**4.5 Femtosecond laser induced crystallization & simultaneous formation of light-trapping nanostructures**

Femtosecond laser induced crystallization & simultaneous formation of lighttrapping nanostructures is a one-step laser process, which could lead to fabricate the highly efficient solar cells [42–51]. Mmicrostructures and small spikes have been spontaneously formed upon laser treatment. Interestingly the a-Si:H films turned completely dark from an original shiny reddish gray color. A similar effect has been extensively studied by Mazur's group and others in crystalline bulk silicon wafers [42–52].
