Enhanced UV stability of perovskite solar cells with a SrO interlayer

Lee, Sang-Won,Kim, Seongtak,Bae, Soohyun,Cho, Kyungjin,Chung, Taewon,Hwang, Jae-Keun,Song, Inseol,Lee, Wonkyu,Park, Sungeun,Jung, Jaebong,Chun, Jihun,Lee, Yoon Jung,Moon, Yeon Ji,Lee, Hae-Seok,Kim, Do Elsevier 2018 Organic Electronics Vol.63 No.-

<P><B>Abstract</B></P> <P>We investigated strontium oxide (SrO) as an interlayer material to enhance the UV stability of a CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> perovskite solar cell. Moisture and over 400 nm wavelength of light were excluded to investigate the effect of UV light only. Two different interlayer fabrication processes were examined to optimize the performance of this solar cell. Devices fabricated by dipping for 30 min in SrO solution exhibited photoconversion efficiencies of 15.5%, whereas those fabricated with 60-min dipping showed photoconversion efficiencies of 15% and exhibited local Sr agglomeration. Devices with SrO displayed lower initial efficiencies than those without any SrO layer (17.6%), However, a device without SrO retained only 34.4% of its initial efficiency after 100 h of UV exposure. In contrast, SrO-incorporated devices retained almost 60.0% of their initial efficiency. Severe μ-PL mapping intensity degradation was observed in devices that did not include the interlayer, but no degradation was observed in those with the SrO interlayer. This can be attributed to the passivation of the degradation sites by SrO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Perovskite UV stability was tested under conditions except moisture, oxygen and wavelengths exceeding 400 nm. </LI> <LI> With high resolution μ-PL mapping technique, direct evidence is provided about the area perovskite UV degradation begins. </LI> <LI> UV degradation is initiated at the ETL/perovskite interface. </LI> <LI> Effect of the SrO interlayer on UV stability was examined in an inert atmosphere. </LI> <LI> UV stability is enhanced by SrO interface passivation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A comparative study of the deviation of the menton on posteroanterior cephalograms and three-dimensional computed tomography

Lee, Hee Jin,Lee, Sungeun,Lee, Eun Joo,Song, In Ja,Kang, Byung-Cheol,Lee, Jae-Seo,Lim, Hoi-Jeong,Yoon, Suk-Ja Korean Academy of Oral and Maxillofacial Radiology 2016 Imaging Science in Dentistry Vol.46 No.1

Purpose: Facial asymmetry has been measured by the severity of deviation of the menton (Me) on posteroanterior (PA) cephalograms and three-dimensional (3D) computed tomography (CT). This study aimed to compare PA cephalograms and 3D CT regarding the severity of Me deviation and the direction of the Me. Materials and Methods: PA cephalograms and 3D CT images of 35 patients who underwent orthognathic surgery (19 males and 16 females, with an average age of $22.1{\pm}3.3years$) were retrospectively reviewed in this study. By measuring the distance and direction of the Me from the midfacial reference line and the midsagittal plane in the cephalograms and 3D CT, respectively, the x-coordinates ($x_1$ and $x_2$) of the Me were obtained in each image. The difference between the x-coordinates was calculated and statistical analysis was performed to compare the severity of Me deviation and the direction of the Me in the two imaging modalities. Results: A statistically significant difference in the severity of Me deviation was found between the two imaging modalities (${\Delta}x=2.45{\pm}2.03mm$, p<0.05) using the one-sample t-test. Statistically significant agreement was observed in the presence of deviation (k=0.64, p<0.05) and in the severity of Me deviation (k=0.27, p<0.05). A difference in the direction of the Me was detected in three patients (8.6%). The severity of the Me deviation was found to vary according to the imaging modality in 16 patients (45.7%). Conclusion: The measurement of Me deviation may be different between PA cephalograms and 3D CT in some patients.

Organic Electroluminescent Devices Based on Polyurethane Derivatives Having Substituted Stilbene Pendants

Lee, Gyu Hyun,Jin, Youngeup,Lee, Sungeun,Lee, Jong Gun,Kim, Jin Young,Lee, Kwanghee,Jin, Sung-Ho,Ha, Chang-Sik,Won, Mi-Sook,Kang, Shin-Won,Suh, Hongsuk 부산대학교 유전공학연구소 2002 분자생물학 연구보 Vol.18 No.-

