Local current transport and surface potential of photovoltaic Cu(In,Ga)Se2 thin films probed by multi-scale imaging methods*

A R Jeong, G Y Kim, W Jo, D H Nam, H Cheong, H J Jo, D-H Kim, S J Sung, J K Kang and D H Lee

Abstract

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Microstructural alteration induces non-uniform device characteristics in polycrystalline thin films. In thin-film solar cells based on Cu(In,Ga)Se₂ (CIGS), local electrical properties are investigated by Raman scattering spectroscopic imaging and scanning probe microscopic tools. Localized and uneven intensity of phonon modes, which represent different orientation and phases, elucidate the nature of non-uniformity of crystallinity, composition and defects in the films. Surface potential mapping at nanoscale is performed by Kelvin probe force microscopy, showing ~40 mV of band-bending at the grain boundaries. Externally biased-current mapping, which is obtained by conductive atomic force microscopy, shows preferred current path in the films