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Sonication Effect on All-Polymer Solar Cell Performance
Barange, Nilesh,Kim, Young Dong,Nam, Minwoo,Park, Byoungnam,Kim, Byunghoon,Han, Il Ki,Ko, Doo-Hyun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>In this paper, we demonstrated an effect of ultrasonication on the photoactive layer solution of polymer solar cell (PSC). We have fabricated the conventional polymer cells with active layer of poly(3-hexylthiophene) (P3HT) and poly[(9,9-dioctyluorene)-2,7-diyl-alt-(4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole)-2',2 ''-diyl] (F8TBT). Ultrasonic irradiation was performed on the blend of active layer solution for different time-period. The PSC with ultrasonic irradiation shows degradation in power conversion efficiency (PCE) with respect to the increase in treatment time period. The PSC with just 3 min ultrasonic irradiation shows a 37% decrease in open circuit voltage as compared to the reference device. Also, the PCE of ultrasonically treated (3 min) PSC is reduced to 0.509% from 0.893%. The overall performance degradation attributed to a mechanical rapid movement of molecule overcomes the intermolecular forces in the solution and breaks the polymer chain. The effect of ultrasonic irradiation on blend solution was confirmed by using optical (UV-vis absorption and PL) and morphological study.</P>
MgF₂ Monoplate 보정기를 사용한 회전보정기형 타원편광분석기의 제작 및 GaAs 연구에 대한 응용
최준호,Nilesh S. Barange,Mangesh S. Diware,김태중,박재찬,김영동 한국물리학회 2014 새물리 Vol.64 No.4
We constructed a rotating compensator type ellipsometer (RCE) and applied it to the study of the optical properties of GaAs. In this work, a MgF₂ monoplate retarder was incorporated into the RCE system to avoid the disadvantages of biplates and Berek plates and a photomultiplier tube (PMT) detector was used to effectively detect the signal of light. To demonstrate the high-precision capability of our home made RCE, we present the dielectric function and the critical point (CP) analysis results for GaAs, and we compare the data with those measured by using conventional ellipsometers. This work show that our home made RCE can resolve several CPs near the E₂ CP at room-temperature, which connot be done using conventional ellipsometers. 본 연구에서는 회전보정기형 타원편광분석기 (Rotating Compensator Ellipsometer, RCE) 를 제작하고 제작된 RCE 를 GaAs 의 광특성 연구에 적용하였다. Biplate (복층구조) 와 Berek plate 보정기의 단점들을 피하기 위하여 MgF₂ monoplate (단층구조) 보정기가 사용되었고, 효과적으로 빛의 신호를 검출하기 위하여 광전자증배관 (photomultiplier tube) 검출기가 사용되었다. 고정밀 측정정밀도를 확인하기 위해서 GaAs 의 유전율 함수를 측정하고, 전이점들을 분석 하였으며, 기존의 타원편광분석기를 통해 얻어낸 결과와 비교하였다. 그 결과 기존의 타원편광분석기들로는 분리가 불가능한 E 전이점 영역 부근의 전이점들을 상온에서 분석할 수 있었다.
Parametrization of the Optical Constants of AlAsxSb1-x Alloys in the Range 0.74-6.0 eV
김태중,변준석,Nilesh Barange,박한결,강유리,박재찬,김영동 한국광학회 2014 Current Optics and Photonics Vol.18 No.4
We report parameters that allow the dielectric functions ε = ε1 + iε2 of AlAsxSb1-x alloys to be calculatedanalytically over the entire composition range 0 ≤ x ≤ 1 in the spectral energy range from 0.74 to 6.0 eVby using the dielectric function parametric model (DFPM). The ε spectra were obtained previously byspectroscopic ellipsometry for x = 0, 0.119, 0.288, 0.681, 0.829, and 1. The ε data are successfullyreconstructed and parameterized by six polynomials in excellent agreement with the data. We can determineε as a continuous function of As composition and energy over the ranges given above, and ε can beconverted to complex refractive indices using a simple relationship. We expect these results to be usefulfor the design of optoelectronic devices and also for in situ monitoring of AlAsSb film growth.
김태중,공태호,윤재진,황순용,Nilesh Barange,김영동,Yia-Chung Chang 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.8
We report the parameters necessary to construct the dielectric functions of Cd1−xMgxTe ternary alloys at room temperature for arbitrary compositions from x = 0 to x = 0.5. The experimental spectra were measured by using vacuum ultraviolet spectroscopic ellipsometry in the spectral range from 0.7 to 9.0 eV. By performing a band structure calculation with the linear augmented Slater-type orbital method, we newly identify the four higher band gaps as E2 + Δ2, E2(Δ), E2(Σ), and E′1 transitions.
