Kwanghee Lee's research while affiliated with Gwangju Institute of Science and Technology and other places

Publications (334)

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Suppressing nonradiative recombination at the interface between the organometal halide perovskite (PVK) and the charge transport layer (CTL) is crucial for improving the efficiency and stability of PVK‐based solar cells (PSCs). Here, we synthesized a new bathocuproine (BCP)‐based nonconjugated polyelectrolyte (poly‐BCP) and introduced this as a “du...
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Solution‐processed transition metal oxides (TMOs) prepared from complex ion precursors are developed as promising scalable interfacial layers for non‐fullerene organic photovoltaics (OPVs); however, challenges remain in achieving defect‐free and highly oriented metal‐oxygen networks without post‐deposition treatments due to the presence of residual...
Article
Non-fullerene acceptors (NFAs) have been crucial in improving the efficiency of organic solar cells (OSCs) due to their attractive properties, such as strong light-harvesting ability, easily tunable energy levels, and high crystallinity. Nevertheless, general NFAs have limited light absorption, and studies on the design of NFAs that can absorb a br...
Article
To realize the commercialization of nonfullerene acceptor‐based efficient organic solar cells, a low‐cost and indium‐tin‐oxide‐free (ITO‐free) flexible electrode‐based module that can be produced by roll‐to‐roll production should be developed. However, the low surface energy of ITO‐free electrodes hinders the formation of a uniform charge transport...
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We prepared a series of D-A-D’ type random copolymers, which are based on PBDB-S-3Cl and PBDB-S-4Cl, PBDB-S-CO-3Cl–4Cl (1:9), PBDB-S-CO-3Cl–4Cl (3:7), PBDB-S-CO-3Cl–4Cl (7:3) and PBDB-S-CO-3Cl–4Cl (9:1) with 3-chloro or 4-chloro and 2-s-alkylated thiophene on benzodithiophene (BDT), to examine the position effects of chlorine substitution of PBDB-S...
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Photoelectrochemical (PEC) water splitting based on organic semiconductors (OSs) is a promising way to enable sustainable hydrogen production because of its high photovoltaic performance and mass productivity by low-cost printing....
Article
Despite the outstanding role of conjugated polyelectrolytes (CPEs) in organic solar cells, the use of CPEs in perovskite solar cells has rarely been reported due to instability issues of the material itself under operating conditions.
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A new series of ITIC-based non-fullerene acceptors (NFAs), namely m-ITTC-Oeh-SM (IT-SM) and m-ITTC-Oeh-DSM (IT-DSM), which contain thiophene-substituted end groups (EGs) with single and double thiomethyl side chains, respectively, were designed, synthesized, and characterized in this study. The IT-SM NFA exhibited a narrower optical band gap, redsh...
Article
We designed and synthesised two fused electron acceptors based on 6,6,12,12-tetrakis(3-hexylphenyl)-indacenobis(benzodithiophene) with two-dimensional alkylthiophene or alkylthiothiophene substituents, named ETBDTIC and ESTBDTIC, respectively. ESTBDTIC exhibited red-shift absorption and deeper the highest occupied molecular orbital (HOMO) and the l...
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The advent of special types of polymeric semiconductors, known as “polymer blends,” presents new opportunities for the development of next‐generation electronics based on these semiconductors' versatile functionalities in device applications. Although these polymer blends contain semiconducting polymers (SPs) mixed with a considerably high content...
Article
The degradation of the perovskite layer in atmospheric air is a critical bottleneck for the commercialization of perovskite solar cells (PSCs). Since the moisture and oxygen in air penetrate the charge transport layer/top metal electrode interface, both adjacent layers and perovskite layers decompose in the PSCs. Here, we demonstrated moisture-stab...
Article
Amine-containing polyelectrolytes such as polyethyleneimine (PEI) are commonly used as cathode interfacial materials (CIMs); however, they are rarely found in non-fullerene acceptor (NFA) organic solar cells due to undesirable chemical reactions between PEI and NFAs. Unveiling the nature of these chemical interactions and developing chemically stab...
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In perovskite solar cells, doped organic semiconductors are often used as charge-extraction interlayers situated between the photoactive layer and the electrodes. The π-conjugated small molecule 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD) is the most frequently used semiconductor in the hole-conducting layer1...
