Tuning spike-like morphologies in Silicon by sustainable fs-laser processing in air for enhanced light absorption

• Size- and period-scalable spike-like structures have been achieved. • Non-hyperdoped black silicon is fabricated in ambient air by fs-laser processing. • An absorptance > 94 % is achieved just by the texturing up to 1100 nm. • Non-zero absorptance by light trapping in the range 1100–2500 nm. • These properties suggest the use of our material in PV, sensing and wettability. In this work, we demonstrate that ultrafast laser processing (1030 nm, 290 fs) of silicon in ambient air strongly improves the material’s performance in terms of absorption, both in the visible and near infrared spectral range, which paves the way for further studies on increasing the sub-bandgap absorption after texturing, suggesting the material developed as a sustainable substitute for black silicon processed in greenhouse gases atmospheres. Our approach is based on the fabrication of spike-like morphologies in ambient air and the subsequent annealing of the material by pulsed laser melting or rapid thermal annealing to recover its crystalline phase. In particular, the influence of three main processing parameters (fluence, pulse number and repetition rate) on the properties of the spike-like structures has been investigated, each of them revealing the possibility of a direct control on the size, shape and period of the spikes, and achieving a total tuning range of the period from 4 μm to 14 μm for a single laser wavelength. Macroscopic areas have been fabricated using short processing times, yielding absorption values A > 94% over the UV–VIS-NIR spectral range (250 nm - 1100 nm) without hyperdoping, and A ≥ 20% for longer wavelengths up to 2500 nm, while preserving the electrical performance of pristine silicon.