Local mapping of the oxygen-boron complex in 2×2 cm2 and 10×10 cm2 high-efficiency CZ-Si solar cells by lock-in thermography and LBIC

If high efficiency solar cells made from Czochralski material are exposed to sunlight or forward bias, their performance degrades due to a rearrangement of complex which most probably contains oxygen and boron. This degradation, which can be reversed by annealing, is reflected not only in the solar cell parameters but also in the dark I-V characteristics. We have imaged the dark forward current across a 4 cm² cell and a 100 cm² cell containing striations by lock-in thermography after annealing the cell at 200°C and after degrading it for 24 hrs. The difference between these two images corresponds to the local action of the B-O complex. We have found that this complex is distributed homogeneously across both cells, and that some observed weak local shunts do not show any recombination-induced degradation. Especially, the striation pattern in the 100 cm² cell did not react on degradation and annealing.