Nondestructive local analysis of current–voltage characteristics of solar cells by lock-in thermography

By evaluating dark lock-in thermography images taken at one reverse and three forward biases, images of all two-diode-parameters J01, J02, n (ideality factor of J02), and Gp (the parallel Ohmic conductivity) of the dark current–voltage characteristic are obtained. A local series resistance is explicitly considered and may be provided as a series resistance image, e.g. resulting from luminescence imaging. The results enable a separate investigation of factors influencing the depletion region recombination current and the diffusion current, which is governed by the bulk lifetime. Local I–V characteristics of special sites may be simulated.

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► Dark current of all industrial solar cells (multi- and monocrystalline) flows inhomogeneous.
► For cell optimization, the local 2-diode parameters of the dark characteristic are needed.
► These are obtained by evaluating four lock-in thermography images taken at various biases.
► Procedure enables the calculation of realistic local current–voltage characteristics.
► The results of this procedure enable a detailed local analysis of the dark current losses.