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Ga/(In+Ga)함량비에 따른 Cu(In,Ga)Se2 박막의 국소적 영역에서의 표면 퍼텐셜과 전류-전압 특성 연구
김지영(G. Y. Kim),정아름(A. R. Jeong),조윌렴(W. Jo),조현준(H. J. Jo),김대환(D. -H. Kim),성시준(S. -J. Sung),황대규(D. -K. Hwang),강진규(J.-K. Kang),이동하(D. H. Lee) 한국태양에너지학회 2012 한국태양에너지학회 학술대회논문집 Vol.2012 No.3
Cu(In, Ga)Se2 (CIGS) is one of the most promising photovoltaic materials because of large conversion efficiency which has been achieved with an optimum Ga/(In+Ga) composition in CuIn1-xGaxSe2 (X~0.3). The Ga/(In+Ga) content is important to determine band gap, solar cell performances and carrier behaviors at grain boundary (GB). Effects of Ga/(In+Ga) content on physical properties of the CIGS layers have been extensively studied. In previous research, it is reported that GB is not recombination center of CIGS thin-film solar cells. However, GB recombination and electron-hole pair behavior studies are still lacking, especially influence of with different X on CIGS thin-films. We obtained the GB surface potential, local current and I-V characteristic of different X (0<X<1) in CIGS thin-films by using the Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). From C-AFM results, we found that CIGS thin-film (X~0.3) with high conversion efficiency flows lower local current. Surface potential was smaller than 80 mV near GBs with X<0.1 and X>0.7 while X~0.3 showed higher potential than 100mV on GBs. Higher potential on GBs appears positive band bending. It can decrease recombination loss because of carrier separation. Therefore, we suggest recombination and electron-hole behaviors at GBs depending on composition of X.
Micro-Raman Scattering Studies of Ge-Sb-Te Bulk Crystals and Nanoparticles
조윌렴,윤석현,H. R. Yoon,W. Jo 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
We measured micro-Raman scattering spectra of commercially available Ge-Sb-Te (GST) bulk crystals and GST nanoparticles which were synthesized using a pulsed laser ablation method. The lack of the amorphous Te-Te stretching mode near 150 cm¡1 from the Raman spectrum of the bulk sample indicated that the sample was well-crystallized. We also measured GST nanoparticles with dierent growth conditions, from which we could get information towards the optimal growth conditions for better crystallinity of the GST nanoparticles. Our results suggest that through local structural information, micro-Raman scattering spectroscopy can be used to study the phases and the phase changes in the GST bulk crystals and nanoparticles which is being developed for low-power non-volatile memory applications.
정아름(Jeong, A.R.),김지영(Kim, G.Y.),조윌렴(Jo, W.),조현준(Jo, H.J.),김대환(Kim, D.H.),성시준(Sung, S.J.),강진규(Kang, J.K.),이동하(Lee, D.H.),남다현(Nam, D.H.),정현식(Cheong, H.) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
We report on a direct measurement of two-dimensional chemical and electrical distribution on the surface of photovoltaic Cu(In,Ga)Se₂ thin-films using a nano-scale spectroscopic and electrical characterization, respectively. The Raman measurement reveals non-uniformed surface phonon vibration which comes from different compositional distribution and defects in the nature of polycrystalline thin-films. On the other hand, potential analysis by scanning Kelvin probe force microscopy shows a higher surface potential or a small work function on grain boundaries of the thin-films than on the grain surfaces. This demonstrates the grain boundary is positively charged and local built-in potential exist on grain boundary, which improve electron-hole separation on grain boundary. Local electrical transport measurements with scanning probe microscopy on the thin-films indicates that as external bias is increases, local current is started to flow from grain boundary and saturated over 0.3 V external bias. This accounts for carrier behavior in the vicinity of grain boundary with regard to defect states. We suggest that electron-hole separation at the grain boundary as well as chemical and electrical distribution of polycrystalline Cu(In,Ga)Se₂ thin-films.