Sn_xGe_1–x Alloy Nanocrystals: A First Step toward Solution-Processed Group IV Photovoltaics

Abstract

Non-toxic, sustainable and cost-effective, Group IV materials are attractive for a broad range of electronic and opto-electronic applications, although the indirect principal band gaps of silicon and germanium (Ge) present complications that impact device design and cost. Previous studies have shown that the band structures of these materials can be modified by the influence of quantum confinement in nanostructures, or by alloying with tin (Sn) in metastable thin films;to date, neither method has produced a material with a direct band gap of appropriate energy for application in, e.g., efficient solar photovoltaics. We have developed a facile colloidal method for the synthesis of size-controlled, homogeneous Sn x Ge 1-x alloy nanocrystals (NCs) with remarkably high tin concentration (x up to 0.42). We demonstrate that NCs of the same size exhibit a pronounced, systematic red-shift in the optical band gap, and a significant increase in molar absorptivity, with increasing Sn-content, and a measurable photoluminescence was observed from NCs with high contents. The indications of at least partial direct-gap character in these NCs, combined with their broad tunability throughout the infrared, suggest their promise for use in solution-processed solar cells.

Facile Deposition of Cu−SnOx Hybrid Nanostructures on Lightly Boron‐Doped Diamond Electrodes for CO2 Reduction

“…Figure b displays Sn 3d indicating similar nature of photoelectron peaks from both SnO x and Cu−SnO x deposited on BDD L . BEs of Sn 3d 5/2 and 3d 3/2 are found to be at 487.2 and 495.7 eV, respectively which can be assigned as Sn(IV) ,. Therefore, EELS and XPS surface analysis suggest that the nanoparticles deposited on BDD L by a potentiodynamic method with suitable experimental conditions are covered with a 3 to 10 nm SnO x ‐rich shell.…”

Investigation of the photophysical properties of energy-relevant inorganic nanocrystals

“…Ge1-xSnx cores were prepared by a modified reported procedure. 10 To prepare core-shell nanocrystals with excess precursors (one-pot synthesis), a batch of freshly prepared Ge1-xSnx cores (in amine or amine/ODE) solution, ODE (1.5 mL, 4.7 mmol), and (octyl)2NH (1.5 mL, 5.0 mmol) were added to a four-neck 250 mL R.B. flask.…”

“…Still, previous work showed the potential for tin doping to create a more direct band gap through strain. 10 The work described in Chapter 2 sought to understand the effect of tin doping on the luminescence properties of germanium nanocrystals.…”

“…49 Ge 2+ , Ge 4+ , Sn 0 , and a broad, overlapping peak for Sn 2+ and Sn 4+ . 10 Relatively high ratios of the metallic peak to the oxidized peaks correlate to very little surface oxidation of these nanocrystals. Esteves and coworkers observed similar results, where three types of peaks were present: metallic Ge 0 and Sn 0 peaks from interior atoms, Ge 2+ and Sn 2+/4+ peaks from atoms bound to passivating ligands, and a small Ge 4+ peak from GeO2 at the surface.…”

“…101 The preparation of Ge-Sn alloy nanocrystals typically follows one of the aforementioned strategies with the addition of a suitable Sn precursor, such as tin(II) chloride (SnCl2) or bis(trimethylsilyl)amide [Sn(HDMS)2]. 10,49 A recent report showed the bottom-up formation of Ge1-xSnx nanowires grown from Sn nanocrystals. 102 The concentration of Sn in these nanowires was found to be 12.4 atom% (x = 0.124).…”