Analysis of the small-signal voltage decay technique in the characterization of Si concentrator solar cells

Detailed analyses of the small-signal voltage decay (SSVD) method of lifetime measurement have been performed. The main difficulty in voltage decay techniques is that the boundary conditions at the junction are coupled. A solution to the time-dependent diffusion equations has been obtained using the quasi-static emitter (QSE) approximation. Assuming a power-law emitter doping profile, a solution to the coupled diffusion equations has also been obtained using a dynamical approach without the QSE approximation. The extent to which effects such as emitter recombination and bandgap narrowing affect the SSVD lifetime has been examined using this solution. The SSVD technique has been applied in investigating the variation of minority-carrier recombination rates in the emitter, base, and back surface of concentrator solar cells with illumination intensities. The experimentally observed degradation in SSVD lifetime with increasing illumination intensity has been accounted for quantitatively