The ever-increasing number of connected objects requires novel ways to power them and make them fully autonomous. In this context, photovoltaic, piezoelectric or thermoelectric energy-harvesting technologies show great promises as...

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We use conventional and aberration-corrected transmission electron microscopy (TEM) and ab initio calculations to investigate the structural and electronic properties of β-FeSi 2 nanoparticles, which are a promising material for photovoltaic applications due to a band gap of <1 eV and a high absorption coefficient. The nanoparticles have average sizes of ß20 nm, form aggregates, and are prepared by gas-phase synthesis. Amorphous SiO x shells with thicknesses of ß1.7 nm around β-FeSi 2 cores are identified on individual nanoparticles using electron energy-loss spectroscopy, while stacking fault domains in the nanoparticles are observed using high-resolution TEM, nanobeam electron diffraction, and automated diffraction tomography. Ab initio calculations indicate only minor changes in band structure in the faulted structure when compared to perfect β-FeSi 2 . The optical properties of imperfect β-FeSi 2 nanoparticles are therefore expected to be the same as those of the perfect structure, suggesting that β-FeSi 2 nanoparticles are suitable candidates for use in optical absorber layers in thin film solar cells.

We have investigated the potential of solution-processed β-phase iron disilicide (FeSi2) nanoparticles as a novel semiconducting material for photovoltaic applications. Combined ultraviolet-visible absorption and photothermal deflection spectroscopy measurements have revealed a direct band gap of 0.85 eV and, therefore, a particularly high absorption in the near infrared. With the help of Fourier-transform infrared and X-ray photoelectron spectroscopy, we have observed that exposure to air primarily leads to the formation of a silicon oxide rather than iron oxide. Mössbauer measurements have confirmed that the nanoparticles possess a phase purity of more than 99%. To diminish the small fraction of metallic iron impurities, which were detected by superconducting quantum interference device magnetometry and which would act as unwanted Auger recombination centers, we present a novel concept to magnetically separate the FeSi2 nanoparticles (NPs). This process leads to a reduction of more than 95% of the iron impurities.

Heat recovery systems based on thermoelectric micro-generators (µ-TEGs) can play a significant role in the development of wireless, energetically autonomous electronics. However, to date, the power density recovered for low temperature differences using µ-TEGs is limited to a few micro-watts or less, which is still insufficient to power a wide-range of wireless devices. To develop more efficient µ-TEGs, material, device and system requirements must be considered simultaneously. In this study, an innovative design of an in-plane µ-TEG integrating bismuth telluride forming sinusoidal-shaped trenches is reported. Using 3D numerical modelling, the influence of boundary conditions, parasitic effects (electrical and thermal contact resistances), and transport properties of thermoelectric materials on the output power of these µ-TEGs are investigated in detail for a small temperature difference of 5 K between the hot and cold sources. Compared to wavy-shaped trenches, this novel shape enables enhancing the output power. The results show that either the thermal conductivity or the Seebeck coefficient of the active n- and p-type semiconductors is the key parameter that should be minimized or maximized, depending on the magnitude of the parasitic effects.