromorphic devices for next-generation wearable medical systems and personalized cardiovascular treatment. |
|
Assistant Professor, |
Material Design of Polymer Acceptors for Efficient and Stable All-Polymer Solar CellsAbstract Organic solar cells (OSCs) have attracted considerable attention from both academia and industry due to their portability, transparency, flexibility, and facile fabrication. Owing to the extensive research efforts devoted to material development and device optimization, the power conversion efficiencies (PCEs) of OSCs based on small-molecular acceptors (SMAs) have exceeded 20% recently. Despite that, the device stability issue still remains a critical factor that limits the commercialization of OSCs. To this end, all-polymer solar cells (all-PSCs), which employ both polymeric donors and acceptors have attracted attention due to their additional advantages of robust mechanical toughness, and excellent light/thermal stability. With the development of Y-series polymerized-SMAs, the all-PSCs have realized decent efficiencies of over 19%. Here we report multiple design strategies for high-performance polymer acceptors, including end-group fluorination[1,2], vinylene-linkage conformational locking[3], core-to-core coupling[4] and ternary complementary strategies[5], which will strengthen the absorption and morphology properties of the active layer, thus achieving simultaneous enhancement in device efficiency and stability. Throughout precise control of the intramolecular charge transfer effect and intermolecular interaction, our all-PSCs can be also fine-tuned to fulfill various application circumstance, such as semitransparent photovoltaics and indoor photovoltaics, to the pressing demand of the ecosystem of Internet-of-Things.
|
|
Research Assistant Professor, |
Circular Bulk Photovoltaic Effect Induced Circularly Polarized Light Detection in Flexible Lead-Free Double Perovskite FerroelectricsAbstract Circular bulk photovoltaic effect (CBPV) of ferroelectric materials can be utilized as a distinctive methodology to detect circularly polarized light (CPL), especially in organic-inorganic hybrid perovskite ferroelectrics. However, most of the reported hybrid perovskite ferroelectrics contain environmentally hazardous lead; and the resultant CPL detectors are generally based on rigid bulk crystals. Here, flexible CPL detection is successfully realized by using lead-free double perovskite ferroelectrics, (C6H5CH2NH3)2CsAgBiBr7 (BCAB). Along with the spontaneous polarization, BCAB presents intriguing CBPV, which drives photovoltaic current highly dependent on the helicity of CPL, leading to a robust anisotropy factor up to 0.68. More notably, BCAB single-crystalline thin films can be mechanically exfoliated from its bulk crystals, allowing for flexible self-powered CPL detection with a high anisotropy factor of 0.63 at specific bending angle. This work would be helpful to design lead-free hybrid perovskite ferroelectrics for other advanced chiroptical devices. |
|
Research Assistant Professor, |
The Design of Thermally Activated Delayed Fluorescence Polymers and Their Application in OLEDsAbstract Thermally activated delayed fluorescence (TADF) conjugated polymers theoretically have the potential to achieve 100% internal quantum efficiency and offer numerous advantages, such as solution-processability, cost-effectiveness and compatibility with large-scale and flexible displays. This makes them highly promising for applications in solid-state lighting and displaying. The development of narrowband TADF conjugated polymers with high color purity is crucial for achieving high-definition displays. However, the currently reported TADF conjugated polymers suffer from the wide luminescence spectra and low color purity. On the other hand, it is a formidable challenge for precisely modulating light colors due to the extended conjugation along the conjugated backbone. Addressing this scientific issue, we plan to synthesize a series of narrowband blue, green and red MR-TADF conjugated polymers with high color purity, by grafting a multi-resonance (MR) effect induced narrowband TADF unit as pendant onto a conjugated backbone through a π bridge, or by embedding MR unit into conjugated backbone. Subsequently, these polymers will be used in the solution-processed organic light-emitting diode (OLED), and a detailed investigation into the structure-properties relationship of MR-TADF conjugated polymers will be conducted. |
|
Research Assistant Professor, |
Metal Halide Perovskite Nanocrystals for Photocatalysis: Interfacial Engineering StrategiesAbstract The evolution of materials chemistry is driven by the functional modification of natural and synthetic systems. Among advanced materials, metal halide perovskite (MHP) nanocrystals hold great promise as photocatalysts, yet their practical application is hindered by intrinsic structural instability. Environmental factors such as moisture, oxygen, light, and heat induce phase transformation, hydration, decomposition, and dissolution of perovskites. To address this, we proposed several stabilization strategies, primarily centered on interfacial engineering modifying the surface without altering the core composition, including ligand modification, surface encapsulation, and scaffolding support. These methods enable precise control from nanocrystal size down to the quantum dot scale, resulting in significantly enhanced stability and photocatalytic performance. Collectively, this work contributes to the growing development for the next-generation photocatalytic materials. |
