Localization of shunts across the floating junction of DSBC solar cells by lock-in thermography

The passivation that is provided by a floating junction (FJ) is degraded by any shunts that occur across the FJ. In Double-Sided Buried-Contact (DSBC) solar cells, shunts have been suspected to occur at various locations of the FJ: at pinholes in the insulating oxide, tunnel currents near the rear fingers, and at the cell edges. However, until recently there has not been a simple technique to precisely localize these shunts, since by definition, the FJ cannot be contacted. Infrared lock-in thermography, performed in the dark by applying a pulsed forward bias to the emitter, can localize FJ shunts with a spacial resolution down to 5 mum. The FJs are "remotely" forward biased via the emitter potential, and the heat dissipation at the shunts is imaged. This technique permits the investigation of any type of leakage phenomena in any type of solar cell within minutes of measuring time by a non-contacting measurement, including the bias-dependent leakage current at the edge of the cells.