DLIT- versus ILIT-based efficiency imaging of solar cells

Efficiency imaging of solar cells means to know which region of an inhomogeneous cell contributes by which degree to the efficiency at maximum power point of the cell. This knowledge allows us to judge how strong certain defect regions influence the efficiency of the whole cell. Efficiency imaging can be performed based on dark lock-in thermography (DLIT) imaging within the model of independent diodes, or based on illuminated lock-in thermography (ILIT), which does not assume any cell model. Moreover, by 2-dimensional finite element simulation of the cell based on DLIT results, an efficiency image can be obtained, which takes into account the distributed nature of the series resistance. In this contribution these three methods are applied to one and the same multicrystalline cell containing ohmic shunts and the results are compared to each other. Conclusions to the accuracy of solely DLIT-based efficiency imaging are drawn.