Article
Π-conjugated polymers (π-CPs) blended with ionic liquids (ILs) have shown great potential for noninvasive diagnostics by transducing dielectric environmental changes induced by volatile organic compound (VOC) biomarkers into distinct electrical signals. However, the role of ILs in VOC sensing remains unclear, limiting further development of organic...
Article
Conjugated small molecular electrolytes (CSMEs), based on carbazole, containing different number of N and F atoms, were synthesized and introduced as the electron transport layer (ETL) for the fabrication of the polymer solar cells. Active-layer materials of bulk heterojunction and synthesized CSMEs were mixed as one solution which was coated on Zn...
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Although organometal halide perovskites (OHPs) have desirable photovoltaic properties, their photoelectrochemical (PEC) water‐splitting application for hydrogen production is limited by the instability originating from their intrinsic ionic defects and hygroscopic vulnerability. Herein, a highly efficient and stable OHP‐based photocathode achieved...
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In article number 2008277, Sanghan Lee, Kwanghee Lee, and co‐workers report a perovskite‐based photocathode for photoelectrochemical hydrogen production. The simultaneous improvement of the photocurrent and stability in organometal halide perovskite photocathode cells is successfully achieved by introducing both a L‐proline zwitterion additive to p...
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A simpler and less expensive fabrication process is one of the essential demands for the commercialization of perovskite solar cells (PeSCs). Especially, inverted PeSCs (I-PeSCs) require a cathode buffer layer (CBL) for fabricating highly efficient and stable PeSCs. However, this increases the number of fabrication step. Here, we demonstrate highly...
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An organometal halide perovskite (OHP) photocathode integrated with a MoS 2 catalyst achieved long-term photoelectrochemical (PEC) stability and high half-cell solar-to-hydrogen conversion efficiency (HC-STH).
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Solution-processed hybrid perovskite solar cells (PeSCs) have achieved remarkably high power conversion efficiencies (PCEs) of over 25%. [1] These excellent PCE results are attributed to the high crystallinity of perovskite materials with strong light absorption, high charge carrier mobility, and long intrinsic Ionic defects (e.g., organic cations...
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A new strongly electron‐accepting end group, 2,1,3‐benzothiadiazole‐4,5,6‐tricarbonitrile (TCNBT), has been prepared by a one‐step sixfold nucleophilic substitution reaction. Cyanation results in a significant enhancement of the electron affinity in comparison to the fluorinated analogue, and the material demonstrates promising n‐type performance i...
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We report a new high electron affinity acceptor end group for organic semiconductors, 2,1,3‐benzothiadiazole‐4,5,6‐tricarbonitrile (TCNBT). An n‐type organic semiconductor with an indacenodithiophene (IDT) core and TCNBT end groups was synthesized by a six‐fold nucleophilic substitution with cyanides on a fluorinated precursor, itself prepared by a...
Article
Conducting polymers (CPs) constitute a promising building block to establish next‐generation stretchable electronics. However, achieving CPs with both high electrical conductivity and outstanding mechanical stretchability beyond flexibility is still a major challenge. Therefore, understanding the key factors controlling such characteristics of CPs...
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Despite recent breakthroughs in the fabrication of spin-coated small-area devices (≤0.1 cm²) with power conversion efficiencies (PCEs) of more than 17%, printed large-area organic solar cells (OSCs) are significantly less efficient because of the intrinsic differences between the coating dynamics of the two types of OSCs. The PCEs of printed large-...
Article
An electric-field driven chemical doping modulation in a blend of solution-processed organic semiconductors (OSC) and solid-state ionic liquids (SSIL) in response to volatile organic compounds (VOC) provides a new exciting opportunity to facilitate printable and low-power chemical gas sensors (chemiresistors). In order to fully exploit this opportu...
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Color filters are essential components to realize next‐generation applications based on organic light‐emitting diodes (OLEDs), such as flexible displays and multipurpose lighting. Although the most widely used color filters that include dyes and pigments have advantageous features, such as their simplicity and color purity, the energy wasted by the...
Article
Printable organic sensors fabricated from solution-processed π-conjugated polymers (π-CPs) are promising candidates to detect volatile organic compounds (VOCs) due to the intriguing physical, chemical and electronic properties of π-CPs. These devices, often termed organic chemiresistors, require good sensing capabilities to transduce stimuli from s...
