Enhanced light absorption in nanotextured amorphous thin-film silicon caused by femtosecond-laser materials processing

Efficient thin-film solar cells balance the reduced absorption occurring in thin absorber layers by means of various photon management strategies that often involve randomly nanotextured interfaces. We report on broadband absorption enhancement in nanotextured amorphous silicon processed by femtosecond laser materials processing. As identified by micro-Raman spectroscopy and surface profilometry, the absorption of a single femtosecond amplifier laser pulse (30 fs, 795 nm, 75 mJ cm−2) creates a thin nanotextured micro-crystalline surface layer. Optical microscopy in transmission and reflection geometry reveals a broadband absorption enhancement in the visual spectrum range for the nanotextured area. Scattered light spectroscopy in combination with spectral interferometry indicates that light trapping for about 100 fs is achieved in the femtosecond-laser processed amorphous silicon area and thus is responsible for the observed enhanced absorption and locally enhanced Raman yields. Thus fs-laser materials processing offers an interesting pathway towards advanced photon management in amorphous silicon based thin-film solar cells.