There have been extensive research efforts on organic electroluminescent devices (OELDs) with the aim of application for the flat panel display (FPD). OELDs have also attracted much interest because of their particular low driving voltage, convenient design of the device structures, possible control of emission band, and low fabrication cost compared with any other devices. OELDs can be classified as either molecular or polymer-based. Molecular-based devices consist of vacuum deposited fluorescent emitter layers whereas polymer-based devices consist of either spinor dip-coated layers. Most of the research in the field of polymer-chain conducting polymers such as poly(plenylene vinylene) (PPV), poly(p-phenylene) (PPP), their copolymers and soluble derivatives. Other groups have reported non-conjugated polymers with pendant chromophores for OELDs. The attachment of the fluorophore as the pendant group of a random-coil polymer presents several advantages: (1) the synthetic route would be simpler than that used for main-chain polymers; (2) the moderate solubility could be obtained by the nature of the backbone; (3) the emission wavelength would be easily controllable. We, recently, reported the PU polymer with the 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye as the pendant. Even though it is known that the PU backbone have many quenching sites, the turn-on voltage of the PU-DCM device was ca. 5 V. Also, the change of the fluorophores in the side chain from para-cyanostilbene(PU-CN) to DCN (PU-DCM) caused the shift of PL emission wavelength. For the PL emission spectra of PU-CN and PU-DCM, the maximum peaks were at ca. 520 and 630 nm, respectively, corresponding to the maximum PL peaks. Therefore, EL, and PL properties can be changed using different lumophore pendant groups possibly caused by the electron withdrawing effect of the DCM prndant. In the present work, PU derivatives with stilbene pendant. In the present work, PU derivatives with stilbene pendant containing one or two fluoro group were introduced on the stilbene side chain. OELDs using polyurethane derivatives with stilbene pendants were fabricated to investigate the effect of the electron withdrawing substituents of the lumophore pendant on the EL and PL properties. Since PU derivatives possess different electron withdrawing substituents on the stilbence pendant, the shift of emission wave-length is expected.

Holocene Climate Variability on the Centennial and Millennial Time Scale

Eun Hee Lee,Dae-Young Lee,Mi-Young Park,Sungeun Kim,Su Jin Park 한국우주과학회 2014 Journal of Astronomy and Space Sciences Vol.31 No.4

There have been many suggestions and much debate about climate variability during the Holocene. However, their complex forcing factors and mechanisms have not yet been clearly identified. In this paper, we have examined the Holocene climate cycles and features based on the wavelet analyses of 14C, 10Be, and 18O records. The wavelet results of the 14C and 10Be data show that the cycles of ~2180-2310, ~970, ~500-520, ~350-360, and ~210-220 years are dominant, and the ~1720 and ~1500 year cycles are relatively weak and subdominant. In particular, the ~2180-2310 year periodicity corresponding to the Hallstatt cycle is constantly significant throughout the Holocene, while the ~970 year cycle corresponding to the Eddy cycle is mainly prominent in the early half of the Holocene. In addition, distinctive signals of the ~210-220 year period corresponding to the de Vries cycle appear recurrently in the wavelet distribution of 14C and 10Be, which coincide with the grand solar minima periods. These de Vries cycle events occurred every ~2270 years on average, implying a connection with the Hallstatt cycle. In contrast, the wavelet results of 18O data show that the cycles of ~1900-2000, ~900-1000, and ~550-560 years are dominant, while the ~2750 and ~2500 year cycles are subdominant. The periods of ~2750, ~2500, and ~1900 years being derived from the 18O records of NGRIP, GRIP and GISP2 ice cores, respectively, are rather longer or shorter than the Hallstatt cycle derived from the 14C and 10Be records. The records of these three sites all show the ~900-1000 year periodicity corresponding to the Eddy cycle in the early half of the Holocene.

Nanostructural analysis of ZnO:Al thin films for carrier-transport mechanisms

Seung-Yoon Lee,Woojin Lee,남창우,Jongmin Kim,Sujin Byun,Taehyun Hwang,Byung-Kee Lee,Young Il Jang,Sungeun Lee,Heon Min Lee,박병우 한국물리학회 2013 Current Applied Physics Vol.13 No.4

The carrier mobility of sputter-deposited Al-doped ZnO transparent-conducting (ZnO:Al) thin films was controlled between 22 and 48 cm2/Vs by varying the ZnO:Al seed layer. The statistical distribution of the [001] grain misorientation was characterized from the X-ray diffraction rocking curve in the range from 0.043 (2.5) to 0.179 rad (10.2). The grain-boundary energy barriers (Eb) from Seto’s model [1] clearly exhibit linear dependence on the grain-boundary misorientation angle (u) according to the equation Eb ¼ 78 4 þ 173 32 u meV.

