3D-MICROSTRUCTURING AND SELECTIVE ETCHING OF SILICON BY NANOSECOND PULSED INFRARED LASER FOR PHOTOVOLTAIC APPLICATIONS

Date

2025-3-13

Author

Demirbaş, Kardelen

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Laser-induced silicon modifications combined with selective chemical etching offer a promising approach for advanced photovoltaic applications. This thesis investigates a maskless, nanosecond infrared (IR) laser-assisted method to achieve precise buried contact openings and flexible silicon wafers without damaging the wafer. A customdeveloped nanosecond-pulsed erbium-doped fiber laser is employed to induce localized modifications through nonlinear absorption processes. These modifications are then selectively removed using a copper-assisted chemical etching (Cu-ACE),widely used Si etchant containing Cu(NO3)2, HNO3, HF, and CH3COOH, process to reveal well-defined three-dimensional (3D) structures. While it offers a high etch rate, its low selectivity and surface roughness limit precise 3D structuring. The study first examines the fundamental mechanisms governing laser-induced modifications in silicon, including carrier dynamics, energy absorption, and material response to nanosecond laser pulses. The impact of laser processing on silicon’s mechanical and electrical properties is assessed, ensuring that the proposed method does not degrade silicon’s minority carrier lifetime, a crucial factor for photovoltaic efficiency. The buried contact opening process is optimized using a combination of laser processing and Cu-ACE etching, achieving precise subsurface structures with high selectivity and minimal surface roughness. This approach eliminates the need for complex photolithography steps and enables cost-effective integration into buried contact solar cells (BCSCs). Additionally, the thesis explores the fabrication of flexible silicon wafers by introducing controlled modifications that enhance mechanical adaptability while maintaining structural stability. The optimized etching process successfully removes modified regions, resulting in flexible silicon wafer.

Subject Keywords

Laser-induced modification, Selective chemical etching, Buried contact solar cells, Flexible silicon wafers, Lazerle modifikasyon, Seçici kimyasal aşındırma, Gömülü kontak güneş hücreleri, Esnek silikon hücreleri

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https://hdl.handle.net/11511/114104

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Graduate School of Natural and Applied Sciences, Thesis