High‐Resolution Printed Ethylene Vinyl Acetate Based Strain Sensor for Impact Sensing

The strongly growing interest in digitalizing society requires simple and reliable strain-sensing concepts. In this work, a highly sensitive stretchable sensor is presented using a straightforward and scalable printing method. The piezoresistive sensor consists of conductive core–shell microspheres embedded in an elastomer. As the elastomer, ethylene vinyl acetate (EVA) is employed as an efficient and cost-effective alternative compared to polydimethylsiloxane (PDMS). EVA allows for a significantly lower percolation threshold and low hysteresis compared with PDMS. Using 35 µm microspheres, a detection limit of 0.01% is achieved. When using 4 µm microspheres, the sensor shows a detection limit of 0.015% and electromechanical robustness against 1000 cycles of 0–1% strain. The stretchable strain sensor is successfully implemented as an impact sensor and a diaphragm expansion monitoring sensor. Fast (20 ms) and high-resolution response as well as mechanical robustness to strain values greater than the linear working range of the sensor are demonstrated. The results of this research indicate the promising potential of employing conductive microspheres embedded in the EVA matrix for fast and precise strain detection applications

Rare-earth coordination polymers with multimodal luminescence on the nano-, micro-, and milli-second time scales

We present a coordination polymer based on rare-earth metal centers and carboxylated 4,4′-diphenyl-2,2′-bipyridine ligands. We investigate Y$^{3+}$, Lu$^{3+}$, Eu$^{3+}$, and a statistical mixture of Y$^{3+}$ with Eu$^{3+}$ as metal centers. When Y$^{3+}$ or Lu$^{3+}$ is exclusively present in the coordination polymer, biluminescence from the ligand is observed: violet emission from the singlet state (417 nm, 0.9 ns lifetime) and orange emission from the triplet state (585 nm, 76 ms (Y$^{3+}$) and 31 ms (Lu$^{3+}$)). When Eu$^{3+}$ is present in a statistical mixture with Y$^{3+}$, red emission from the Eu$^{3+}$ (611 nm, ∼500μs) is observed in addition to the ligand emissions. We demonstrate that this multi-mode emission is enabled by the immobility of singlet and triplet states on the ligand. Eu$^{3+}$ only receives energy from adjacent ligands. Meanwhile, in the broad inhomogeneous distribution of ligand energies, higher energy states favor singlet emission, whereas faster intersystem crossing in the more stabilized ligands enhances their contribution to triplet emission

Piezoresistive Free‐standing Microfiber Strain Sensor for High‐resolution Battery Thickness Monitoring

Highly sensitive microfiber strain sensors are promising for the detection of mechanical deformations in applications where limited space is available. In particular for in situ battery thickness monitoring where high resolution and low detection limit are key requirements. Herein, the realization of a highly sensitive strain sensor for in situ lithium-ion (Li-ion) battery thickness monitoring is presented. The compliant fiber-shaped sensor is fabricated by an upscalable wet-spinning method employing a composite of microspherical core-shell conductive particles embedded in an elastomer. The electrical resistance of the sensor changes under applied strain, exhibiting a high strain sensitivity and extremely low strain detection limit of 0.00005 with high durability of 10 000 cycles. To demonstrate the accuracy and ease of applicability of this sensor, the real-time thickness change of a Li-ion battery pouch cell is monitored during the charge and discharge cycles. This work introduces a promising approach with the least material complexity for soft microfiber strain gauges

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8_{0.8}MA0.2_{0.2}Sn0.5_{0.5}Pb0.5_{0.5}I3_{3}) for All‐Perovskite Tandem Solar Cells

All-perovskite multijunction photovoltaics, combining a wide-bandgap (WBG) perovskite top solar cell (EG ≈1.6–1.8 eV) with a low-bandgap (LBG) perovskite bottom solar cell (EG 33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum-assisted growth control (VAGC) of solution-processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well-established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge-carrier lifetime. The improved optoelectronic characteristics enable high-performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four-terminal all-perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active-area solar cells up to 1 cm²