Textured Stainless Steel as a Platform for Black Mg2Si/Si Heterojunction Solar Cells with Advanced Photovoltaic Performance

Abstract

This paper reports on a facile bottom-up method for the direct integration of a silicon (Si)-magnesium silicide (Mg2Si) heterojunction solar cell (HSC) with a textured rear reflector made of stainless steel (SS). Modified wet chemical etching and post processing of SS substrates resulted in the formation of both a rough surface texture and diffusion barrier layer, consisting of magnetite (Fe3O4) with reduced optical reflection. Then, Si, Mg2Si and CaSi2 layers were stepwise thermally evaporated onto the textured SS surface. No traces of Fe and Cr silicide phases were detected by Raman spectroscopy, confirming effective suppression of impurity diffusion from the SS to the upper layers at least at temperatures required for Si deposition, as well as Mg2Si and CaSi2 formation. The obtained black-SS/Fe3O4/Si/Mg2Si/CaSi2 sample preserved, to some extent, its underlying textured morphology and demonstrated an averaged reflection of 15% over the spectral range of 200–1800 nm, while its prototype HSC possessed a wideband photoresponse with a photoelectric conversion efficiency of 7.5% under AM1.5 illumination. Moreover, Si layers deposited alone onto a black-SS substrate demonstrated competitive antireflection properties compared with black Si (b-Si) obtained by traditional top-down etching approaches, and hybrid b-Si/textured-SS structures with a glue-bonded interlayer.

Alternative Look at Calcium Digermanide CaGe2: A High-Performing Semimetal Transparent Conducting Material for Ge Optoelectronics

“…That is why, correlated metals and semimetals became the systems of interest, , which infrared transparency has been recently validated for the thin films of calcium disilicide (CaSi 2 ) and tungsten ditelluride (WTe 2 ) both possessing layered crystal structure and classified as trivial and type-II Weyl semimetals, respectively. , High intrinsic transparency in the optical telecommunication spectral range of the former material was shown in addition to a very low sheet resistance, which resulted in a record near-infrared (NIR) figure of merit (FOM) competitive with state-of-the-art TCOs and other TCMs. Moreover, a prototype photovoltaic device utilizing a CaSi 2 top electrode instead of conventional metal-finger contacts was demonstrated resulting in enhanced photovoltaic performance and clearly confirming the reliability of the semimetal approach …”