Multicrystalline, Highly Oriented Thick‐Film Silicon from Reduction of Soda‐Lime Glass

• Published in: Advanced materials interfaces 2023-12, Vol.10 (35), p.n/a
• Main Authors: Schall, Ingrid, Ebbinghaus, Stefan G., Strelow, Christian, Peiner, Erwin
• Format: Article
• Language: English
• Subjects: Aluminothermic reduction; Bonding strength; Carrier density; Compressive properties; crystal growth; Crystallinity; Electric contacts; Emitters; Glass substrates; glasses; Low concentrations; multicrystalline layers; Photovoltaic cells; Raman spectroscopy; Secondary ion mass spectrometry; Silicon; silicon‐on‐glass; Spalling
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.202300681

The study describes synthesis and characterization of > 10 µm thick multicrystalline (mc), highly oriented, p‐doped silicon layers by aluminothermic reduction of low‐cost soda‐lime glass. X‐ray diffraction shows a highly preferred (111)‐orientation and excellent crystallinity. Low compressive stress and very good crystallinity are confirmed by the peak position and width of the Raman LO‐phonon line, approaching the one of bulk single‐crystalline wafer material. Due to strong bonding to the glass substrate layer, spalling is not observed. A conductive aluminum‐rich oxide layer is formed underneath the silicon, serving as an electrical back‐contact for electronic devices. Using secondary ion mass spectrometry very low concentrations of 1014–1015 cm−3 of impurities are found originating from the soda‐lime glass with an iron content below the detection limit. Furthermore, a plateau‐like, very homogenous Al concentration of ≈4 × 1018 cm−3 over a thickness of ≈10 µm is found, which corresponds to the solubility of Al in Si at the process temperature. Complete electronic activation within the plateau region is confirmed by carrier concentration measurements using electrochemical capacitance–voltage profiling and Raman spectroscopy. Hole concentrations in the range of few 1018 cm−3 are beneficial for the p‐type base material of full‐emitter cell mc‐silicon photovoltaic devices. Ten‐micron‐thick silicon synthesized by aluminothermic reduction from low‐cost soda‐lime glass shows unprecedented crystallinity and purity suitable for photovoltaics. Incorporated Al is fully ionized forming a p‐type‐conductive silicon layer. The underlying glass containing silica is converted to porous alumina, which is likely filled by metallic aluminum. The thereby formed back‐contacted silicon enables vertical device architectures.