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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>
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>
Highly Efficient Polymer Light-Emitting Diodes Using Graphene Oxide as a Hole Transport Layer
Lee, Bo Ram,Kim, Jung-woo,Kang, Dongwoo,Lee, Dong Wook,Ko, Seo-Jin,Lee, Hyun Jung,Lee, Chang-Lyoul,Kim, Jin Young,Shin, Hyeon Suk,Song, Myoung Hoon American Chemical Society 2012 ACS NANO Vol.6 No.4
<P>We present an investigation of polymer light-emitting diodes (PLEDs) with a solution-processable graphene oxide (GO) interlayer. The GO layer with a wide band gap blocks electron transport from an emissive polymer to an ITO anode while reducing the exciton quenching between the GO and the active layer in place of poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS). This GO interlayer maximizes hole–electron recombinations within the emissive layer, finally enhancing device performance and efficiency levels in PLEDs. It was found that the thickness of the GO layer is an important factor in device performance. PLEDs with a 4.3 nm thick GO interlayer are superior to both those with PEDOT:PSS layers as well as those with rGO, showing maximum luminance of 39 000 Cd/m<SUP>2</SUP>, maximum luminous efficiencies of 19.1 Cd/A (at 6.8 V), and maximum power efficiency as high as 11.0 lm/W (at 4.4 V). This indicates that PLEDs with a GO layer show a 220% increase in their luminous efficiency and 280% increase in their power conversion efficiency compared to PLEDs with PEDOT:PSS.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-4/nn300280q/production/images/medium/nn-2012-00280q_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn300280q'>ACS Electronic Supporting Info</A></P>
Introducing paired electric dipole layers for efficient and reproducible perovskite solar cells
Lee, Jong-Hoon,Kim, Junghwan,Kim, Geunjin,Shin, Dongguen,Jeong, Song Yi,Lee, Jinho,Hong, Soonil,Choi, Jin Woo,Lee, Chang-Lyoul,Kim, Heejoo,Yi, Yeonjin,Lee, Kwanghee The Royal Society of Chemistry 2018 ENERGY AND ENVIRONMENTAL SCIENCE Vol.11 No.7
<P>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 (<I>E</I>in) across the photoactive layer with a pair of strong electric dipole layers (EDLs). The paired EDLs significantly intensify the <I>E</I>in across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges. As a result, our low-temperature processed P-I-N planar PeSC devices using the paired EDLs exhibit a higher power conversion efficiency (<I>η</I>max ∼ 19.4%) and a smaller device-to-device variation with a standard deviation (S.D.) of 0.70%, which far surpass those (<I>η</I>max ∼ 17.8%, S.D. ∼ 1.1%) of the devices with typical charge transport layers.</P>
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>