Article
Wavelength-selective harvesting by organic solar cells (OSCs) has attracted significant research attention due to the unique potential of these materials for smart photovoltaic window applications. Here, a visibly transparent OSC is demonstrated by utilizing both near-infrared (NIR)-absorbing polymer donor and nonfullerene acceptor (NFA) materials...
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Integrated perovskite/organic bulk heterojunction (BHJ) solar cells have the potential to enhance the efficiency of perovskite solar cells by a simple one‐step deposition of an organic BHJ blend photoactive layer on top of the perovskite absorber. It is found that inverted structure integrated solar cells show significantly increased short‐circuit...
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Sol-gel’-processed transition metal oxide (TMO) thin films sandwiched by an organic photoactive layer and metal electrodes have proven to be a versatile interlayer for photovoltaics with long-term stability on the laboratory scale; however, chemical defects and dewetting (or shrinkage) processes during sol-gel synthesis on top of the photoactive la...
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We fabricated window-film-type organic photovoltaics with flexible transparent electrodes (FTEs). By overcoming the poor adhesion between layers, we created ultra-thin metal electrodes (bottom FTE) on flexible substrates and transferred conducting polymers onto the photoactive layer (top FTE), providing power conversion efficiencies of 4.9% (7.4%)...
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Spirobifluorene based non-fullerene acceptors NFAs having meta-ethylhexyl oxy (m-OEh) substituents (PBDB-T: spiro-bridged NFAs) were synthesized. The orthogonal molecular structure of the m-OEh-substituted spirobifluorene with different end groups provided high solubility and kept the stable morphology between donor-acceptor. Organic Photovoltaic (...
Article
Recent breakthroughs in molecular design have allowed for remarkable achievement in the field of non-fullerene acceptor (NFA)-based organic solar cells (OSCs) with high power conversion efficiencies (PCEs) of over 15%. However, despite such promising advances, the inferior stability of OSCs under operational conditions remains a prominent challenge...
Article
A cost‐effective, flexible, and transparent gas barrier has been a main pursuit of research into plastics electronics. However, it is difficult to realize a high‐performance gas barrier on a plastic substrate via a solution process at low temperature. Here, by introducing an interfacial photocatalytic reduction between TiOx and graphene oxide (GO)...
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Alternating different donor units like ethyldioxy-thiophene (ED)/thiophenes (T) and acceptor units isoindigo (ID) /benzothiadiazle (BT) were attached together with the aid of Pd catalyzed C–H activation condition and forming [A(DA`nD`)2] based two π-bridged small molecules, ID(EDBT2TH)2 and ID(EDBT3T)2. Even the new materials have a significant hig...
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Despite the promise of a simple manufacturing via entire solution process at low temperature (< 100 °C), the planar-type inverted perovskite solar cells (PeSCs) based on methylammonium lead tri-iodide (MAPbI3) still suffer from a notorious instability problem under operational conditions. Here, we found that the operational stability of PeSCs with...
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The origin of performance enhancements in p‐i‐n perovskite solar cells (PSCs) when incorporating low concentrations of the bulky cation 1‐naphthylmethylamine (NMA) are discussed. A 0.25 vol % addition of NMA increases the open circuit voltage (Voc) of methylammonium lead iodide (MAPbI3) PSCs from 1.06 to 1.16 V and their power conversion efficiency...
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In article number 1906109, Kwanghee Lee, Bong‐Joong Kim, and co‐workers synthesize a polymorph of a single crystalline 2,7‐dioctyl[1] benzothieno[3,2‐b][1]benzothio‐phene (C8‐BTBT) rod on a low molecular weight poly(methyl methacrylate) (PMMA), which exhibits a reversible change in resistivity by 5.5 orders with hysteresis during thermal cycling. V...
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Semi-transparent organic solar cells (ST-OSCs) are considered to be an influential tool for aesthetic and economic building-integrated photovoltaics (BIPVs), which can be fabricated by printing technology. A poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and ionic liquid (IL) composite has been considered as an electrode for ST-O...
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Organic semiconductors (OSCs) are highly susceptible to the formation of metastable polymorphs that are often transformed by external stimuli. However, thermally reversible transformations in OSCs with stability have not been achieved due to weak van der Waals forces, and poor phase homogeneity and crystallinity. Here, a polymorph of a single cryst...
