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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.
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.