Characterization of laser edge isolation in multicrystalline silicon solar cells

We report on a characterization study of laser edge isolation in multicrystalline silicon (mc-Si) solar cells using microscopic electrical, structural, and morphological tools of scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM), electron backscattering diffraction (EBSD), and scanning electron microscopy (SEM), as well as a macroscopic electrical characterization of lock-in thermography (LIT). SCM and C-AFM measurements revealed that the emitter was not completely removed by the laser ablation, and considerable amounts of emitter dopant were driven into the material. A portion of the ablated or molten material was redeposited or recrystallized on top of the laser groove, forming either single- or polycrystalline stripes. Si particles with either polycrystalline or amorphous structures were also formed on the grooves. LIT measurement on a shunted device exhibits a high-temperature region centered on the groove line, indicating inadequate isolation. SEM observations show a significant different morphological/structural surface of the groove from that of the isolated devices. These techniques provide useful characterizations for failure analysis of the laser edge isolation.