Analysis of thin-film inhomogeneities using electroluminescence and LBIC measurements

Electroluminescence (EL) and light-beam-induced-current (LBIC) mapping are used to study lab-size thin-film photovoltaic devices. Inhomogeneities seen in individual cells with these two characterization techniques are compared and analyzed. Features of interest in CdTe cells include signal variations across large areas of the cell as well as local, well-defined regions with little or no EL signal and/or reduced quantum efficiency (QE). CIGS devices exhibit these inhomogeneities as well as current crowding around the gridlines, where the current immediately around the front contacts is highest and decreases as the distance from the contacts increases. Other inhomogeneities seen using both EL and LBIC and across both technologies show variations in sheet resistance, mostly in the TCO layer.