Properties of ultrafast laser textured silicon for photovoltaics

In this work, we report a detailed material study of ultrafast laser textured silicon surfaces to gain insight into the impact of ultrafast laser processing conditions on photovoltaic device properties. A comprehensive study of the ultrafast laser processed silicon is achieved by determination of crystal structure and elemental compositional changes using transmission electron microscopy, compositional mapping by energy dispersive X-ray spectroscopy and depth profiling compositional determination using X-ray photoelectron spectroscopy. We have observed material non-homogeneity, impurity incorporation and strained silicon, all limited to the surface. A combination of chemical etching and thermal annealing was used to remove the laser induced changes and the material was restored to its starting quality. Further, silicon solar cell devices on such defect-etched surfaces are fabricated. These devices are characterized through dark i–v analysis and Fourier transform deep level transient spectroscopy for defect analysis.