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Jeong, Inyoung,Park, Yun Hee,Bae, Seunghwan,Park, Minwoo,Jeong, Hansol,Lee, Phillip,Ko, Min Jae American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.42
<P>The electron transport layer (ETL) is a key component of perovskite solar cells (PSCs) and must provide efficient electron extraction and collection while minimizing the charge recombination at interfaces in order to ensure high performance. Conventional bilayered TiO2 ETLs fabricated by depositing compact TiO2 (c-TiO2) and mesoporous TiO2 (mp-TiO2) in sequence exhibit resistive losses due to the contact resistance at the c-TiO2/mp-TiO2 interface and the series resistance arising from the intrinsically low conductivity TiO2 of TiO2. Herein, to minimize such resistive losses, we developed a novel ETL consisting of an ultrathin c-TiO2 layer hybridized with mp-TiO2, which is fabricated by performing one-step spin-coating of a mp-TiO2 solution containing a small amount of titanium diisopropoxide bis(acetylacetonate) (TAA). By using electron microscopies and elemental mapping analysis, we establish that the optimal concentration of TAA produces an ultrathin blocking layer with a thickness of similar to 3 nm and ensures that the mp-TiO2 layer has a suitable porosity for efficient perovskite infiltration. We compare PSCs based on mesoscopic ETLs with and without compact layers to determine the role of the hole-blocking layer in their performances. The hybrid ETLs exhibit enhanced electron extraction and reduced charge recombination, resulting in better photovoltaic performances and reduced hysteresis of PSCs compared to those with conventional bilayered ETLs.</P>
A fluorinated polythiophene hole-transport material for efficient and stable perovskite solar cells
Jeong, Inyoung,Jo, Jea Woong,Bae, Seunghwan,Son, Hae Jung,Ko, Min Jae Elsevier 2019 Dyes and pigments Vol.164 No.-
<P><B>Abstract</B></P> <P>Charge-transport materials for use in highly efficient and stable perovskite solar cells (PSCs) must exhibit energy levels appropriate for high charge selectivity, sufficiently high charge-transport ability for efficient charge collection, and high humidity resistance for long-term device stability. Polythiophenes are a promising class of hole-transport layer (HTL) materials that could satisfy these requirements. However, PSCs fabricated using conventional poly(3-hexylthiophene) (P3HT) HTLs show limited efficiencies of <16% owing to the shallow highest occupied molecular orbital (HOMO) energy level and poor charge extraction ability of P3HT. Herein, we demonstrate that the fluorinated polythiophene derivative FEH is a suitable replacement for P3HT and a promising HTL material for perovskite solar cells. The FEH was found to have a deeper HOMO and exhibit more efficient charge-extraction ability at the perovskite/HTL interface than P3HT. This is attributed to the electron-withdrawing nature of the fluorine atoms in FEH and its ability to form more uniform films on the perovskite layer. Thus, when FEH was employed as the HTL, the corresponding PSC showed an improved efficiency of 18.0% and an enhancement of all device parameters compared with control devices fabricated using P3HT (10.8%) and Spiro-OMeTAD (17.0%) HTLs. Moreover, fluorination on the conjugated backbone of the polymer increases its hydrophobicity, and the resulting hydrophobic surface of the FEH HTL prevents the ingress of water, resulting in an improvement of the long-term stability of the corresponding PSCs under air exposure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fluorinated polythiophene derivative was used as hole-transport layer (HTL) of perovskite solar cells (PSCs). </LI> <LI> The fluorinated polymeric HTL shows efficient charge extraction and hydrophobic surface property. </LI> <LI> The PSCs based on the HTL exhibit a best efficiency of 18.0% and better stability compared to conventional Spiro-OMeTAD HTL. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jeong, Inyoung,Jung, Heesuk,Park, Minwoo,Park, Joon Suh,Son, Hae Jung,Joo, Jin,Lee, Jinwoo,Ko, Min Jae Elsevier 2016 Nano energy Vol.28 No.-
<P><B>Abstract</B></P> <P>To realize high-performance flexible perovskite solar cells (PSCs), electron selective layers (ESL) that can be processed at low temperatures are required. Here, we develop UV-assisted solution process to prepare highly compact Nb-doped TiO<SUB>2</SUB> (UV-Nb:TiO<SUB>2</SUB>) ESLs at low temperature (<50°C). Highly crystalline TiO<SUB>2</SUB> nanocrystals (NCs) stabilized with oleic acid are synthesized and the highly dispersed TiO<SUB>2</SUB> NCs solution is spin-coated, followed by UV treatment. The UV exposure induces photocatalytic removal of the organic ligands and spontaneous coalescence of the TiO<SUB>2</SUB> NCs, resulting in highly uniform and compact TiO<SUB>2</SUB> thin films. The UV-processed TiO<SUB>2</SUB> layer (UV-TiO<SUB>2</SUB>) shows higher transmittance and a better blocking effect, compared to a conventional TiO<SUB>2</SUB> layer (HT-TiO<SUB>2</SUB>) prepared by high temperature sintering process. Furthermore, Nb