Erratum to: Charge transfer in graphene/polymer interfaces for CO2 detection

Kim, Kihyeun,Son, Myungwoo,Pak, Yusin,Chee, Sang-Soo,Auxilia, Francis Malar,Lee, Byung-Kee,Lee, Sungeun,Kang, Sun Kil,Lee, Chaedeok,Lee, Jeong Soo,Kim, Ki Kang,Jang, Yun Hee,Lee, Byoung Hun,Jung, Gun- Springer-Verlag 2018 NANO RESEARCH Vol.11 No.7

Charge transfer in graphene/polymer interfaces for CO2 detection

Son, Myungwoo,Pak, Yusin,Chee, Sang-Soo,Auxilia, Francis Malar,Kim, Kihyeun,Lee, Byung-Kee,Lee, Sungeun,Kang, Sun Kil,Lee, Chaedeok,Lee, Jeong Soo,Kim, Ki Kang,Jang, Yun Hee,Lee, Byoung Hun,Jung, Gun- Springer-Verlag 2018 NANO RESEARCH Vol.11 No.7

Average SNR and ergodic capacity analysis for opportunistic DFrelaying with outage over rayleigh fading channels

Sungeun Lee,Myeongsu Han,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.6

<P>In the paper, we deal with a single-selection opportunistic relaying with the decode-and-forward (DF) protocol over Rayleigh fading channels. The exact end-to-end average signal-to-noise ratios (SNR) and ergodic capacities of both proactive and reactive opportunistic relaying are derived as a closed-form for arbitrary link SNR. In addition, the effective ergodic capacity satisfying the minimum required data rate without outage is also identified for both relaying schemes. The analysis results are used to demonstrate which relaying scheme outperforms the other for given system parameters.</P>

The Effects of Weight-Bearing Exercise on Upper Extremity Activities Performance in the Female Stroke Patients

Lee, SungEun,Cho, SungHyoun,Kim, Kyoung The Korea Contents Association 2013 International Journal of Contents Vol.9 No.1

The purpose in the present study was to examine the effects of weight-bearing exercises on stroke patients' ability to perform upper extremity activities. Experiments were conducted with 24 female stroke patients who were randomly assigned to either a control group (CG) that performed general exercise or an experimental group that performed weight-bearing exercise (WBG). The experiments were conducted for 30 minutes per time, three times per week for six weeks. The upper extremity functions, grasping power, and the ability to manipulate the fingers were measured for both groups before the experiments and again six weeks after the beginning of the experiments. Although the scores for upper extremity functions relating to raising the arms that correspond to proximal upper extremity functions increased in both groups, the WBG showed more significant improvement. The WBG showed significant changes in grasping power compared to the CG. Based on these results, weight-bearing exercise can be effective in improving the ability to perform upper extremity movements and grasping power and thus can be used in stroke rehabilitation.

Theca-specific estrogen receptor-alpha knockout mice lose fertility prematurely.

Lee, Sungeun,Kang, Dong-Wook,Hudgins-Spivey, Susan,Krust, Andree,Lee, Eun-Young,Koo, Youngbum,Cheon, Yongpil,Gye, Myung Chan,Chambon, Pierre,Ko, ChemYong Association for the Study of Internal Secretions 2009 Endocrinology Vol.150 No.8

<P>Estrogen receptor-alpha (Esr1) mediates estrogen action in regulating at all levels of the hypothalamic-pituitary-ovarian axis. Whereas the importance of Esr1 in hypothalamus and pituitary has been demonstrated by loss of fertility in the neuron- and pituitary-specific Esr1 knockout mice, whether Esr1 plays a critical role in the ovary remains to be determined. In the ovary, Esr1 is mainly expressed in the theca/interstitial cells and germinal epithelium and thus is believed to mediate estrogen action in these cells. In this study, we assessed the importance of Esr1 in the ovarian theca cells in regulating female reproduction. The Cre-LoxP approach was used to selectively delete the Esr1 gene in the theca cells, and the reproductive consequence of the deletion was measured. Adolescent theca-specific Esr1 knockout (thEsr1KO) mice (<4 months of age) are fertile and cycling. However, they begin to display an erratic pattern of estrous cycles and become infertile before they reach the age of 6 months. The ovaries of thEsr1KOmice (>or=4 months) have fewer corpora lutea but more antral follicles than the age-matching wild-type mice. The numbers of 17-hydroxylase-expressing cells are largely increased in the interstitium of the thEsr1KO mouse ovary. Interestingly, whereas basal levels of serum testosterone and FSH were mildly elevated, LH level was either markedly lower or undetectable in the thEsr1KO mice. When superstimulated by exogenous gonadotropins, thEsr1KO mice released significantly fewer oocytes that wild-type littermates and developed multiple hemorrhagic cysts. Taken together, this study demonstrates that theca Esr1 plays a critical role in regulating female reproduction.</P>