New technique for characterizing floating-junction-passivated solar cells from their dark IV curves

The incorporation of a floating junction (FJ) at the surface of a solar cell is a proven means of attaining excellent surface passivation. The development of FJ passivation for commercial use, however, has been hindered by an inherent difficulty in characterizing the FJ itself; to measure FJ parameters directly requires that electrical contact be made to the floating (i.e. uncontacted) layer that forms the FJ, and this is an irreversible process that can alter the properties of the FJ. This paper presents a new, simple technique to characterize an FJ that does not require electrical contact to the floating layer. The Ebers-Moll equivalent circuit is used to derive relationships between the cell parameters of an FJ-passivated solar cell and the shape of its dark IV curve. With these relationships, lumped, one-dimensional values can be determined for the current gains and the dark saturation currents of both the contacted and the floating junction, and the shunt resistance across the FJ. The technique is verified with device simulation and then demonstrated on two experimental FJ-passivated solar cells.