Nano-scale observation of charge transport and potential distribution of photovoltaic Cu(In,Ga)Se2 thin-films

Understanding of grain boundary (GB) is critical for photovoltaic applications since electron-hole recombination at GBs determines the conversion efficiency. However, our local electrical and optical analysis shows positive potential at GBs in Cu(In,Ga)Se2 (CIGS), which suppresses the recombination at GBs. We report on a direct measurement of potential distribution and local electrical transport on the surface of photovoltaic CIGS using a nano-scale electrical characterization of Kelvin probe microscopy and conductive atomic force microscopy. This reveals that the positively charged surface potential at GB is expected to increase the minority carrier collection and the enhanced current at GB leads to large carrier mobility and electron-hole separation at the GBs. Micro-Raman scattering results helps to analyze electrical behavior from defect analysis.