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Here, we report that a chemically p-doped conjugated small-molecule electrolyte (CSE) can be used as a strong and uniform dipole array for highly efficient optoelectronic devices via electrostatically induced molecular alignment and surface coverage on metal electrodes. Based on the structural and electrical characterization as well as evaluation o...
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Increasing the open circuit voltage (Voc) is one of the key strategies for further improvement of the efficiency of perovskite solar cells. It requires fundamental understanding of the complex optoelectronic processes related to charge carrier generation, transport, extraction and their loss mechanisms inside a device upon illumination. Herein we r...
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We analyse organic solar cells with four different photoactive blends exhibiting differing dependencies of short-circuit current upon photoactive layer thickness. These blends and devices are analysed by transient optoelectronic techniques of carrier kinetics and densities, air photoemission spectroscopy of material energetics, Kelvin probe measure...
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The tailoring of the chromaticity of white organic light‐emitting diodes (WOLEDs) has presented a significant challenge in their application in smart lighting sources to improve the quality of life and human performance. Here, a new microcavity WOLED (M‐WOLED) structure to modulate the chromaticity of the emitted light is demonstrated by only adjus...
Article
4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole (ED-BT-ED) is used as π (Donor-acceptor-Donor) bridge between two arms of (E)-1-(2-octyldodecyl)-3-(1-(2-octyldodecyl)-2-oxo-6-(5-(5-(thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)indolin-3-ylidene)indolin-2-one (ID-T3) to form a novel medium-sized molecule BT(EDIDT3)2, Using P...
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Carbazole-based conjugated small molecule electrolytes (CSEs) containing different numbers of amine groups were synthesized and applied to bulk-heterojunction (BHJ) organic solar cells for the formation of a spontaneous self-assembled electron transporting layer (ETL). The active layer was spin-coated with a mixture solution containing the BHJ mate...
Article
A new series of protected isoindigo (ID) based solution processable donor-acceptor type of small molecules was synthesized. Tert-butoxycarbonyl (t-Boc) substituted isoindigo is used as the acceptor unit and oligothiophene derivatives as the donor units. Thermal decarboxylation of small molecules films at 200 °C eliminated the t-Boc side groups. The...
Article
Doping is a widely implemented strategy for enhancing the inherent electronic properties of charge transport layers in photovoltaic (PV) devices. Here, in direct contrast to existing understanding, we find that a reduction in p-doping of the organic hole transport layer (HTL) leads to substantial improvements in PV performance in planar p-i-n perov...
Chapter
This chapter contains sections titled: Introduction Electrolytes Transition Metal Oxides (TMOs) Organic Semiconductors Outlook Acknowledgement
Article
Although high power conversion efficiency of over 14% has been achieved using nonfullerene acceptors (NFAs) in organic photovoltaics (OPVs), securing their insensitive device performance to the thickness of the photoactive layer remains an indispensable requirement for their successful commercialization via printing technologies. In this study, by...
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Owing to the mixed electron/hole and ion transport in the aqueous environment, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based organic electrochemical transistor has been regarded as one of the most promising device platforms for bioelectronics. Nonetheless, there exist very few in-depth studies on how intrinsic channel material prope...
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Realizing industrial-scale, large-area photovoltaic modules without any considerable performance losses compared with the performance of laboratory-scale, small-area perovskite solar cells (PSCs) has been a challenge for practical applications of PSCs. Highly sophisticated patterning processes for achieving series connections, typically fabricated...
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UV phototransistors based on ZnO, a material considered promising owing to its wide direct bandgap and high stability in harsh environments, have been intensively investigated. However, ZnO single-layer UV phototransistors, especially solution-processed devices, still exhibit poor electrical and UV photoresponse characteristics. Herein, we report t...
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Elimination of charge trapping at defects is highly challenging for poly-crystalline organometal halide perovskites. Here, we report a new architecture for reinforcing the built-in electric field (Ein) across the photoactive layer with a pair of strong electric dipole layers (EDLs). The paired EDLs significantly intensify Ein across the perovskite...
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Correction to:NPG Asia Materials (2018) https://doi.org/10.1038/s41427-018-0014-9published online on 16 April 2018