Structural and optical property tailoring of black silicon with fs-laser pulses

Abstract

ABSTRACTIrradiating a planar silicon surface with femtosecond laser pulses under a sulfuric atmosphere creates first a structured surface featuring cones of up to 20 microns in height, and second a 0.1 – 1 μ m thick layer of multi-crystalline silicon on theses cones containing up to 1 at.% sulfur acting as n-type dopant. Further, the sulfur establishes energy states within the band gap of silicon allowing for the absorption of infrared (IR) light with energies below the band gap energy of silicon. This black silicon process is distinguished by the fact that only one single laser process is required to tailor three material characteristics in on step: the surface structure, the doping and the light absorption. In this work we study structural and optical material characteristics of black silicon. For the first time this work presents properties of black silicon processed with shaped femtosecond laser pulses. Finally, black silicon substrate is used as substrate for manufacturing a black silicon solar cell with a femtosecond laser pulse formed sulfur emitter. For such a black silicon solar cell we achieved a record efficiency of η =4.5%