EVALUATION OF LOCAL ELECTRICAL PARAMETERS OF SOLAR-CELLS BY DYNAMIC (LOCK-IN) THERMOGRAPHY

The local current flow through biased solar cells can be monitored by measuring the local heating at the cell surface. Based on the discussi on of heat diffusion phenomena and on practical aspects, optimum strat egies for dynamic local current density measurements are derived. The practical realization of dynamic contact thermography is reviewed. Loc al inhomogeneities of the injected current density can be measured by this technique with a spatial resolution of down to 100 mu m and a sen sitivity of about 200 mu A/cm(2) in forward direction of a silicon cel l. Moreover, local I-V characteristics can be measured thermally in a non-destructive way. The applicability of this technique is demonstrat ed by investigating shunts in multicrystalline silicon solar cells. Dy namic thermography is shown to be a useful supplement to LBIC and EBIC investigations, since it reveals the locations limiting the open circ uit voltage and the fill factor of solar cells.