Inorganic double-helix compounds for energy conversion

• Applicant: Professor Dr. Tom Nilges
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 389011793

Semiconducting compounds with the composition SnXPn (with X = Br, I and Pn = P, As) exhibit an exceptional structural chemistry for inorganic substances. [SnX]+ and [Pn]- helices form double-helical SnIP and SnIAs structures, which have been identified as promising compounds for solar cells and as catalysts in photocatalysis due to their mechanical and electronic properties. Quantum chemical calculations suggest that SnIP and SnIAs exhibit comparable or even more promising properties for solar cell applications than the currently heavily researched (Ma)PbX3 perovskites. We have demonstrated through measurements that the charge carrier mobilities for h+ perpendicular to the double helices and for e- parallel to the helices in SnIP are comparable to the values found in MaPbI3. For SnIP@C3N4 hybrids, an up to fourfold increase in water splitting activity compared to the pure substances has been demonstrated. In mesoporous TiO2, a sixfold increase has even been observed. Based on the findings of the predecessor project, we will synthesize the semiconducting double-helix compounds SnIP, SnBrP, and SnIAs, and combine them with 2D materials such as h-BN, phosphorene, MoQ2 (Q = S, Se), terminated silicene, and terminated germanene to form SnXPn@2D material hybrids. For hybrid formation, the double-helix compounds and 2D materials will be delaminated, transformed into nanoparticulate form, and then assembled into hybrids through self-organization processes. In the case of the SnXPn compounds, the development and optimization of a thin-film deposition process is planned to obtain the compounds, which crystallize in an extremely anisotropic form (needles with a tendency to self-delaminate), as compact, dense, and firmly adhering layers on suitable substrates for subsequent applications. The above-mentioned SnXPn double-helix compounds, deposited as thin films, and selected hybrid systems will be studied for their water splitting properties, with the aim of creating solar cells from them. For this purpose, collaborations with experts in Canada and at TUM are planned. The goal is to understand and optimize heterojunction formation in the water splitting catalysts, thereby developing efficient, non-precious metal-based catalysts. For the solar cell subproject, the first functioning SnXPn solar cell will be fabricated, thereby confirming the quantum chemical predictions. This could expand the field of inorganic solar cell materials by introducing an interesting new class of materials.

• DFG Programme: Research Grants