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Microcrystalline silicon deposited from SiF4/H2/Ar plasmas and its application to photovoltaics

Abstract : Silicon tetrafluoride is a good candidate to replace silane as silicon precursor in plasmas used to deposit thin films. It has been demonstrated by previous Ph.D. thesis at LPICM that microcrystalline silicon, grown from SiF4/H2/Ar gas mixtures, leads to excellent thin film transistors. This thesis is dedicated to another application: photovoltaic devices. A new challenge arises because several micron thick layers are required in microcrystalline silicon thin film PIN solar cells. Therefore a better and deeper understanding of SiF4/H2/Ar plasmas is necessary to optimize the deposition rate of microcrystalline silicon. SiF4/H2/Ar plasmas have been studied thanks to mass spectrometry and the specificity of such gas mixtures is demonstrated to be the formation HF molecules via the recombination of atomic F and molecular H2. We found that a H2-limited process is associated to amorphous growth and all H2 is used to form HF. On the contrary, an excess of H2 leads to microcrystalline growth. A simple yet accurate model, strongly based on experimental data, has been developed to explain the amorphous-to-microcrystalline transition and enables a controlled tuning of plasma parameters leading to an increase of deposition rate. Moreover, the contribution of plasma generated nanoparticles has been clarified, in particular their crystallization in the plasma phase. The microcrystalline silicon, fabricated from SiF4/H2/Ar, is a high quality material: a density of defects as low as 3x10-3cm-1 has been deduced from absorption below the bandgap (at 0.8eV). By using the fluorinated chemistry for the deposition of the intrinsic absorber layers in thin film PIN solar cells, open-circuit voltage as high as 536mV has been obtained for highly crystallized layers, leading to an efficiency of 9.2%.
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Contributor : Jean-Christophe Dornstetter Connect in order to contact the contributor
Submitted on : Thursday, January 29, 2015 - 4:31:25 PM
Last modification on : Wednesday, March 27, 2019 - 4:20:04 PM
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  • HAL Id : tel-01111141, version 1



Jean-Christophe Dornstetter. Microcrystalline silicon deposited from SiF4/H2/Ar plasmas and its application to photovoltaics. Materials Science [cond-mat.mtrl-sci]. Ecole Polytechnique, 2014. English. ⟨tel-01111141⟩



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