doping of the TiO<SUB>2</SUB> NCs improves the electrical conductivity and gives rise to a downward shift of the conduction band, enhancing the charge extraction. Thanks to the advantages, PSCs based on UV-Nb:TiO<SUB>2</SUB> ESLs show improved photovoltaic performances and less hysteresis, compared to the HT-TiO<SUB>2</SUB> ESL. The best-performing PSCs based on UV-Nb:TiO<SUB>2</SUB> ESL exhibit outstanding power conversion efficiencies of 19.57% and 16.01% for rigid and flexible substrates, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Low-temperature solution processed TiO<SUB>2</SUB> ESL is developed for high-performance PSCs. </LI> <LI> Nb doping of TiO<SUB>2</SUB> ESL improves photovoltaic performances of PSCs. </LI> <LI> Champion cells exhibit PCE of 19.57% for rigid and 16.01% for flexible substrates. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
mRNA expression and metabolic regulation of <i>npy</i> and <i>agrp1/2</i> in the zebrafish brain
Jeong, Inyoung,Kim, Eunmi,Kim, Suhyun,Kim, Hwan-Ki,Lee, Dong-Won,Seong, Jae Young,Park, Hae-Chul Elsevier 2018 Neuroscience Letters Vol.668 No.-
<P><B>Abstract</B></P> <P>Neuropeptide Y (NPY) is an evolutionarily conserved neuropeptide implicated in feeding regulation in vertebrates. In mammals, NPY neurons coexpress Agouti-related protein (AgRP) in the arcuate nucleus of the hypothalamus, and NPY/AgRP neurons activate orexigenic signaling to increase food intake. Zebrafish express <I>npy</I> and two <I>agrp</I> genes, <I>agrp1</I> and <I>agrp2</I>, in the brain. Similar to mammals, NPY and AgRP1 act as orexigenic factors in zebrafish, but the exact distribution of NPY and AgRP neurons in the zebrafish brain and the regulation of these genes by metabolic states remain unclear. In this study, we analyzed the tissue distribution of <I>npy, agrp1</I>, and <I>agrp2</I> mRNA in the brain of larval and adult zebrafish. We detected the expression of <I>agrp1</I>, but not <I>npy</I>, in the hypothalamus of larval zebrafish. In the adult zebrafish brain, <I>npy</I> mRNA expression was detected in the dorsal area of the periventricular and lateral hypothalamus, but fasting induced upregulation of <I>npy</I> only in the lateral hypothalamus, indicating that NPY neurons in this area are implicated in feeding regulation. However, consistent with the findings in larval zebrafish, NPY neurons in the hypothalamus did not coexpress AgRP1. In contrast, fasting resulted in a dramatic increase in AgRP1 neurons in the ventral periventricular hypothalamus, which do not coexpress NPY. In addition, we found for the first time that <I>npy</I>- and <I>agrp1</I>-expressing neurons function as GABAergic inhibitory neurons in zebrafish, as they do in mammals. Taken together, our results show that the zebrafish NPY/AgRP system is involved in appetite regulation. In addition, our data suggest that although <I>npy</I> and <I>agrp1</I> were initially expressed in distinct neurons, evolution has resulted in their coexpression in mammalian hypothalamic neurons.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We analyzed <I>npy, agrp1,</I> and <I>agrp2</I> mRNA distribution in larval/adult zebrafish brains. </LI> <LI> NPY and AGRP1 neurons function as GABAergic inhibitory neurons in larval zebrafish. </LI> <LI> <I>Npy</I> and <I>agrp1/2</I> are expressed in distinct neurons in the hypothalamus. </LI> <LI> Metabolic state regulated NPY neurons in the lateral hypothalamus of adult zebrafish. </LI> <LI> Metabolic state regulated AgRP1 neurons in the adult zebrafish ventral hypothalamus. </LI> </UL> </P>
Jeong, Inyoung,Jo, Changshin,Anthonysamy, Arockiam,Kim, Jung-Min,Kang, Eunae,Hwang, Jongkook,Ramasamy, Easwaramoorthi,Rhee, Shi-Woo,Kim, Jin Kon,Ha, Kyoung-Su,Jun, Ki-Won,Lee, Jinwoo Wiley-VCH 2013 ChemSusChem Vol.6 No.2
<P>A disulfide/thiolate (T(2)/T(-)) redox-couple electrolyte, which is a promising iodine-free electrolyte owing to its transparent and noncorrosive properties, requires alternative counter-electrode materials because conventional Pt shows poor catalytic activity in such an electrolyte. Herein, ordered mesoporous tungsten suboxide (m-WO(3-x)), synthesized by using KIT-6 silica as a hard template followed by a partial reduction, is used as a catalyst for a counter electrode in T(2)/T(-)-electrolyte-based dye-sensitized solar cells (DSCs). The mesoporous tungsten suboxide, which possesses interconnected pores of 4 and 20 nm, provides a large surface area and efficient electrolyte penetration into the m-WO(3-x) pores. In addition to the advantages conferred by the mesoporous structure, partial reduction of tungsten oxide creates oxygen vacancies that can function as active catalytic sites, which causes a high electrical conductivity because of intervalence charge transfer between the W(5+) and W(6+) ions. m-WO(3-x) shows a superior photovoltaic performance (79 % improvement in the power conversion efficiency) over Pt in the T(2)/T(-) electrolyte. The superior catalytic activity of m-WO(3-x) is investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization curve analysis.</P>