Structural, optical, and electrical properties on Cu(In,Ga)$Se_2$ thin-films with Cu-defects and In/(In+Ga) ratio

Cu(In,Ga)$Se_2$ 박막의 Cu 결함 및 In, Ga 비율의 변화에 따른 구조적, 광학적, 전기적 특성 연구

  • Published : 2011.11.16

Abstract

We report on a direct measurement of two-dimensional chemical and electrical distribution on the surface of photovoltaic Cu(In,Ga)$Se_2$ 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)$Se_2$ thin-films.

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