Effect of laser annealing on defected silicon solar cells

The effect of pulsed Nd-YAG laser annealing (λ = 1.06 μm), on the efficiency of defected polycrystalline silicon solar cells has been studied. Cells performance measurement and microscopic structure examinations of the surface using optical and scanning electron microscopy (SEM) have been done before and after irradiation with different laser fluences (2.3 - 25 J/cm2) and for successive times until a steady state has been reached. It is found that the annealing causes a change in the topography of the cells, resulting in an increase in grain size at low fluences and beginning of crystal growth at higher fluences up to an optimum value of 7.5 J/cm2. These processes cause an improvement in the electrical output characteristics of the defect-rich solar cells; hence an increase in the cell efficiency is obtained. The maximum change in efficiency value is found to be about 5 times greater than its initial value. For fluences of more than 16 J/cm2, SEM micrographs show slightly deeper melt front penetration which affects the junction interface and a reduction in light output characteristics of the cells has been detected.