Temperature Dependence of the Dielectric Function and Critical-point Energies of InAs
김태중,황순용,Jun Seok Byun,Nilesh S. Barange,Jun Young Kim,김영동 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.1
We report the complex dielectric function of InAs for energies from 0.74 to 6.54 eV and temperatures from 22 to 675 K. The complex dielectric function was determined by using spectroscopic ellipsometry. The critical-point (CP) structures at low temperatures are blue-shifted and are sharpened significantly relative to those observed at high temperatures, which can be explained by using the reduction of the electron-phonon interaction and the thermal expansion. The CP energies are determined by using lineshape fittings to numerically calculated second energy derivatives of the dielectric function. The obtained CP energies are fit to a phenomenological expression that contains the Bose-Einstein statistical factor and to a linear equation.
Effect of the Ga Ratio on the Dielectric Function of Solution-processed InGaZnO Films
김태중,윤재진,Tae Ho Ghong,Nilesh Barange,Jun Young Kim,Soon Young Hwang,김영동,황수민,Jun Hyuk Choi,Jinho Joo 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6
Optical properties of InGaZnO (IGZO) films grown by the sol-gel process for various Ga ratios were investigated by spectroscopic ellipsometry (SE). The IGZO precursor sols were prepared at a molar ratio of In:Ga:Zn = 3:x:1 (0.0 ≤ x ≤ 1.5), deposited on SiO_2/Si substrates by spin coating, and sintered at 400 °C for 6 h in an ambient atmosphere. The optical properties were measured from 1.12 to 6.52 eV by variable-angle SE at room temperature. The angle of incidence was varied from 50° to 70° in steps of 5°. We clearly observed a blue shift of the bandgap energies and changes in the dielectric functions of the films with increasing Ga fraction. The change of optical properties might be understood by the concentration of oxygen vacancies, which can be modulated by varing the Ga content in IGZO.
Choi, Minjung,Kang, Gumin,Shin, Dongheok,Barange, Nilesh,Lee, Chang-Won,Ko, Doo-Hyun,Kim, Kyoungsik American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.20
<P>Strategies to confine electromagnetic field within ultrathin film emerge as essential technologies for applications from thin-film solar cells to imaging and sensing devices. We demonstrate a lithography-free, low-cost, large-scale method to realize broadband ultrathi-film metal dielectric-metal (MDM) absorbers, by exploiting gap-plasmon resonances for strongly confined electromagnetic field. A two-steps method, first organizing Au nanoparticles via thermal dewetting and then transferring the nanoparticles to a spacer - reflector substrate, is used to achieve broader absorption bandwidth by manipulating geometric shapes of the top metallic layer into hemiellipsoids. A fast-deposited nominal Au film, instead of a conventional slow one, is employed in the Ostwald ripening process to attain hemiellipsoidal nanoparticles. A polymer supported transferring step allows a wider range of dewetting temperature to manipulate the nanoparticles' shape. By incorporating circularity with ImageJ software, the geometries of hemiellipsoidal nanoparticles are quantitatively characterized. Controlling the top geometry of MDM structure from hemisphere to hemiellipsoid increases the average absorption at 500-900 nm from 23.1% to 43.5% in the ultrathin film and full width at half maximum of 132-324 nm, which is consistently explained by finite-difference time-domain simulation. The structural advantages of our scheme are easily applicable to thin-film photovoltaic devices because metal electrodes can act as metal reflectors and semiconductor layers as dielectric spacers.</P>
Kim, T.J.,Park, J.C.,Barange, N.S.,Park, H.G.,Kang, Y.R.,Nam, K.H.,Kim, Y.D. Elsevier 2015 Current Applied Physics Vol.15 No.suppl2
We report analytic expressions that accurately represent the dielectric functions ε = ε<SUB>1</SUB> + iε<SUB>2</SUB> of In<SUB>x</SUB>Al<SUB>1-x</SUB>As from 1.5 to 6 eV. We use the dielectric function parametric model, which portrays ε as a sum of polynomials and can accommodate the asymmetric nature of critical-point transitions. The ε spectra were obtained previously by spectroscopic ellipsometry for compositions x = 0, 0.10, 0.43, 0.62, 0.75, and 1. The ε data are successfully reconstructed and parameterized in excellent agreement with the data by seven polynomials. Our results allow ε to be determined as a continuous function of In composition and energy over the ranges given above, and ε can be converted to the complex refractive index using a simple relationship.
Temperature dependence of the critical points of monolayer MoS2 by ellipsometry
Park, Han Gyeol,Kim, Tae Jung,Kim, Hwa Seob,Yoo, Chang Hyun,Barange, Nilesh S.,Le, Van Long,Kim, Hyoung Uk,Senthilkumar, Velusamy,Le, Chinh Tam,Kim, Yong Soo,Seong, Maeng-Je,Kim, Young Dong Taylor Francis 2016 Applied spectroscopy reviews Vol.51 No.7