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Choi, Jin Woo,Cho, Namchul,Woo, Hee Chul,Oh, Byeong M.,Almutlaq, Jawaher,Bakr, Osman M.,Kim, Sung-Hoon,Lee, Chang-Lyoul,Kim, Jong H. The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.12
<P>Thermochromism of organic/inorganic halide perovskites has attracted particular interest due to their potential applications as photoluminescence (PL)-based temperature sensors. However, despite the outstanding PL characteristics, their use as a thermochromic material in practical temperature ranges has been limited because of their poor thermal stability. In this study, we used the quantum confinement effect and exceptional PL quantum efficiency of the Cs4PbBr6 perovskite to demonstrate their high on/off ratio (20) and reversible PL thermochromism in the solid state in practical temperature ranges including room temperature (RT). Systematic photophysical and optical characterization studies, including exciton-phonon scattering, exciton binding energy, exciton decay dynamics, and crystal structure change, were performed to investigate the origin of this unique thermochromic PL property. The results showed that the efficient and highly reversible thermochromic PL emission of the Cs4PbBr6 perovskite is due to its desirable optical properties such as highly luminescent emission, efficient PL quenching at high temperatures, and thermally reversible structural changes.</P>
Chang-Lyoul Lee 한국진공학회(ASCT) 2015 Applied Science and Convergence Technology Vol.24 No.6
In this work, the electrical bistability of an organic CT complex is demonstrated and the possible switching mechanism is proposed. 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and tetracyanoquinodimethane (TCNQ) are used as an organic donor and acceptor, respectively, and poly-methamethylacrylate (PMMA) is used as a polymeric matrix for spin-coating. A device with the Al/(Al₂O₃)/PMMA:BCP:TCNQ[1:1:0.5 wt%]/Al configuration demonstrated bistable and switching characteristics similar to Ovshinsky switching with a low threshold voltage and a high ON/OFF ratio. An analysis of the current-voltage curves of the device suggested that electrical switching took place due to the charge transfer mechanism.
Triplet Exciton and Polaron Dynamics in Phosphorescent Dye Blended Polymer Photovoltaic Devices
Lee, Chang‐,Lyoul,Hwang, In‐,Wook,Byeon, Clare Chisu,Kim, Bok Hyeon,Greenham, Neil C. WILEY‐VCH Verlag 2010 Advanced Functional Materials Vol.20 No.17
<P><B>Abstract</B></P><P>The triplet exciton and polaron dynamics in phosphorescent dye (PtOEP) blended polymer (MEH‐PPV) photovoltaic devices are investigated by quasi‐steady‐state photo‐induced absorption (PIA) spectroscopy. According to the low‐temperature PIA and photoluminescence (PL) results, the increase in strength of the triplet‐triplet (<I>T</I><SUB>1</SUB>‐<I>T<SUB>n</SUB></I>) absorption of MEH‐PPV in the blend system originates from the triplet‐triplet energy transfer from PtOEP to MEH‐PPV. The PtOEP blended MEH‐PPV/C<SUB>60</SUB> bilayer photovoltaic device shows a roughly 30%–40% enhancement in photocurrent and power‐conversion efficiency compared to the device without PtOEP. However, in contrast to the bilayer device results, the bulk heterojunction photovoltaic devices do not show a noticeable change in photocurrent and power‐conversion efficiency in the presence of PtOEP. The PIA intensity, originating from the polaron state, is only slightly higher (within the experimental error), indicating that carrier generation in the bulk heterojunction is not enhanced in the presence of PtOEP. The rate and probability of the exciton dissociation between PtOEP and PCBM is much faster and higher than that of the triplet‐triplet energy transfer between PtOEP and MEH‐PPV.</P>
Electroluminescence from monolayer of quantum dots formed by multiple dip-coating processes
Lee, Chang-Lyoul,Nam, Sung-Wook,Kim, Viena,Kim, Jang-Joo,Kim, Ki-Bum WILEY-VCH Verlag 2009 Physica Status Solidi. B Vol.246 No.4
<P>The monolayer of 4.3 nm-size CdSe(ZnS) core-shell quantum dots (QDs) was formed by multiple dip-coating processes to fabricate the electroluminescent device. The particle adsorption was found to depend on both the substrate and the dipping number. The surface coverage was about 73% on PEDOT and 40% on PVK substrate, respectively. Self-assembled monolayer of QDs showed the hexagonal close-packed array by the van der Waals attraction between QDs. The monolayer quantum dots based organic (polymer) light emitting diodes (QD-O(P)LEDs) showed the maximum external quantum efficiency (η<SUB>ex</SUB>) of 0.05% and luminous power efficiency (η<SUB>p</SUB>) of 0.45 lm/W in the structure of ITO/ PEDOT(40 nm)/PVK(40 nm)/CdSe(ZnS) QDs/BCP(30 nm)/ Alq<SUB>3</SUB>(30 nm)/Mg:Ag/Ag. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>