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Cho, Yunae,Cho, Byungjin,Kim, Yonghun,Lee, Jihye,Kim, Eunah,Nguyen, Trang Thi Thu,Lee, Ju Hyun,Yoon, Seokhyun,Kim, Dong-Ho,Choi, Jun-hyuk,Kim, Dong-Wook American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.7
<P>There has been growing research interest in realizing optoelectronic devices based on the two-dimensional atomically thin semiconductor MoS2 owing to its distinct physical properties that set it apart from conventional semiconductors. However, there is little optical absorption in these extremely thin MoS2 layers, which presents an obstacle toward applying them for use in high efficiency light-absorbing devices. We synthesized trilayers of MoS2 directly on SiO2/Si nanocone (NC) arrays using chemical vapor deposition and investigated their photodetection characteristics. The photoresponsivity of the MoS2/NC structure was much higher than that of the flat counterpart across the whole visible wavelength range (for example, it was almost an order of magnitude higher at lambda = 532 nm). Strongly concentrated light near the surface that originated from a Fabry-Perot interference in the SiO2 thin layers and a Mie-like resonance caused by the Si NCs boosted the optical absorption in MoS2. Our work demonstrates that MoS2/NC structures could provide a useful means to realize high-performance optoelectronic devices.</P>
Cho, Yunae,Sohn, Ahrum,Kim, Sujung,Hahm, Myung Gwan,Kim, Dong-Ho,Cho, Byungjin,Kim, Dong-Wook American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.33
<P>Molybdenum disulfide (MoS2) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS2 is crucial for its application in electronic and optoelectronic devices. Because the MoS2 layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N-2, H-2/N-2, and O-2) choice on the resistance (R) and surface work function (WF) of trilayer MoS2 thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS, thin films; their R value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, R was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS2 thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable R change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS2.</P>
Cho, Ara,Banu, Shahara,Cho, Yunae,Ahn, Seung Kyu,Yun, Jae Ho,Cho, Jun-Sik Elsevier 2019 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.185 No.-
<P><B>Abstract</B></P> <P>Hybrid inks with a chelating agent were prepared and coated by a spin-coating method to form Cu<SUB>2</SUB>SnS<SUB>3</SUB> (CTS) thin films. After the coating, a subsequent sulfurizing process via rapid thermal annealing was performed. During the sulfurization, the Cu and Sn precursors in the hybrid inks exist in complex forms with chelates and these complexes help to form the CTS thin films by controlling the reaction rate of the metal precursors. Additionally, even though the complexes with chelates were formed, the oxidation numbers of the metal precursors were affected by the ionization tendency of each metal in the hybrid inks to form the semiconducting CTS thin films. After obtaining the optimum sulfurizing condition by controlling the reaction pressure and temperature, the CTS thin films were characterized and CTS solar cells were fabricated under these conditions. The best conversion efficiency of the fabricated cells was 2.953% and the temperature-dependent photovoltaic performances were also examined to investigate the carrier transport mechanisms of the devices. According to admittance spectroscopy, the dominant defect energy level was determined as 0.09 eV above the valence band minimum, which accords with the copper vacancy (<I>V<SUB>Cu</SUB> </I>) level. In addition, capacitance–voltage measurements and drive-level capacitance profiling were applied to demonstrate the carrier densities and defect behaviors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The chelating effect of metal-chelate complexes in hybrid ink can control reaction rate to form pure Cu<SUB>2</SUB>SnS<SUB>3</SUB> thin films. </LI> <LI> Metal-chelate complex helped to form pure Cu<SUB>2</SUB>SnS<SUB>3</SUB> by maintaining oxidation number of Cu and Sn. </LI> <LI> To investigate the carrier transport mechanisms, temperature-dependent As and DLCP analyses were conducted. </LI> <LI> The main defects were related to the <I>V<SUB>Cu</SUB> </I> acceptor. </LI> </UL> </P>
Cho, Yunae,Jeong, Inyoung,Gang, Myeng Gil,Kim, Jin Hyeok,Song, Soomin,Eo, Young-Joo,Ahn, Seung Kyu,Shin, Dong Hyeop,Cho, Jun-Sik,Yun, Jae Ho,Gwak, Jihye,Kim, Kihwan Elsevier 2018 Solar energy materials and solar cells Vol.188 No.-
<P><B>Abstract</B></P> <P>The structural, optical, and electrical properties of molybdenum (Mo) layers play a major role in Cu(In,Ga)Se<SUB>2</SUB> (CIGS) solar cell performance. The Mo layer works as a transport gate for diffusion of alkali ion from the soda-lime glass substrate to the back contact in CIGS solar cells. In the present work, Mo back contacts are controlled to exhibit two different orientations: (110)-oriented and randomly oriented. The influence of these orientations on CIGS absorbers and resulting solar cells is investigated. <I>In situ</I> thermo-Raman spectroscopy and secondary ion mass spectrometry results indicate that the greater amount of alkali ions are found in the CIGS absorber with randomly oriented Mo back contact than in the (110)-orientated Mo back contact. The resulting different Na incorporations significantly affect the performance of the resulting devices. Devices with the randomly oriented Mo back contact exhibit superior device performances to the devices with (110)-oriented Mo back contact. With comprehensive device characterizations, an alkali ion release determined by the orientation of the Mo back contact affects the recombination mechanism in the CIGS bulk and the back contact properties at the CIGS/Mo interface.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal orientation of Mo greatly affects alkali incorporation into CIGS films. </LI> <LI> Alkali incorporation by the orientation of Mo is dynamically observed via Thermo-Raman spectroscopy technique. </LI> <LI> Alkali incorporation influences not only the CIGS bulk but also CIGS/Mo interface. </LI> <LI> Correlation between device performance and alkali incorporation is discussed. </LI> </UL> </P>